RFC 6038
Two-Way Active Measurement Protocol (TWAMP) Reflect Octets and Symmetrical Size Features
📜 RFC 6038: TWAMP Reflect Octets and Symmetrical Size Features ✨
Bestie, this one's a sequel-type spec. It's by A. Morton and L. Ciavattone from AT&T Labs, dated October 2010, and it's a Standards Track doc with ISSN 2070-1721. It updates RFC 5357 (that's TWAMP's core spec, Updates: 5357). Nothing about obsoleting another RFC shows up in the title block, so I'm not adding one 🙈
Abstract 🌸
Okay so this memo adds two features that go together, and both sit on top of the TWAMP core spec. Feature one is an optional move where the responding host bounces some of the command octets or padding octets back to the sender. Feature two is an optional sender packet format that makes sure the test packets are the same size in both directions. Iconic, honestly 🦋
Status of This Memo 🎀
This is an Internet Standards Track document, aka the real deal. 💅
It's a product of the Internet Engineering Task Force (IETF), so it represents the consensus of the IETF community. It went through public review and got the green light from the Internet Engineering Steering Group (IESG). If you want more on Internet Standards, check out Section 2 of RFC 5741.
For the current status, any errata, and how to send feedback, go to http://www.rfc-editor.org/info/rfc6038.
Copyright Notice 🔥
Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. 🫶
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://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 document. Any Code Components pulled out of this document have to include the Simplified BSD License text described in Section 4.e of the Trust Legal Provisions, and they come with no warranty, per the Simplified BSD License.
Heads up on the old stuff: this document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The people who control copyright in some of that material may not have given the IETF Trust permission to allow modifications outside the IETF Standards Process. So unless you get an adequate license from those copyright holders, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process. The exceptions are formatting it for publication as an RFC, or translating it into languages other than English. 🙈
Table of Contents 🧚
1. Introduction ....................................................3
2. Requirements Language ...........................................3
3. Purpose and Scope ...............................................4
4. TWAMP Control Extensions ........................................4
4.1. Connection Setup with New Features .........................5
4.2. Reflect Octets: Request-TW-Session Packet Format ...........6
4.3. Reflect Octets: Accept Session Packet Format ...............7
4.4. Additional Considerations ..................................9
5. Extended TWAMP Test .............................................9
5.1. Sender Behavior ............................................9
5.1.1. Packet Timings ......................................9
5.1.2. Reflect Octets: Packet Formats and Contents .........9
5.1.3. Reflect Octets: Interaction with Padding
Truncation .........................................11
5.1.4. Symmetrical Size: Session-Sender Packet Format .....13
5.1.5. Symmetrical Size AND Reflect Octets:
Session-Sender Packet ..............................14
5.2. Reflector Behavior ........................................14
5.2.1. Reflect Octets: Session-Reflector Packet
Format and Contents ................................15
5.2.2. Symmetrical Size: Session-Reflector Packet Format ..16
5.2.3. Symmetrical Size AND Reflect Octets:
Session-Sender Packet Format .......................16
6. Security Considerations ........................................17
7. IANA Considerations ............................................17
7.1. Registry Specification ....................................17
7.2. Registry Contents .........................................17
8. Acknowledgements ...............................................17
9. Normative References ...........................................181. Introduction ✨
Okay so TWAMP [RFC5357] is basically an extension of OWAMP, the One-way Active Measurement Protocol [RFC4656]. The TWAMP spec got a ton of review as it was getting finished, and that review turned up a bunch of recommendations for new features. Main character energy 👑
This memo describes two closely related features for TWAMP. 🦋
Feature one is an OPTIONAL capability. The responder host can send back a limited number of unassigned (padding) octets to the Control-Client or Session-Sender, over both the TWAMP-Control and TWAMP-Test protocols. So the Control-Client or Session-Sender can tuck in octets it finds useful, and it gets the assurance that the matching reply or test packet will carry that info back when it's reflected and returned by the Server or Session-Reflector. Okay that's giving reliability 🎀
Feature two is also an OPTIONAL capability, and it makes sure reflected test packets are the same size in both directions. The way it works is a brand new TWAMP-Test Session-Sender packet format. Now here's the tea 🍓 TWAMP [RFC5357] already recommends padding truncation to get symmetrical sizes, which compensates for the Session-Reflector's bigger test packet header. But it's not guaranteed that the Session-Reflector will actually truncate the padding, and it's not possible at all if there's not enough padding. 😭
This memo updates the TWAMP core protocol specified in [RFC5357]. Measurement systems don't have to implement the features in this memo to claim compliance with [RFC5357].
