IPv6: IS-IS or OSPFv3

devang patel devangnp at gmail.com
Mon Jan 5 18:23:11 UTC 2009

Thanks all for sharing information!

Devang Patel

On Mon, Jan 5, 2009 at 11:43 AM, Justin Shore <justin at justinshore.com>wrote:

> Kevin Oberman wrote:
>> I would hope you have a backbone well enough secured that you don't need
>> to rely on this, but it does make me a bit more relaxed and makes me
>> wish we were using ISIS for IPv4, as well. The time and disruption
>> involved in converting is something that will keep us running OSPF for
>> IPv4 for a long time, though. I remember the 'fun' of converting from
>> IGRP to OSPF about 13 years ago and I'd prefer to retire before a
>> repeat.
> I did the OSPF --> IS-IS migration some time back and here's some of the
> info I found at the time.
> http://www.nanog.org/meetings/nanog29/abstracts.php?pt=Njg2Jm5hbm9nMjk=&nm=nanog29
> Vijay did a nice presentation on AOL's migration to IS-IS.  IIRC AOL
> migrated everything in 2 days.  Day 1 was to migrate their test POP and hone
> their script.  All remaining POPs were migrated on Day 2.  I believe he said
> it went well.  There have been several other documented migrations too:
> http://www.geant.net/upload/pdf/GEANT-OSPF-to-ISIS-Migration.pdf
> http://www.ripe.net/ripe/meetings/ripe-47/presentations/ripe47-eof-ospf.pdf
> I migrated my SP from a flat OSPF network (end to end area 0) to IS-IS.
>  The OSPF setup was seriously screwed up.  Someone got the bright idea to
> changes admin distances on some OSPF speakers, introduce a default in some
> places with static defaults in others, redistributing like it was going out
> of style, redisting a static for a large customer subnet on P2 instead of P1
> which is what PE1 actually connected to (and not advertising the route from
> PE1 for some unknown reason), etc.  The old setup was a nightmare.
> The IS-IS migration went fairly well after I got some major bugs worked out
> on our 7600s.  I implemented IS-IS overtop of OSPF.  Some OSPF speakers had
> admin distances of 80 and some were default.  IS-IS slipped in over top with
> no problems.  I raised IS-IS to 254 for the initial phase anyway just to be
> safe.  Once I had IS-IS up I verified it learned all the expected routes via
> IS-IS.  Then I lowered its admin distance back to the default and bumped
> OSPF up to 254.  Shortly thereafter I nuked OSPF from each device.  It was
> hitless.  I never could get IS-IS to work with multiple areas.  The 7600s
> made a smelly mess on the CO floor every time I tried.  In the end I went
> with a L2-only IS-IS network.  Still it works well for the most part.  I've
> had about as much trouble with IS-IS as I have had with OSPF.  Occasionally
> some random router will get a burr under it's saddle and jack up the MTU on
> the CLNS packets beyond the interface's max.  The receiving router will drop
> the padded frame as too big.  Fixing this can sometimes happen with a
> shut/no shut.  Sometimes I can nuke the entire IS-IS config and re-add the
> config.  Other times I simply have to reboot.  This doesn't happen too
> often; it's usually several hours after I rock the IS-IS boat so to speak.
>  Still, I wouldn't go back to OSPF for this SP.
> Justin

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