RFC 8540
Stream Control Transmission Protocol: Errata and Issues in RFC 4960
RFC 8540: Stream Control Transmission Protocol: Errata and Issues in RFC 4960 🦋
Okay bestie, the header tea 🫶 This is RFC 8540, titled "Stream Control Transmission Protocol: Errata and Issues in RFC 4960." It was published in February 2019 and sits in the Informational category, so it's not a standards-track spec. The ISSN is 2070-1721. The authors are R. Stewart (Netflix, Inc.), M. Tuexen (Muenster Univ. of Appl. Sciences), and M. Proshin (Ericsson). The header doesn't list anything it obsoletes or updates.
Abstract 💖
This doc is a roundup of all the issues people found since RFC 4960 dropped in September 2007. The findings come from actually building, testing, and using the Stream Control Transmission Protocol (SCTP), and each one comes with a suggested fix. It's written as a set of deltas to RFC 4960, arranged in time order, so the issues appear in the order they were raised. Some text got edited more than once, so the last delta in the text is the one that should be applied 🔥 Along with the deltas, you get a description of each problem and the details of each solution.
Status of This Memo 🌸
Not an Internet Standards Track spec, just published for informational purposes.
This is an IETF product and represents IETF community consensus. It got public review and was approved for publication by the Internet Engineering Steering Group (IESG). Not every IESG-approved doc is a candidate for any level of Internet Standard, so check Section 2 of RFC 7841 if you want the full picture.
For the current status, any errata, and how to send feedback, head to https://www.rfc-editor.org/info/rfc8540.
Copyright Notice 🎀
Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved.
This doc is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info), as they stand on the publication date. Read those carefully, because they spell out your rights and restrictions for this doc. Any Code Components pulled out of this doc must include Simplified BSD License text, as described in Section 4.e of the Trust Legal Provisions, and they come with no warranty, as the Simplified BSD License describes.
Table of Contents 🧚
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Corrections to RFC 4960 . . . . . . . . . . . . . . . . . . . 4
3.1. Path Error Counter Threshold Handling . . . . . . . . . . 4
3.2. Upper-Layer Protocol Shutdown Request Handling . . . . . 5
3.3. Registration of New Chunk Types . . . . . . . . . . . . . 6
3.4. Variable Parameters for INIT Chunks . . . . . . . . . . . 7
3.5. CRC32c Sample Code on 64-Bit Platforms . . . . . . . . . 8
3.6. Endpoint Failure Detection . . . . . . . . . . . . . . . 9
3.7. Data Transmission Rules . . . . . . . . . . . . . . . . . 10
3.8. T1-Cookie Timer . . . . . . . . . . . . . . . . . . . . . 11
3.9. Miscellaneous Typos . . . . . . . . . . . . . . . . . . . 12
3.10. CRC32c Sample Code . . . . . . . . . . . . . . . . . . . 19
3.11. partial_bytes_acked after T3-rtx Expiration . . . . . . . 19
3.12. Order of Adjustments of partial_bytes_acked and cwnd . . 20
3.13. HEARTBEAT ACK and the Association Error Counter . . . . . 21
3.14. Path for Fast Retransmission . . . . . . . . . . . . . . 22
3.15. Transmittal in Fast Recovery . . . . . . . . . . . . . . 23
3.16. Initial Value of ssthresh . . . . . . . . . . . . . . . . 24
3.17. Automatically CONFIRMED Addresses . . . . . . . . . . . . 25
3.18. Only One Packet after Retransmission Timeout . . . . . . 26
3.19. INIT ACK Path for INIT in COOKIE-WAIT State . . . . . . . 27
3.20. Zero Window Probing and Unreachable Primary Path . . . . 28
3.21. Normative Language in Section 10 of RFC 4960 . . . . . . 29
3.22. Increase of partial_bytes_acked in Congestion Avoidance . 32
3.23. Inconsistent Handling of Notifications . . . . . . . . . 33
3.24. SACK.Delay Not Listed as a Protocol Parameter . . . . . . 37
3.25. Processing of Chunks in an Incoming SCTP Packet . . . . . 39
3.26. Increasing the cwnd in the Congestion Avoidance Phase . . 41
3.27. Refresh of cwnd and ssthresh after Idle Period . . . . . 43
3.28. Window Updates after Receiver Window Opens Up . . . . . . 45
3.29. Path of DATA and Reply Chunks . . . . . . . . . . . . . . 46
3.30. "Outstanding Data", "Flightsize", and "Data in Flight"
Key Terms . . . . . . . . . . . . . . . . . . . . . . . . 47
3.31. Degradation of cwnd due to Max.Burst . . . . . . . . . . 49
3.32. Reduction of RTO.Initial . . . . . . . . . . . . . . . . 50
3.33. Ordering of Bundled SACK and ERROR Chunks . . . . . . . . 51
3.34. Undefined Parameter Returned by RECEIVE Primitive . . . . 52
3.35. DSCP Changes . . . . . . . . . . . . . . . . . . . . . . 53
3.36. Inconsistent Handling of ICMPv4 and ICMPv6 Messages . . . 55
3.37. Handling of Soft Errors . . . . . . . . . . . . . . . . . 56
3.38. Honoring cwnd . . . . . . . . . . . . . . . . . . . . . . 57
3.39. Zero Window Probing . . . . . . . . . . . . . . . . . . . 58
3.40. Updating References regarding ECN . . . . . . . . . . . . 60
3.41. Host Name Address Parameter Deprecated . . . . . . . . . 62
3.42. Conflicting Text regarding the 'Supported Address Types'
Parameter . . . . . . . . . . . . . . . . . . . . . . . . 66
3.43. Integration of RFC 6096 . . . . . . . . . . . . . . . . . 67
3.44. Integration of RFC 6335 . . . . . . . . . . . . . . . . . 70
3.45. Integration of RFC 7053 . . . . . . . . . . . . . . . . . 72
3.46. CRC32c Code Improvements . . . . . . . . . . . . . . . . 76
3.47. Clarification of Gap Ack Blocks in SACK Chunks . . . . . 87
3.48. Handling of SSN Wraparounds . . . . . . . . . . . . . . . 89
3.49. Update to RFC 2119 Boilerplate Text . . . . . . . . . . . 90
3.50. Removal of Text (Previously Missed in RFC 4960) . . . . . 91
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 91
5. Security Considerations . . . . . . . . . . . . . . . . . . . 92
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 92
6.1. Normative References . . . . . . . . . . . . . . . . . . 92
6.2. Informative References . . . . . . . . . . . . . . . . . 92
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 94
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 941. Introduction ✨
This doc is a compilation of every defect found in [RFC4960] ("Stream Control Transmission Protocol") up until it was published. The defects can be editorial or technical. Think of it as a companion doc for anyone implementing SCTP, helping clear up mistakes in the original SCTP spec 💅
It also keeps a history of the changes that will eventually be folded into a bis document for [RFC4960], and it's structured the same way as [RFC4460].
Each error gets detailed in this doc with:
- The problem description,
- The text quoted from [RFC4960],
- The replacement text that should go into an upcoming bis document, and
- A description of the solution.
Be careful when you read this, okay? Make sure a field or item doesn't get updated later on in the document. This doc is a historical record of the changes that were needed over time, from interop events and discussion on the Transport Area Working Group mailing list. So the last delta in the text is the one that should be applied 🙈
2. Conventions 💜
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" are interpreted as described in BCP 14 [RFC2119] [RFC8174], but only when they show up in all capitals, like this. 🎀
3. Corrections to RFC 4960 🌈
3.1. Path Error Counter Threshold Handling 🦋
3.1.1. Description of the Problem
RFC 4960 handles the 'Path.Max.Retrans' parameter in two places, Sections 8.2 and 8.3, and they don't agree. Section 8.2 of [RFC4960] says a path gets marked inactive when the path error counter exceeds the threshold. Section 8.3 of [RFC4960] says it gets marked inactive when the counter reaches the threshold. Those are different things, bestie 😭
This was reported as an errata for [RFC4960] as Errata ID 1440.
3.1.2. Text Changes to the Document
Here's the before and after, word for word, since implementers need the exact wording:
---------
Old text: (Section 8.3)
---------
When the value of this counter reaches the protocol parameter
'Path.Max.Retrans', the endpoint should mark the corresponding
destination address as inactive if it is not so marked, and may also
optionally report to the upper layer the change of reachability of
this destination address. After this, the endpoint should continue
HEARTBEAT on this destination address but should stop increasing the
counter.
---------
New text: (Section 8.3)
---------
When the value of this counter exceeds the protocol parameter
'Path.Max.Retrans', the endpoint SHOULD mark the corresponding
destination address as inactive if it is not so marked and MAY also
optionally report to the upper layer the change in reachability of
this destination address. After this, the endpoint SHOULD continue
HEARTBEAT on this destination address but SHOULD stop increasing the
counter.This text has been modified by multiple errata. It gets further updated in Section 3.23.
3.1.3. Solution Description
The state change is supposed to happen when the threshold is exceeded. The intended state change should happen when the threshold is exceeded. 💅
3.2. Upper-Layer Protocol Shutdown Request Handling 🌸
3.2.1. Description of the Problem
Section 9.2 of [RFC4960] describes how to handle SHUTDOWN chunks received while in the SHUTDOWN-RECEIVED state. It doesn't say what to do with shutdown requests coming from the upper layer while in that state, which is the actual gap 🙈
This was reported as an errata for [RFC4960] as Errata ID 1574.
3.2.2. Text Changes to the Document
---------
Old text: (Section 9.2)
---------
Once an endpoint has reached the SHUTDOWN-RECEIVED state, it MUST NOT
send a SHUTDOWN in response to a ULP request, and should discard
subsequent SHUTDOWN chunks.
---------
New text: (Section 9.2)
---------
Once an endpoint has reached the SHUTDOWN-RECEIVED state, it MUST
ignore ULP shutdown requests but MUST continue responding to SHUTDOWN
chunks from its peer.This text is in final form and isn't further updated in this document. ✨
3.2.3. Solution Description
The text never meant for the SCTP endpoint to ignore SHUTDOWN chunks from its peer. If it did, endpoints could never gracefully terminate associations in some cases. That would be a whole mess 😭
3.3. Registration of New Chunk Types 🧚
3.3.1. Description of the Problem
Section 14.1 of [RFC4960] should deal with new chunk types, but the text only mentions parameter types. Iconic of it to miss that, honestly 💀
This was reported as an errata for [RFC4960] as Errata ID 2592.
More parts are coming, so stay tuned, bestie 💖
3. Corrections to RFC 4960 ✨
3.3.2. Text Changes to the Document 💅
okay so the chunk type section gets a glow-up 🎀 here's the old text and the new text, bestie:
---------
Old text: (Section 14.1)
---------
The assignment of new chunk parameter type codes is done through an
IETF Consensus action, as defined in [RFC2434]. Documentation of the
chunk parameter MUST contain the following information:
---------
New text: (Section 14.1)
---------
The assignment of new chunk type codes is done through an IETF
Consensus action, as defined in [RFC8126]. Documentation for the
chunk type MUST contain the following information:this text has been through multiple errata 😭 and it's further updated in Section 3.43, so keep that in your back pocket 🧚
3.3.3. Solution Description 🦋
the new text finally talks about chunk types the way it's supposed to, and the reference gets switched over to [RFC8126]. iconic 👑
3.4. Variable Parameters for INIT Chunks 🌸
3.4.1. Description of the Problem 🙈
ngl the table in Section 3.3.2 of [RFC4960] is a mess 💀 newlines showing up in the wrong places totally break the layout of the table of variable parameters for the INIT chunk.
this got reported as an errata for [RFC4960] with Errata ID 3291 and Errata ID 3804 🍓
3.4.2. Text Changes to the Document 🎀
here's the messy old table and the cleaned-up new one:
Variable Parameters Status Type Value
-------------------------------------------------------------
IPv4 Address (Note 1) Optional 5 IPv6 Address
(Note 1) Optional 6 Cookie Preservative
Optional 9 Reserved for ECN Capable (Note 2) Optional
32768 (0x8000) Host Name Address (Note 3) Optional
11 Supported Address Types (Note 4) Optional 12---------
New text: (Section 3.3.2)
---------
Variable Parameters Status Type Value
-------------------------------------------------------------
IPv4 Address (Note 1) Optional 5
IPv6 Address (Note 1) Optional 6
Cookie Preservative Optional 9
Reserved for ECN Capable (Note 2) Optional 32768 (0x8000)
Host Name Address (Note 3) Optional 11
Supported Address Types (Note 4) Optional 12this text is in final form and is not further updated in this document ✨ no more edits, we're done here 💅
3.4.3. Solution Description 🧚
the formatting of the table gets fixed. the vibes are restored 🌈
3.5. CRC32c Sample Code on 64-Bit Platforms 💜
3.5.1. Description of the Problem 😭
the CRC32c sample code in [RFC4960] assumes that a variable of type unsigned long uses 32 bits. that's not true on some 64-bit platforms, like the ones that use LP64 🙈 so the code isn't it for them.
this issue was reported as an errata for [RFC4960] with Errata ID 3423 🔥
3.5.2. Text Changes to the Document 🎀
here's the old code next to the new code 👀
unsigned long
generate_crc32c(unsigned char *buffer, unsigned int length)
{
unsigned int i;
unsigned long crc32 = ~0L; unsigned long
generate_crc32c(unsigned char *buffer, unsigned int length)
{
unsigned int i;
unsigned long crc32 = 0xffffffffL;this text has been modified by multiple errata 💀 it's further updated in Section 3.10 and again in Section 3.46, so watch out for those 🧚
3.5.3. Solution Description ✨
the new text uses 0xffffffffL instead of ~0L. that gives the same value whether the platform uses 32 bits or 64 bits for variables of type unsigned long. no cap, that's a clean fix 💅
3.6. Endpoint Failure Detection 🦋
3.6.1. Description of the Problem 🙈
here's the tea ☕ the association error counter handling in Section 8.1 of [RFC4960] can cause an association failure even when the path used for data transmission is available, just idle. that's lowkey unfair 😭
this issue was reported as an errata for [RFC4960] with Errata ID 3788 🍓
3.6.2. Text Changes to the Document 🎀
here's the old rule and the new rule, and the new one is way more refined 💅
---------
Old text: (Section 8.1)
---------
An endpoint shall keep a counter on the total number of consecutive
retransmissions to its peer (this includes retransmissions to all the
destination transport addresses of the peer if it is multi-homed),
including unacknowledged HEARTBEAT chunks.
---------
New text: (Section 8.1)
---------
An endpoint SHOULD keep a counter on the total number of consecutive
retransmissions to its peer (this includes data retransmissions to
all the destination transport addresses of the peer if it is
multi-homed), including the number of unacknowledged HEARTBEAT chunks
observed on the path that is currently used for data transfer.
Unacknowledged HEARTBEAT chunks observed on paths different from the
path currently used for data transfer SHOULD NOT increment the
association error counter, as this could lead to association closure
even if the path that is currently used for data transfer is
available (but idle).this text has been modified by multiple errata 😭 and it's further updated in Section 3.23, so don't forget to check that one 🫶
3.6.3. Solution Description 👑
a more refined handling of the association error counter is defined. main character energy 💅
3.7. Data Transmission Rules 🌈
3.7.1. Description of the Problem 💀
so when the changes to Section 6.1 A) of [RFC2960] got integrated, as described in Section 2.15.2 of [RFC4460], some text got duplicated and ended up as the final paragraph of Section 6.1 A) of [RFC4960]. oops 🙈
this issue was reported as an errata for [RFC4960] with Errata ID 4071 🍓
3.7.2. Text Changes to the Document 🎀
here's the before and after 👀
---------
Old text: (Section 6.1 A))
---------
The sender MUST also have an algorithm for sending new DATA chunks to
avoid silly window syndrome (SWS) as described in [RFC0813]. The
algorithm can be similar to the one described in Section 4.2.3.4 of
[RFC1122].
However, regardless of the value of rwnd (including if it is 0), the
data sender can always have one DATA chunk in flight to the receiver
if allowed by cwnd (see rule B below). This rule allows the sender
to probe for a change in rwnd that the sender missed due to the SACK
having been lost in transit from the data receiver to the data
sender.
---------
New text: (Section 6.1 A))
---------
The sender MUST also have an algorithm for sending new DATA chunks to
avoid silly window syndrome (SWS) as described in [RFC1122]. The
algorithm can be similar to the algorithm described in
Section 4.2.3.4 of [RFC1122].
