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

Hannes Gredler <hannes@juniper.net> Wed, 14 May 2014 15:58 UTC

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Date: Wed, 14 May 2014 17:57:39 +0200
From: Hannes Gredler <hannes@juniper.net>
To: "Nobo Akiya (nobo)" <nobo@cisco.com>
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References: <20140508144606.23448.98448.idtracker@ietfa.amsl.com> <F3ADE4747C9E124B89F0ED2180CC814F23D873B9@xmb-aln-x02.cisco.com> <9DDF3832-A276-40F1-AF24-2CEAB31E63DC@juniper.net> <F3ADE4747C9E124B89F0ED2180CC814F23DB5518@xmb-aln-x02.cisco.com> <922372D3-6CE8-461E-9BD4-94C2B050C37D@juniper.net> <20140514153641.GC13993@pfrc> <CECE764681BE964CBE1DFF78F3CDD3941E14ED44@xmb-aln-x01.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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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 ?