Throughout this memo, the bits marked MBZ (Must Be Zero) MUST be set to zero by senders and MUST be ignored by receivers. 💖 Also, the HMAC (Hashed Message Authentication Code) MUST be calculated as defined in Section 3.2 of [RFC4656].
2. Requirements Language 💜
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]. 🫶
3. Purpose and Scope 🌈
Here's the vibe check. The whole point of this memo is to define two OPTIONAL, closely related features for TWAMP [RFC5357]. These features upgrade the TWAMP host so it can do a simple operation on control and test packets. The operation is either reflecting octets or padding, or making sure TWAMP-Test packets come out symmetrical in size. The motivations are letting the controller host tag packets with an index so they're easy to spot, and/or confirming that the same size test packets will be used in each direction. Bestie, that's so smart 🧚
The scope is limited to these two features:
- Reflect Octets: the capability of the Server/Session-Reflector to reflect specific octets back to the Client/Session-Sender, plus a similar service that the Client and Session-Sender provide.
- Symmetrical Size: the capability to make sure the TWAMP-Test protocol uses the same packet size in both directions. It does this with a new TWAMP-Test Session-Sender test packet format, which both the Session-Sender and the Session-Reflector support. Only the Session-Sender test packet format is new. ✨
This memo extends the modes of operation by assigning two new values in the Modes field (check Section 3.1 of [RFC4656] for the format of the Server Greeting message). It keeps backward compatibility with core TWAMP [RFC5357] implementations too. The two new values line up with the two features in this memo. 🦋
When the Server and Control-Client agree to use the Reflect Octets mode during control connection setup, the Control-Client, the Server, the Session-Sender, and the Session-Reflector MUST all conform to the requirements of that mode, as listed below. 💅
When the Server and Control-Client agree to use the Symmetrical Size mode during control connection setup, the Control-Client, the Server, the Session-Sender, and the Session-Reflector MUST all conform to the requirements of that mode, as listed below. 🔥
4. TWAMP Control Extensions 🌸
The TWAMP-Control protocol [RFC5357] uses the Modes field to identify and select specific communication capabilities. This field is a recognized extension mechanism, and the next sections describe two extensions that use it. 🎀
4.1. Connection Setup with New Features 🧚
TWAMP connection establishment follows the procedure in Section 3.1 of [RFC4656] and Section 3.1 of [RFC5357]. The new features need two new bit positions (and values). One identifies the Server/Session-Reflector's ability to reflect specific octets back to the Control-Client/Session-Sender. The other supports the new Session-Sender packet format in the TWAMP-Test protocol. Check the IANA section for the assigned values and bit positions. 💖
The Server sets one or both of the new bit positions in the Modes field of the Server Greeting message, which tells the world what it can do and that it's willing to operate in either mode (or both) if it wants to. 👑
If the Control-Client plans to run all test sessions invoked with this control connection in one or both of the new modes, it MUST set the Mode field bit that corresponds to each function in the Setup Response message. With this and other extensions, the Control-Client MAY set multiple Mode field bits in the Setup Response message. 🌈
4.2. Reflect Octets: Request-TW-Session Packet Format ✨