This text is in final form and is not further updated in this
document.this text is in final form and is not further updated in this document ✨ the duplicate is gone and the citation gets cleaned up 💅
3.7.3. Solution Description 🦋
the last paragraph of Section 6.1 A) is removed, just like was intended in Section 2.15.2 of [RFC4460]. bye bye, duplicate 🫶
3.8. T1-Cookie Timer 🌸
3.8.1. Description of the Problem 🙈
Figure 4 of [RFC4960] shows the SCTP association setup, but it says the T1-init timer runs in the COOKIE-ECHOED state. that's wrong 💀 the T1-cookie timer is the one that belongs there.
this issue was reported as an errata for [RFC4960] with Errata ID 4400 🍓
3.8.2. Text Changes to the Document 🎀
the figure gets a glow-up, so here's the old one and the new one 🦋
---------
Old text: (Section 5.1.6, Figure 4)
---------
COOKIE ECHO [Cookie_Z] ------\
(Start T1-init timer) \
(Enter COOKIE-ECHOED state) \---> (build TCB enter ESTABLISHED
state)
/---- COOKIE-ACK
/
(Cancel T1-init timer, <-----/
Enter ESTABLISHED state)---------
New text: (Section 5.1.6, Figure 4)
---------
COOKIE ECHO [Cookie_Z] ------\
(Start T1-cookie timer) \
(Enter COOKIE-ECHOED state) \---> (build TCB, enter ESTABLISHED
state)
/---- COOKIE-ACK
/
(Cancel T1-cookie timer, <---/
enter ESTABLISHED state)this text has been modified by multiple errata 😭 and it's further updated in Section 3.9, so keep going 🧚
3.8.3. Solution Description ✨
the figure changes so the T1-cookie timer is used instead of the T1-init timer. correct timer, correct vibes 💅👑
3.9. Miscellaneous Typos 💜
3.9.1. Description of the Problem 💀
while processing [RFC4960], a few typos slipped past everyone 🙈 bestie happens to the best of us 🫶
one typo got reported as an errata for [RFC4960] with Errata ID 5003 🍓
3.9.2. Text Changes to the Document ✨
okay bestie, this is the big list of wording fixes 💅 every old and new text is copied exactly, so nothing shifts under anyone's feet 🔒
Old text: (Section 1.6)
Transmission Sequence Numbers wrap around when they reach 2**32 - 1.
That is, the next TSN a DATA chunk MUST use after transmitting TSN =
2*32 - 1 is TSN = 0.New text: (Section 1.6)
Transmission Sequence Numbers wrap around when they reach 2**32 - 1.
That is, the next TSN a DATA chunk MUST use after transmitting
TSN = 2**32 - 1 is TSN = 0.This text is in final form and is not further updated in this document. 🌸
Old text: (Section 3.3.10.9)
No User Data: This error cause is returned to the originator of a
DATA chunk if a received DATA chunk has no user data.New text: (Section 3.3.10.9)
No User Data: This error cause is returned to the originator of a
DATA chunk if a received DATA chunk has no user data.This text is in final form and is not further updated in this document. 🎀
Old text: (Section 6.7, Figure 9)
Endpoint A Endpoint Z {App
sends 3 messages; strm 0} DATA [TSN=6,Strm=0,Seq=2] ----------
-----> (ack delayed) (Start T3-rtx timer)
DATA [TSN=7,Strm=0,Seq=3] --------> X (lost)
DATA [TSN=8,Strm=0,Seq=4] ---------------> (gap detected,
immediately send ack)
/----- SACK [TSN Ack=6,Block=1,
/ Start=2,End=2]
<-----/ (remove 6 from out-queue,
and mark 7 as "1" missing report)New text: (Section 6.7, Figure 9)
Endpoint A Endpoint Z
{App sends 3 messages; strm 0}
DATA [TSN=6,Strm=0,Seq=2] ---------------> (ack delayed)
(Start T3-rtx timer)
DATA [TSN=7,Strm=0,Seq=3] --------> X (lost)
DATA [TSN=8,Strm=0,Seq=4] ---------------> (gap detected,
immediately send ack)
/----- SACK [TSN Ack=6,Block=1,
/ Start=2,End=2]
<-----/
(remove 6 from out-queue,
and mark 7 as "1" missing report)This text is in final form and is not further updated in this document. 🦋
Old text: (Section 6.10)
An endpoint bundles chunks by simply including multiple chunks in one
outbound SCTP packet. The total size of the resultant IP datagram,
including the SCTP packet and IP headers, MUST be less that or equal
to the current Path MTU.New text: (Section 6.10)
An endpoint bundles chunks by simply including multiple chunks in one
outbound SCTP packet. The total size of the resultant IP datagram,
including the SCTP packet and IP headers, MUST be less than or equal
to the current Path MTU (PMTU).This text is in final form and is not further updated in this document. ✨
Old text: (Section 10.1 O))
o Receive Unacknowledged Message
Format: RECEIVE_UNACKED(data retrieval id, buffer address, buffer
size, [,stream id] [, stream sequence number] [,partial
flag] [,payload protocol-id])New text: (Section 10.1 O))
O) Receive Unacknowledged Message
Format: RECEIVE_UNACKED(data retrieval id, buffer address, buffer
size [,stream id] [,stream sequence number] [,partial
flag] [,payload protocol-id])This text is in final form and is not further updated in this document. 💖
Old text: (Section 10.1 M))
M) Set Protocol Parameters
Format: SETPROTOCOLPARAMETERS(association id,
[,destination transport address,]
protocol parameter list)New text: (Section 10.1 M))
M) Set Protocol Parameters
Format: SETPROTOCOLPARAMETERS(association id,
[destination transport address,]
protocol parameter list)This text is in final form and is not further updated in this document. 🧚
Old text: (Appendix C)
ICMP2) An implementation MAY ignore all ICMPv6 messages where the
type field is not "Destination Unreachable", "Parameter
Problem",, or "Packet Too Big".New text: (Appendix C)
ICMP2) An implementation MAY ignore all ICMPv6 messages where the
type field is not "Destination Unreachable", "Parameter
Problem", or "Packet Too Big".This text is in final form and is not further updated in this document. 🌈
Old text: (Appendix C)
ICMP7) If the ICMP message is either a v6 "Packet Too Big" or a v4
"Fragmentation Needed", an implementation MAY process this
information as defined for PATH MTU discovery.New text: (Appendix C)
ICMP7) If the ICMP message is either a v6 "Packet Too Big" or a v4
"Fragmentation Needed", an implementation MAY process this
information as defined for PMTU discovery.This text is in final form and is not further updated in this document. 🫶
Old text: (Section 5.4)
2) For the receiver of the COOKIE ECHO, the only CONFIRMED address
is the one to which the INIT-ACK was sent.New text: (Section 5.4)
2) For the receiver of the COOKIE ECHO, the only CONFIRMED address
is the address to which the INIT ACK was sent.This text is in final form and is not further updated in this document. 🌸
Old text: (Section 5.1.6, Figure 4)
COOKIE ECHO [Cookie_Z] ------\
(Start T1-init timer) \
(Enter COOKIE-ECHOED state) \---> (build TCB enter ESTABLISHED
state)
/---- COOKIE-ACK
/
(Cancel T1-init timer, <-----/
Enter ESTABLISHED state)New text: (Section 5.1.6, Figure 4)
COOKIE ECHO [Cookie_Z] ------\
(Start T1-cookie timer) \
(Enter COOKIE-ECHOED state) \---> (build TCB, enter ESTABLISHED
state)
/---- COOKIE ACK
/
(Cancel T1-cookie timer, <---/
enter ESTABLISHED state)This text has been modified by multiple errata. It includes modifications from Section 3.8. It is in final form and is not further updated in this document. 🔥
Old text: (Section 5.2.5)
5.2.5. Handle Duplicate COOKIE-ACK.New text: (Section 5.2.5)
5.2.5. Handle Duplicate COOKIE ACK.This text is in final form and is not further updated in this document. 💜
Old text: (Section 8.3)
By default, an SCTP endpoint SHOULD monitor the reachability of the
idle destination transport address(es) of its peer by sending a
HEARTBEAT chunk periodically to the destination transport
address(es). HEARTBEAT sending MAY begin upon reaching the
ESTABLISHED state and is discontinued after sending either SHUTDOWN
or SHUTDOWN-ACK. A receiver of a HEARTBEAT MUST respond to a
HEARTBEAT with a HEARTBEAT-ACK after entering the COOKIE-ECHOED state
(INIT sender) or the ESTABLISHED state (INIT receiver), up until
reaching the SHUTDOWN-SENT state (SHUTDOWN sender) or the SHUTDOWN-
ACK-SENT state (SHUTDOWN receiver).New text: (Section 8.3)
By default, an SCTP endpoint SHOULD monitor the reachability of the
idle destination transport address(es) of its peer by sending a
HEARTBEAT chunk periodically to the destination transport
address(es). HEARTBEAT sending MAY begin upon reaching the
ESTABLISHED state and is discontinued after sending either SHUTDOWN
or SHUTDOWN ACK. A receiver of a HEARTBEAT MUST respond to a
HEARTBEAT with a HEARTBEAT ACK after entering the COOKIE-ECHOED state
(INIT sender) or the ESTABLISHED state (INIT receiver), up until
reaching the SHUTDOWN-SENT state (SHUTDOWN sender) or the
SHUTDOWN-ACK-SENT state (SHUTDOWN receiver).This text is in final form and is not further updated in this document. 🙈
3.9.3. Solution Description
Several typos have been fixed. ✨
3.10. CRC32c Sample Code 🌈
3.10.1. Description of the Problem
The CRC32c computation is described in Appendix B of [RFC4960]. However, the corresponding sample code and its explanation appear at the end of Appendix C of [RFC4960], which deals with ICMP handling. 💅
3.10.2. Text Changes to the Document
The text in Appendix C of [RFC4960], starting with the following sentence, needs to be moved to the end of Appendix B.
The following non-normative sample code is taken from an
open-source CRC generator [WILLIAMS93], using the "mirroring"
technique and yielding a lookup table for SCTP CRC32c with
256 entries, each 32 bits wide.This text has been modified by multiple errata. It includes modifications from Section 3.5. It is further updated in Section 3.46. 🦋
3.10.3. Solution Description
The text is moved to the appropriate location. 🎀
3.11. partial_bytes_acked after T3-rtx Expiration 🔥
3.11.1. Description of the Problem
Section 7.2.3 of [RFC4960] explicitly states that partial_bytes_acked should be reset to 0 after packet loss detection from selective acknowledgment (SACK), but this information is not accounted for in the case of T3-rtx timer expiration. 🙈
3.11.2. Text Changes to the Document
Old text: (Section 7.2.3)
When the T3-rtx timer expires on an address, SCTP should perform slow
start by:
ssthresh = max(cwnd/2, 4*MTU)
cwnd = 1*MTUNew text: (Section 7.2.3)
When the T3-rtx timer expires on an address, SCTP SHOULD perform slow
start by:
ssthresh = max(cwnd/2, 4*MTU)
cwnd = 1*MTU
partial_bytes_acked = 0This text is in final form and is not further updated in this document. 🌸
3.11.3. Solution Description
The new text specifies that partial_bytes_acked should be reset to 0 after T3-rtx timer expiration. 💖
3.12. Order of Adjustments of partial_bytes_acked and cwnd 👑
3.12.1. Description of the Problem
Section 7.2.2 of [RFC4960] likely implies the wrong order of adjustments applied to partial_bytes_acked and cwnd in the congestion avoidance phase. 🧚
3.12.2. Text Changes to the Document
Old text: (Section 7.2.2)
o When partial_bytes_acked is equal to or greater than cwnd and
before the arrival of the SACK the sender had cwnd or more bytes
of data outstanding (i.e., before arrival of the SACK, flightsize
was greater than or equal to cwnd), increase cwnd by MTU, and
reset partial_bytes_acked to (partial_bytes_acked - cwnd).New text: (Section 7.2.2)
o (1) when partial_bytes_acked is equal to or greater than cwnd and
(2) before the arrival of the SACK the sender had cwnd or more
bytes of data outstanding (i.e., before the arrival of the SACK,
flightsize was greater than or equal to cwnd), partial_bytes_acked
is reset to (partial_bytes_acked - cwnd). Next, cwnd is increased
by 1*MTU.This text has been modified by multiple errata. It is further updated in Section 3.26. 🌈
3.12.3. Solution Description
The new text defines the exact order of adjustments of partial_bytes_acked and cwnd in the congestion avoidance phase. 💜
3.13. HEARTBEAT ACK and the Association Error Counter ⭐
3.13.1. Description of the Problem ✨
Okay so, [RFC4960] says that when the receiver of a HEARTBEAT ACK gets one, it has to reset the association overall error count, which is in Sections 8.1 and 8.3 🫶. But sometimes that's kinda not ideal. Like, imagine a router that drops DATA chunks but still lets the smaller HEARTBEAT chunks through because DATA chunks are bigger 🙈. If you reset the counter on every HEARTBEAT ACK, the association could get stuck. So the better move might be to not clear the association error counter when a HEARTBEAT ACK comes in, and only reset it when a SACK arrives. That way nothing stalls 💀
3.13.2. Text Changes to the Document 🎀
Here's the before-and-after for Section 8.1 and Section 8.3, copied exactly so nothing gets lost in translation 💅
---------
Old text: (Section 8.1)
---------
The counter shall be reset each time a DATA chunk sent to that peer
endpoint is acknowledged (by the reception of a SACK) or a HEARTBEAT
ACK is received from the peer endpoint.
---------
New text: (Section 8.1)
---------
The counter MUST be reset each time a DATA chunk sent to that peer
endpoint is acknowledged (by the reception of a SACK). When a
HEARTBEAT ACK is received from the peer endpoint, the counter SHOULD
also be reset. The receiver of the HEARTBEAT ACK MAY choose not to
clear the counter if there is outstanding data on the association.
This allows for handling the possible difference in reachability
based on DATA chunks and HEARTBEAT chunks.
This text is in final form and is not further updated in this
document.
---------
Old text: (Section 8.3)
---------
Upon the receipt of the HEARTBEAT ACK, the sender of the HEARTBEAT
should clear the error counter of the destination transport address
to which the HEARTBEAT was sent, and mark the destination transport
address as active if it is not so marked. The endpoint may
optionally report to the upper layer when an inactive destination
address is marked as active due to the reception of the latest
HEARTBEAT ACK. The receiver of the HEARTBEAT ACK must also clear
the association overall error count as well (as defined in Section 8.1).
---------
New text: (Section 8.3)
---------
Upon the receipt of the HEARTBEAT ACK, the sender of the HEARTBEAT
MUST clear the error counter of the destination transport address to
which the HEARTBEAT was sent and mark the destination transport
address as active if it is not so marked. The endpoint MAY
optionally report to the upper layer when an inactive destination
address is marked as active due to the reception of the latest
HEARTBEAT ACK. The receiver of the HEARTBEAT ACK SHOULD also clear
the association overall error count (as defined in Section 8.1).
This text has been modified by multiple errata. It is further
updated in Section 3.23.So the 8.1 text is final and won't be touched again in this doc 🔒, but the 8.3 text got tweaked by a few errata and gets another update in Section 3.23 👀
3.13.3. Solution Description 🦋
The new wording makes it possible to skip resetting the association overall error count when a HEARTBEAT ACK comes in, as long as there are valid reasons to skip it 🧚
3.14. Path for Fast Retransmission 🌸
3.14.1. Description of the Problem
[RFC4960] is super clear about where to retransmit data that timed out when the peer is multi-homed 🙌 but it doesn't say the same thing about fast retransmissions. Hmm, we need that spelled out 🤔
3.14.2. Text Changes to the Document 🍓
---------
Old text: (Section 6.4)
---------
Furthermore, when its peer is multi-homed, an endpoint SHOULD try to
retransmit a chunk that timed out to an active destination transport
address that is different from the last destination address to which
the DATA chunk was sent.
---------
New text: (Section 6.4)
---------
Furthermore, when its peer is multi-homed, an endpoint SHOULD try to
retransmit a chunk that timed out to an active destination transport
address that is different from the last destination address to which
the DATA chunk was sent.
When its peer is multi-homed, an endpoint SHOULD send fast
retransmissions to the same destination transport address to which
the original data was sent. If the primary path has been changed and
the original data was sent to the old primary path before the Fast
Retransmit, the implementation MAY send it to the new primary path.
This text is in final form and is not further updated in this
document.The timed-out retransmission text stays the same, and the new paragraph adds the fast retransmission rules right under it ✨ This bit is final too 💖
3.14.3. Solution Description 💜
The new text makes it clear where fast retransmissions should go 🎯
3.15. Transmittal in Fast Recovery 🌈
3.15.1. Description of the Problem
The Fast Retransmit on Gap Reports algorithm is meant to let only the very first packet go out in the Fast Recovery phase, no matter what cwnd says 🏃♀️ But rule 3) in Section 7.2.4 of [RFC4960] doesn't mention that, so it's missing the clarification 🙄
3.15.2. Text Changes to the Document 🫧
3) If not in Fast Recovery, determine how many of the earliest
(i.e., lowest TSN) DATA chunks marked for retransmission will fit
into a single packet, subject to constraint of the PMTU of
the destination transport address to which the packet is being
sent. Call this value K. Retransmit those K DATA chunks in a
single packet. When a Fast Retransmit is being performed, the
sender SHOULD ignore the value of cwnd and SHOULD NOT delay
retransmission for this single packet.Here's the old version of rule 3), which is the one you get when you read Section 7.2.4 as-is 📜
3) Determine how many of the earliest (i.e., lowest TSN) DATA chunks
marked for retransmission will fit into a single packet, subject
to constraint of the path MTU of the destination transport
address to which the packet is being sent. Call this value K.
