Re: RFC 2370 Update and a Proposed Change to Stub Area Behavior
Dave Katz <dkatz@JUNIPER.NET> Fri, 12 August 2005 02:33 UTC
Received: from odin.ietf.org ([132.151.1.176] helo=ietf.org) by megatron.ietf.org with esmtp (Exim 4.32) id 1E3PMk-0006fd-Ru for ospf-archive@megatron.ietf.org; Thu, 11 Aug 2005 22:33:50 -0400
Received: from cherry.ease.lsoft.com (cherry.ease.lsoft.com [209.119.0.109]) by ietf.org (8.9.1a/8.9.1a) with ESMTP id WAA13594 for <ospf-archive@LISTS.IETF.ORG>; Thu, 11 Aug 2005 22:33:48 -0400 (EDT)
Received: from vms.dc.lsoft.com (209.119.0.2) by cherry.ease.lsoft.com (LSMTP for Digital Unix v1.1b) with SMTP id <1.010C8A1C@cherry.ease.lsoft.com>; Thu, 11 Aug 2005 22:33:46 -0400
Received: by PEACH.EASE.LSOFT.COM (LISTSERV-TCP/IP release 14.4) with spool id 82224445 for OSPF@PEACH.EASE.LSOFT.COM; Thu, 11 Aug 2005 22:33:44 -0400
Received: from 207.17.137.57 by WALNUT.EASE.LSOFT.COM (SMTPL release 1.0m) with TCP; Thu, 11 Aug 2005 22:33:44 -0400
Received: from merlot.juniper.net (merlot.juniper.net [172.17.27.10]) by colo-dns-ext1.juniper.net (8.11.3/8.9.3) with ESMTP id j7C2Xh979184 for <OSPF@PEACH.EASE.LSOFT.COM>; Thu, 11 Aug 2005 19:33:43 -0700 (PDT) (envelope-from dkatz@juniper.net)
Received: from [172.16.12.13] (nimbus-sc.juniper.net [172.16.12.13]) by merlot.juniper.net (8.11.3/8.11.3) with ESMTP id j7C2XcG72385 for <OSPF@PEACH.EASE.LSOFT.COM>; Thu, 11 Aug 2005 19:33:38 -0700 (PDT) (envelope-from dkatz@juniper.net)
Mime-Version: 1.0 (Apple Message framework v733)
References: <42778DFC.4060107@cisco.com> <42FBBD03.6090004@cisco.com> <42FBE8A5.916FCADE@earthlink.net>
Content-Type: text/plain; charset="WINDOWS-1252"; delsp="yes"; format="flowed"
Content-Transfer-Encoding: quoted-printable
X-Mailer: Apple Mail (2.733)
Message-ID: <D04CF6BF-A60F-4F61-AC4A-5EFCC488A7A1@juniper.net>
Date: Thu, 11 Aug 2005 19:33:45 -0700
Reply-To: Mailing List <OSPF@PEACH.EASE.LSOFT.COM>
Sender: Mailing List <OSPF@PEACH.EASE.LSOFT.COM>
From: Dave Katz <dkatz@JUNIPER.NET>
Subject: Re: RFC 2370 Update and a Proposed Change to Stub Area Behavior
To: OSPF@PEACH.EASE.LSOFT.COM
In-Reply-To: <42FBE8A5.916FCADE@earthlink.net>
Precedence: list
Content-Transfer-Encoding: quoted-printable
I guess the broader question is, does this really matter at all? Are stub areas even useful any longer? Once upon a time, routers were memory-starved little boxes, but it's not clear to me at this point why anybody actually needs stub areas, unless they're still running AGS+'s someplace. Stub areas were a hack 15+ years ago (along with a bunch of other sort-sighted optimizations) but they don't seem all that useful these days... --Dave On Aug 11, 2005, at 5:09 PM, Erblichs wrote: > Group, > > I vote NOT to remove the restriction on the > flooding of unknown LSAs into stub area. I vote for > #2 or #3. Sorry, I have not spent any major time looking > at the pros / cons between the later 2. > > Why? > 1) The primary reason is that some of the these LSAs > are unknown to a percentage of the routers within > the stub area. Even the "attempt" to limit them > would follow the reason to limit the database size, > memory requirements, sizing of OSPF control packets, > etc... This limit is suggested in the 1st paragraph > of every OSPF v2 RFC. A copy is in the middle of this > email. > > 2) What is an unknown LSA? What LSA type greater than > X is an unknown? What help is it by having just 1 > router understand it? Can they equal in number > over time External-LSAs and be totally useless in > our env? Where should we put the older routers that > we want to isolate from our network? > > 3) Is is possible to have 30% - 90% of LSAs in a router's > db be present in a stub area, be unknown LSAs? Shouldn't > their be an attempt to limit this percentage? > > 3b) Could we be using / spending a large percentage > of our OSPF control packet time / resources > handling unknown LSAs? > > 4) Backward compatibility.. I would assume that most > environments would not like to just start seeing > something new in their network just show up. > > "An area can be configured as a stub when there is a single exit > point from the area, or when the choice of exit point need not > be made on a per-external-destination basis." > > Lets look at the third word, can. It would be different > if we used the word SHOULD or MUST. > > Thus, if a area that CAN be configured as a stub wishes > to process unknown LSAs, then why not configure the > without the STUB area identification? Wouldn't this