Re: [Idr] Capability Advertisement in draft-ietf-idr-bgp-extended-messages

Robert Raszuk <robert@raszuk.net> Fri, 09 August 2019 16:23 UTC

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From: Robert Raszuk <robert@raszuk.net>
Date: Fri, 09 Aug 2019 12:23:04 -0400
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To: Alvaro Retana <aretana.ietf@gmail.com>
Cc: "idr@ietf. org" <idr@ietf.org>, idr-chairs@ietf.org, draft-ietf-idr-bgp-extended-messages@ietf.org, Susan Hares <shares@ndzh.com>
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Subject: Re: [Idr] Capability Advertisement in draft-ietf-idr-bgp-extended-messages
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Hi Alvaro,

So imagine that BGP Operational Message draft get's standardized and one
TLV will ask to replay back the received message to the sender.

Example: 3.4.3.3
<https://tools.ietf.org/html/draft-ietf-idr-operational-message-00#section-3.4.3.3>.
Malformed Update Dump (MUD)

How is this going to work in this case when I receive over 4K PDU and can
not mirror it back to sender per his request ?

Aren't we getting ourselves into the trap here and "Oooops" condition by
allowing this asymmetry ?

Thx,
R.


On Fri, Aug 9, 2019 at 9:28 AM Alvaro Retana <aretana.ietf@gmail.com> wrote:

> Hi!
>
> Thank you for everyone’s opinion and discussion!
>
> The current text in -35 says this:
>
>    A BGP speaker that is capable of receiving BGP Extended Messages
>    SHOULD advertise the BGP Extended Message Capability to its peers
>    using BGP Capabilities Advertisement [RFC5492].  A BGP speaker MAY
>    send Extended Messages to a peer only if the Extended Message
>    Capability was received from that peer.
>
>    An implementation that advertises the BGP Extended Message capability
>    MUST be capable of receiving a message with a Length up to and
>    including 65,535 octets.
>
>
> From the thread, the consensus is to keep the asymmetric capability
> advertisement.  As written, operators have the flexibility to advertise (or
> not) the capability to meet their local policy.
>
>
> Jeff brought up the point that rfc4271 (§6.3 / UPDATE Message Error
> Handling) says that, for some errors, the NOTIFICATION "Data field MUST
> contain the attribute (type, length, and value)."  The problem is that if
> an Extended UPDATE (> 4k) with an erroneous attribute is received from a
> speaker that hasn't advertised the Capability (which is ok because of the
> asymmetry), then that peer may not be able to handle an Extended
> NOTIFICATION (> 4k).
>
> NEW (to be inserted as the 3rd paragraph in §5 (Error Handling))>
>    The UPDATE Message Error Handling, as specified in Section 6.3 of
> [RFC4271],
>    is not changed.  However, if a NOTIFICATION is to be sent to a BGP
> speaker
>    that hasn't advertised the BGP Extended Message Capability, the maximum
> size
>    of the message MUST NOT exceed 4096 octets.
>
>
> Authors: If no word-smithing suggestions are received in the next couple
> of days, please submit a revised draft by the middle of next week.
>
> Thanks!
>
> Alvaro.
>
> On July 31, 2019 at 4:06:04 PM, Alvaro Retana (aretana.ietf@gmail.com)
> wrote:
>
> On July 31, 2019 at 1:31:11 PM, Susan Hares (shares@ndzh.com) wrote:
>
> Dear WG:
>
> As I hope all of you know, the Extended Messages draft is being processed
> by the IESG.
>
> Enke had brought up [1] some confusion in the text in rfc5492 related to
> the need, or not, for both BGP speakers to advertise a Capability before it
> can be used.  I discussed this point with Enke and John Scudder last week
> in Montreal — we looked at the text in the RFC and how recent Capabilities
> had been specified — and concluded that the intent of the RFC was to
> require at least one speaker to advertise the Capability…but that it should
> be the responsibility of any document defining a Capability to explicitly
> specify any changes.
>
> IOW, in some cases it may be enough for one of the peers to advertise a
> Capability, but in other cases it may be required for both to do so.
>  [Enke/John will work on an Update to rfc5492 to clarify.]
>
> Related to Extended Messages, here’s is what Enke proposed on the list [2]:
>
>    As long as Speaker A is able and willing to receive large messages (by
> advertising
>    the capability), its neighbor would be allowed to send such messages to
> Speaker A.
>    Such behavior does not depend on whether Speaker A is able / willing /
> need to
>    send any large messages to its neighbors.
>
>
> We have modified the text in draft-ietf-idr-bgp-extended-messages to
> reflect Enke’s proposal (from -35):
>
>    A BGP speaker that is capable of receiving BGP Extended Messages
>    SHOULD advertise the BGP Extended Message Capability to its peers
>    using BGP Capabilities Advertisement [RFC5492].  A BGP speaker MAY
>    send Extended Messages to a peer only if the Extended Message
>    Capability was received from that peer.
>
>    An implementation that advertises the BGP Extended Message capability
>    MUST be capable of receiving a message with a Length up to and
>    including 65,535 octets.
>
>
> During the IESG Evaluation, Sue pointed out that we removed the piece of
> text below:
>
> Just to let you know that the text below:
>
>
>
> “A peer which does not advertise this capability MUST NOT send BGP
>
>
>    Extended Messages, and BGP Extended Messages MUST NOT be sent to it.”
>
>
>
> was added due to comments on the IDR WG list from reviewers and
> operators.
>
> Given that Extended Messages is a very important extension to BGP, and
> even though I didn’t see objections in the thread mentioned above, I want
> to confirm one more time that the current text is ok with the WG.  The
> effective change is really related to the piece that says "A peer which
> does not advertise this capability MUST NOT send BGP Extended Messages”,
> which would require that both peers advertise the Capability before it can
> be used.
>
> Please reply with any comments by end-of-day on August 8, 2019.  Please
> explain any arguments against what is currently specified in -35.   The
> document is scheduled to be considered by the IESG on Aug/8, but I will
> hold approving publication until there is consensus on this thread.
>
> Thanks!
>
> Alvaro.
>
> [1] https://mailarchive.ietf.org/arch/msg/idr/vaBLOKHQZlRCiJOMTT8VjJrWp7c
> [2] https://mailarchive.ietf.org/arch/msg/idr/K5rA5rVci6VhMv5-UqXXaoRlvXo
>
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