Retransmit those K DATA chunks in a single packet. When a Fast
Retransmit is being performed, the sender SHOULD ignore the value
of cwnd and SHOULD NOT delay retransmission for this single
packet.Ah, and the new one starts with "If not in Fast Recovery," which is the whole fix 🙌 This text is final, and it won't get changed again in this document 🔒
3.15.3. Solution Description 🌷
The new text says outright that only the first packet in Fast Recovery gets sent, and that cwnd limits don't apply to it 🚀
3.16. Initial Value of ssthresh 👑
3.16.1. Description of the Problem
The initial value of ssthresh should be set arbitrarily high 📈 Using the peer's advertised receiver window isn't the right move if the peer grows its window after the handshake 🙅♀️ Also, a higher requirement level needs to be used here, because ignoring the advice can lead to performance problems 😬
3.16.2. Text Changes to the Document 🍒
---------
Old text: (Section 7.2.1)
---------
o The initial value of ssthresh MAY be arbitrarily high (for
example, implementations MAY use the size of the receiver
advertised window).
---------
New text: (Section 7.2.1)
---------
o The initial value of ssthresh SHOULD be arbitrarily high (e.g.,
the size of the largest possible advertised window).
This text is in final form and is not further updated in this
document.The old text was softer, and the new one is firmer, with the example now pointing at the largest possible advertised window 🌟 This part is final too 💅
3.16.3. Solution Description 💫
The same initial value suggested in [RFC5681], Section 3.1, is now the one used as the sensible starting point 🎀 The requirement level matches too 🫶
3.17. Automatically CONFIRMED Addresses 🦋
3.17.1. Description of the Problem
The Path Verification procedure of [RFC4960] says that any address the upper layer hands to the sender of the INIT gets automatically CONFIRMED 🔍 But it's not clear whether that covers (1) only the addresses in the request to set up an association, or (2) any addresses the upper layer gives in any request, like in 'Set Primary' 🤷♀️
3.17.2. Text Changes to the Document 🌸
---------
Old text: (Section 5.4)
---------
1) Any address passed to the sender of the INIT by its upper layer
is automatically considered to be CONFIRMED.
---------
New text: (Section 5.4)
---------
1) Any addresses passed to the sender of the INIT by its upper layer
in the request to initialize an association are automatically
considered to be CONFIRMED.
This text is in final form and is not further updated in this
document.The new text narrows it down to the addresses given in the request to initialize an association 🎯 And yep, this one's final too 🔒
3.17.3. Solution Description 🧁
The new text makes it clear that only the addresses the upper layer provides in the request to initialize an association get automatically CONFIRMED ✨
3.18. Only One Packet after Retransmission Timeout 🌙
3.18.1. Description of the Problem
[RFC4960] isn't totally clear about sending data after the T3-rtx timer expires 😵💫 Section 7.2.1 of [RFC4960] doesn't say how many packets can go out after expiry when more than one packet fits in cwnd 🤔 Meanwhile, Section 7.2.3 of [RFC4960] has some non-normative text saying SCTP should make sure no more than one packet is in flight after T3-rtx expiry until it gets acknowledged 📦 Those two bits don't agree with each other, so yeah, inconsistent 💀
3.18.2. Text Changes to the Document 🍓
---------
Old text: (Section 7.2.1)
---------
o The initial cwnd after a retransmission timeout MUST be no more
than 1*MTU.
---------
New text: (Section 7.2.1)
---------
o The initial cwnd after a retransmission timeout MUST be no more
than 1*MTU, and only one packet is allowed to be in flight until
successful acknowledgement.
This text is in final form and is not further updated in this
document.The new version tacks on the one-packet-in-flight rule right after the cwnd limit 🚧 This text is final, so no more changes 💖
3.18.3. Solution Description 🫧
The new text clearly says only one packet can be sent after T3-rtx expiry until it's acknowledged 🙌
3.19. INIT ACK Path for INIT in COOKIE-WAIT State 🧚
3.19.1. Description of the Problem
When an INIT shows up in the COOKIE-WAIT state, [RFC4960] says the INIT ACK should go back to the same destination address the original INIT went to 📨 But [RFC4960] doesn't deal with the case where the upper layer gives several remote IP addresses when it asks for the association to be set up 🤯 If only some of those addresses are supported by the peer, the original INIT's destination might not show up in the incoming INIT at all, and sending the INIT ACK there is pointless 🙃
3.19.2. Text Changes to the Document 🎀
---------
Old text: (Section 5.2.1)
---------
Upon receipt of an INIT in the COOKIE-WAIT state, an endpoint MUST
respond with an INIT ACK using the same parameters it sent in its
original INIT chunk (including its Initiate Tag, unchanged). When
responding, the endpoint MUST send the INIT ACK back to the same
address that the original INIT (sent by this endpoint) was sent.
---------
New text: (Section 5.2.1)
---------
Upon receipt of an INIT in the COOKIE-WAIT state, an endpoint MUST
respond with an INIT ACK using the same parameters it sent in its
original INIT chunk (including its Initiate Tag, unchanged). When
responding, the following rules MUST be applied:
1) The INIT ACK MUST only be sent to an address passed by the upper
layer in the request to initialize the association.
2) The INIT ACK MUST only be sent to an address reported in the
incoming INIT.
3) The INIT ACK SHOULD be sent to the source address of the received
INIT.
This text is in final form and is not further updated in this
document.So now the INIT ACK has to follow the three rules in the new text 📋 The old "send it back to the same address" rule is gone, and this text is final 🔒
3.19.3. Solution Description 🌈
The new text says the INIT ACK has to go to a destination address that the upper layer provided and that also appears in the incoming INIT 💌 If the INIT's source address meets both of those conditions, then sending the INIT ACK to that source address is the preferred move ✨
3.20. Zero Window Probing and Unreachable Primary Path 🌸
3.20.1. Description of the Problem ✨
okay so, Section 6.1 of [RFC4960] says that when SCTP is sending zero window probes, it's supposed to skip bumping the association counter AND the destination address error counter as long as it keeps getting new packets from the peer 💅. ngl that sounds fine until you realize that getting new packets doesn't actually prove the peer is reachable 😭. so if the destination address goes unreachable during zero window probing, SCTP can't get an updated rwnd until it switches the destination address for probes. 💀
3.20.2. Text Changes to the Document 🎀
Here's the before and after 👀
---------
Old text: (Section 6.1 A))
---------
If the sender continues to receive new packets from the receiver
while doing zero window probing, the unacknowledged window probes
should not increment the error counter for the association or any
destination transport address. This is because the receiver MAY keep
its window closed for an indefinite time. Refer to Section 6.2 on
the receiver behavior when it advertises a zero window.
---------
New text: (Section 6.1 A))
---------
If the sender continues to receive SACKs from the peer while doing
zero window probing, the unacknowledged window probes SHOULD NOT
increment the error counter for the association or any destination
transport address. This is because the receiver could keep its
window closed for an indefinite time. Section 6.2 describes the
receiver behavior when it advertises a zero window.This text is in final form and is not further updated in this document.
Wait, the old version said "should not increment" in lowercase and "MAY keep" in caps, and the new version swaps "new packets" for "SACKs" and goes with "SHOULD NOT" in caps. big glow-up energy 🦋
3.20.3. Solution Description 🌸
The new text makes it clear that if the receiver keeps sending SACKs, the sender of the probes should not bump the error counter for the association OR the destination address, even if those SACKs don't acknowledge the probes. no more punishing the path for something that's actually fine 🙌
3.21. Normative Language in Section 10 of RFC 4960 📚
3.21.1. Description of the Problem 🧐
Section 10 of [RFC4960] is informative. Therefore, normative language such as MUST and MAY cannot be used there. However, there are several places in Section 10 of [RFC4960] where MUST and MAY are used. the vibes are a little messy here, bestie 🙈
3.21.2. Text Changes to the Document 🧁
---------
Old text: (Section 10.1 E))
---------
o no-bundle flag - instructs SCTP not to bundle this user data with
other outbound DATA chunks. SCTP MAY still bundle even when this
flag is present, when faced with network congestion.
---------
New text: (Section 10.1 E))
---------
o no-bundle flag - instructs SCTP not to bundle this user data with
other outbound DATA chunks. When faced with network congestion,
SCTP may still bundle the data, even when this flag is present.This text is in final form and is not further updated in this document.
---------
Old text: (Section 10.1 G))
---------
o Stream Sequence Number - the Stream Sequence Number assigned by
the sending SCTP peer.
o partial flag - if this returned flag is set to 1, then this
Receive contains a partial delivery of the whole message. When
this flag is set, the stream id and Stream Sequence Number MUST
accompany this receive. When this flag is set to 0, it indicates
that no more deliveries will be received for this Stream Sequence
Number.
---------
New text: (Section 10.1 G))
---------
o stream sequence number - the Stream Sequence Number assigned by
the sending SCTP peer.
o partial flag - if this returned flag is set to 1, then this
primitive contains a partial delivery of the whole message. When
this flag is set, the stream id and stream sequence number must
accompany this primitive. When this flag is set to 0, it
indicates that no more deliveries will be received for this stream
sequence number.This text is in final form and is not further updated in this document.
---------
Old text: (Section 10.1 N))
---------
o Stream Sequence Number - this value is returned indicating the
Stream Sequence Number that was associated with the message.
o partial flag - if this returned flag is set to 1, then this
message is a partial delivery of the whole message. When this
flag is set, the stream id and Stream Sequence Number MUST
accompany this receive. When this flag is set to 0, it indicates
that no more deliveries will be received for this Stream Sequence
Number.
---------
New text: (Section 10.1 N))
---------
o stream sequence number - this value is returned indicating the
Stream Sequence Number that was associated with the message.
o partial flag - if this returned flag is set to 1, then this
message is a partial delivery of the whole message. When this
flag is set, the stream id and stream sequence number must
accompany this primitive. When this flag is set to 0, it
indicates that no more deliveries will be received for this stream
sequence number.This text is in final form and is not further updated in this document.
---------
Old text: (Section 10.1 O))
---------
o Stream Sequence Number - this value is returned indicating the
Stream Sequence Number that was associated with the message.
o partial flag - if this returned flag is set to 1, then this
message is a partial delivery of the whole message. When this
flag is set, the stream id and Stream Sequence Number MUST
accompany this receive. When this flag is set to 0, it indicates
that no more deliveries will be received for this Stream Sequence
Number.
---------
New text: (Section 10.1 O))
---------
o stream sequence number - this value is returned indicating the
Stream Sequence Number that was associated with the message.
o partial flag - if this returned flag is set to 1, then this
message is a partial delivery of the whole message. When this
flag is set, the stream id and stream sequence number must
accompany this primitive. When this flag is set to 0, it
indicates that no more deliveries will be received for this stream
sequence number.This text is in final form and is not further updated in this document.
3.21.3. Solution Description ✨
The normative language is removed from Section 10, and the consistency of the text is improved too. clean and iconic 👑
3.22. Increase of partial_bytes_acked in Congestion Avoidance 📈
3.22.1. Description of the Problem 🔍
Two issues have been discovered in the text in Section 7.2.2 of [RFC4960] regarding partial_bytes_acked handling:
- If the Cumulative TSN Ack Point is not advanced but the SACK chunk acknowledges new TSNs in the Gap Ack Blocks, these newly acknowledged TSNs are not considered for
partial_bytes_ackedeven though these TSNs were successfully received by the peer. - Duplicate TSNs are not considered in
partial_bytes_ackedeven though they confirm that the DATA chunks were successfully received by the peer.
3.22.2. Text Changes to the Document 🧩
---------
Old text: (Section 7.2.2)
---------
o Whenever cwnd is greater than ssthresh, upon each SACK arrival that
advances the Cumulative TSN Ack Point, increase partial_bytes_acked
by the total number of bytes of all new chunks acknowledged in that
SACK including chunks acknowledged by the new Cumulative TSN Ack and
by Gap Ack Blocks.
---------
New text: (Section 7.2.2)
---------
o Whenever cwnd is greater than ssthresh, upon each SACK arrival,
increase partial_bytes_acked by the total number of bytes of all
new chunks acknowledged in that SACK, including chunks
acknowledged by the new Cumulative TSN Ack, by Gap Ack Blocks,
and by the number of bytes of duplicated chunks reported in
Duplicate TSNs.This text has been modified by multiple errata. It is further updated in Section 3.26.
3.22.3. Solution Description 🦋
In the new text, partial_bytes_acked gets increased by TSNs reported as duplicated, AND by TSNs newly acknowledged in Gap Ack Blocks, even if the Cumulative TSN Ack Point hasn't moved. the counting finally counts everything that actually got through 💖
3.23. Inconsistent Handling of Notifications 🔔
3.23.1. Description of the Problem 🙃
[RFC4960] uses inconsistent normative and non-normative language when describing rules for sending notifications to the upper layer. For example, Section 8.2 of [RFC4960] says that when a destination address becomes inactive due to an unacknowledged DATA chunk or HEARTBEAT chunk, SCTP SHOULD send a notification to the upper layer; however, Section 8.3 of [RFC4960] says that when a destination address becomes inactive due to an unacknowledged HEARTBEAT chunk, SCTP may send a notification to the upper layer.
These inconsistent descriptions need to be corrected. bestie this section is giving "pick a lane" 😭🌈
3.23.2. Text Changes to the Document 💅
Old text (Section 8.1):
okay so the old version says an endpoint shall keep a counter of the total consecutive retransmissions to its peer. That counts retransmissions to every destination transport address of the peer if it's multi-homed, and it includes unacknowledged HEARTBEAT chunks. 🌸
New text (Section 8.1):
this is the glow-up bestie 🦋 An endpoint SHOULD keep a counter of the total consecutive retransmissions to its peer. This counts data retransmissions to all the destination transport addresses of the peer if it's multi-homed, and it includes the number of unacknowledged HEARTBEAT chunks seen on the path that's currently being used for data transfer. Unacknowledged HEARTBEAT chunks on any other path SHOULD NOT increment the association error counter, because that could close the association even while the path doing the data transfer is totally fine (just idle) 🙈 If the value of this counter exceeds the limit in Association.Max.Retrans, the endpoint SHOULD consider the peer endpoint unreachable and SHALL stop transmitting any more data to it, so the association enters the CLOSED state. ✨ The endpoint SHOULD also report the failure to the upper layer and can optionally report back all the outstanding user data still sitting in its outbound queue. The association gets closed automatically when the peer endpoint becomes unreachable.
This text has been modified by multiple errata. It includes modifications from Section 3.6. It is in final form and is not further updated in this document. 🔒
Old text (Section 8.2):
when an outstanding TSN is acknowledged, or a HEARTBEAT sent to that address gets a HEARTBEAT ACK back, the endpoint shall clear the error counter of the destination transport address that the DATA chunk was last sent to (or the HEARTBEAT was sent to). If the peer is multi-homed and the last chunk sent to it was a retransmission to an alternate address, it's unclear whether the acknowledgement should be credited to the address of that last chunk. This doesn't seem to matter much for SCTP behavior, though. If it bugs you, the transmitter may choose not to clear the error counter when the last chunk sent was a retransmission. 🤷♀️
New text (Section 8.2):
okay this one's giving clarity ✨ When an outstanding TSN is acknowledged, or a HEARTBEAT sent to that address is acknowledged with a HEARTBEAT ACK, the endpoint SHOULD clear the error counter of the destination transport address that the DATA chunk was last sent to (or the HEARTBEAT was sent to). It SHOULD also report to the upper layer when an inactive destination address gets marked as active. If the peer is multi-homed and the last chunk sent to it was a retransmission to an alternate address, it's still a bit ambiguous whether the acknowledgement could be credited to the address of that last chunk. But this ambiguity doesn't seem to have significant consequences for SCTP behavior 💅 If it's undesirable, the transmitter MAY choose not to clear the error counter if the last chunk sent was a retransmission.
