Re: [Isis-wg] Requesting WG adoption of draft-baker-ipv6-isis-dst-src-routing-06
"Les Ginsberg (ginsberg)" <ginsberg@cisco.com> Thu, 27 October 2016 14:58 UTC
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From: "Les Ginsberg (ginsberg)" <ginsberg@cisco.com>
To: David Lamparter <equinox@diac24.net>, Chris Bowers <cbowers@juniper.net>
Thread-Topic: [Isis-wg] Requesting WG adoption of draft-baker-ipv6-isis-dst-src-routing-06
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Date: Thu, 27 Oct 2016 14:57:56 +0000
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Subject: Re: [Isis-wg] Requesting WG adoption of draft-baker-ipv6-isis-dst-src-routing-06
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David - > -----Original Message----- > From: Isis-wg [mailto:isis-wg-bounces@ietf.org] On Behalf Of David > Lamparter > Sent: Thursday, October 27, 2016 7:12 AM > To: Chris Bowers > Cc: isis-chairs@tools.ietf.org; FredBaker.IETF@gmail.com; isis-wg@ietf.org > list (isis-wg@ietf.org) > Subject: Re: [Isis-wg] Requesting WG adoption of draft-baker-ipv6-isis-dst- > src-routing-06 > > Hi Chris, > > On Thu, Oct 27, 2016 at 12:51:19PM +0000, Chris Bowers wrote: > > I have two main comments/questions on this. > > Useful feedback, Thanks! > > > 1) If I understand correctly, one reason to use existing > > multi-topology routing mechanisms for this is the requirement to > > support deployments where only a partial subset of routers support > > source address dependent routing. Ideally, this would allow an enterprise > site to start by upgrading a subset of routers to support SADR, starting at the > site egress routers. > > Yes, that's the intent. > > > However, this statement from section 2.3 seems to imply that all of > > the routers in the enterprise network would need to support multi- > topology even if they don't support SADR. > > No, non-MT routers would be ignorant of the MT information and would not > see any of the SADR routes -- which is exactly the intended goal. I'll update > the draft to say this very clearly. > [Les:] For my taste the best way to do this is simply to remove the statement: " Even installations that previously used only MTID 0 (i.e. no M-ISIS) would need to start using MTID TBD-MT0." You don't need to explain the way MT works because you are making no changes to RFC 5120. Trying to "explain" is only going put you at risk for misinterpretation - and this thread is an existence proof for that. :-) It is the first sentence of the same paragraph which is important: " As this compatibility mechanism is not considered optional, M-ISIS MUST therefore be implemented for supporting the protocol outlined in this document." (though I would prefer replacing "protocol" with "extensions") Les > > As this compatibility mechanism is not considered optional, M-ISIS > > MUST therefore be implemented for supporting the protocol outlined in > > this document. Even installations that previously used only MTID 0 > > (i.e. no M-ISIS) would need to start using MTID TBD-MT0. > > Ah, I see where I misworded that. It needs to say "need to start using MTID > TBD-MT0 *for transporting SADR routes*". > > Sidenote: at some point, the draft allowed non-usage of MT for greenfield > setups (all routers with SADR support and everything in zero MTID / no M- > ISIS used at all), with homenet in mind for that. I'm now thinking that was a > stupid idea. However, there might be leftover weird wording in the draft > from that. > > > It would be good to clarify this statement. I interpret it to mean > > that all prefix advertisements to use TLV#237, so that even routers > > that are currently using TLV#236 to advertise IPv6 prefixes would need > > to start using TLV#237 instead. But it is not clear what MT-ID a router not > supporting SADR should use when advertising a prefix in TLV#237, since it > can't use MT-ID=0. > > No -- all non-SADR routing information stays in MTID 0/TLV 236 (or 2/237, if > you're using separate IPv4/IPv6 MT topologies). There is no change to non- > SADR routes, and by using a separate MTID for SADR, they will be routed > "around" as non-participants in the SADR topology to ensure proper SADR > operation. (That's the core idea why MT is used > here.) > > > As a nice side-effect, the operator also has some good control here in > feeding information to non-SADR systems. For example, they can advertise > non-SADR default routes at one or more selected SADR routers, so traffic > towards the internet flows towards the "SADR subdomain", where it can > then be SADR-routed to the proper exit. > > (MT makes sure SADR-routed traffic, once in the "SADR subdomain", will > never be routed back towards non-SADR routers. They're not in the MT > topology, thus not in SPF, thus not in the shortest path used for SADR > routes.) > > > In any case, it would be good to clarify overall if and how this > > solution achieves the goal of requiring only a subset of routers to be > upgraded from a basic non-MT deployment of ISIS. > > As part of this, it would be good to explain how TLV#222 and TLV#229 > > (the other multi-topology > > TLVs) are used in the partial deployment case. > > > > 2) For addressing PA multi-homing for IPv6 w/o NAT in existing > > enterprises, I would guess that >90% of enterprises running a > > link-state routing protocol are running OSPF as opposed to ISIS. Is the > expectation that enterprises will switch to ISIS > > in order to address this problem? I would like to better understand what > use cases this work > > is targeted at from a practical point of view. > > There is/was a companion OSPF draft: > https://datatracker.ietf.org/doc/draft-baker-ipv6-ospf-dst-src-routing/ > which we need to revive I guess. The OSPF version has the additional > constraint that it is built on another draft in progress: > https://datatracker.ietf.org/doc/draft-ietf-ospf-ospfv3-lsa-extend/ > which led to (my personal) decision to focus on the IS-IS draft and "fix OSPF > later." Sorry, OSPF ;) > > > Updating the doc -- also planning to explain some protocol-agnostic MT > considerations in the rtgwg document -- expect another mail from me soon > (with a diff attached), > > > -David > > _______________________________________________ > Isis-wg mailing list > Isis-wg@ietf.org > https://www.ietf.org/mailman/listinfo/isis-wg
- [Isis-wg] Requesting WG adoption of draft-baker-i… David Lamparter
- Re: [Isis-wg] Requesting WG adoption of draft-bak… Fred Baker
- Re: [Isis-wg] Requesting WG adoption of draft-bak… Chris Bowers
- Re: [Isis-wg] Requesting WG adoption of draft-bak… David Lamparter
- Re: [Isis-wg] Requesting WG adoption of draft-bak… Les Ginsberg (ginsberg)
- Re: [Isis-wg] Requesting WG adoption of draft-bak… Tony Przygienda
- Re: [Isis-wg] Requesting WG adoption of draft-bak… David Lamparter
- Re: [Isis-wg] Requesting WG adoption of draft-bak… Tony Przygienda