From: Joseph D. Phillips (josephdphillips@fastmail.us)
Date: Wed Jul 07 2004 - 18:24:57 GMT-3
Cisco seems big on tags to prevent route feedback. Why not try tags?
I've done it so often I've memorized it:
router ei 1
red os 1 ma in ex metric 1500 1 255 1 1500 route-map o2e
router os 1
red ei 1 sub metric 100 metric-ty 1 route-map e2o
route-map e2o deny 10
match tag 110
route-map e2o perm 20
set tag 90
route-map o2e deny 10
match tag 90
route-map o2e perm 20
set tag 110
----- Original message -----
From: "James" <james@towardex.com>
To: "Daniel Sheedy" <dansheedy@gmx.net>
Date: Wed, 7 Jul 2004 06:37:13 -0400
Subject: Re: Redistribution Methodology
Dan,
The only way to test this is to see this yourself. While the backup
logic works
when the feedback is being received from a routing protocol with higher
distance[1]
, it will become an issue when feedback is being received from a
protocol with
lower distance than the active one. In that case, feedback will be
preferred
over active routing protocol, which could set the potential for routing
loops or
unintended routing instability/oddities.
The point of distribute list or route-map filtering is to not filter all
of
these feedback potential prefixes, but filter any of these that could
cause
trouble with your network. So it is completely up to you in deciding
which
prefixes should become candidates of being filtered before entering the
RIB.
-J
[1] Only on same prefix length. More specifics will override distance.
On Wed, Jul 07, 2004 at 08:54:41AM +0200, Daniel Sheedy wrote:
> Hi everyone,
>
> Maybe a silly question here, but I never did understand the reasoning behind
> restricting routes with an access list/prefix list. Maybe someone could
> explain the logic to me.
>
> I was always under the impression that if you are in a situation where you
> could have potential routing loops, then this is an opportunity to have a
> backup route, if the first route disappears. Isn't it better to use
> Distance to prefer one route over another? This way, if your preferred
> route disappears out of town, you can still get to the target with the
> backup route, as your backup routes with the higher and nonprefered distance
> suddenly begin to look desirable to the router. If you have filtered out
> the route on the backup route, then what happens when your primary route
> goes down? Sort of leaves a hole doesn't it?
>
>
> Any comments as to what I'm not seeing?
>
> Dan Sheedy
>
>
> ----- Original Message -----
> From: "Rohan Grover" <rohang@cisco.com>
> To: "'Mike Dickson'" <Mike@dicksonnetworks.com>; "'group study'"
> <ccielab@groupstudy.com>
> Sent: Wednesday, July 07, 2004 8:26 AM
> Subject: RE: Redistribution Methodology
>
>
> > Hi,
> >
> > A related question.
> >
> > If the specific redistribution scenario restricts the use of access-lists,
> would prefix-list be an alternative?
> >
> > Or would route-tagging be the expected answer?
> >
> > Thanks
> > Rohan
>
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-- 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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