This text is in final form and is not further updated in this document. 🌈
Old text (Section 8.3):
when the value of this counter reaches the protocol parameter Path.Max.Retrans, the endpoint should mark the corresponding destination address as inactive if it isn't already, and it may also optionally report the change in reachability of that destination address to the upper layer. After that, the endpoint should keep sending HEARTBEAT on this destination address, but it should stop increasing the counter. 🫠
New text (Section 8.3):
this is where it gets spicy 🌶️ When the value of this counter exceeds the protocol parameter Path.Max.Retrans, the endpoint SHOULD mark the corresponding destination address as inactive if it isn't already marked that way, and SHOULD also report the change in reachability of this destination address to the upper layer. After that, the endpoint SHOULD continue HEARTBEAT on this destination address, but SHOULD stop increasing the counter. 💖
This text has been modified by multiple errata. It includes modifications from Section 3.1. It is in final form and is not further updated in this document. 🎀
Old text (Section 8.3):
when a HEARTBEAT ACK comes in, the sender of the HEARTBEAT should clear the error counter of the destination transport address the HEARTBEAT was sent to, and mark that address as active if it isn't already. The endpoint may optionally report to the upper layer when an inactive destination address gets marked as active because of the latest HEARTBEAT ACK. The receiver of the HEARTBEAT ACK must also clear the association overall error count (as defined in Section 8.1). 🧚
New text (Section 8.3):
the HEARTBEAT ACK glow-up 🍓 Upon receipt of the HEARTBEAT ACK, the sender of the HEARTBEAT SHOULD clear the error counter of the destination transport address the HEARTBEAT was sent to, and mark that address as active if it isn't already marked that way. The endpoint SHOULD report to the upper layer when an inactive destination address is marked as active due to the reception of the latest HEARTBEAT ACK. The receiver of the HEARTBEAT ACK SHOULD also clear the association overall error count (as defined in Section 8.1). ✨
This text has been modified by multiple errata. It includes modifications from Section 3.13. It is in final form and is not further updated in this document. 🌸
Old text (Section 9.2):
an endpoint should limit the number of retransmissions of the SHUTDOWN chunk to the protocol parameter Association.Max.Retrans. If that threshold is exceeded, the endpoint should destroy the TCB and MUST report the peer endpoint unreachable to the upper layer (and the association enters the CLOSED state). 💀
New text (Section 9.2):
okay the SHUTDOWN chunk needs boundaries too 👑 An endpoint SHOULD limit the number of retransmissions of the SHUTDOWN chunk to the protocol parameter Association.Max.Retrans. If that threshold is exceeded, the endpoint SHOULD destroy the TCB and SHOULD report the peer endpoint unreachable to the upper layer (and the association enters the CLOSED state).
This text is in final form and is not further updated in this document. 🔒
Old text (Section 9.2):
the sender of the SHUTDOWN ACK should limit the number of retransmissions of the SHUTDOWN ACK chunk to the protocol parameter Association.Max.Retrans. If that threshold is exceeded, the endpoint should destroy the TCB and may report the peer endpoint unreachable to the upper layer (and the association enters the CLOSED state). 🫶
New text (Section 9.2):
same energy for the SHUTDOWN ACK 💅 The sender of the SHUTDOWN ACK SHOULD limit the number of retransmissions of the SHUTDOWN ACK chunk to the protocol parameter Association.Max.Retrans. If that threshold is exceeded, the endpoint SHOULD destroy the TCB and SHOULD report the peer endpoint unreachable to the upper layer (and the association enters the CLOSED state).
This text is in final form and is not further updated in this document. 🦋
3.23.3. Solution Description ✨
The inconsistencies get cleared up by consistently using SHOULD. Simple, iconic, done 💖
3.24. SACK.Delay Not Listed as a Protocol Parameter 🎀
3.24.1. Description of the Problem 🧐
SCTP as specified in [RFC4960] supports delaying SACKs. The timer value for this is a parameter, and Section 6.2 of [RFC4960] gives it a default and a maximum value. However, two things are missing: (1) a name for this parameter, and (2) an entry for it in the table of protocol parameters in Section 15 of [RFC4960]. Not great, not terrible, just lowkey messy 😭
This issue was reported as an errata for [RFC4960] with Errata ID 4656. 📝
3.24.2. Text Changes to the Document 💅
Old text (Section 6.2):
An implementation MUST NOT allow the maximum delay to be configured
to be more than 500 ms. In other words, an implementation MAY lower
this value below 500 ms but MUST NOT raise it above 500 ms.New text (Section 6.2):
now the maximum delay has a name, and it's SACK.Delay 🧚 An implementation MUST NOT allow the maximum delay (protocol parameter SACK.Delay) to be configured to be more than 500 ms. In other words, an implementation MAY lower the value of SACK.Delay below 500 ms, but MUST NOT raise it above 500 ms.
This text is in final form and is not further updated in this document. 🔒
Old text (Section 15):
The following protocol parameters are RECOMMENDED:
RTO.Initial - 3 seconds
RTO.Min - 1 second
RTO.Max - 60 seconds
Max.Burst - 4
RTO.Alpha - 1/8
RTO.Beta - 1/4
Valid.Cookie.Life - 60 seconds
Association.Max.Retrans - 10 attempts
Path.Max.Retrans - 5 attempts (per destination address)
Max.Init.Retransmits - 8 attempts
HB.interval - 30 seconds
HB.Max.Burst - 1New text (Section 15):
the list of protocol parameters is getting its missing bestie 📋
The following protocol parameters are RECOMMENDED:
RTO.Initial: 3 seconds
RTO.Min: 1 second
RTO.Max: 60 seconds
Max.Burst: 4
RTO.Alpha: 1/8
RTO.Beta: 1/4
Valid.Cookie.Life: 60 seconds
Association.Max.Retrans: 10 attempts
Path.Max.Retrans: 5 attempts (per destination address)
Max.Init.Retransmits: 8 attempts
HB.interval: 30 seconds
HB.Max.Burst: 1
SACK.Delay: 200 millisecondsThis text has been modified by multiple errata. It is further updated in Section 3.32. 🌈
3.24.3. Solution Description ✨
The parameter gets the name SACK.Delay and is added to the list of protocol parameters. Finally, it's on the list 🎉
3.25. Processing of Chunks in an Incoming SCTP Packet 🍓
3.25.1. Description of the Problem 🧐
There are a few places in [RFC4960] where the text says the receiver of a packet must discard it while processing the packet's chunks. It's unclear whether the receiver has to roll back any state changes it already made while processing that packet 🙈
The intention of [RFC4960] is to process an incoming packet chunk by chunk, without any prescreening of the chunks in the received packet. So if the receiver discards one chunk, it also ends up discarding every chunk after it. Main character energy for the first chunk, but the rest get ghosted 👻
3.25.2. Text Changes to the Document ✨
okay bestie, here's the before-and-after for the chunk-handling text 💅
Old text (Section 3.2):
00 - Stop processing this SCTP packet and discard it, do not
process any further chunks within it.
01 - Stop processing this SCTP packet and discard it, do not
process any further chunks within it, and report the
unrecognized chunk in an 'Unrecognized Chunk Type'.New text (Section 3.2): 🎀
00 - Stop processing this SCTP packet; discard the unrecognized
chunk and all further chunks.
01 - Stop processing this SCTP packet, discard the unrecognized
chunk and all further chunks, and report the unrecognized
chunk in an 'Unrecognized Chunk Type'.This text is in final form and is not further updated in this document. 🔒
Old text (Section 11.3): 🙈
It is helpful for some firewalls if they can inspect just the first
fragment of a fragmented SCTP packet and unambiguously determine
whether it corresponds to an INIT chunk (for further information,
please refer to [RFC1858]). Accordingly, we stress the requirements,
stated in Section 3.1, that (1) an INIT chunk MUST NOT be bundled
with any other chunk in a packet, and (2) a packet containing an INIT
chunk MUST have a zero Verification Tag. Furthermore, we require
that the receiver of an INIT chunk MUST enforce these rules by
silently discarding an arriving packet with an INIT chunk that is
bundled with other chunks or has a non-zero verification tag and
contains an INIT-chunk.New text (Section 11.3): 🌸
It is helpful for some firewalls if they can inspect just the first
fragment of a fragmented SCTP packet and unambiguously determine
whether it corresponds to an INIT chunk (for further information,
please refer to [RFC1858]). Accordingly, we stress the requirements,
as stated in Section 3.1, that (1) an INIT chunk MUST NOT be bundled
with any other chunk in a packet and (2) a packet containing an INIT
chunk MUST have a zero Verification Tag. The receiver of an INIT
chunk MUST silently discard the INIT chunk and all further chunks if
the INIT chunk is bundled with other chunks or the packet has a
non-zero Verification Tag.This text is in final form and is not further updated in this document.
3.25.3. Solution Description 🧚
the new wording makes it crystal clear that chunks get processed from beginning to end, and that there's no rollback or prescreening needed. no backtracking, no drama 🙌
3.26. Increasing the cwnd in the Congestion Avoidance Phase
3.26.1. Description of the Problem 🦋
okay so [RFC4960] says cwnd goes up by 1*MTU per RTT when the sender has cwnd or more bytes outstanding to that address during congestion avoidance (Section 7.2.2). the catch? it's written without normative language 🙃. and the algorithm in Section 7.2.2 of [RFC4960] is underspecified, which means it actually lets cwnd grow by more than 1*MTU per RTT. not iconic behaviour, ngl 💀
3.26.2. Text Changes to the Document 💖
Old text (Section 7.2.2):
When cwnd is greater than ssthresh, cwnd should be incremented by
1*MTU per RTT if the sender has cwnd or more bytes of data
outstanding for the corresponding transport address.New text (Section 7.2.2): ✨
When cwnd is greater than ssthresh, cwnd SHOULD be incremented by
1*MTU per RTT if the sender has cwnd or more bytes of data
outstanding for the corresponding transport address. The basic
guidelines for incrementing cwnd during congestion avoidance are as
follows:
o SCTP MAY increment cwnd by 1*MTU.
o SCTP SHOULD increment cwnd by 1*MTU once per RTT when the sender
has cwnd or more bytes of data outstanding for the corresponding
transport address.
o SCTP MUST NOT increment cwnd by more than 1*MTU per RTT.This text is in final form and is not further updated in this document. 🔒
Old text (Section 7.2.2): 🥺
o Whenever cwnd is greater than ssthresh, upon each SACK arrival
that advances the Cumulative TSN Ack Point, increase
partial_bytes_acked by the total number of bytes of all new chunks
acknowledged in that SACK including chunks acknowledged by the new
Cumulative TSN Ack and by Gap Ack Blocks.
o When partial_bytes_acked is equal to or greater than cwnd and
before the arrival of the SACK the sender had cwnd or more bytes
of data outstanding (i.e., before arrival of the SACK, flightsize
was greater than or equal to cwnd), increase cwnd by MTU, and
reset partial_bytes_acked to (partial_bytes_acked - cwnd).New text (Section 7.2.2): 💅
o Whenever cwnd is greater than ssthresh, upon each SACK arrival,
increase partial_bytes_acked by the total number of bytes of all
new chunks acknowledged in that SACK, including chunks
acknowledged by the new Cumulative TSN Ack, by Gap Ack Blocks,
and by the number of bytes of duplicated chunks reported in
Duplicate TSNs.
o (1) when partial_bytes_acked is greater than cwnd and (2) before
the arrival of the SACK the sender had less than cwnd bytes of
data outstanding (i.e., before the arrival of the SACK, flightsize
was less than cwnd), reset partial_bytes_acked to cwnd.
o (1) when partial_bytes_acked is equal to or greater than cwnd and
(2) before the arrival of the SACK the sender had cwnd or more
bytes of data outstanding (i.e., before the arrival of the SACK,
flightsize was greater than or equal to cwnd), partial_bytes_acked
is reset to (partial_bytes_acked - cwnd). Next, cwnd is increased
by 1*MTU.This text has been modified by multiple errata. It includes modifications from Sections 3.12 and 3.22. It is in final form and is not further updated in this document.
3.26.3. Solution Description 🌈
the basic guidelines for growing cwnd during congestion avoidance got added into Section 7.2.2, with the normative language included and lined up with [RFC5681] 🎯. the algorithm from Section 7.2.2 also got improved, so it now doesn't let cwnd jump by more than 1*MTU per RTT. chef's kiss 👑
3.27. Refresh of cwnd and ssthresh after Idle Period
3.27.1. Description of the Problem 😭
so [RFC4960] says cwnd gets adjusted per RTO when the endpoint isn't sending data on a transport address. on top of that, it says cwnd goes back to the initial value after a long enough idle period. honestly that's excessive 🙄, and "sufficiently long" is super vague too.
[RFC4960] also doesn't say what happens to ssthresh when idle. if ssthresh gets lowered because of packet loss, it never recovers 💔. so traffic can end up stuck in congestion avoidance forever, which means a low sending rate and bad performance. it's even worse for SCTP: in a multi-homed association, traffic that switches back to the old primary path that had failed also ends up stuck in congestion avoidance 😩.
3.27.2. Text Changes to the Document 🎀
Old text (Section 7.2.1):
o The initial cwnd before DATA transmission or after a sufficiently
long idle period MUST be set to min(4*MTU, max (2*MTU, 4380
bytes)).New text (Section 7.2.1): 🌷
o The initial cwnd before data transmission MUST be set to
min(4*MTU, max (2*MTU, 4380 bytes)).Old text (Section 7.2.1): 🍓
o When the endpoint does not transmit data on a given transport
address, the cwnd of the transport address should be adjusted to
max(cwnd/2, 4*MTU) per RTO.New text (Section 7.2.1): 🦋
o While the endpoint does not transmit data on a given transport
address, the cwnd of the transport address SHOULD be adjusted to
max(cwnd/2, 4*MTU) once per RTO. Before the first cwnd
adjustment, the ssthresh of the transport address SHOULD be set to
the cwnd.This text is in final form and is not further updated in this document.
3.27.3. Solution Description 🧠
the rule about adjusting cwnd after a sufficiently long idle period is gone 🗑️. the text now covers ssthresh too. when the idle period is detected, the cwnd value gets copied into ssthresh. no more getting stuck in congestion avoidance forever 🫶
3.28. Window Updates after Receiver Window Opens Up
3.28.1. Description of the Problem 🌟
the sending of SACK chunks for window updates is only indirectly mentioned in Section 6.2 of [RFC4960]. that section says an SCTP receiver must not generate more than one SACK for every incoming packet, other than to update the offered window 🤏.
but to avoid performance problems, window updates need to get sent when the receiver window opens up 🪟.
3.28.2. Text Changes to the Document 💜
Old text (Section 6.2):
An SCTP receiver MUST NOT generate more than one SACK for every
incoming packet, other than to update the offered window as the
receiving application consumes new data.New text (Section 6.2): ✨
An SCTP receiver MUST NOT generate more than one SACK for every
incoming packet, other than to update the offered window as the
receiving application consumes new data. When the window opens up,
an SCTP receiver SHOULD send additional SACK chunks to update the
window even if no new data is received. The receiver MUST avoid
sending a large number of window updates -- in particular, large
bursts of them. One way to achieve this is to send a window update
only if the window can be increased by at least a quarter of the
receive buffer size of the association.This text is in final form and is not further updated in this document.
3.28.3. Solution Description 🍭
the new text makes it clear that extra SACK chunks for window updates are totally fine to send, as long as they don't turn into excessive bursts 🌊.
3.29. Path of DATA and Reply Chunks
3.29.1. Description of the Problem 🤔
Section 6.4 of [RFC4960] describes the transmission policy for multi-homed SCTP endpoints. but this policy has a couple of issues 😬:
- It states that a SACK should be sent to the source address of an incoming DATA. however, other SACK policies (e.g., always sending SACKs to the primary path) are known to be more beneficial in some situations 🫠.
- Also, it initially states that an endpoint should always transmit DATA chunks to the primary path, but then says the rule for transmitting reply chunks should also be followed if the endpoint is bundling DATA chunks together with the reply chunk. that second statement contradicts the first one 🙃. some implementations had problems with it and sent DATA chunks bundled with reply chunks to a different destination address than the primary path, which caused many gaps 🕳️.
3.29.2. Text Changes to the Document
okay so the reply-chunk rules in Section 6.4 get a full glow-up 💅 The old version said reply chunks SHOULD go back to the same address the DATA or control chunk came from, and it also covered bundling. The new version narrows that rule to control chunks like INIT ACK, COOKIE ACK, and HEARTBEAT ACK. SACK gets its own vibe: the destination is implementation dependent, with a SHOULD NOT against changing it for DATA from one source address. And when one SACK acknowledges DATA from different source addresses, it MAY go to any of the addresses those chunks came from 🦋
---------
Old text: (Section 6.4)
---------
An endpoint SHOULD transmit reply chunks (e.g., SACK, HEARTBEAT ACK,
etc.) to the same destination transport address from which it
received the DATA or control chunk to which it is replying. This
rule should also be followed if the endpoint is bundling DATA chunks
together with the reply chunk.
However, when acknowledging multiple DATA chunks received in packets
from different source addresses in a single SACK, the SACK chunk may
be transmitted to one of the destination transport addresses from
which the DATA or control chunks being acknowledged were received.
---------
New text: (Section 6.4)
---------
An endpoint SHOULD transmit reply chunks (e.g., INIT ACK, COOKIE ACK,
HEARTBEAT ACK) in response to control chunks to the same destination
transport address from which it received the control chunk to which
it is replying.
The selection of the destination transport address for packets
containing SACK chunks is implementation dependent. However, an
endpoint SHOULD NOT vary the destination transport address of a SACK
when it receives DATA chunks coming from the same source address.
When acknowledging multiple DATA chunks received in packets from
different source addresses in a single SACK, the SACK chunk MAY be
transmitted to one of the destination transport addresses from which
the DATA or control chunks being acknowledged were received.
This text is in final form and is not further updated in this
document.3.29.3. Solution Description
The SACK sending policy is still implementation dependent, but the new text says the policy should not change the destination address of a packet with a SACK chunk unless there's a good reason, because switching addresses can mess up RTT measurement 🍓 The confusing line about bundling DATA with reply chunks is gone too.
