From: Erick B. (erickbe@xxxxxxxxx)
Date: Thu Jan 18 2001 - 19:58:39 GMT-3
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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