okay so this is where the Request-TW-Session command gets its Reflect Octets bits 💅 here's the layout bestie:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 5 | MBZ | IPVN | Conf-Sender | Conf-Receiver |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Number of Schedule Slots |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. ... Many fields (66 octets) not shown ... .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Padding Length (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Start Time (8 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timeout (8 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type-P Descriptor |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Octets to be reflected | Length of padding to reflect |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| HMAC (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ok this next bit is super important 🫶 the Padding Length field still tells you how many padding octets the Session-Sender tacks onto ALL TWAMP-Test packets in this test session. the minimum-length rules are coming right after the two new fields that sit behind the Type-P Descriptor 🎀
the padding count on the Session-Reflector's side depends on whether the truncation process TWAMP recommends is supported, see Section 4.2.1 of [RFC5357] 🦋
- Octets to be reflected: this field SHALL be 2 octets long (as shown!) and holds the octets the Server MUST reflect in the Accept Session message, as spelled out below 🌸
- Length of padding to reflect: this one SHALL be 2 octets long and is an unsigned binary value in units of octets 💖 it tells the Session-Reflector how long the padding in the TWAMP-Test Packet should be, which the Session-Sender expects to be reflected, and how many octets the Session-Reflector SHALL return in its TWAMP-Test packet format (see Section 5.2). by putting this length in the Request-TW-Session message, a Server can figure out whether it can comply with a request to reflect padding and get the Session-Reflector ready in advance 🧚
now the Padding Length rules, bestie, read these carefully 👑
- unauthenticated TWAMP-Test mode: the Padding Length SHOULD be >= 27 octets, so truncation can happen as TWAMP recommends, see Section 4.2.1 of [RFC5357] ✨
- Authenticated or Encrypted TWAMP-Test modes: the Padding Length SHOULD be >= 56 octets, for that same truncation process, see Section 4.2.1 of [RFC5357] 💜
- OPTIONAL Reflect Octets mode: the Padding Length SHALL be > the Length of padding to reflect 🍓
- unauthenticated mode with both the OPTIONAL Reflect Octets mode and truncation: the Padding Length SHALL be >= 27 + Length of padding to reflect octets, see Section 4.2.1 of [RFC5357] 🌈
- Authenticated or Encrypted modes with both the OPTIONAL Reflect Octets mode and truncation: the Padding Length SHALL be >= 56 + Length of padding to reflect octets, see Section 4.2.1 of [RFC5357] 😭
4.3. Reflect Octets: Accept Session Packet Format 🦋
okay now the Accept Session command, where the Reflect Padding bits live 💅 check out the layout:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Accept | MBZ | Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| |
| SID (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reflected octets | Server octets |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (8 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| HMAC (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- Reflected octets: this field SHALL contain the octets from the Request-TW-Session Octets to be reflected field, and it's 2 octets long, as shown 🌸
- Server octets: this field SHALL contain info the Server wants returned in the TWAMP-Test Packet Padding (to be reflected) field, OR SHALL be zero. it's 2 octets long too, as shown 🍓 even though the Server determines the SID, this field is very long (16 octets) and does not normally appear in TWAMP-Test packets 💀
these items MUST be part of compliant implementations using the Reflect Octets feature, no cap 👑
- when a Server does not require octets to be returned in TWAMP-Test packets, it MUST send all zeros in the Server octets field.
- when a Server intends octets to be returned in TWAMP-Test packets, it MUST send a non-zero value in the Server octets field, and the TWAMP-Test Sender MUST include those octets at the beginning of the Packet Padding (to be reflected) field.
