From: ccie2be (ccie2be@nyc.rr.com)
Date: Wed Oct 13 2004 - 19:29:24 GMT-3
Hey James,
Thanks for getting back to me.
It sounds like you had a similar scenario. Compared to mine, its a little
different thought. In my scenario, when I first looked at sw2's route
table, it had 2 paths to almost all the routes. But, then, a few minutes
later, sw2's route table only had 1 path to the various routes with a couple
of exceptions. After that, sw2's route table remained stable even after I
cleared the the route tables of R1 and R2 at different times in different
sequences.
So, I'm kinda stumped.
I don't know why at 1st I had 2 paths and then a few minutes later only 1
path.
Hopefully, one of the guru's will shed some light on this at some point.
Thanks again, Tim
PS: If we don't get a chance to talk again before your lab, the best of
luck, buddy.
----- Original Message -----
From: "James" <james@towardex.com>
To: "ccie2be" <ccie2be@nyc.rr.com>
Cc: "Group Study" <ccielab@groupstudy.com>
Sent: Wednesday, October 13, 2004 12:36 PM
Subject: Re: Rip v2 path selection criteria
> On Wed, Oct 13, 2004 at 10:10:26AM -0400, ccie2be wrote:
>
> > Now, I noticed that R1 is only sending 3 routes to sw2 but I'm not sure
why.
> > R1's route table is the same as R3's and both are redist the same routes
into
> > rip. Could this be a timing issue? In other words, is this possibly
because
> > when R3 redist it's isis routes into rip and advertises them to sw2, sw2
in
> > turn advertises these same routes to R1 and because of split horizon R1
> > doesn't advertise these same routes back to SW2?
> >
> > If this is the case, then why are there any exceptions? Why does sw2
have 2
> > paths for 3 routes instead of just 1 path for these routes?
>
> I think you are bumping into the similar problem I had a while ago with a
bit
> same topology (ISIS->RIP redist on two routers, and two routers and a L3
switch
> are sitting on shared ethernet running RIP, just like yours). If I recall
> correctly, the split horizon +/- route poisoning issue of RIP keeps the
routing
> table on the devices pretty unstable (e.g. routes would flap, all
isis->rip
> redistributed routes would appear with one router as nexthop, then all
flap
> again, etc). As far as why it does that, I think your assertion above may
be is
> correct..
>
> Anyway the solution that I used to fix this was to make switch the
> "authoritative" rip router on both routers. I've set distance to 114 on
the
> switch's address, and 125 for routes from other router. This made RIP on
each
> router to have higher pref on the routes via the switch instead. Switch
going
> down would make it select the other router.
>
> This had been a while since I did this, so I'm sure I may be missing some
> memory here, in which someone can point additional insights to this
matter.. :)
>
> HTH,
> -J
>
> >
> > Any insight would be greatly appreciated.
> >
> > Thanks, Tim
> >
> > _______________________________________________________________________
> > Subscription information may be found at:
> > http://www.groupstudy.com/list/CCIELab.html
>
> --
> James Jun TowardEX
Technologies, Inc.
> Technical Lead Network Design, Consulting, IT
Outsourcing
> james@towardex.com Boston-based Colocation & Bandwidth
Services
> cell: 1(978)-394-2867 web: http://www.towardex.com , noc:
www.twdx.net
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