3.30. "Outstanding Data", "Flightsize", and "Data in Flight" Key Terms
3.30.1. Description of the Problem
[RFC4960] uses the key terms "outstanding data", "flightsize", and "data in flight" in its formulas and statements, but Section 1.3 ("Key Terms") of [RFC4960] never actually defines them 🙈 Worse, outstanding data doesn't include DATA chunks that have been classified as lost but haven't been retransmitted yet, and one paragraph in Section 6.1 of [RFC4960] contradicts that. Not it 💀
3.30.2. Text Changes to the Document
---------
Old text: (Section 1.3)
---------
o Congestion window (cwnd): An SCTP variable that limits the data,
in number of bytes, a sender can send to a particular destination
transport address before receiving an acknowledgement.
...
o Outstanding TSN (at an SCTP endpoint): A TSN (and the associated
DATA chunk) that has been sent by the endpoint but for which it
has not yet received an acknowledgement.
---------
New text: (Section 1.3)
---------
o Congestion window (cwnd): An SCTP variable that limits outstanding
data, in number of bytes, that a sender can send to a particular
destination transport address before receiving an acknowledgement.
...
o Flightsize: The amount of bytes of outstanding data to a
particular destination transport address at any given time.
...
o Outstanding data (or "data outstanding" or "data in flight"): The
total amount of the DATA chunks associated with outstanding TSNs.
A retransmitted DATA chunk is counted once in outstanding data. A
DATA chunk that is classified as lost but that has not yet been
retransmitted is not in outstanding data.
o Outstanding TSN (at an SCTP endpoint): A TSN (and the associated
DATA chunk) that has been sent by the endpoint but for which it
has not yet received an acknowledgement.
This text is in final form and is not further updated in this
document.
---------
Old text: (Section 6.1)
---------
C) When the time comes for the sender to transmit, before sending new
DATA chunks, the sender MUST first transmit any outstanding DATA
chunks that are marked for retransmission (limited by the current
cwnd).
---------
New text: (Section 6.1)
---------
C) When the time comes for the sender to transmit, before sending new
DATA chunks, the sender MUST first transmit any DATA chunks that
are marked for retransmission (limited by the current cwnd).
This text is in final form and is not further updated in this
document.3.30.3. Solution Description
Section 1.3 now actually explains "outstanding data", "data in flight", and "flightsize" 🎀 Section 6.1 also drops the word "outstanding" in "any outstanding DATA chunks", so it now says "any DATA chunks" instead.
3.31. Degradation of cwnd due to Max.Burst
3.31.1. Description of the Problem
Some implementations were seeing their cwnd degrade because of the Max.Burst limit 😭 That came from reading the suggestion in Section 6.1 of [RFC4960] the wrong way when working out how many packets to send.
3.31.2. Text Changes to the Document
---------
Old text: (Section 6.1)
---------
D) When the time comes for the sender to transmit new DATA chunks,
the protocol parameter Max.Burst SHOULD be used to limit the
number of packets sent. The limit MAY be applied by adjusting
cwnd as follows:
if((flightsize + Max.Burst*MTU) < cwnd) cwnd = flightsize +
Max.Burst*MTU
Or it MAY be applied by strictly limiting the number of packets
emitted by the output routine.
---------
New text: (Section 6.1)
---------
D) When the time comes for the sender to transmit new DATA chunks,
the protocol parameter Max.Burst SHOULD be used to limit the
number of packets sent. The limit MAY be applied by adjusting
cwnd temporarily, as follows:
if ((flightsize + Max.Burst*MTU) < cwnd)
cwnd = flightsize + Max.Burst*MTU
Or, it MAY be applied by strictly limiting the number of packets
emitted by the output routine. When calculating the number of
packets to transmit, and particularly when using the formula
above, cwnd SHOULD NOT be changed permanently.
This text is in final form and is not further updated in this
document.3.31.3. Solution Description
The new text makes it clear that cwnd shouldn't be changed while applying the Max.Burst limit ✨ That cuts down on packet bursts triggered by receiving SACK chunks, but it doesn't touch bursts from an application sending a flood of user messages 🌸
3.32. Reduction of RTO.Initial
3.32.1. Description of the Problem
[RFC4960] uses 3 seconds as the default RTO.Initial, following Section 4.2.3.1 of [RFC1122] 🕰️ [RFC6298] updates [RFC1122] and drops the initial retransmission timer value from 3 seconds to 1 second.
3.32.2. Text Changes to the Document
---------
Old text: (Section 15)
---------
The following protocol parameters are RECOMMENDED:
RTO.Initial - 3 seconds
RTO.Min - 1 second
RTO.Max - 60 seconds
Max.Burst - 4
RTO.Alpha - 1/8
RTO.Beta - 1/4
Valid.Cookie.Life - 60 seconds
Association.Max.Retrans - 10 attempts
Path.Max.Retrans - 5 attempts (per destination address)
Max.Init.Retransmits - 8 attempts
HB.interval - 30 seconds
HB.Max.Burst - 1
---------
New text: (Section 15)
---------
The following protocol parameters are RECOMMENDED:
RTO.Initial: 1 second
RTO.Min: 1 second
RTO.Max: 60 seconds
Max.Burst: 4
RTO.Alpha: 1/8
RTO.Beta: 1/4
Valid.Cookie.Life: 60 seconds
Association.Max.Retrans: 10 attempts
Path.Max.Retrans: 5 attempts (per destination address)
Max.Init.Retransmits: 8 attempts
HB.interval: 30 seconds
HB.Max.Burst: 1
SACK.Delay: 200 milliseconds
This text has been modified by multiple errata. It includes
modifications from Section 3.24. It is in final form and is not
further updated in this document.3.32.3. Solution Description
RTO.Initial is now 1 second, which lines up with [RFC6298] and is totally on-trend 🦋
3.33. Ordering of Bundled SACK and ERROR Chunks
3.33.1. Description of the Problem
When an SCTP endpoint gets a DATA chunk with an invalid stream identifier, it shall acknowledge that chunk with a SACK chunk and also say the stream identifier was invalid by sending an ERROR chunk 📦 Those two can be bundled. But when they are, [RFC4960] requires the ERROR chunk to come after the SACK chunk. That ordering rule isn't necessary, and it could get in the way of interoperability 🙄
3.33.2. Text Changes to the Document
---------
Old text: (Section 6.5)
---------
Every DATA chunk MUST carry a valid stream identifier. If an
endpoint receives a DATA chunk with an invalid stream identifier, it
shall acknowledge the reception of the DATA chunk following the
normal procedure, immediately send an ERROR chunk with cause set to
"Invalid Stream Identifier" (see Section 3.3.10), and discard the
DATA chunk. The endpoint may bundle the ERROR chunk in the same
packet as the SACK as long as the ERROR follows the SACK.
---------
New text: (Section 6.5)
---------
Every DATA chunk MUST carry a valid stream identifier. If an
endpoint receives a DATA chunk with an invalid stream identifier, it
SHOULD acknowledge the reception of the DATA chunk following the
normal procedure, immediately send an ERROR chunk with cause set to
"Invalid Stream Identifier" (see Section 3.3.10), and discard the
DATA chunk. The endpoint MAY bundle the ERROR chunk and the SACK
chunk in the same packet.
This text is in final form and is not further updated in this
document.3.33.3. Solution Description
The pointless rule about the order of the SACK and ERROR chunks has been removed 🎉
3.34. Undefined Parameter Returned by RECEIVE Primitive
3.34.1. Description of the Problem
[RFC4960] describes an abstract API 🧩 Its RECEIVE primitive mentions an optional parameter called "delivery number". But [RFC4960] never defines that parameter, and it isn't needed anyway.
3.34.2. Text Changes to the Document
---------
Old text: (Section 10.1 G))
---------
G) Receive
Format: RECEIVE(association id, buffer address, buffer size
[,stream id])
-> byte count [,transport address] [,stream id] [,stream sequence
number] [,partial flag] [,delivery number] [,payload protocol-id]
---------
New text: (Section 10.1 G))
---------
G) Receive
Format: RECEIVE(association id, buffer address, buffer size
[,stream id])
-> byte count [,transport address] [,stream id] [,stream sequence
number] [,partial flag] [,payload protocol-id]
This text is in final form and is not further updated in this
document.3.34.3. Solution Description
The undefined parameter is gone, and the RECEIVE line is cleaner for it 💜
3.35. DSCP Changes
3.35.1. Description of the Problem 💅
Okay so the upper layer is allowed to change the Differentiated Services Code Point (DSCP) on the packets it sends 🦋. Here's the tea: changing the DSCP can drop packets into different queues along the path, so congestion control should be initialized when the upper layer does this. [RFC4960] doesn't say this, which is literally why this section exists 🙈
3.35.2. Text Changes to the Document 🎀
Here's the glow-up for the text 💖
---------
New text: (Section 7.2.5)
---------
7.2.5. Making Changes to Differentiated Services Code Points
SCTP implementations MAY allow an application to configure the
Differentiated Services Code Point (DSCP) used for sending
packets. If a DSCP change might result in outgoing packets being
queued in different queues, the congestion control parameters for
all affected destination addresses MUST be reset to their initial
values.Locked in and final 🔒 this document won't touch this text again.
---------
Old text: (Section 10.1 M))
---------
Mandatory attributes:
o association id - local handle to the SCTP association.
o protocol parameter list - the specific names and values of the
protocol parameters (e.g., Association.Max.Retrans; see
Section 15) that the SCTP user wishes to customize.---------
New text: (Section 10.1 M))
---------
Mandatory attributes:
o association id - local handle to the SCTP association.
o protocol parameter list - the specific names and values of the
protocol parameters (e.g., Association.Max.Retrans (see
Section 15), or other parameters like the DSCP) that the SCTP user
wishes to customize.This one's final too 🌸 no more edits from this document.
3.35.3. Solution Description ✨
We added text that spells out the required action for DSCP changes 🎀
3.36. Inconsistent Handling of ICMPv4 and ICMPv6 Messages 🧚
3.36.1. Description of the Problem
Appendix C of [RFC4960] covers how ICMPv4 and ICMPv6 messages get handled 🫶. But the handling of ICMP messages that say the port number is unreachable (the enumerated procedures) doesn't match what [RFC4960] says after those procedures. Even worse, the text spells out what to do with ICMPv6 reachability problems but says nothing about the matching ICMPv4 packets 😭
3.36.2. Text Changes to the Document 💜
---------
Old text: (Appendix C)
---------
ICMP3) An implementation MAY ignore any ICMPv4 messages where the
code does not indicate "Protocol Unreachable" or
"Fragmentation Needed".---------
New text: (Appendix C)
---------
ICMP3) An implementation SHOULD ignore any ICMP messages where the
code indicates "Port Unreachable".Final form, no further updates in this document 🔒
---------
Old text: (Appendix C)
---------
ICMP9) If the ICMPv6 code is "Destination Unreachable", the
implementation MAY mark the destination into the unreachable
state or alternatively increment the path error counter.---------
New text: (Appendix C)
---------
ICMP9) If the ICMP type is "Destination Unreachable", the
implementation MAY move the destination to the unreachable
state or, alternatively, increment the path error counter.This one has been through multiple errata 🌈 and it gets another update in Section 3.37.
3.36.3. Solution Description 🍓
We rewrote the third rule so it describes the intended handling of ICMP messages that say the port number is unreachable 💅. We also took out the ICMPv6-only limit from the ninth rule, so it covers ICMP in general now 👑
3.37. Handling of Soft Errors 🌷
3.37.1. Description of the Problem
[RFC1122] defines how soft errors and hard errors are handled for TCP 📚. Appendix C of [RFC4960] only deals with hard errors 🙄
3.37.2. Text Changes to the Document 🩷
---------
Old text: (Appendix C)
---------
ICMP9) If the ICMPv6 code is "Destination Unreachable", the
implementation MAY mark the destination into the unreachable
state or alternatively increment the path error counter.---------
New text: (Appendix C)
---------
ICMP9) If the ICMP type is "Destination Unreachable", the
implementation MAY move the destination to the unreachable
state or, alternatively, increment the path error counter.
SCTP MAY provide information to the upper layer indicating
the reception of ICMP messages when reporting a network status
change.This has been through multiple errata too 🫧 It includes the changes from Section 3.36. It's in final form and this document won't update it again.
3.37.3. Solution Description 🎀
We added text that lets SCTP tell the application about soft errors 🔥
3.38. Honoring cwnd 🌙
3.38.1. Description of the Problem
When SCTP uses slow start, it only grows the congestion window when the window is fully used 😤. SCTP sends DATA chunks and doesn't use the congestion window to fragment user messages, so some overbooking of the congestion window has to be allowed 🍓
3.38.2. Text Changes to the Document 💅
---------
Old text: (Section 6.1)
---------
B) At any given time, the sender MUST NOT transmit new data to a
given transport address if it has cwnd or more bytes of data
outstanding to that transport address.---------
New text: (Section 6.1)
---------
B) At any given time, the sender MUST NOT transmit new data to a
given transport address if it has cwnd + (PMTU - 1) or more bytes
of data outstanding to that transport address. If data is
available, the sender SHOULD exceed cwnd by up to (PMTU - 1) bytes
on a new data transmission if the flightsize does not currently
reach cwnd. The breach of cwnd MUST constitute one packet only.This text is final and won't be updated again in this document 🔒
---------
Old text: (Section 7.2.1)
---------
o Whenever cwnd is greater than zero, the endpoint is allowed to
have cwnd bytes of data outstanding on that transport address.---------
New text: (Section 7.2.1)
---------
o Whenever cwnd is greater than zero, the endpoint is allowed to
have cwnd bytes of data outstanding on that transport address. A
limited overbooking as described in Section 6.1 B) SHOULD be
supported.Also final, no more changes in this document 💖
3.38.3. Solution Description ✨
We added text to clarify how the cwnd limit should be handled 🦋
3.39. Zero Window Probing 🧸
3.39.1. Description of the Problem
The text in Section 6.1 of [RFC4960] about zero window probing doesn't clearly cover the case where the window isn't zero but is too small for the next DATA chunk to be sent 😵💫. Even then, zero window probing has to happen to avoid deadlocks 💀
3.39.2. Text Changes to the Document 🌈
---------
Old text: (Section 6.1)
---------
A) At any given time, the data sender MUST NOT transmit new data to
any destination transport address if its peer's rwnd indicates
that the peer has no buffer space (i.e., rwnd is 0; see Section
6.2.1). However, regardless of the value of rwnd (including if it
is 0), the data sender can always have one DATA chunk in flight to
the receiver if allowed by cwnd (see rule B, below). This rule
allows the sender to probe for a change in rwnd that the sender
missed due to the SACK's having been lost in transit from the data
receiver to the data sender.
When the receiver's advertised window is zero, this probe is
called a zero window probe. Note that a zero window probe SHOULD
only be sent when all outstanding DATA chunks have been
cumulatively acknowledged and no DATA chunks are in flight. Zero
window probing MUST be supported.---------
New text: (Section 6.1)
---------
A) At any given time, the data sender MUST NOT transmit new data to
any destination transport address if its peer's rwnd indicates
that the peer has no buffer space (i.e., rwnd is smaller than the
size of the next DATA chunk; see Section 6.2.1). However,
regardless of the value of rwnd (including if it is 0), the data
sender can always have one DATA chunk in flight to the receiver
if allowed by cwnd (see rule B, below). This rule allows the
sender to probe for a change in rwnd that the sender missed
due to the SACK's having been lost in transit from the data
receiver to the data sender.
When the receiver has no buffer space, this probe is called a
zero window probe. Note that a zero window probe SHOULD only be
sent when all outstanding DATA chunks have been cumulatively
acknowledged and no DATA chunks are in flight. Zero window
probing MUST be supported.This text is final and won't be updated again in this document 🔒
3.39.3. Solution Description 🌸
The terminology is cleaner now 🧚
3.40. Updating References regarding ECN 💜
3.40.1. Description of the Problem
For Explicit Congestion Notification (ECN), [RFC4960] only refers to [RFC3168], and [RFC8311] has since updated that one 📌. So whenever the text talks about ECN, it needs to say so too 🫶
3.40.2. Text Changes to the Document 🦋
Okay, bestie, time for the ECN glow-up 💅 Here's the before and after.
Old text (Appendix A): ECN [RFC3168] describes a proposed extension to IP that details a method to become aware of congestion outside of datagram loss.
New text (Appendix A): ECN as specified in [RFC3168] (updated by [RFC8311]) describes an extension to IP that details a method for becoming aware of congestion outside of datagram loss.
This text is in final form and isn't updated again in this document 🔒
Old text (Appendix A): In general, [RFC3168] should be followed with the following exceptions.
New text (Appendix A): In general, [RFC3168] (updated by [RFC8311]) SHOULD be followed, with the following exceptions.
This text is in final form and isn't updated again in this document 🔒
Old text (Appendix A): [RFC3168] details negotiation of ECN during the SYN and SYN-ACK stages of a TCP connection.
New text (Appendix A): [RFC3168] (updated by [RFC8311]) details the negotiation of ECN during the SYN and SYN-ACK stages of a TCP connection.
