RFC 2023

IP Version 6 over PPP

📅 published October 1996, from ietf

IP Version 6 over PPP ✨

Okay bestie, this one is RFC 2023 🎀 and it's from October 1996. It's by D. Haskin and E. Allen from Bay Networks, Inc. 💖 It's a Standards Track doc, so it's a real Internet standard, not just a vibe. The header doesn't list anything it obsoletes or updates, so no drama there 🫶

Status of This Memo 🌸

Okay so this is an Internet standards track protocol for the Internet community, and the authors want people to talk about it and suggest improvements 💅 If you want to know where it stands officially, check the current "Internet Official Protocol Standards" (STD 1) edition. And the best part: distribution of this memo is totally unlimited 🦋

Abstract ✨

So PPP (the Point-to-Point Protocol) [1] is the standard way to wrap up Network Layer protocol info and send it over point-to-point links 🔗 It also has an extensible Link Control Protocol, plus a whole family of Network Control Protocols (NCPs) for setting up and configuring different network-layer protocols 👑

This doc is the one that explains how to send IP Version 6 [2] packets over PPP links 🧚 It also covers the NCP that sets up and configures IPv6 over PPP, and it spells out how to form IPv6 link-local addresses on PPP links too 💜

Table of Contents 🍓

   1.     Introduction ..........................................    2
        1.1.  Specification of Requirements ......................   2
   2.     Sending IPv6 Datagrams ................................    3
   3.     A PPP Network Control Protocol for IPv6 ...............    3
   4.     IPV6CP Configuration Options ..........................    4
        4.1.  Interface-Token ...................................    4
        4.2.  IPv6-Compression-Protocol..........................    7
   5.     Stateless Autoconfiguration and Link-Local Addresses ..    9
   A.     IPV6CP Recommended Options .............................   9
   Security Considerations .......................................  10
   References ....................................................  10
   Acknowledgments ...............................................  10
   Authors' Addresses ............................................  10

1. Introduction 🌈

Okay so PPP has three main parts 💅

A way to encapsulate datagrams over serial links.
A Link Control Protocol (LCP) for establishing, configuring, and testing the data-link connection.
A family of Network Control Protocols (NCPs) for establishing and configuring different network-layer protocols.

Here's the tea 🫖 To get communication going over a point-to-point link, each end of the PPP link must first send LCP packets to configure and test the data link. Once the link is up and any optional facilities the LCP negotiated are sorted, PPP must send NCP packets to choose and configure one or more network-layer protocols. After each chosen network-layer protocol is configured, its datagrams can finally be sent over the link 🦋

In this doc, the NCP that sets up and configures IPv6 over PPP is called the IPv6 Control Protocol (IPV6CP) 🎀

The link stays configured for communications until explicit LCP or NCP packets shut it down, or until some outside event happens (power failure at the other end, carrier drop, and so on) ⚡

1.1. Specification of Requirements 💖

Okay so this section is about the key words in the spec 🔑 These words are usually written in capitals, and they mean:

MUST — This word, or the adjective "required", means that the definition is an absolute requirement of the specification.
MUST NOT — This phrase means that the definition is an absolute prohibition of the specification.
SHOULD — This word, or the adjective "recommended", means that there may exist valid reasons in particular circumstances to ignore this item, but the full implications must be understood and carefully weighed before choosing a different course.
MAY — This word, or the adjective "optional", means that this item is one of an allowed set of alternatives. An implementation which does not include this option MUST be prepared to inter-operate with another implementation which does include the option. 🫶

2. Sending IPv6 Datagrams 🚀

Before any IPv6 packets may be communicated, PPP must reach the Network-Layer Protocol phase, and the IPv6 Control Protocol must reach the Opened state 🙈 No shortcuts, bestie.

Exactly one IPv6 packet gets encapsulated in the Information field of PPP Data Link Layer frames where the Protocol field says type hex 0057 (Internet Protocol Version 6) 💜

The maximum length of an IPv6 packet sent over a PPP link is the same as the maximum length of the Information field of a PPP data link layer frame. PPP links that support IPv6 must allow at least 576 octets in the information field of a data link layer frame 🍓

3. A PPP Network Control Protocol for IPv6 🧚

So the IPv6 Control Protocol (IPV6CP) handles configuring, enabling, and disabling the IPv6 protocol modules on both ends of the point-to-point link 👑 It uses the same packet exchange mechanism as LCP. IPV6CP packets may not be exchanged until PPP has reached the Network-Layer Protocol phase. If IPV6CP packets show up before that phase is reached, they should be silently discarded 🙈

The IPv6 Control Protocol is exactly the same as the Link Control Protocol [1], with the following exceptions 💅

Data Link Layer Protocol Field ✨

Exactly one IPV6CP packet is encapsulated in the Information field of PPP Data Link Layer frames where the Protocol field says type hex 8057 (IPv6 Control Protocol) 🎀

Code field 🦋

Only Codes 1 through 7 are used: Configure-Request, Configure-Ack, Configure-Nak, Configure-Reject, Terminate-Request, Terminate-Ack and Code-Reject 💖 Other Codes should be treated as unrecognized, and should result in Code-Rejects ⚠️

Timeouts ⏰

IPV6CP packets may not be exchanged until PPP has reached the Network-Layer Protocol phase. An implementation should be prepared to wait for Authentication and Link Quality Determination to finish before timing out while waiting for a Configure-Ack or other response. It is suggested that an implementation give up only after user intervention or a configurable amount of time 🌸

Configuration Option Types 🌈

IPV6CP has its own distinct set of Configuration Options, which are defined below 🫶

4. IPV6CP Configuration Options 💎

IPV6CP Configuration Options let the two ends negotiate the IPv6 parameters they'd like to use 🔥 IPV6CP uses the same Configuration Option format defined for LCP [1], just with its own separate set of Options. If a Configuration Option is not included in a Configure-Request packet, the default value for that Configuration Option is assumed 💅

Up-to-date values of the IPV6CP Option Type field are listed in the most recent "Assigned Numbers" RFC [5]. Right now the values are assigned like this 👑

    1       Interface-Token
    2       IPv6-Compression-Protocol

Part 1 wraps up here, and Part 2 picks up the rest of Section 4, from Interface-Token and IPv6-Compression-Protocol onward 🦋

4.1. Interface-Token 🎀

Description

okay so this Configuration Option is how you negotiate a unique 32-bit interface token 🦋 for address autoconfiguration [3] at the local end of the link (see section 5). The interface token MUST be unique within the PPP link, meaning once the negotiation is done, the two ends have to pick different Interface-Token values. no twins allowed 😭

before you even request this option, your implementation needs to pick its tentative Interface-Token. it's recommended to go with a non-zero value chosen in the most random way possible, so you get a super high chance of landing on something unique 🌈 a good move is to start with a unique seed. suggested sources of uniqueness include machine serial numbers, other network hardware addresses, system clocks, etc. ngl a link-layer address alone might not be enough as a seed, because it won't always be unique. so the seed should be built from a bunch of sources that are likely to differ even between identical systems, and you should use as many sources as you can at the same time ✨ good sources of uniqueness or randomness are required for the Interface-Token negotiation to succeed. if you can't find a good source of randomness, it's recommended to send a zero value for the Interface-Token in the Configure-Request. then the PPP peer can give you a valid non-zero Interface-Token in its response, as described below. and the tea is that as long as at least one of the PPP peers can generate a unique random number, the token negotiation will succeed 💅

when a Configure-Request comes in with the Interface-Token Configuration Option and the receiving peer implements this option, the received Interface-Token gets compared with the Interface-Token of the last Configure-Request sent to the peer. depending on what that comparison shows, an implementation MUST respond in one of the following ways:

if the two Interface-Tokens are different but the received Interface-Token is zero, send a Configure-Ack with a non-zero Interface-Token value suggested for use by the remote peer. that suggested Interface-Token MUST be different from the Interface-Token of the last Configure-Request sent to the peer 🫶

if the two Interface-Tokens are different and the received Interface-Token is not zero, the Interface-Token MUST be acknowledged. that means a Configure-Ack goes out with the requested Interface-Token, which says "yep, I agree with the token you asked for" 💖

if the two Interface-Tokens are equal and are not zero, a Configure-Nak MUST be sent specifying a different non-zero Interface-Token value suggested for use by the remote peer 🙈

if the two Interface-Tokens are equal to zero, the Interface-Tokens negotiation MUST be terminated by transmitting the Configure-Reject with the Interface-Token value set to zero. in this case a unique Interface-Token can not be negotiated 💀

if a Configure-Request comes in with the Interface-Token Configuration Option and the receiving peer does not implement this option, send a Configure-Rej 🍓

a new Configure-Request SHOULD NOT be sent to the peer until normal processing would cause it to be sent (that is, until a Configure-Nak is received or the Restart timer runs out) ⏰

a new Configure-Request MUST NOT contain the Interface-Token option if a valid Interface-Token Configure-Reject is received 🚫

receiving a Configure-Nak with a suggested Interface-Token that's different from the one in the last Configure-Nak sent to the peer means a unique Interface-Token has been found 🎉 in that case a new Configure-Request MUST be sent with the token value suggested in the last Configure-Nak from the peer. but if the received Interface-Token is equal to the one sent in the last Configure-Nak, a new Interface-Token MUST be chosen. then a new Configure-Request SHOULD be sent with the new tentative Interface-Token. this back-and-forth (transmit Configure-Request, receive Configure-Request, transmit Configure-Nak, receive Configure-Nak) might happen a few times, but it's extremely unlikely to keep going forever. more likely, the Interface-Tokens picked at either end will quickly diverge, and that ends the loop 🙌

if negotiating the Interface-Token is required, and the peer didn't include the option in its Configure-Request, the option SHOULD be appended to a Configure-Nak. the tentative value you give has to be acceptable as the remote Interface-Token, so it should be different from the token value picked for the local end of the PPP link. the next Configure-Request from the peer may include this option. if that next Configure-Request does NOT include this option, the peer MUST NOT send another Configure-Nak with this option included, and it should assume the peer's implementation doesn't support this option 🧚

by default, an implementation SHOULD attempt to negotiate the Interface-Token for its end of the PPP connection 💜

the summary of the Interface-Token Configuration Option format is below. fields go left to right ✨

