From: David FAHED (dfahed@xxxxxxxxxxxx)
Date: Thu Jan 18 2001 - 22:24:20 GMT-3
First thanks for your answer.
But I already know the risk of this. I just want to know why in the
cisco cd they say that it isn't possible? For me it is possible with
some care!
"Erick B." wrote:
> Hi,
>
> The issue with distribute-list in on OSPF is that you
> need to be careful what you filter out else you can
> break your routing. This command filters routes that
> get put into the main routing table.
>
> For example:
>
> Topology: R1 ---- R2 ---- R3
>
> OSPF running on all 3 in area 0 announcing the
> loopback address.
>
> Router 1 loopback: 1.1.1.1
> Router 2 loopback: 2.2.2.2
> Router 3 loopback: 3.3.3.3
> No default routes anywhere.
>
> Without a distribute list, router 3 can ping 1.1.1.1
> just fine. All routers have routes to every loopback.
>
> Now we put a distribute-list in on Router2 denying
> 1.1.1.1 from being put in router 2's routing table.
> Router 2 has routes to 2 and 3.
> Router 1 has routes to 1, 2, and 3.
> Router 3 has routes to 1, 2, and 3.
>
> Router 3 can't ping 1.1.1.1 because when the packet
> gets to router 2, router 2 doesn't have a route to the
> 1 network because it was filtered out.
>
> HTH, Erick
>
> --- David FAHED <dfahed@outremer.com> wrote:
> > I couldn't understand the doc on the CD about
> > distribute-list.
> >
> > The cd say :
> > Control the Processing of Routing Updates
> > You might want to avoid processing certain routes
> > listed in incoming
> > updates. This feature does not apply to OSPF or
> > IS-IS. Use the following
> > command in router
> > configuration mode:
> >
> > distribute-list {access-list-number | name} in
> > [interface-name]
> >
> > But I use in lot of my distribution Lab this command
> > apply to an
> > interface in a ospf routing process (with a ASBR) to
> > filter external
> > route. And it works find!
> > I understand that you can't use a distribute-list
> > out interface with a
> > link state protocol but not why you can't do that
> > with a distribute-list
> > in interface....
> >
> > Any help will be welcome
>
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