This text is in final form and isn't updated again in this document 🔒
Old text (Appendix A): [RFC3168] details a specific bit for a receiver to send back in its TCP acknowledgements to notify the sender of the Congestion Experienced (CE) bit having arrived from the network.
New text (Appendix A): [RFC3168] (updated by [RFC8311]) details a specific bit for a receiver to send back in its TCP acknowledgements to notify the sender of the Congestion Experienced (CE) bit that the CE bit has arrived from the network.
This text is in final form and isn't updated again in this document 🔒
Old text (Appendix A): [RFC3168] details a specific bit for a sender to send in the header of its next outbound TCP segment to indicate to its peer that it has reduced its congestion window.
New text (Appendix A): [RFC3168] (updated by [RFC8311]) details a specific bit for a sender to send in the header of its next outbound TCP segment to indicate to its peer that it has reduced its congestion window.
This text is in final form and isn't updated again in this document 🔒
3.40.3. Solution Description ✨
References to [RFC8311] have been added. Some wordsmithing was also done while making those updates 🫶
3.41. Host Name Address Parameter Deprecated 💀
3.41.1. Description of the Problem
[RFC4960] defines three types of address parameters to be used with INIT and INIT ACK chunks:
- IPv4 Address parameters.
- IPv6 Address parameters.
- Host Name Address parameters.
The first two parameter types are supported by the SCTP kernel implementations of FreeBSD, Linux, and Solaris, but the third is not. In addition, the first two were successfully tested in all nine interoperability tests for SCTP, but the third has never been successfully tested. Therefore, the Host Name Address parameter should be deprecated 🥀
3.41.2. Text Changes to the Document
Old text (Section 3.3.2):
Note 3: An INIT chunk MUST NOT contain more than one Host Name Address parameter. Moreover, the sender of the INIT MUST NOT combine any other address types with the Host Name Address in the INIT. The receiver of INIT MUST ignore any other address types if the Host Name Address parameter is present in the received INIT chunk.
New text (Section 3.3.2):
Note 3: An INIT chunk MUST NOT contain the Host Name Address parameter. The receiver of an INIT chunk containing a Host Name Address parameter MUST send an ABORT and MAY include an "Unresolvable Address" error cause.
This text is in final form and isn't updated again in this document 🔒
Old text (Section 3.3.2.1):
The sender of INIT uses this parameter to pass its Host Name (in place of its IP addresses) to its peer. The peer is responsible for resolving the name. Using this parameter might make it more likely for the association to work across a NAT box.
New text (Section 3.3.2.1):
The sender of an INIT chunk MUST NOT include this parameter. The usage of the Host Name Address parameter is deprecated.
This text is in final form and isn't updated again in this document 🔒
Old text (Section 3.3.2.1):
Address Type: 16 bits (unsigned integer)
This is filled with the type value of the corresponding address TLV (e.g., IPv4 = 5, IPv6 = 6, Host name = 11).
New text (Section 3.3.2.1):
Address Type: 16 bits (unsigned integer)
This is filled with the type value of the corresponding address TLV (e.g., IPv4 = 5, IPv6 = 6). The value indicating the Host Name Address parameter (Host name = 11) MUST NOT be used.
This text is in final form and isn't updated again in this document 🔒
Old text (Section 3.3.3):
Note 3: The INIT ACK chunks MUST NOT contain more than one Host Name Address parameter. Moreover, the sender of the INIT ACK MUST NOT combine any other address types with the Host Name Address in the INIT ACK. The receiver of the INIT ACK MUST ignore any other address types if the Host Name Address parameter is present.
New text (Section 3.3.3):
Note 3: An INIT ACK chunk MUST NOT contain the Host Name Address parameter. The receiver of INIT ACK chunks containing a Host Name Address parameter MUST send an ABORT and MAY include an "Unresolvable Address" error cause.
This text is in final form and isn't updated again in this document 🔒
Old text (Section 5.1.2):
B) If there is a Host Name parameter present in the received INIT or INIT ACK chunk, the endpoint shall resolve that host name to a list of IP address(es) and derive the transport address(es) of this peer by combining the resolved IP address(es) with the SCTP source port.
The endpoint MUST ignore any other IP Address parameters if they are also present in the received INIT or INIT ACK chunk.
The time at which the receiver of an INIT resolves the host name has potential security implications to SCTP. If the receiver of an INIT resolves the host name upon the reception of the chunk, and the mechanism the receiver uses to resolve the host name involves potential long delay (e.g., DNS query), the receiver may open itself up to resource attacks for the period of time while it is waiting for the name resolution results before it can build the State Cookie and release local resources.
Therefore, in cases where the name translation involves potential long delay, the receiver of the INIT MUST postpone the name resolution till the reception of the COOKIE ECHO chunk from the peer. In such a case, the receiver of the INIT SHOULD build the State Cookie using the received Host Name (instead of destination transport addresses) and send the INIT ACK to the source IP address from which the INIT was received.
The receiver of an INIT ACK shall always immediately attempt to resolve the name upon the reception of the chunk.
The receiver of the INIT or INIT ACK MUST NOT send user data (piggy-backed or stand-alone) to its peer until the host name is successfully resolved.
If the name resolution is not successful, the endpoint MUST immediately send an ABORT with "Unresolvable Address" error cause to its peer. The ABORT shall be sent to the source IP address from which the last peer packet was received.
New text (Section 5.1.2):
B) If there is a Host Name Address parameter present in the received INIT or INIT ACK chunk, the endpoint MUST immediately send an ABORT and MAY include an "Unresolvable Address" error cause to its peer. The ABORT SHALL be sent to the source IP address from which the last peer packet was received.
This text is in final form and isn't updated again in this document 🔒
Old text (Section 11.2.4.1):
The use of the host name feature in the INIT chunk could be used to flood a target DNS server. A large backlog of DNS queries, resolving the host name received in the INIT chunk to IP addresses, could be accomplished by sending INITs to multiple hosts in a given domain. In addition, an attacker could use the host name feature in an indirect attack on a third party by sending large numbers of INITs to random hosts containing the host name of the target. In addition to the strain on DNS resources, this could also result in large numbers of INIT ACKs being sent to the target. One method to protect against this type of attack is to verify that the IP addresses received from DNS include the source IP address of the original INIT. If the list of IP addresses received from DNS does not include the source IP address of the INIT, the endpoint MAY silently discard the INIT. This last option will not protect against the attack against the DNS.
New text (Section 11.2.4.1):
Support for the Host Name Address parameter has been removed from the protocol. Endpoints receiving INIT or INIT ACK chunks containing the Host Name Address parameter MUST send an ABORT chunk in response and MAY include an "Unresolvable Address" error cause.
This text is in final form and isn't updated again in this document 🔒
3.41.3. Solution Description 🌸
The usage of the Host Name Address parameter has been deprecated.
3.42. Conflicting Text regarding the 'Supported Address Types' Parameter 🎀
3.42.1. Description of the Problem
Section 5.1.2 of [RFC4960] contains conflicting text regarding the receipt of an SCTP packet containing an INIT chunk sent from an address for which the corresponding address type is not listed in the 'Supported Address Types' parameter. The text states that the association MUST be aborted, but it also states that the association SHOULD be established and there SHOULD NOT be any error indication.
3.42.2. Text Changes to the Document
Old text (Section 5.1.2):
The sender of INIT may include a 'Supported Address Types' parameter in the INIT to indicate what types of address are acceptable. When this parameter is present, the receiver of INIT (initiate) MUST either use one of the address types indicated in the Supported Address Types parameter when responding to the INIT, or abort the association with an "Unresolvable Address" error cause if it is unwilling or incapable of using any of the address types indicated by its peer.
New text (Section 5.1.2):
The sender of INIT chunks MAY include a 'Supported Address Types' parameter in the INIT to indicate what types of addresses are acceptable.
This text is in final form and isn't updated again in this document 🔒
3.42.3. Solution Description ✨
The conflicting text has been removed.
3.43. Integration of RFC 6096 🧚
3.43.1. Description of the Problem
[RFC6096] updates [RFC4960] by adding the "Chunk Flags" registry. This should be integrated into the base specification.
3.43.2. Text Changes to the Document 🎀
Old text: (Section 14.1)
14.1. IETF-Defined Chunk Extension ✨
Okay so, new chunk parameter type codes get assigned through an IETF Consensus action, as defined in [RFC2434]. Documentation of the chunk parameter MUST contain the following info:
a) A long and short name for the new chunk type.
b) A detailed description of the structure of the chunk, which MUST conform to the basic structure defined in Section 3.2.
c) A detailed definition and description of the intended use of each field within the chunk, including the chunk flags if any.
d) A detailed procedural description of the use of the new chunk type within the operation of the protocol.
The last chunk type (255) is reserved for future extension if necessary. 🌸
New text: (Section 14.1)
14.1. IETF-Defined Chunk Extension 💅
Now new chunk type codes are assigned through an IETF Review action, as defined in [RFC8126]. Documentation for a new chunk MUST contain the following info:
a) A long and short name for the new chunk type.
b) A detailed description of the structure of the chunk, which MUST conform to the basic structure defined in Section 3.2.
c) A detailed definition and description of the intended use of each field within the chunk, including the chunk flags (if any). Defined chunk flags will be used as initial entries in the chunk flags table for the new chunk type.
d) A detailed procedural description of the use of the new chunk type within the operation of the protocol.
The last chunk type (255) is reserved for future extension if necessary.
For each new chunk type, IANA creates a registration table for the chunk flags of that type. The procedure for registering particular chunk flags is described in Section 14.2. 🦋
This text has been modified by multiple errata. It includes modifications from Section 3.3. It is in final form and is not further updated in this document. 💜
New text: (Section 14.2)
14.2. New IETF Chunk Flags Registration 🧚
Chunk flags get assigned through an RFC Required action, as defined in [RFC8126]. Documentation for the chunk flags MUST contain the following info:
a) A name for the new chunk flag.
b) A detailed procedural description of the use of the new chunk flag within the operation of the protocol. It MUST be considered that implementations not supporting the flag will send '0' on transmit and just ignore it on receipt.
IANA selects a chunk flags value. This MUST be one of 0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, or 0x80, which MUST be unique within the chunk flag values for the specific chunk type. 🔥
This text is in final form and is not further updated in this document.
Please note that Sections 14.2, 14.3, 14.4, and 14.5 as shown in [RFC4960] will need to be renumbered when [RFC4960] is updated. 🙈
3.43.3. Solution Description ✨
[RFC6096] has been integrated, and the reference has been updated to [RFC8126]. Slay, it's all tidied up! 💖
3.44. Integration of RFC 6335 🌈
3.44.1. Description of the Problem
[RFC6335] updates [RFC4960] by updating procedures for the "Service Name and Transport Protocol Port Number Registry". This should be integrated into the base specification. Also, the "Guidelines for Writing an IANA Considerations Section in RFCs" reference needs to be changed to [RFC8126]. 🎀
3.44.2. Text Changes to the Document 🍓
Old text: (Section 14.5)
SCTP services may use contact port numbers to provide service to unknown callers, as in TCP and UDP. IANA is therefore requested to open the existing Port Numbers registry for SCTP using the following rules, which we intend to mesh well with existing Port Numbers registration procedures. An IESG-appointed Expert Reviewer supports IANA in evaluating SCTP port allocation requests, according to the procedure defined in [RFC2434].
Port numbers are divided into three ranges. The Well Known Ports are those from 0 through 1023, the Registered Ports are those from 1024 through 49151, and the Dynamic and/or Private Ports are those from 49152 through 65535. Well Known and Registered Ports are intended for use by server applications that desire a default contact point on a system. On most systems, Well Known Ports can only be used by system (or root) processes or by programs executed by privileged users, while Registered Ports can be used by ordinary user processes or programs executed by ordinary users. Dynamic and/or Private Ports are intended for temporary use, including client-side ports, out-of-band negotiated ports, and application testing prior to registration of a dedicated port; they MUST NOT be registered. 🌙
The Port Numbers registry should accept registrations for SCTP ports in the Well Known Ports and Registered Ports ranges. Well Known and Registered Ports SHOULD NOT be used without registration. Although in some cases -- such as porting an application from TCP to SCTP -- it may seem natural to use an SCTP port before registration completes, we emphasize that IANA will not guarantee registration of particular Well Known and Registered Ports. Registrations should be requested as early as possible. 😭
Each port registration SHALL include the following information:
- A short port name, consisting entirely of letters (A-Z and a-z), digits (0-9), and punctuation characters from
"-_+./*"(not including the quotes). - The port number that is requested for registration.
- A short English phrase describing the port's purpose.
- Name and contact information for the person or entity performing the registration, and possibly a reference to a document defining the port's use. Registrations coming from IETF working groups need only name the working group, but indicating a contact person is recommended.
Registrants are encouraged to follow these guidelines when submitting a registration. 🫶
- A port name SHOULD NOT be registered for more than one SCTP port number.
- A port name registered for TCP MAY be registered for SCTP as well. Any such registration SHOULD use the same port number as the existing TCP registration.
- Concrete intent to use a port SHOULD precede port registration. For example, existing TCP ports SHOULD NOT be registered in advance of any intent to use those ports for SCTP. 👑
New text: (Section 14.5)
SCTP services can use contact port numbers to provide service to unknown callers, as in TCP and UDP. IANA is therefore requested to open the existing "Service Name and Transport Protocol Port Number Registry" for SCTP using the following rules, which we intend to mesh well with existing port-number registration procedures. An IESG-appointed expert reviewer supports IANA in evaluating SCTP port allocation requests, according to the procedure defined in [RFC8126]. The details of this process are defined in [RFC6335]. 💅
This text is in final form and is not further updated in this document.
3.44.3. Solution Description ✨
[RFC6335] has been integrated, and the reference has been updated to [RFC8126]. Look at that glow-up! 🌸
3.45. Integration of RFC 7053 🦋
3.45.1. Description of the Problem
[RFC7053] updates [RFC4960] by adding the I bit to the DATA chunk. This should be integrated into the base specification. 💜
3.45.2. Text Changes to the Document ✨
okay bestie, this is where the DATA chunk gets its new little superpower 🦋
Old text: (Section 3.3.1)
The following format MUST be used for the DATA chunk:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0 | Reserved|U|B|E| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Identifier S | Stream Sequence Number n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Protocol Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ User Data (seq n of Stream S) /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Reserved: 5 bits. It should be set to all '0's and ignored by the receiver.
New text: (Section 3.3.1)
The following format MUST be used for the DATA chunk:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 0 | Res |I|U|B|E| Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TSN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Stream Identifier S | Stream Sequence Number n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Protocol Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
\ \
/ User Data (seq n of Stream S) /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+Res: 4 bits. It SHOULD be set to all '0's and ignored by the receiver.
I bit: 1 bit. The (I)mmediate bit MAY be set by the sender whenever the sender of a DATA chunk can benefit from the corresponding SACK chunk being sent back without delay. See Section 4 of [RFC7053] for a discussion of the benefits.
This text is in final form and is not further updated in this document.
New text: (Append to Section 6.1)
Whenever the sender of a DATA chunk can benefit from the corresponding SACK chunk being sent back without delay, the sender MAY set the I bit in the DATA chunk header. Please note that why the sender has set the I bit is irrelevant to the receiver.
Reasons for setting the I bit include, but are not limited to, the following (see Section 4 of [RFC7053] for a discussion of the benefits):
- The application requests that the I bit of the last DATA chunk of a user message be set when providing the user message to the SCTP implementation (see Section 7).
- The sender is in the SHUTDOWN-PENDING state.
- The sending of a DATA chunk fills the congestion or receiver window.
This text is in final form and is not further updated in this document.
Old text: (Section 6.2)
Note: The SHUTDOWN chunk does not contain Gap Ack Block fields. Therefore, the endpoint should use a SACK instead of the SHUTDOWN chunk to acknowledge DATA chunks received out of order.
New text: (Section 6.2)
Note: The SHUTDOWN chunk does not contain Gap Ack Block fields. Therefore, the endpoint SHOULD use a SACK instead of the SHUTDOWN chunk to acknowledge DATA chunks received out of order.
Upon receipt of an SCTP packet containing a DATA chunk with the I bit set, the receiver SHOULD NOT delay the sending of the corresponding SACK chunk, i.e., the receiver SHOULD immediately respond with the corresponding SACK chunk.
Please note that this change is only about adding a paragraph. 💅
This text is in final form and is not further updated in this document.
Old text: (Section 10.1 E))
E) Send
Format: SEND(association id, buffer address, byte count [,context]
[,stream id] [,life time] [,destination transport address]
[,unordered flag] [,no-bundle flag] [,payload protocol-id] )
-> resultNew text: (Section 10.1 E))
E) Send
Format: SEND(association id, buffer address, byte count [,context]
[,stream id] [,life time] [,destination transport address]
[,unordered flag] [,no-bundle flag] [,payload protocol-id]
[,sack-immediately])
-> resultThis text is in final form and is not further updated in this document.
New text: (Append optional parameter in item E) of Section 10.1)
- sack-immediately flag - set the I bit on the last DATA chunk used for the user message to be transmitted.
