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

[<[e-mail]>]

Sue,

Please see 1 comment inline [Bruno]

From: Susan Hares [mailto:[e-mail]]
Sent: Tuesday, January 29, 2019 5:42 PM
To: DECRAENE Bruno TGI/OLN
Cc: [e-mail]
Subject: RE: [Idr] WG Last Call on Extened Message Support

Bruno:

Thank you for your comments on this topic - as I think

I did receive reports privately that we have 1 full implementations of draft-ietf-idr-bgp-extended-messages off list which is not listed in this report.   I hope those implementers will volunteer this information on the list.   If not, I will share this information with Alvaro and the IESG.

The SIDR work did define draft-ietf-bgp-extended-messages as a requirement and only moved to not specifying it when we could not quickly pass this through WG LC.

The real needs are a growing BGP-LS that may run out of BGP message space.  As my previous email to IDR indicates, I was hoping this handles an BGP message whose length is bigger than 4096 bytes.   Thank you for the correction of:

"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."


As to your comment:

"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."

This problem has been true for years, and thus as co-chairs had hoped to have the draft-ietf-bgp-extended-messages passed years ago.   As BGP-LS attributes grow use and in number, the potential of exceeding the BGP message limit increases.  It seems like a good direction to prevent issues.
[Bruno] I understand the BGP-LS issue and more generally I support removing such limitation even before we hit it. But IMHO a bigger issue is the potential impact in networks supporting many services and users such as the Internet and VPN ones. The document is applicable to all AFI/SAFI so I'd like the document to define how such routes would be handled when received with a set of attributes larger than the current 4271 limit and having to be sent to speakers not supporting Extend Message. One possible option may be to treat as withdraw, possibly on RR/over IBGP (i.e., within the AS) which would translates in routing inconsistencies within the AS. Another option would be to drop some attributes or some attribute content (which ones). There are probably other reasons. As of today the behavior is undefined and the document does not even refer to this problem. I'm sorry to say that is not good enough for me. Again is not even about error handling, but regular behavior of this specification.

Thanks
Cheers,
--Bruno


I hope the authors will comment on the changes you suggested to the text.

Cheers,
Susan Hares



From: [e-mail] [mailto:[e-mail]]
Sent: Tuesday, January 29, 2019 8:33 AM
To: Susan Hares
Cc: [e-mail]
Subject: RE: [Idr] WG Last Call on Extened Message Support

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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pas etre diffuses, exploites ou copies sans autorisation. Si vous avez recu ce message par erreur, veuillez le signaler
a l'expediteur et le detruire ainsi que les pieces jointes. Les messages electroniques etant susceptibles d'alteration,
Orange decline toute responsabilite si ce message a ete altere, deforme ou falsifie. Merci.

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