- Section 4.1.2 defines how Server octets MUST be included in the TWAMP-Test packet padding when this service is desired by the Server (indicated in the second of two figures in this section). 🫶
when you're doing the truncation process TWAMP recommends (see Section 4.2.1 of [RFC5357]) and the padding math shows there aren't enough octets to make equal-length Session-Sender and Session-Reflector test packets, then the Accept field MUST be set to 3 to indicate that some aspect of the request is not supported. 💀
4.4. Additional Considerations ✨
the Modes field the Server sends in its Server Greeting message is the bit-wise OR of the mode values it's willing to support during this session 🌈
okay so with this memo published as an RFC, the last 7 bit positions of the Modes 32-bit field are in use 🦋 a Control-Client conforming to this extension of [RFC5357] MAY ignore the values in the higher bits of the Modes field, or it MAY support other features communicated in those bit positions. the other bits are reserved for future protocol extensions, so they're giving possibility 🧚
5. Extended TWAMP Test 💖
the TWAMP-Test protocol is kinda like the OWAMP [RFC4656] test protocol, except the Session-Reflector sends test packets back to the Session-Sender in response to each test packet it receives 🔥 TWAMP, see Section 4 of [RFC5357], defines two additional test packet formats for packets sent by the Session-Reflector. which format applies depends on the security mode chosen. the new modes here either use some of the padding octets inside each test packet format or require truncation of those octets, depending on the security mode in use 💅
5.1. Sender Behavior 🌸
this section describes extensions to the behavior of the TWAMP Session-Sender 🎀
5.1.1. Packet Timings 🦋
the Send Schedule isn't used in TWAMP, and this memo doesn't change that 🙈
5.1.2. Reflect Octets: Packet Formats and Contents ✨
Okay so the Session-Sender packet format and content follow the same procedure and guidelines as Section 4.1.2 of [RFC4656] (as indicated in Section 4.1.2 of [RFC5357]). No need to reinvent the wheel here, bestie 💅
The Reflect Octets mode re-designates the original TWAMP-Test Packet Padding field (see Section 4.1.2 of [RFC4656]), as shown below for Unauthenticated mode: 🦋
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
| Packet Padding (to be reflected) |
. (length in octets specified in command) .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. Additional Packet Padding .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+The Packet Padding (to be reflected) field SHALL correspond to the length of octets specified in the Request-TW-Session Length of padding to reflect field to this test session. These are the octets that the Session-Sender expects will be returned by the Session-Reflector. 💖
The length of the Additional Packet Padding field is the difference between two fields in the Request-TW-Session command, as follows:
Additional Packet Padding, in octets =
Padding Length - Length of padding to reflectWhen a Server intends octets to be returned in TWAMP-Test packets, it MUST send a non-zero value in the Server octets field, and the TWAMP-Test Session-Sender MUST include those octets in the first 2 octets of the Packet Padding (to be reflected) field as shown below: 🎀
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Server octets |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Remaining Packet Padding (to be reflected) |
. (total length in octets specified in command) .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+The Server octets field contains the same information that the Server returned to the Control-Client in the Accept-Session message corresponding to this specific test session (see Section 4.3). At the Session-Reflector, these octets MUST be reflected the same as the rest of the Packet Padding (to be reflected) field. 🫶
Note that it is permissible for the Session-Sender to insert the same octets used in the Octets to be reflected field of the Request-TW-Session command elsewhere in the Packet Padding (to be reflected) field. 🌸
5.1.3. Reflect Octets: Interaction with Padding Truncation 🧚