This text is in final form and is not further updated in this document.
3.45.3. Solution Description
[RFC7053] has been integrated. 🎀
3.46. CRC32c Code Improvements 🦋
3.46.1. Description of the Problem
The code given for the CRC32c computations uses types such as "long", which may have different lengths on different operating systems or processors. Therefore, the code needs to be changed, so that it uses specific types such as uint32_t.
Some syntax errors and a comment also need to be fixed.
We remind the reader that per Section 3.10.2 of this document most of Appendix C of RFC 4960 will be moved to Appendix B in the bis document (thus the "Old text: (Appendix C)" and "New text: (Appendix B)" items in this section).
3.46.2. Text Changes to the Document
Old text: (Appendix C)
/*************************************************************/
/* Note Definition for Ross Williams table generator would */
/* be: TB_WIDTH=4, TB_POLLY=0x1EDC6F41, TB_REVER=TRUE */
/* For Mr. Williams direct calculation code use the settings */
/* cm_width=32, cm_poly=0x1EDC6F41, cm_init=0xFFFFFFFF, */
/* cm_refin=TRUE, cm_refot=TRUE, cm_xorort=0x00000000 */
/*************************************************************/
/* Example of the crc table file */
#ifndef __crc32cr_table_h__
#define __crc32cr_table_h__
#define CRC32C_POLY 0x1EDC6F41
#define CRC32C(c,d) (c=(c>>8)^crc_c[(c^(d))&0xFF])
unsigned long crc_c[256] =
{
0x00000000L, 0xF26B8303L, 0xE13B70F7L, 0x1350F3F4L,
0xC79A971FL, 0x35F1141CL, 0x26A1E7E8L, 0xD4CA64EBL,
0x8AD958CFL, 0x78B2DBCCL, 0x6BE22838L, 0x9989AB3BL,
0x4D43CFD0L, 0xBF284CD3L, 0xAC78BF27L, 0x5E133C24L,
0x105EC76FL, 0xE235446CL, 0xF165B798L, 0x030E349BL,
0xD7C45070L, 0x25AFD373L, 0x36FF2087L, 0xC494A384L,
0x9A879FA0L, 0x68EC1CA3L, 0x7BBCEF57L, 0x89D76C54L,
0x5D1D08BFL, 0xAF768BBCL, 0xBC267848L, 0x4E4DFB4BL,
0x20BD8EDEL, 0xD2D60DDDL, 0xC186FE29L, 0x33ED7D2AL,
0xE72719C1L, 0x154C9AC2L, 0x061C6936L, 0xF477EA35L,
0xAA64D611L, 0x580F5512L, 0x4B5FA6E6L, 0xB93425E5L,
0x6DFE410EL, 0x9F95C20DL, 0x8CC531F9L, 0x7EAEB2FAL,
0x30E349B1L, 0xC288CAB2L, 0xD1D83946L, 0x23B3BA45L,
0xF779DEAEL, 0x05125DADL, 0x1642AE59L, 0xE4292D5AL,
0xBA3A117EL, 0x4851927DL, 0x5B016189L, 0xA96AE28AL,
0x7DA08661L, 0x8FCB0562L, 0x9C9BF696L, 0x6EF07595L,
0x417B1DBCL, 0xB3109EBFL, 0xA0406D4BL, 0x522BEE48L,
0x86E18AA3L, 0x748A09A0L, 0x67DAFA54L, 0x95B17957L,
0xCBA24573L, 0x39C9C670L, 0x2A993584L, 0xD8F2B687L,
0x0C38D26CL, 0xFE53516FL, 0xED03A29BL, 0x1F682198L,
0x5125DAD3L, 0xA34E59D0L, 0xB01EAA24L, 0x42752927L,
0x96BF4DCCL, 0x64D4CECFL, 0x77843D3BL, 0x85EFBE38L,
0xDBFC821CL, 0x2997011FL, 0x3AC7F2EBL, 0xC8AC71E8L,
0x1C661503L, 0xEE0D9600L, 0xFD5D65F4L, 0x0F36E6F7L,
0x61C69362L, 0x93AD1061L, 0x80FDE395L, 0x72966096L,
0xA65C047DL, 0x5437877EL, 0x4767748AL, 0xB50CF789L,
0xEB1FCBADL, 0x197448AEL, 0x0A24BB5AL, 0xF84F3859L,
0x2C855CB2L, 0xDEEEDFB1L, 0xCDBE2C45L, 0x3FD5AF46L,
0x7198540DL, 0x83F3D70EL, 0x90A324FAL, 0x62C8A7F9L,
0xB602C312L, 0x44694011L, 0x5739B3E5L, 0xA55230E6L,
0xFB410CC2L, 0x092A8FC1L, 0x1A7A7C35L, 0xE811FF36L,
0x3CDB9BDDL, 0xCEB018DEL, 0xDDE0EB2AL, 0x2F8B6829L,
0x82F63B78L, 0x709DB87BL, 0x63CD4B8FL, 0x91A6C88CL,
0x456CAC67L, 0xB7072F64L, 0xA457DC90L, 0x563C5F93L,
0x082F63B7L, 0xFA44E0B4L, 0xE9141340L, 0x1B7F9043L,
0xCFB5F4A8L, 0x3DDE77ABL, 0x2E8E845FL, 0xDCE5075CL,
0x92A8FC17L, 0x60C37F14L, 0x73938CE0L, 0x81F80FE3L,
0x55326B08L, 0xA759E80BL, 0xB4091BFFL, 0x466298FCL,
0x1871A4D8L, 0xEA1A27DBL, 0xF94AD42FL, 0x0B21572CL,
0xDFEB33C7L, 0x2D80B0C4L, 0x3ED04330L, 0xCCBBC033L,
0xA24BB5A6L, 0x502036A5L, 0x4370C551L, 0xB11B4652L,
0x65D122B9L, 0x97BAA1BAL, 0x84EA524EL, 0x7681D14DL,
0x2892ED69L, 0xDAF96E6AL, 0xC9A99D9EL, 0x3BC21E9DL,
0xEF087A76L, 0x1D63F975L, 0x0E330A81L, 0xFC588982L,
0xB21572C9L, 0x407EF1CAL, 0x532E023EL, 0xA145813DL,
0x758FE5D6L, 0x87E466D5L, 0x94B49521L, 0x66DF1622L,
0x38CC2A06L, 0xCAA7A905L, 0xD9F75AF1L, 0x2B9CD9F2L,
0xFF56BD19L, 0x0D3D3E1AL, 0x1E6DCDEEL, 0xEC064EEDL,
0xC38D26C4L, 0x31E6A5C7L, 0x22B65633L, 0xD0DDD530L,
0x0417B1DBL, 0xF67C32D8L, 0xE52CC12CL, 0x1747422FL,
0x49547E0BL, 0xBB3FFD08L, 0xA86F0EFCL, 0x5A048DFFL,
0x8ECEE914L, 0x7CA56A17L, 0x6FF599E3L, 0x9D9E1AE0L,
0xD3D3E1ABL, 0x21B862A8L, 0x32E8915CL, 0xC083125FL,
0x144976B4L, 0xE622F5B7L, 0xF5720643L, 0x07198540L,
0x590AB964L, 0xAB613A67L, 0xB831C993L, 0x4A5A4A90L,
0x9E902E7BL, 0x6CFBAD78L, 0x7FAB5E8CL, 0x8DC0DD8FL,
0xE330A81AL, 0x115B2B19L, 0x020BD8EDL, 0xF0605BEEL,
0x24AA3F05L, 0xD6C1BC06L, 0xC5914FF2L, 0x37FACCF1L,
0x69E9F0D5L, 0x9B8273D6L, 0x88D28022L, 0x7AB90321L,
0xAE7367CAL, 0x5C18E4C9L, 0x4F48173DL, 0xBD23943EL,
0xF36E6F75L, 0x0105EC76L, 0x12551F82L, 0xE03E9C81L,
0x34F4F86AL, 0xC69F7B69L, 0xD5CF889DL, 0x27A40B9EL,
0x79B737BAL, 0x8BDCB4B9L, 0x988C474DL, 0x6AE7C44EL,
0xBE2DA0A5L, 0x4C4623A6L, 0x5F16D052L, 0xAD7D5351L,
};
#endifNew text: (Appendix B)
<CODE BEGINS>
/****************************************************************/
/* Note: The definitions for Ross Williams's table generator */
/* would be TB_WIDTH=4, TB_POLY=0x1EDC6F41, TB_REVER=TRUE. */
/* For Mr. Williams's direct calculation code, use the settings */
/* cm_width=32, cm_poly=0x1EDC6F41, cm_init=0xFFFFFFFF, */
/* cm_refin=TRUE, cm_refot=TRUE, cm_xorot=0x00000000. */
/****************************************************************/
/* Example of the crc table file */
#ifndef __crc32cr_h__
#define __crc32cr_h__
#define CRC32C_POLY 0x1EDC6F41UL
#define CRC32C(c,d) (c=(c>>8)^crc_c[(c^(d))&0xFF]) uint32_t crc_c[256] =
{
0x00000000UL, 0xF26B8303UL, 0xE13B70F7UL, 0x1350F3F4UL,
0xC79A971FUL, 0x35F1141CUL, 0x26A1E7E8UL, 0xD4CA64EBUL,
0x8AD958CFUL, 0x78B2DBCCUL, 0x6BE22838UL, 0x9989AB3BUL,
0x4D43CFD0UL, 0xBF284CD3UL, 0xAC78BF27UL, 0x5E133C24UL,
0x105EC76FUL, 0xE235446CUL, 0xF165B798UL, 0x030E349BUL,
0xD7C45070UL, 0x25AFD373UL, 0x36FF2087UL, 0xC494A384UL,
0x9A879FA0UL, 0x68EC1CA3UL, 0x7BBCEF57UL, 0x89D76C54UL,
0x5D1D08BFUL, 0xAF768BBCUL, 0xBC267848UL, 0x4E4DFB4BUL,
0x20BD8EDEUL, 0xD2D60DDDUL, 0xC186FE29UL, 0x33ED7D2AUL,
0xE72719C1UL, 0x154C9AC2UL, 0x061C6936UL, 0xF477EA35UL,
0xAA64D611UL, 0x580F5512UL, 0x4B5FA6E6UL, 0xB93425E5UL,
0x6DFE410EUL, 0x9F95C20DUL, 0x8CC531F9UL, 0x7EAEB2FAUL,
0x30E349B1UL, 0xC288CAB2UL, 0xD1D83946UL, 0x23B3BA45UL,
0xF779DEAEUL, 0x05125DADUL, 0x1642AE59UL, 0xE4292D5AUL,
0xBA3A117EUL, 0x4851927DUL, 0x5B016189UL, 0xA96AE28AUL,
0x7DA08661UL, 0x8FCB0562UL, 0x9C9BF696UL, 0x6EF07595UL,
0x417B1DBCUL, 0xB3109EBFUL, 0xA0406D4BUL, 0x522BEE48UL,
0x86E18AA3UL, 0x748A09A0UL, 0x67DAFA54UL, 0x95B17957UL,
0xCBA24573UL, 0x39C9C670UL, 0x2A993584UL, 0xD8F2B687UL,
0x0C38D26CUL, 0xFE53516FUL, 0xED03A29BUL, 0x1F682198UL,
0x5125DAD3UL, 0xA34E59D0UL, 0xB01EAA24UL, 0x42752927UL,
0x96BF4DCCUL, 0x64D4CECFUL, 0x77843D3BUL, 0x85EFBE38UL,
0xDBFC821CUL, 0x2997011FUL, 0x3AC7F2EBUL, 0xC8AC71E8UL,
0x1C661503UL, 0xEE0D9600UL, 0xFD5D65F4UL, 0x0F36E6F7UL,
0x61C69362UL, 0x93AD1061UL, 0x80FDE395UL, 0x72966096UL,
0xA65C047DUL, 0x5437877EUL, 0x4767748AUL, 0xB50CF789UL,
0xEB1FCBADUL, 0x197448AEUL, 0x0A24BB5AUL, 0xF84F3859UL,
0x2C855CB2UL, 0xDEEEDFB1UL, 0xCDBE2C45UL, 0x3FD5AF46UL,
0x7198540DUL, 0x83F3D70EUL, 0x90A324FAUL, 0x62C8A7F9UL,
0xB602C312UL, 0x44694011UL, 0x5739B3E5UL, 0xA55230E6UL,
0xFB410CC2UL, 0x092A8FC1UL, 0x1A7A7C35UL, 0xE811FF36UL,
0x3CDB9BDDUL, 0xCEB018DEUL, 0xDDE0EB2AUL, 0x2F8B6829UL,
0x82F63B78UL, 0x709DB87BUL, 0x63CD4B8FUL, 0x91A6C88CUL,
0x456CAC67UL, 0xB7072F64UL, 0xA457DC90UL, 0x563C5F93UL,
0x082F63B7UL, 0xFA44E0B4UL, 0xE9141340UL, 0x1B7F9043UL,
0xCFB5F4A8UL, 0x3DDE77ABUL, 0x2E8E845FUL, 0xDCE5075CUL,
0x92A8FC17UL, 0x60C37F14UL, 0x73938CE0UL, 0x81F80FE3UL,
0x55326B08UL, 0xA759E80BUL, 0xB4091BFFUL, 0x466298FCUL,
0x1871A4D8UL, 0xEA1A27DBUL, 0xF94AD42FUL, 0x0B21572CUL,
0xDFEB33C7UL, 0x2D80B0C4UL, 0x3ED04330UL, 0xCCBBC033UL,
0xA24BB5A6UL, 0x502036A5UL, 0x4370C551UL, 0xB11B4652UL,
0x65D122B9UL, 0x97BAA1BAUL, 0x84EA524EUL, 0x7681D14DUL,
0x2892ED69UL, 0xDAF96E6AUL, 0xC9A99D9EUL, 0x3BC21E9DUL,
0xEF087A76UL, 0x1D63F975UL, 0x0E330A81UL, 0xFC588982UL,
0xB21572C9UL, 0x407EF1CAUL, 0x532E023EUL, 0xA145813DUL,
0x758FE5D6UL, 0x87E466D5UL, 0x94B49521UL, 0x66DF1622UL,
0x38CC2A06UL, 0xCAA7A905UL, 0xD9F75AF1UL, 0x2B9CD9F2UL,
0xFF56BD19UL, 0x0D3D3E1AUL, 0x1E6DCDEEUL, 0xEC064EEDUL,
0xC38D26C4UL, 0x31E6A5C7UL, 0x22B65633UL, 0xD0DDD530UL,
0x0417B1DBUL, 0xF67C32D8UL, 0xE52CC12CUL, 0x1747422FUL,
0x49547E0BUL, 0xBB3FFD08UL, 0xA86F0EFCUL, 0x5A048DFFUL,
0x8ECEE914UL, 0x7CA56A17UL, 0x6FF599E3UL, 0x9D9E1AE0UL,
0xD3D3E1ABUL, 0x21B862A8UL, 0x32E8915CUL, 0xC083125FUL,
0x144976B4UL, 0xE622F5B7UL, 0xF5720643UL, 0x07198540UL,
0x590AB964UL, 0xAB613A67UL, 0xB831C993UL, 0x4A5A4A90UL,
0x9E902E7BUL, 0x6CFBAD78UL, 0x7FAB5E8CUL, 0x8DC0DD8FUL,
0xE330A81AUL, 0x115B2B19UL, 0x020BD8EDUL, 0xF0605BEEUL,
0x24AA3F05UL, 0xD6C1BC06UL, 0xC5914FF2UL, 0x37FACCF1UL,
0x69E9F0D5UL, 0x9B8273D6UL, 0x88D28022UL, 0x7AB90321UL,
0xAE7367CAUL, 0x5C18E4C9UL, 0x4F48173DUL, 0xBD23943EUL,
0xF36E6F75UL, 0x0105EC76UL, 0x12551F82UL, 0xE03E9C81UL,
0x34F4F86AUL, 0xC69F7B69UL, 0xD5CF889DUL, 0x27A40B9EUL,
0x79B737BAUL, 0x8BDCB4B9UL, 0x988C474DUL, 0x6AE7C44EUL,
0xBE2DA0A5UL, 0x4C4623A6UL, 0x5F16D052UL, 0xAD7D5351UL,
};
#endifOkay so this table has been through multiple errata, which are basically fixes that got layered on over time 🙈 It includes modifications from Section 3.10, and it is in final form, so it is NOT getting updated again in this document. Officially done, no notes 💅✨
---------
Old text: (Appendix C)
---------
/* Example of table build routine */
#include <stdio.h>
#include <stdlib.h>
#define OUTPUT_FILE "crc32cr.h"
#define CRC32C_POLY 0x1EDC6F41L
FILE *tf;
unsigned long
reflect_32 (unsigned long b)
{
int i;
unsigned long rw = 0L;
for (i = 0; i < 32; i++){
if (b & 1)
rw |= 1 << (31 - i);
b >>= 1;
}
return (rw);
}
unsigned long
build_crc_table (int index)
{
int i;
unsigned long rb;
rb = reflect_32 (index);
for (i = 0; i < 8; i++){
if (rb & 0x80000000L)
rb = (rb << 1) ^ CRC32C_POLY;
else
rb <<= 1;
}
return (reflect_32 (rb));
}
main ()
{
int i;
printf ("\nGenerating CRC-32c table file <%s>\n",
OUTPUT_FILE);
if ((tf = fopen (OUTPUT_FILE, "w")) == NULL){
printf ("Unable to open %s\n", OUTPUT_FILE);
exit (1);
}
fprintf (tf, "#ifndef __crc32cr_table_h__\n");
fprintf (tf, "#define __crc32cr_table_h__\n\n");
fprintf (tf, "#define CRC32C_POLY 0x%08lX\n",
CRC32C_POLY);
fprintf (tf,
"#define CRC32C(c,d) (c=(c>>8)^crc_c[(c^(d))&0xFF])\n");
fprintf (tf, "\nunsigned long crc_c[256] =\n{\n");
for (i = 0; i < 256; i++){
fprintf (tf, "0x%08lXL, ", build_crc_table (i));
if ((i & 3) == 3)
fprintf (tf, "\n");
}
fprintf (tf, "};\n\n#endif\n");
if (fclose (tf) != 0)
printf ("Unable to close <%s>." OUTPUT_FILE);
else
printf ("\nThe CRC-32c table has been written to <%s>.\n",
OUTPUT_FILE);
}
---------
New text: (Appendix B)
---------
/* Example of table build routine */
#include <stdio.h>
#include <stdlib.h>
#define OUTPUT_FILE "crc32cr.h"
#define CRC32C_POLY 0x1EDC6F41UL
static FILE *tf;
static uint32_t
reflect_32(uint32_t b)
{
int i;
uint32_t rw = 0UL;
for (i = 0; i < 32; i++) {
if (b & 1)
rw |= 1 << (31 - i);
b >>= 1;
}
return (rw);
}
static uint32_t
build_crc_table (int index)
{
int i;
uint32_t rb;
rb = reflect_32(index);
for (i = 0; i < 8; i++) {
if (rb & 0x80000000UL)
rb = (rb << 1) ^ (uint32_t)CRC32C_POLY;
else
rb <<= 1;
}
return (reflect_32(rb));
}
int
main (void)
{
int i;
printf("\nGenerating CRC32c table file <%s>.\n",
OUTPUT_FILE);
if ((tf = fopen(OUTPUT_FILE, "w")) == NULL) {
printf("Unable to open %s.\n", OUTPUT_FILE);
exit (1);
}
fprintf(tf, "#ifndef __crc32cr_h__\n");
fprintf(tf, "#define __crc32cr_h__\n\n");
fprintf(tf, "#define CRC32C_POLY 0x%08XUL\n",
(uint32_t)CRC32C_POLY);
fprintf(tf,
"#define CRC32C(c,d) (c=(c>>8)^crc_c[(c^(d))&0xFF])\n");
fprintf(tf, "\nuint32_t crc_c[256] =\n{\n");
for (i = 0; i < 256; i++) {
fprintf(tf, "0x%08XUL,", build_crc_table (i));
if ((i & 3) == 3)
fprintf(tf, "\n");
else
fprintf(tf, " ");
}
fprintf(tf, "};\n\n#endif\n");
if (fclose(tf) != 0)
printf("Unable to close <%s>.\n", OUTPUT_FILE);
else
printf("\nThe CRC32c table has been written to <%s>.\n",
OUTPUT_FILE);
}Right, so that's the table builder, and it's giving "build it yourself if you don't trust the list" energy 🧚 The text has been modified by multiple errata, includes modifications from Section 3.10, and is in final form, not updated further here 🌸
---------
Old text: (Appendix C)
---------
/* Example of crc insertion */
#include "crc32cr.h"
unsigned long
generate_crc32c(unsigned char *buffer, unsigned int length)
{
unsigned int i;
unsigned long crc32 = ~0L;
unsigned long result;
unsigned char byte0,byte1,byte2,byte3;
for (i = 0; i < length; i++){
CRC32C(crc32, buffer[i]);
}
result = ~crc32;
/* result now holds the negated polynomial remainder;
* since the table and algorithm is "reflected" [williams95].
