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

["Susan Hares" <[e-mail]>]

Bruno: 

 

Good catch on this point. 

 

“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”. 

 

While we discussed this earlier, the current version of the draft does not
have anything regarding it.  Randy indicated he would be replying regarding
your long message. 

 

Susan Hares 

 

From: Idr [mailto:[e-mail]] On Behalf Of
[e-mail]
Sent: Tuesday, January 29, 2019 12:26 PM
To: Susan Hares
Cc: [e-mail]
Subject: Re: [Idr] WG Last Call on Extened Message Support

 

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-implementati
ons 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., [
<https://tools.ietf.org/html/draft-ietf-idr-bgp-extended-messages-27#ref-I-D
.ietf-sidr-bgpsec-protocol> 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

 

 

[
<https://tools.ietf.org/html/draft-ietf-idr-bgp-extended-messages-27#ref-I-D
.ietf-sidr-bgpsec-protocol> 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/>
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-implementat
ions>
https://trac.ietf.org/trac/idr/wiki/draft-ietf-idr-bgp-extended-implementati
ons

 

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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electroniques etant susceptibles d'alteration,
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