When the Reflect Octets mode is selected, and performing the truncation process that TWAMP recommends, see Section 4.2.1 of [RFC5357], the Session-Sender MUST anticipate a minimum padding required to achieve equal-size test packets in both directions. The amount of padding needed to achieve symmetrical packet size depends on both the security mode (Unauthenticated/Authenticated/Encrypted) and whether the Reflect Octets mode is selected simultaneously. 🌈
When using the truncation process in TWAMP alone, see Section 4.2.1 of [RFC5357], the Session-Sender MUST append sufficient Packet Padding octets to allow the same IP packet payload lengths to be used in each direction of transmission (this is usually desirable). To compensate for the Session-Reflector's larger test packet format, the Session-Sender MUST append at least 27 octets of padding in Unauthenticated mode, and at least 56 octets in Authenticated and Encrypted modes. The sizes of TWAMP-Test protocol packets and the resulting truncated padding to achieve equal packet sizes in both directions are shown in the table below: 📊
+-------------------+----------------------+---------------------+
| Octets in: | Unauthenticated Mode | Auth/Encrypted Mode |
+-------------------+----------------------+---------------------+
| Reflector Header | 41 | 104 |
| Sender Header | 14 | 48 |
| Truncated Padding | 27 | 56 |
+-------------------+----------------------+---------------------+
TWAMP-Test Padding TruncationWhen using the Reflect Octets mode simultaneously with the truncation process that TWAMP recommends in Section 4.2.1 of [RFC5357], the Session-Sender MUST append at least 27 octets of padding plus the Length of the padding to reflect octets when operating in Unauthenticated mode. The Session-Sender MUST append at least 56 octets of padding plus the Length of the padding to reflect octets when operating in Authenticated and Encrypted modes. 👑
5.1.4. Symmetrical Size: Session-Sender Packet Format 💅
When the Symmetrical Size mode is selected, the Session-Sender SHALL use the following TWAMP-Test Packet Format in Unauthenticated mode:
Unauthenticated Mode
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
| |
| MBZ (27 octets) |
| |
| |
| |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+ +
. .
. Packet Padding .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+This feature needs only a new Session-Sender test packet format, the Session-Reflector test packet format is unchanged. 🔥
5.1.5. Symmetrical Size AND Reflect Octets: Session-Sender Packet Format 🌸
When both the Symmetrical Size mode and the Reflect Octets mode are selected, the Session-Sender SHALL use the following TWAMP-Test Packet Format in Unauthenticated mode:
Unauthenticated Mode
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
| |
| MBZ (27 octets) |
| |
| |
| |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+ +
| Packet Padding (to be reflected) |
. (length in octets specified in command) .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. Additional Packet Padding .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+In this combined mode, the Packet Padding to be reflected follows the 27 MBZ octets. In Authenticated or Encrypted modes, the Packet Padding to be reflected follows the 56 MBZ octets. 🦋
5.2. Reflector Behavior 🧚♀️
The TWAMP Reflector follows the procedures and guidelines in Section 4.2 of [RFC5357], with the following additional functions: 💖
- Reflect Octets mode: Designated octets in the Packet Padding (to be reflected) field of the Session-Sender's test packet MUST be included in the Session-Reflector's test packet. ✨
- Symmetrical Size mode: The Session-Reflector MUST operate using the Session_Reflector Packet Format defined in Section 5.1.4, where the Padding Octets are separated from the information fields. 🌈
5.2.1. Reflect Octets: Session-Reflector Packet Format and Contents
Okay so the Reflect Padding feature basically re-designates the Packet Padding field 💅, as shown below. When the Reflect Octets mode is selected, the Session-Sender SHALL use the following TWAMP-Test Packet Format in Unauthenticated mode: 🎀
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receive Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Error Estimate | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender TTL | Packet Padding (from Session-Sender) |
+-+-+-+-+-+-+-+-+ +
. .
