Re: [Idr] WG Last Call on Extened Message Support

[<[e-mail]>]

Hi WG,

Please find below some comments.
As of today, I don't believe this specification is ready to be progressed to IESG/RFC, especially for a document updating RFC 4271 (core BGP spec).

> The WG chairs intend to forward this draft to the IESG with the current level of implementation.

https://trac.ietf.org/trac/idr/wiki/draft-ietf-idr-bgp-extended-implementations says : 5a

Does not send Extended Message capability

Yes

Yes

Yes


I may be misunderstanding the implementation report, but my reading of the above is that none of the reported implementations sends the capability hence no implementation supports draft-ietf-idr-bgp-extended-messages.. Here this document is updating RFC 4271, so it is not a minor extension for a niche use case. So I don't see the arguments for not requiring the IDR's usual two interoperable implementations.

----
§ 1
" As BGP is extended to support newer AFI/SAFIs and
   newer capabilities (e.g., [I-D.ietf-sidr-bgpsec-protocol<https://tools.ietf.org/html/draft-ietf-idr-bgp-extended-messages-27#ref-I-D.ietf-sidr-bgpsec-protocol>]), there is
   a need to extend the maximum message size beyond 4096 octets.  "

https://tools.ietf.org/html/draft-ietf-idr-bgp-extended-messages-27#section-1


[I-D.ietf-sidr-bgpsec-protocol<https://tools.ietf.org/html/draft-ietf-idr-bgp-extended-messages-27#ref-I-D.ietf-sidr-bgpsec-protocol> is now RFC 8205 (thanks for updating the reference). It has removed the normative/any reference to draft-ietf-idr-bgp-extended-messages. So presumably BGP Sec does not need draft-ietf-idr-bgp-extended-messages.
Can we have an update on this?
Can the introduction of draft-ietf-idr-bgp-extended-messages be updated to introduce on the real reasons/needs?

----
§4

§3 says "A peer which does not advertise this capability MUST NOT send BGP
   Extended Messages, and BGP Extended Messages MUST NOT be sent to it."

Fine. Text in §4 should probably be aligned with the above .e.g.

OLD: A BGP speaker
   MAY send Extended Messages to its peer only if it has received the
   Extended Message Capability from that peer.

NEW:
A BGP speaker
   MAY send Extended Messages to its peer only if it has sent and received the
   Extended Message Capability to and from that peer.

----

"   Applications generating information which might be encapsulated
   within BGP messages MUST limit the size of their payload to take the
   maximum message size into account."

I don't see what new behavior is been defined here. If there is none, I would suggest to remove this sentence

----
   A BGP announcement will, in the normal case, propagate throughout the
   BGP speaking Internet; and there will undoubtedly be BGP speakers
   which do not have the Extended Message capability.  Therefore,
   putting an attribute which can not be decomposed to 4096 octets or
   less in an Extended Message is a likely path to routing failure.


The issue is not specific to attributes bigger than 4096 octets, but to BGP message whose length is bigger than 4096, irrespective of the size of each attribute.
Please elaborate on what you mean by "an attribute which can not be decomposed to 4096 octets"

---
"   It is RECOMMENDED that BGP protocol developers and implementers are
   conservative in their application and use of Extended Messages."

What does this mean exactly? That they don't use this extension? That they don't use this extension unless XX_TO BE SPECIFIED_XX?

---
  Future protocol specifications will need to describe how to handle
   peers which can only accommodate 4096 octet messages.

Why is this limited to future specifications? A priori, using existing BGP mechanism (AFI/SAFI, attributes, * communities) one could exceed the size of 4096 octets. How does the BGP speaker supposed to behave in this case? This should be described in this specification. Note that this is not a case of error handling, as every BGP speaker is behaving as specified.
----
Depending on the above specification, a section describing the operational consequences in a network (such as the Internet, BGP Enabled ServiceS/VPN networks) is probably needed. Possible consequences could be BGP NLRI being removed in the middle of such network, or (extended) community (such as Route Targets) been removed. Both having significant consequences on the availability provided by the network.

---
§4
OLD: The Extended Message Capability only applies to all messages except for the OPEN message.
Probably
NEW: The Extended Message Capability applies to all message types except for the OPEN message (type 1).
----
§8

"This extension to BGP does not change BGP's underlying security issues »

Before evaluating this, I think this document should first specified how a BGP messages bigger than 4096 octets is handled when it needs to be sent to a received not supporting this extension.

Nits:
OLD : to reduce compexity
NEW : to reduce complexity

Thanks,
--Bruno

From: Idr [mailto:[e-mail]] On Behalf Of Susan Hares
Sent: Tuesday, January 29, 2019 12:33 PM
To: [e-mail]
Subject: [Idr] WG Last Call on Extened Message Support


This begins a 2 week WG LC on Extended Message Support for BGP (draft-ietf-idr-bgp-extended-messages-27).  You can access the draft at:

https://datatracker.ietf.org/doc/draft-ietf-idr-bgp-extended-messages/

The authors should indicate whether they know of any IPR.   Implementers are encouraged to update the  implementation data at:

https://trac.ietf.org/trac/idr/wiki/draft-ietf-idr-bgp-extended-implementations

The draft provides a means for expanding the BGP message to 65535 octets for all messages except OPEN messages.  BGP message space is running short for all of the potential attributes or additions proposed by BGP-LS features.

The WG chairs intend to forward this draft to the IESG with the current level of implementation.

As you comment on the draft, please consider if: a) the technology is mature, b) the additional space in a BGP message would be helpful for those deploying BGP-LS or SR, and c) if the specification is ready for publication.

Sue Hares (WG Chair, Shepherd)



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