    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      |    Length     |        Interface-Token
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         Interface-Token (cont)    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Type: 1

Length: 6

Interface-Token: the 32-bit Interface-Token, which is very likely to be unique on the link, or zero if a good source of uniqueness can't be found 🔥

Default Token Value

if no valid interface token can be successfully negotiated, no default Interface-Token value should be assumed. the procedures for recovering from that case are unspecified. one approach is to manually configure the interface token of the interface 🌸

4.2. IPv6-Compression-Protocol 🦋

Description

this Configuration Option lets you negotiate the use of a specific IPv6 packet compression protocol. the IPv6-Compression-Protocol Configuration Option indicates that you're able to receive compressed packets. each end of the link has to request this option separately if you want bi-directional compression. by default, compression is not enabled 🙅‍♀️

IPv6 compression negotiated with this option is specific to IPv6 datagrams. don't mix it up with the compression that comes from negotiations via Compression Control Protocol (CCP), which can potentially affect all datagrams 👑

the summary of the IPv6-Compression-Protocol Configuration Option format is below. fields go left to right 💅

    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      |    Length     |   IPv6-Compression-Protocol   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Data ...
   +-+-+-+-+

Type: 2

Length: >= 4

IPv6-Compression-Protocol: this two-octet field indicates the compression protocol you want. its values are always the same as the PPP Data Link Layer Protocol field values for that same compression protocol 🧁

the up-to-date values of the IPv6-Compression-Protocol field are in the most recent "Assigned Numbers" RFC [5] 📚

current values are assigned like this:

Value (in hex)          Protocol

004f                    IPv6 Header Compression

Data: zero or more octets, holding additional data as determined by the particular compression protocol ✨

Default

no IPv6 compression protocol enabled 🙈

5. Stateless Autoconfiguration and Link-Local Addresses 🌈

the interface token, which is used for forming IPv6 addresses of a PPP interface, SHOULD be negotiated in the IPV6CP phase of the PPP connection setup (see section 4.1). if no valid interface token has been successfully negotiated, the procedures for recovering from that case are unspecified. one approach is to manually configure the interface token of the interface 🔧

as long as the interface token is negotiated in the IPV6CP phase of the PPP connection setup, it's redundant to run duplicate address detection as part of the IPv6 Stateless Autoconfiguration protocol [3]. so it's recommended that, for PPP links with the IPV6CP Interface-Token option enabled, the default value of the DupAddrDetectTransmits autoconfiguration variable [3] be zero 💖

link-local addresses of PPP interfaces have this format:

| 10 bits  |              86 bits               |     32 bits     |
+----------+--------------+---------------------+-----------------+
|1111111010|              0                     | Interface Token |
+----------+--------------+---------------------+-----------------+

the most significant 10 bits of the address are the Link-Local prefix FE80::. 86 zero bits pad out the address between the Link-Local prefix and the Interface Token fields 🦢

A. IPV6CP Recommended Options ✨

the following Configurations Options are recommended:

Interface-Token
IPv6-Compression-Protocol

Security Considerations

🚨 Security issues are not discussed in this memo. 🚨 Literally nothing about security is covered here, so please go into any deployment with your eyes wide open 👀

References

[1] Simpson, W., "The Point-to-Point Protocol", STD 51, RFC 1661, July 1994.

[2] Deering, S., and R. Hinden, Editors, "Internet Protocol, Version 6 (IPv6) Specification", RFC 1883, December 1995.

[2] Hinden, R., and S. Deering, "IP Version 6 Addressing Architecture", RFC 1884, December 1995.

[3] Thomson, S., and T. Narten, "IPv6 Stateless Address Autoconfiguration", RFC 1971, August 1996.

[4] Narten, T., Nordmark, E., and W. Simpson, "Neighbor Discovery for IP Version 6 (IPv6)", RFC 1970, August 1996.

[5] Reynolds, J., and J. Postel, "Assigned Numbers", STD 2, RFC 1700, October 1994.

Acknowledgments 🫶

this document borrows from the Magic-Number LCP option, so it's partially based on previous work done by the PPP working group 🌷

Authors' Addresses 💜

Dimitry Haskin
Bay Networks, Inc.
2 Federal Street
Billerica, MA 01821
email: dhaskin@baynetworks.com

Ed Allen
Bay Networks, Inc.
2 Federal Street
Billerica, MA 01821
email: eallen@baynetworks.com

📦 where this page comes from

ietf: rfc2023 1996-10
💖 girlified by claude-haiku-5-5 on 2026-10-15: a language model's rewrite of the original, under its terms