+ +-+-+-+-+-+-+-+-+
| Packet Padding (from Session-Sender) | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
| |
. Additional Packet Padding .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+The Packet Padding (from Session-Sender) field MUST be the same octets as the Packet Padding (to be reflected) field in the Session-Sender's test packet, and therefore MUST conform to the length specified in the Request-TW-Session message. 🧚
When the Server has returned a non-zero value in the Server octets field of the Accept Session message (as described in Section 4.3), then the Session-Reflector SHALL reflect these octets the same as the rest of the Packet Padding (to be reflected) field. 💜
Section 4.2.1 of [RFC5357] recommends a padding truncation process for use in TWAMP. When using that process in conjunction with the Reflect Octets mode, the Session-Reflector MUST reflect the designated octets from the Session-Sender's test packet in the Packet Padding (from Session-Sender) field, and MAY re-use additional Packet Padding from the Session-Sender. The Session-Reflector MUST truncate the padding such that the highest number octets are discarded, and the test packet length equals the Session-Sender's packet length. When using the recommended truncation process, the Session-Reflector MUST truncate exactly 27 octets of padding in Unauthenticated mode, and exactly 56 octets in Authenticated and Encrypted modes. ✂️
In any case, the Session-Reflector MAY re-use the Sender's Packet Padding (since the requirements for padding generation are the same for each). 🌸
5.2.2. Symmetrical Size: Session-Reflector Packet Format
When Symmetrical Size mode is selected, the Session-Reflector packet formats for Unauthenticated and Authenticated/Encrypted modes are identical to the core TWAMP specification, see Section 4.2.1 of [RFC5357]. Thus, the Session-Reflector test packet format is unchanged. 🦋
The Session-Reflector MUST construct its test packet using the information in the Session-Sender's test packet. The length of the Session-Reflector's test packet SHALL equal the length of the Session-Sender's test packet. 🍓
5.2.3. Symmetrical Size AND Reflect Octets: Session-Sender Packet Format
When both the Symmetrical Size mode and the Reflect Octets mode are selected, the Session-Reflector MUST operate using the Session-Sender Packet Format defined in Section 5.1.5, where the Padding Octets are separated from the information fields, and the Packet Padding (to be reflected) field precedes the Additional Padding. 👑
The Session-Reflector SHALL use the same TWAMP-Test Packet Format as specified in Section 5.2.1, above. ✨
6. Security Considerations 🔥
These extended modes of operation do not appear to permit any new attacks on hosts communicating with core TWAMP [RFC5357].
The security considerations that apply to any active measurement of live networks are relevant here as well. See [RFC4656] and [RFC5357]. This is serious, bestie, so don't skip it 🙈
7. IANA Considerations 🌈
This memo adds two modes to the IANA registry for the TWAMP Modes field, and describes behavior when the new modes are used. This field is a recognized extension mechanism for TWAMP. 🧚
7.1. Registry Specification
IANA has created a TWAMP-Modes registry (as requested in [RFC5618]). TWAMP-Modes are specified in TWAMP Server Greeting messages and Setup Response messages, as described in Section 3.1 of [RFC5357], consistent with Section 3.1 of [RFC4656], and extended by this memo. Modes are indicated by setting bits in the 32-bit Modes field that correspond to values in the Modes registry. For the TWAMP-Modes registry, we expect that new features will be assigned increasing registry values that correspond to single bit positions, unless there is a good reason to do otherwise (more complex encoding than single-bit positions may be used in the future to access the 2^32 value space). 🦋
7.2. Registry Contents
The TWAMP-Modes registry has been augmented as follows: 💖
Value Description Semantics Definition
--------------------------------------------------------
32 Reflect Octets this memo, Section 3.1
Capability new bit position (5)
64 Symmetrical Size this memo, Section 3.1
Sender Test Packet Format new bit position (6)8. Acknowledgements 🫶
The authors thank Steve Baillargeon, Walt Steverson, and Stina Ross for helpful review and comments. 💅
9. Normative References 📚
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
Zekauskas, "A One-way Active Measurement Protocol
(OWAMP)", RFC 4656, September 2006.
[RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
RFC 5357, October 2008.
[RFC5618] Morton, A. and K. Hedayat, "Mixed Security Mode for the
Two-Way Active Measurement Protocol (TWAMP)", RFC 5618,
August 2009.Authors' Addresses 🍓
Al Morton
AT&T Labs
200 Laurel Avenue South
Middletown, NJ 07748
USA
Phone: +1 732 420 1571
Fax: +1 732 368 1192
EMail: acmorton@att.com
URI: http://home.comcast.net/~acmacm/
Len Ciavattone
AT&T Labs
200 Laurel Avenue South
Middletown, NJ 07748
USA
Phone: +1 732 420 1239
EMail: lencia@att.com📦 where this page comes from
- ietf: rfc6038 2010-10
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms