RFC 7902

Registry and Extensions for P-Multicast Service Interface Tunnel Attribute Flags

📅 published June 2016, from ietf

RFC 7902 💖 Registry and Extensions for P-Multicast Service Interface Tunnel Attribute Flags

Part 1 of 2 🎀

Okay so this one's a Standards Track doc from June 2016, which means it's the real deal 🔥. E. Rosen from Juniper Networks, Inc. and T. Morin from Orange wrote it 🫶. It updates RFC 6514, and it doesn't obsolete anything 👑. The ISSN is 2070-1721.

Abstract

Okay so the BGP control procedures for MVPNs lean on a BGP attribute called the "P-Multicast Service Interface (PMSI) Tunnel" attribute 🦋. It has a one-octet "Flags" field. This doc sets up an IANA registry so the bits in that field get assigned properly. Since the "Flags" field only has eight bits (eight, bestie 😭), this doc also defines a brand-new BGP Extended Community called "Additional PMSI Tunnel Attribute Flags" that can carry extra flags for the PMSI Tunnel attribute. This document updates RFC 6514.

Status of This Memo

This is an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841.

Info about the current status of this doc, any errata, and how to send feedback is at http://www.rfc-editor.org/info/rfc7902 🌸.

Copyright (c) 2016 IETF Trust and the persons identified as the document authors. All rights reserved. ✨

Legal stuff, but it matters 💅: 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 in effect on the date this document was published. Please review those carefully, because they spell out your rights and restrictions for this doc. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions, and they come without warranty as described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Extending the "PMSI Tunnel" Attribute "Flags" Field . . . . .   3
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   5.  Normative References  . . . . . . . . . . . . . . . . . . . .   6
   Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1. Introduction ✨

Okay bestie, so there's a BGP attribute called "P-Multicast Service Interface (PMSI) Tunnel" that's defined in [RFC6514] 🦋. From here on I'll just call it the "PMSI Tunnel" attribute. It has a one-octet "Flags" field. That RFC only defines one flag, but now we need more, and that's where things get spicy 🌶️. The catch is that [RFC6514] never made an IANA registry for who gets which bit in the "Flags" field. So this doc creates one 💜.

There's also a chance we'll need more than eight flags, so this doc defines a new BGP Extended Community, "Additional PMSI Tunnel Attribute Flags", to carry extra flags for the "PMSI Tunnel" attribute. We also make a registry for that Extended Community, so IANA can hand out flag bits from its six-octet value field 🎀.

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 [RFC2119] 🤓.

2. Extending the "PMSI Tunnel" Attribute "Flags" Field

So in [RFC6514], only a single octet in the "PMSI Tunnel" attribute is set aside for bit flags. That gives you eight flags total, which is lowkey not enough for future stuff 💀.

This doc defines a new Transitive Opaque Extended Community ([RFC4360] [RFC7153]) called "Additional PMSI Tunnel Attribute Flags". It also defines a new bit flag in the "PMSI Tunnel" attribute "Flags" field, called the "Extension" flag 🌸.

The "Additional PMSI Tunnel Attribute Flags" Extended Community MUST NOT be carried by a given BGP UPDATE message unless both of these conditions hold:

  • the given BGP UPDATE message is also carrying a "PMSI Tunnel" attribute, and
  • the "Extension" flag of that "PMSI Tunnel" attribute's "Flags" field is set.

The six-octet value field of the "Additional PMSI Tunnel Attribute Flags" Extended Community is treated as a string of 48 one-bit flags 🧚. The leftmost bit (the most significant bit of the most significant octet) is bit 0, and the rightmost bit (the least significant bit of the least significant octet) is bit 47. Check out the figure below, it's giving clarity 👑.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |               |               |               |               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      3               4
      2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |               |               |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

               Figure 1: Value Field of the "Additional PMSI
                Tunnel Attribute Flags" Extended Community

A BGP speaker MUST NOT attach more than one "Additional PMSI Tunnel Attribute Flags" Extended Community to a given BGP UPDATE. If a given BGP UPDATE already contains an "Additional PMSI Tunnel Attribute Flags" Extended Community, then a BGP speaker MUST NOT attach any additional such Extended Communities. Rule of thumb: one per UPDATE, no sneaking in extras 🙅‍♀️.

If a BGP speaker receives a BGP UPDATE with more than one "Additional PMSI Tunnel Attribute Flags" Extended Community attached, only the flag settings in the first occurrence of the Extended Community are significant. Flag settings in subsequent occurrences MUST be ignored. When propagating the UPDATE, all instances of the Extended Community other than the first SHOULD be removed 🧹.

Now suppose a BGP speaker receives an UPDATE message that contains a "PMSI Tunnel" attribute, but does not contain an "Additional PMSI Tunnel Attribute Flags" Extended Community. If the "Extension" flag of the "PMSI Tunnel" attribute is set, the UPDATE is considered to be malformed, and the "treat-as-withdraw" procedure of [RFC7606] MUST be applied 😭.

If a BGP speaker receives an UPDATE message that contains one or more "Additional PMSI Tunnel Attribute Flags" Extended Communities, but either (a) that UPDATE message does not contain a "PMSI Tunnel" attribute, or (b) the "Extension" flag of the "PMSI Tunnel" attribute is not set, then the Extended Community(ies) SHOULD be removed and SHOULD NOT be redistributed. The BGP UPDATE message MUST be processed (and if necessary, redistributed) as if the Extended Community(ies) had not been present. Basically, it gets treated like the extra community was never there 🫠.

A BGP speaker that supports the current document, but does not recognize a particular flag (either in the "PMSI Tunnel" attribute "Flags" field or in the "Additional PMSI Tunnel Attribute Flags" Extended Community), MUST simply ignore that flag. If the BGP speaker propagates the "PMSI Tunnel" attribute, the "Additional PMSI Tunnel Attribute Flags" Extended Community, or both along with the UPDATE message, it SHOULD leave the setting of the flag unchanged 🦋.

It's possible that a particular application will require all members of a particular set of BGP speakers to support a particular flag. How it is determined whether all such BGP speakers support that flag is outside the scope of this document 🤷‍♀️.

In some situations, a BGP speaker may need to modify or replace the "PMSI Tunnel" attribute before propagating an UPDATE. If the "Extension" flag of the "PMSI Tunnel" attribute was set before the attribute was modified or replaced, but that flag is no longer set after the attribute is modified or replaced, then any "Additional PMSI Tunnel Attribute Flags" Extended Communities MUST be removed before the UPDATE is propagated. If the "PMSI Tunnel" attribute is removed entirely before an UPDATE is propagated, the "Additional PMSI Tunnel Attribute Flags" Extended Communities (if any) MUST also be removed 💅.

5. Normative References ✨

okay so this is where the receipts live 📚 the normative references are the other RFCs and docs this one leans on, and each one is listed with all its details so you can go find it yourself 🫶

Acknowledgments

the authors wanted to give a shoutout to Martin Vigoureux for reviewing this doc 🙌 and also thank Christian Huitema and Alexey Melnikov for their review and comments. the people who read it closely are the real MVPs 👑

Authors' Addresses

here's who wrote it and where to find them 🎀

Eric C. Rosen
Juniper Networks, Inc.
10 Technology Park Drive
Westford, Massachusetts  01886
United States

Email: erosen@juniper.net


Thomas Morin
Orange
2, avenue Pierre-Marzin
22307 Lannion Cedex
France

Email: thomas.morin@orange.com
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