From: Gregory Gombas (ggombas@gmail.com)
Date: Sat Sep 08 2007 - 19:09:46 ART
On which router?
Let me re-state the restrictions:
1. Can't do any filtering on the ASBR that's doing the redistribution
- that includes distribute lists, route maps, the "summary address
no-advertise" command, distance, or anything on the ASBR itself.
2. No stub/NSSA/totally/NSSA totally areas allowed
3. Since you have 100 routers in the area, its not feasible to do
distribute-list inbound on every router in the area.
By the way, I made this scenario up myself , but its quite possible to
come across this in the real world. Say you have a large network with
multiple connections to external vendors (or even just multiple
routing protocols) that you are redistributing into OSPF. And you
wanted to prevent certain external routes from being
sent to a specific a area - let say its your customer network.
Stub/NSSA areas may not be a good solution for you because you do want
allow certain external routes in and you didn't want sub-optimal
routing inherent in default or summary routes.
The problem is that if you filter the prefix on the ASBR doing the
redistribution,
your entire organization will be cut off from those external routes.
And it may not be feasible to do distribute-list inbound on every
router in the area (especially if its a large area).
How could you accomplish this?
On 9/8/07, Herbert Maosa <asawilunda@googlemail.com> wrote:
> I believe distribute-list route-map out should do.
>
> Herbert.
>
>
>
> On 9/8/07, Gregory Gombas <ggombas@gmail.com > wrote:
> >
> > Yup - only works on Type 3 LSA's...
> >
> > On 9/8/07, Shine Joseph < shinepjoseph@iprimus.com.au> wrote:
> > > Did you consider area filter-list?
> > >
> > > Regards,
> > > Shine
> > >
> > >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> > > Gregory Gombas
> > > Sent: Sunday, 9 September 2007 6:22 AM
> > > To: Toh Soon, Lim
> > > Cc: groupstudy
> > > Subject: Re: Filtering OSPF external routes - tough one
> > >
> > > Hi Lim,
> > >
> > > The goal is to filter the route so no router in the specific area you
> > > want to filter it from will have it in its OSPF database. Distribute
> > > list is only locally significant :-(
> > >
> > > Oh and I forgot to mention stub/totally/NSSA are not allowed for this
> > > solution :-)
> > >
> > > I can't believe OSPF is so inflexible! This is quite easily
> > > accomplished with any distance vector protocol!
> > >
> > >
> > >
> > > On 9/8/07, Toh Soon, Lim < tohsoon28@gmail.com> wrote:
> > > >
> > > >
> > > > Hi Gregory,
> > > >
> > > > At which point in the network do you want to filter the external
> routes?
> > > In
> > > > multi-area OSPF, you can consider deploying stub, totally stubby or
> NSSA
> > > > areas.
> > > >
> > > > AFAIK, Type 5 LSAs are flooded to the entire OSPF domain (whichever
> areas
> > > > that can accept Type 5 LSAs). IMO I don't think we can filter some
> Type 5
> > > > LSAs on only certain routers due to the fact that they must be
> identical
> > > > across the domain. You can try "distribute-list" to prevent them from
> > > > entering the RIB.
> > > >
> > > > Just my 2cents. I may understand it wrongly. Let's hear other opinion.
> > > >
> > > >
> > > > Thank you.
> > > >
> > > > B.Rgds,
> > > > