Re: [trill] TRILL OAM Requirements: available paths
Donald Eastlake <d3e3e3@gmail.com> Mon, 30 April 2012 01:27 UTC
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From: Donald Eastlake <d3e3e3@gmail.com>
Date: Sun, 29 Apr 2012 21:26:50 -0400
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Subject: Re: [trill] TRILL OAM Requirements: available paths
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I don't think the wording "all paths" should ever be used. If you the it literally, it would even include paths that go through some RBridges more than once. I don't particularly like "all ECMP paths" either. I think the clearest wording is "all least cost paths" if you are talking about known unicast. (And "all distribution tree paths" if you were talking about multi-destination frames.) Thanks, Donald ============================= Donald E. Eastlake 3rd +1-508-333-2270 (cell) 155 Beaver Street, Milford, MA 01757 USA d3e3e3@gmail.com On Sat, Apr 28, 2012 at 11:45 PM, Erik Nordmark <nordmark@acm.org> wrote: > On 4/27/12 5:12 PM, Tissa Senevirathne (tsenevir) wrote: >> >> Of course it is possible. The IS-IS topology table provide the >> information on all available ECMP paths to a specific destination when >> the egress RBRidge nickname is known. That is what TRILL unicast >> forwarding table all about. Not sure why you are saying it is not >> possible to know all ECMP paths. > > > You are talking about what Santosh called "all theoretically available > paths". Those can be determined from IS-IS. > > But the document talks about "all available paths" and I don't know what > that is supposed to mean. Do you have a succinct definition? > > What is clear to me is that there can be a subset of the paths that are > determined from IS-IS that would never be used, because no entropy in a > packet would every pick that path. > > Is the requirement in the document that the OAM solution should be able to > test those paths? > > >> What path among available paths to be selected for a specified is a >> local matter. That is what all about flow entropy discovery. Like I >> stated earlier how it is discovered is a framework and solution issue. > > > Agreed. > > >> If you need some reference how it is done in the MPLS world RFC 4379 is >> a good reference. > > > AFAIK MPLS doesn't have a locally defined ECMP hash function in every hop. > TRILL does, which makes these aspects different. > > Regards, > Erik > > >> -----Original Message----- >> From: trill-bounces@ietf.org [mailto:trill-bounces@ietf.org] On Behalf >> Of Erik Nordmark >> Sent: Friday, April 27, 2012 4:07 PM >> To: Santosh Rajagopalan >> Cc: trill@ietf.org >> Subject: Re: [trill] TRILL OAM Requirements: available paths >> >> On 4/27/12 2:15 PM, Santosh Rajagopalan wrote: >>> >>> I agree, the wording needs to be tightened to say "all possible ecmp >>> paths" rather than "all available paths". An operator working out >>> R1-R2 communication is interested in all possible paths data traffic >>> could take rather than all theoretically available paths. >> >> >> The issue is that there is nothing in the TRILL dataplane nor IS-IS >> control plane which helps the operator determine that some paths >> (through RB121 and RB112 in the example) are not possible; the ECMP >> input and hashing is a completely local matter on each RBridge. >> >> It isn't useful to state a requirement around something that can't be >> determined. >> >> Erik >> >>> >>> >>> From: Erik Nordmark<nordmark@acm.org> >>> To: trill@ietf.org >>> Date: 04/27/2012 09:53 AM >>> Subject: [trill] TRILL OAM Requirements: available paths Sent by: >>> trill-bounces@ietf.org >>> ---------------------------------------------------------------------- >>> -- >>> >>> >>> >>> >>> Two requirements use the wording "all available paths." and "all >>> available ECMP paths.", respectively and I'm not sure I know what that >> >> >>> means. >>> >>> Take the following example picture: >>> >>> R1 >>> / \ >>> / \ >>> / \ >>> / \ >>> / \ >>> RB11 RB12 >>> / \ / \ >>> / \ / \ >>> RB111 RB112 RB121 RB122 >>> \ \ / / >>> \ \ / / >>> \ \/ / >>> ------R2------ >>> >>> We can see that there are 4 paths with 3 hops to get from R1 to R2, >>> with two layers of ECMP decisions. But how many available paths are >> >> there? >>> >>> >>> Given that the RBridges make independent ECMP decisions, and how they >>> do that is a local matter, it could be the case that for any packet, >>> if R1 picks the left link, then R11 would also pick the left link; if >>> R1 picks the right link, then R12 also picks the right link. >>> Thus there would be no packet (data or OAM) that would cause packets >>> between R1 and R2 to pass via RB112 or RB121. >>> >>> Even if we ignore that as unlikely, there is still the fact that R1 >>> can't easily tell how many (shortest) paths there might be between it >>> and R2. With single-level TRILL the LSDB could be used to tell, but if >> >> >>> we ever go to multi-level that wouldn't be the case any more. >>> And even if R1 knows that there are 4 potential paths, it can't format >> >> >>> a data packet (or format the flow entropy in an OAM packet) in such a >>> way that particular paths get chosen by downstream ECMP decisions. >>> >>> Thus for any notion of "all available paths" that make sense to me, >>> we'd need an OAM approach that can explore the topology one hop at a >>> time and at each hop explore all the possible ECMP choices. Using the >>> entropy doesn't help with this (but the entropy is critical for >>> following the path taken by a particular flow of data packets). >>> >>> Hence it would be good to clarify what the assumptions are behind this >> >> >>> notion of all available paths. >>> >>> Thanks, >>> Erik >>> >>> _______________________________________________ >>> trill mailing list >>> trill@ietf.org >>> https://www.ietf.org/mailman/listinfo/trill >>> >>> >> >> _______________________________________________ >> trill mailing list >> trill@ietf.org >> https://www.ietf.org/mailman/listinfo/trill >> > > _______________________________________________ > trill mailing list > trill@ietf.org > https://www.ietf.org/mailman/listinfo/trill
- [trill] TRILL OAM Requirements: available paths Erik Nordmark
- Re: [trill] TRILL OAM Requirements: available pat… Tissa Senevirathne (tsenevir)
- Re: [trill] TRILL OAM Requirements: available pat… Santosh Rajagopalan
- Re: [trill] TRILL OAM Requirements: available pat… Erik Nordmark
- Re: [trill] TRILL OAM Requirements: available pat… Tissa Senevirathne (tsenevir)
- Re: [trill] TRILL OAM Requirements: available pat… Sam Aldrin
- Re: [trill] TRILL OAM Requirements: available pat… Erik Nordmark
- Re: [trill] TRILL OAM Requirements: available pat… Tissa Senevirathne (tsenevir)
- Re: [trill] TRILL OAM Requirements: available pat… Sam Aldrin
- Re: [trill] TRILL OAM Requirements: available pat… Erik Nordmark
- Re: [trill] TRILL OAM Requirements: available pat… Sam Aldrin
- Re: [trill] TRILL OAM Requirements: available pat… Sam Aldrin
- Re: [trill] TRILL OAM Requirements: available pat… Donald Eastlake
- Re: [trill] TRILL OAM Requirements: available pat… Tissa Senevirathne (tsenevir)
- Re: [trill] TRILL OAM Requirements: available pat… David M Bond
- Re: [trill] TRILL OAM Requirements: available pat… James Carlson
- Re: [trill] TRILL OAM Requirements: available pat… Puneet Agarwal
- Re: [trill] TRILL OAM Requirements: available pat… Santosh Rajagopalan
- Re: [trill] TRILL OAM Requirements: available pat… Tissa Senevirathne (tsenevir)
- Re: [trill] TRILL OAM Requirements: available pat… Santosh Rajagopalan
- Re: [trill] TRILL OAM Requirements: available pat… Tissa Senevirathne (tsenevir)
- Re: [trill] TRILL OAM Requirements: available pat… Santosh Rajagopalan
- Re: [trill] TRILL OAM Requirements: available pat… Tissa Senevirathne (tsenevir)
- Re: [trill] TRILL OAM Requirements: available pat… Donald Eastlake