* That is, result has the same value as if we mapped the message
* to a polynomial, computed the host-bit-order polynomial
* remainder, performed final negation, then did an end-for-end
* bit-reversal.
* Note that a 32-bit bit-reversal is identical to four inplace
* 8-bit reversals followed by an end-for-end byteswap.
* In other words, the bytes of each bit are in the right order,
* but the bytes have been byteswapped. So we now do an explicit
* byteswap. On a little-endian machine, this byteswap and
* the final ntohl cancel out and could be elided.
*/
byte0 = result & 0xff;
byte1 = (result>>8) & 0xff;
byte2 = (result>>16) & 0xff;
byte3 = (result>>24) & 0xff;
crc32 = ((byte0 << 24) |
(byte1 << 16) |
(byte2 << 8) |
byte3);
return ( crc32 );
}
int
insert_crc32(unsigned char *buffer, unsigned int length)
{
SCTP_message *message;
unsigned long crc32;
message = (SCTP_message *) buffer;
message->common_header.checksum = 0L;
crc32 = generate_crc32c(buffer,length);
/* and insert it into the message */
message->common_header.checksum = htonl(crc32);
return 1;
}
int
validate_crc32(unsigned char *buffer, unsigned int length)
{
SCTP_message *message;
unsigned int i;
unsigned long original_crc32;
unsigned long crc32 = ~0L;
/* save and zero checksum */
message = (SCTP_message *) buffer;
original_crc32 = ntohl(message->common_header.checksum);
message->common_header.checksum = 0L;
crc32 = generate_crc32c(buffer,length);
return ((original_crc32 == crc32)? 1 : -1);
}
---------
New text: (Appendix B)
---------
/* Example of crc insertion */
#include "crc32cr.h"
uint32_t
generate_crc32c(unsigned char *buffer, unsigned int length)
{
unsigned int i;
uint32_t crc32 = 0xffffffffUL;
uint32_t result;
uint8_t byte0, byte1, byte2, byte3;
for (i = 0; i < length; i++) {
CRC32C(crc32, buffer[i]);
}
result = ~crc32;
/* result now holds the negated polynomial remainder,
* since the table and algorithm are "reflected" [williams95].
* That is, result has the same value as if we mapped the message
* to a polynomial, computed the host-bit-order polynomial
* remainder, performed final negation, and then did an
* end-for-end bit-reversal.
* Note that a 32-bit bit-reversal is identical to four in-place
* 8-bit bit-reversals followed by an end-for-end byteswap.
* In other words, the bits of each byte are in the right order,
* but the bytes have been byteswapped. So, we now do an explicit
* byteswap. On a little-endian machine, this byteswap and
* the final ntohl cancel out and could be elided.
*/
byte0 = result & 0xff;
byte1 = (result>>8) & 0xff;
byte2 = (result>>16) & 0xff;
byte3 = (result>>24) & 0xff;
crc32 = ((byte0 << 24) |
(byte1 << 16) |
(byte2 << 8) |
byte3);
return (crc32);
}
int
insert_crc32(unsigned char *buffer, unsigned int length)
{
SCTP_message *message;
uint32_t crc32;
message = (SCTP_message *) buffer;
message->common_header.checksum = 0UL;
crc32 = generate_crc32c(buffer,length);
/* and insert it into the message */
message->common_header.checksum = htonl(crc32);
return 1;
}
int
validate_crc32(unsigned char *buffer, unsigned int length)
{
SCTP_message *message;
unsigned int i;
uint32_t original_crc32;
uint32_t crc32;3.46.3. Solution Description
The fix is literally that the code now uses platform-independent types 💅✨ no more surprises depending on which machine you're running on 🫶
3.47. Clarification of Gap Ack Blocks in SACK Chunks
3.47.1. Description of the Problem
okay so the Gap Ack Blocks in the SACK chunk are supposed to be isolated 🦋 but the spec never actually said that with proper normative text 😭 that's the whole drama
this got reported as part of an errata for [RFC4960] with Errata ID 5202 📝
3.47.2. Text Changes to the Document
here's the glow-up, word for word (we don't touch the exact text, obviously 💖)
---------
Old text: (Section 3.3.4)
---------
The SACK also contains zero or more Gap Ack Blocks. Each Gap Ack
Block acknowledges a subsequence of TSNs received following a break
in the sequence of received TSNs. By definition, all TSNs
acknowledged by Gap Ack Blocks are greater than the value of the
Cumulative TSN Ack.
---------
New text: (Section 3.3.4)
---------
The SACK also contains zero or more Gap Ack Blocks. Each Gap Ack
Block acknowledges a subsequence of TSNs received following a break
in the sequence of received TSNs. The Gap Ack Blocks SHOULD be
isolated. This means that the TSN just before each Gap Ack Block and
the TSN just after each Gap Ack Block have not been received. By
definition, all TSNs acknowledged by Gap Ack Blocks are greater than
the value of the Cumulative TSN Ack.This text is in final form and is not further updated in this document. ✨
---------
Old text: (Section 3.3.4)
---------
Gap Ack Blocks:
These fields contain the Gap Ack Blocks. They are repeated for
each Gap Ack Block up to the number of Gap Ack Blocks defined in
the Number of Gap Ack Blocks field. All DATA chunks with TSNs
greater than or equal to (Cumulative TSN Ack + Gap Ack Block
Start) and less than or equal to (Cumulative TSN Ack + Gap Ack
Block End) of each Gap Ack Block are assumed to have been received
correctly.
---------
New text: (Section 3.3.4)
---------
Gap Ack Blocks:
These fields contain the Gap Ack Blocks. They are repeated for
each Gap Ack Block up to the number of Gap Ack Blocks defined in
the Number of Gap Ack Blocks field. All DATA chunks with TSNs
greater than or equal to (Cumulative TSN Ack + Gap Ack Block
Start) and less than or equal to (Cumulative TSN Ack + Gap Ack
Block End) of each Gap Ack Block are assumed to have been received
correctly. Gap Ack Blocks SHOULD be isolated. This means that
the DATA chunks with TSNs equal to (Cumulative TSN Ack + Gap Ack
Block Start - 1) and (Cumulative TSN Ack + Gap Ack Block End + 1)
have not been received.This text is in final form and is not further updated in this document. 🫶
3.47.3. Solution Description
normative text about how Gap Ack Blocks are meant to be used has finally been added 🎀 no more guessing!
3.48. Handling of SSN Wraparounds
3.48.1. Description of the Problem
so the Stream Sequence Number (SSN) keeps the order of user messages inside each SCTP stream 📦 but it's only 16 bits, so it can wrap around multiple times inside the current send window 🌀 for the receiver to still deliver things in the right order, the sender should limit how many user messages it sends per stream 🧚
3.48.2. Text Changes to the Document
---------
Old text: (Section 6.1)
---------
Note: The data sender SHOULD NOT use a TSN that is more than 2**31 -
1 above the beginning TSN of the current send window.
---------
New text: (Section 6.1)
---------
Note: The data sender SHOULD NOT use a TSN that is more than
2**31 - 1 above the beginning TSN of the current send window.
Note: For each stream, the data sender SHOULD NOT have more than
2**16 - 1 ordered user messages in the current send window.This text is in final form and is not further updated in this document. 💅
3.48.3. Solution Description
the data sender is required to limit the number of ordered user messages within the current send window 🔥
3.49. Update to RFC 2119 Boilerplate Text
3.49.1. Description of the Problem
the text used to talk about the key words defined in [RFC2119] got updated by [RFC8174] 📣 so that new wording needs to be merged into the base spec, obvi 🌈
3.49.2. Text Changes to the Document
---------
Old text: (Section 2)
---------
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
---------
New text: (Section 2)
---------
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.This text is in final form and is not further updated in this document. 🦋
3.49.3. Solution Description
the text has been updated to the text specified in [RFC8174] 💖
3.50. Removal of Text (Previously Missed in RFC 4960)
3.50.1. Description of the Problem
when the changes to Section 7.2.4 of [RFC2960] got integrated, as described in Section 2.8.2 of [RFC4460], some text was missed 🙈 so it's still hanging out in [RFC4960] lol
3.50.2. Text Changes to the Document
---------
Old text: (Section 7.2.4)
---------
A straightforward implementation of the above keeps a counter for
each TSN hole reported by a SACK. The counter increments for each
consecutive SACK reporting the TSN hole. After reaching 3 and
starting the Fast-Retransmit procedure, the counter resets to 0.
Because cwnd in SCTP indirectly bounds the number of outstanding
TSN's, the effect of TCP Fast Recovery is achieved automatically with
no adjustment to the congestion control window size.
---------
New text: (Section 7.2.4)
---------This text is in final form and is not further updated in this document. 💀
3.50.3. Solution Description
the text has finally been removed 🧹✨
4. IANA Considerations
Section 3.44 of this document suggests new text that would update the "Service Name and Transport Protocol Port Number Registry" for SCTP to be consistent with [RFC6335]. 📋
IANA has confirmed that it is OK to make the proposed text change in an upcoming Standards Track document that will update [RFC4960]. IANA is not asked to perform any other action, and this document does not request that IANA make a change to any registry. 🫶
5. Security Considerations
This document does not add any security considerations to those given in [RFC4960]. 🔐 no new security plot twists here, but the ones in [RFC4960] are still very much in play, so stay alert, bestie 👑
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<https://www.rfc-editor.org/info/rfc4960>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.6.2. Informative References
[RFC1122] Braden, R., Ed., "Requirements for Internet Hosts -
Communication Layers", STD 3, RFC 1122,
DOI 10.17487/RFC1122, October 1989,
<https://www.rfc-editor.org/info/rfc1122>.
[RFC1858] Ziemba, G., Reed, D., and P. Traina, "Security
Considerations for IP Fragment Filtering", RFC 1858,
DOI 10.17487/RFC1858, October 1995,
<https://www.rfc-editor.org/info/rfc1858>.
[RFC2960] Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
Schwarzbauer, H., Taylor, T., Rytina, I., Kalla, M.,
Zhang, L., and V. Paxson, "Stream Control Transmission
Protocol", RFC 2960, DOI 10.17487/RFC2960, October 2000,
<https://www.rfc-editor.org/info/rfc2960>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<https://www.rfc-editor.org/info/rfc3168>.
[RFC4460] Stewart, R., Arias-Rodriguez, I., Poon, K., Caro, A., and
M. Tuexen, "Stream Control Transmission Protocol (SCTP)
Specification Errata and Issues", RFC 4460,
DOI 10.17487/RFC4460, April 2006,
<https://www.rfc-editor.org/info/rfc4460>.
[RFC5681] Allman, M., Paxson, V., and E. Blanton, "TCP Congestion
Control", RFC 5681, DOI 10.17487/RFC5681, September 2009,
<https://www.rfc-editor.org/info/rfc5681>.
[RFC6096] Tuexen, M. and R. Stewart, "Stream Control Transmission
Protocol (SCTP) Chunk Flags Registration", RFC 6096,
DOI 10.17487/RFC6096, January 2011,
<https://www.rfc-editor.org/info/rfc6096>.
[RFC6298] Paxson, V., Allman, M., Chu, J., and M. Sargent,
"Computing TCP's Retransmission Timer", RFC 6298,
DOI 10.17487/RFC6298, June 2011,
<https://www.rfc-editor.org/info/rfc6298>.
[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165,
RFC 6335, DOI 10.17487/RFC6335, August 2011,
<https://www.rfc-editor.org/info/rfc6335>.
[RFC7053] Tuexen, M., Ruengeler, I., and R. Stewart, "SACK-
IMMEDIATELY Extension for the Stream Control Transmission
Protocol", RFC 7053, DOI 10.17487/RFC7053, November 2013,
<https://www.rfc-editor.org/info/rfc7053>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8311] Black, D., "Relaxing Restrictions on Explicit Congestion
Notification (ECN) Experimentation", RFC 8311,
DOI 10.17487/RFC8311, January 2018,
<https://www.rfc-editor.org/info/rfc8311>.Acknowledgements
the authors wish to thank Pontus Andersson, Eric W. Biederman, Cedric Bonnet, Spencer Dawkins, Gorry Fairhurst, Benjamin Kaduk, Mirja Kuehlewind, Peter Lei, Gyula Marosi, Lionel Morand, Jeff Morriss, Karen E. E. Nielsen, Tom Petch, Kacheong Poon, Julien Pourtet, Irene Ruengeler, Michael Welzl, and Qiaobing Xie for their invaluable comments 🫶💜
Authors' Addresses
Randall R. Stewart
Netflix, Inc.
Chapin, SC 29036
United States of America
Email: randall@lakerest.net
Michael Tuexen
Muenster University of Applied Sciences
Stegerwaldstrasse 39
48565 Steinfurt
Germany
Email: tuexen@fh-muenster.de
Maksim Proshin
Ericsson
Kistavaegen 25
Stockholm 164 80
Sweden
Email: mproshin@tieto.mera.ru📦 where this page comes from
- ietf: rfc8540 2019-02
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms