Re: [Isis-wg] Proposed isis-wg documents - draft-ginsberg-isis-sbfd-discriminator-00

"Les Ginsberg (ginsberg)" <ginsberg@cisco.com> Thu, 21 August 2014 21:02 UTC

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From: "Les Ginsberg (ginsberg)" <ginsberg@cisco.com>
To: "Nobo Akiya (nobo)" <nobo@cisco.com>, Uma Chunduri <uma.chunduri@ericsson.com>, Christian Hopps <chopps@rawdofmt.org>, "isis-wg@ietf.org list" <isis-wg@ietf.org>
Thread-Topic: [Isis-wg] Proposed isis-wg documents - draft-ginsberg-isis-sbfd-discriminator-00
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Date: Thu, 21 Aug 2014 21:02:46 +0000
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Cc: Hannes Gredler <hannes@juniper.net>
Subject: Re: [Isis-wg] Proposed isis-wg documents - draft-ginsberg-isis-sbfd-discriminator-00
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Uma/Nobo -

The MT question has nothing to do w S-BFD - it is a generic issue for any type of BFD multi-hop session. If you have multiple topologies for a given address family and you would like the BFD packets to traverse a specific topology then you have to "mark"  BFD packets in the same way that data packets are marked for a given topology.  Then the packets will be processed at each hop along the way based on topology specific forwarding. What this marking is has nothing to do with BFD - and it certainly would NOT be a BFD discriminator as this would be specific to BFD packets only - which is not at all what you want.

   Les


> -----Original Message-----
> From: Nobo Akiya (nobo)
> Sent: Thursday, August 21, 2014 6:05 AM
> To: Uma Chunduri; Les Ginsberg (ginsberg); Christian Hopps; isis-
> wg@ietf.org list
> Cc: Hannes Gredler
> Subject: RE: [Isis-wg] Proposed isis-wg documents - draft-ginsberg-isis-sbfd-
> discriminator-00
> 
> Hi Uma, Les,
> 
> Pardon me for jumping in.
> Please see [NOBO] in-line.
> 
> > -----Original Message-----
> > From: Isis-wg [mailto:isis-wg-bounces@ietf.org] On Behalf Of Uma
> > Chunduri
> > Sent: Thursday, August 21, 2014 3:00 AM
> > To: Les Ginsberg (ginsberg); Christian Hopps; isis-wg@ietf.org list
> > Cc: Hannes Gredler
> > Subject: Re: [Isis-wg] Proposed isis-wg documents - draft-ginsberg-isis-
> sbfd-
> > discriminator-00
> >
> > Les,
> >
> > In-line [Uma1]:
> >
> > ===
> > > Support this.
> > >
> > > Qs:
> > >
> > > 1. What happened to the discussion on-  if this discriminator is a
> > > link property or node property as defined (asked originally in OSPF WG
> > > by Hannes).
> >
> > The question was answered - discriminators are a node property.
> >
> > [Uma1]: I saw SR use cases for SBFD and with ADJ-SID's (link specific)  this
> > can be a problem.
> 
> [NOBO] Couple of comments.
> 1. S-BFD document for Segment Routing is very stale. Authors should be
> able to roll out a revised and updated document this weekend.
> 2. S-BFD authors wanted to build in some connectivity test aspect into the S-
> BFD mechanism, particularly to allow verifying where Adj-SID terminates on
> the nextshop. However, there were strong push backs from the BFD WG
> regarding usage of BFD or S-BFD for connectivity test. Thus, S-BFD focuses
> only on continuity check, which is a node reachability check.
> 
> >
> > > 2. If MTs are on the same physical topology, I don't see the
> > > association of Discriminator to the logical topology/MT.  Is it
> > > already though and discounted ? If yes rationale will be helpful.
> >
> > Just as IP/IPv6 addresses are NOT topology specific, S-BFD discriminators
> are
> > NOT topology specific. The paths to reach a node may differ between
> > topologies - but that is not a property of the discriminator.
> >
> > [Uma1]:  A node may  be part of any  logical topology (MT) or may not be.
> > But, if the discriminator doesn't represent the same then the receiving
> node
> > (participating in multiple logical topologies) has no idea  for which topo
> the
> > same has been received or In other words  sending node may not be part
> of
> > the particular logical topo.
> >
> > Do you see this as an issue?
> 
> [NOBO] This is a very good comment Uma. My response would be that
> there's nothing in S-BFD documents that prevents tying of local S-BFD
> discriminator to set of incoming interfaces. i.e. a local S-BFD discriminator
> for an MT can programmed to process S-BFD packets coming in only from set
> of interfaces which belong in the MT. If such strict checks are desired,
> implementations are free to do so.
> 
> Thanks!
> 
> -Nobo
> 
> >
> > --
> > Uma C.
> >
> > _______________________________________________
> > Isis-wg mailing list
> > Isis-wg@ietf.org
> > https://www.ietf.org/mailman/listinfo/isis-wg