allow > for backward capability? Yes, we then allow AS-external-LSAs > in this non named stubby area. > > Or create a new "stubby area" type that accepts or > not accept, xyz type LSAs. This new area type would then be > allowed to accept new LSAs as they show up? The diff > would be that "unknown LSAs" have no restrictions and > could consume the majority of the router's LSDB. > > > Mitchell Erblich > ----------------------- > > > RFC 1247, 1583, 2178, 2328 : OSPFv2. > --------- > 3.6 Supporting stub areas > > In some Autonomous Systems, the majority of the topological > database may > consist of external advertisements. An OSPF external advertisement is > usually flooded throughout the entire AS. However, OSPF allows > certain > areas to be configured as "stub areas". External advertisements > are not > flooded into/throughout stub areas; routing to AS external > destinations > in these areas is based on a (per-area) default only. This reduces > the > topological database size, and therefore the memory requirements, > for a > stub area's internal routers. > > > ========================== > > ======================== > > Acee Lindem wrote: > >> >> At the 63rd IETF in Paris, I proposed that we remove the >> restriction on the >> flooding of unknown LSAs into stub areas. Here is an excerpt from the >> presentation: >> >> - Section 2.9 mandates that an OSPFv3 router should NOT advertise an >> unknown LSA if the U bit is set to “1” – flood as if known. >> ->Should be removed in RFC 2740 respin. >> ->Limits backward compatibility for new LSA types >> ->No corresponding rule for opaque LSAs >> ->Fact that LSA is flooded at all implies one router is stub/NSSA >> understands it. >> ->Ineffective/non-deterministic database limit >> ->As long as there is an intra-area spanning tree of routers that >> understand the LSA type - The LSA will be in everyones database >> >> Comments? Speak now if you wish to retain the current stub area >> restriction. >> My intent is to deprecate it with an appendix documenting it's >> removal. >> >> Thanks, >> Acee >> >> Acee Lindem wrote: >> >> >>> In the evolution of the OSPFv2 protocol specification >>> (RFC 1247->RFC 1583 -> RFC 2178 -> RFC 2328) numerous >>> bugs were fixed and some protocol behaviors were altered. Examples >>> include the metric cost for area ranges and the selection of the >>> ASBR for AS external route computation. >>> >>> In the context of documenting the OSPFv3 NSSA differences I've >>> looked again at section 2.10 and I really think the idea of not >>> flooding >>> unknown LSA types with the U-bit set to 1 is broken. I think it >>> breaks >>> the whole idea of being able to introduce new LSA types in a >>> backward >>> compatible fashion. Furthermore, it won't stop the leakage of these >>> unknown LSAs when some routers understand them and others do not - >>> it all depends on whether you have a spanning tree of routers that >>> understand them. Since the LSAs in question are area scoped or link >>> scoped, it implies that at least one router (the originator) >>> understands the >>> new type and you will have a mixture. IMHO, this is broken. I've had >>> some discussions with others who agree. At this juncture, >>> we have 3 alternatives: >>> >>> 1) Remove the restriction for that unknown LSAs with the U-bit >>> set to 0 for stub areas. >>> 2) Extend the broken restriction to NSSAs in the update. >>> 3) Limit the damage to stub areas and only restrict AS scoped LSAs >>> from NSSAs. >>> >>> Of course, I'd vote for #1 or I wouldn't be sending this E-mail. >>> >>> Thanks, >>> Acee >>> >>> > >
- RFC 2370 Update and a Proposed Change to Stub Are… Acee Lindem
- Re: RFC 2370 Update and a Proposed Change to Stub… Acee Lindem
- Re: RFC 2370 Update and a Proposed Change to Stub… Acee Lindem
- Re: RFC 2370 Update and a Proposed Change to Stub… Erblichs
- Re: RFC 2370 Update and a Proposed Change to Stub… Dave Katz
- Re: RFC 2370 Update and a Proposed Change to Stub… Mike Fox
- Re: RFC 2370 Update and a Proposed Change to Stub… Andrew Smith
- Re: RFC 2370 Update and a Proposed Change to Stub… Acee Lindem
- Re: RFC 2370 Update and a Proposed Change to Stub… Acee Lindem
- Re: RFC 2370 Update and a Proposed Change to Stub… Erblichs
- Re: RFC 2370 Update and a Proposed Change to Stub… Acee Lindem
- Re: RFC 2370 Update and a Proposed Change to Stub… Sina Mirtorabi
- Re: RFC 2370 Update and a Proposed Change to Stub… Russ White
- Re: RFC 2370 Update and a Proposed Change to Stub… Acee Lindem