Re: [Isis-wg] New Version Notification for draft-ginsberg-isis-sbfd-discriminator-00.txt

Hannes Gredler <hannes@juniper.net> Wed, 14 May 2014 16:23 UTC

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From: Hannes Gredler <hannes@juniper.net>
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Date: Wed, 14 May 2014 18:22:57 +0200
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To: "Nobo Akiya (nobo)" <nobo@cisco.com>
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Cc: Jeffrey Haas <jhaas@pfrc.org>, "Les Ginsberg \(ginsberg\)" <ginsberg@cisco.com>, "rtg-bfd@ietf.org" <rtg-bfd@ietf.org>, "isis-wg@ietf.org" <isis-wg@ietf.org>
Subject: Re: [Isis-wg] New Version Notification for draft-ginsberg-isis-sbfd-discriminator-00.txt
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nobo,

assume that the advertising node only supports BFD4
and the receiving node does support only BFD6. - 
how to detect such a condition ?

/hannes


On May 14, 2014, at 6:15 PM, Nobo Akiya (nobo) wrote:

> Hi Hannes,
> 
> Please see in-line.
> 
>> -----Original Message-----
>> From: Hannes Gredler [mailto:hannes@juniper.net]
>> Sent: Wednesday, May 14, 2014 11:58 AM
>> To: Nobo Akiya (nobo)
>> Cc: Jeffrey Haas; Les Ginsberg (ginsberg); rtg-bfd@ietf.org; isis-wg@ietf.org
>> Subject: Re: [Isis-wg] New Version Notification for draft-ginsberg-isis-sbfd-
>> discriminator-00.txt
>> 
>> On Wed, May 14, 2014 at 03:48:10PM +0000, Nobo Akiya (nobo) wrote:
>> | Hi Jeff,
>> |
>> | > On Wed, May 14, 2014 at 05:26:52PM +0200, Hannes Gredler wrote:
>> | > > On May 14, 2014, at 5:22 PM, Les Ginsberg (ginsberg) wrote:
>> | > > > Thanx for the comments.
>> | > > > I don't see how your proposal solves the problem you are
>> | > > > attempting to
>> | > address. The sender of the S-BFD packet has no control over what
>> | > interface is used to receive the packet on the target node.
>> | > Associating it with a prefix will not help in that regard.
>> | > >
>> | > > well it would help first endpoint discovery and pinning down BFD
>> | > > traffic to
>> | > particular line card.
>> | >
>> | > Indeed.  In the SPRING related case (or even some MPLS scenarios),
>> | > traffic may be heavily steered to a given interface.  This interface
>> | > may not even be to a router, but may be an ingress for a SFC device
>> | > and that ingress is critical for the execution of the chain.
>> |
>> | In those cases, one should be sending S-BFD packet in-band, which would
>> go through the specific interface/LC to reach the reflector session on the
>> target node (i.e. outage will be detected regardless of the discriminator
>> used). So having separate reflector discriminator won't be adding further
>> benefit.
>> |
>> | Flip side is, if a reflector is hosted on LC 1 and traffic engineered tunnel is
>> terminating on LC2, then outage of LC1 can cause the "no S-BFD response"
>> on the tunnel terminating on LC2. However, I would think this is a limitation
>> with implementation.
>> 
>> what about AF discovery ? - how would a receiver know what AF a S-BFD
>> session to bring up with ?
> 
> I was under the impression that IP header (i.e version) can distinguish the AF if implementations required demux'ing received S-BFD packet based on AF. If I missed your point/question, do clarify.
> 
> -Nobo
> 
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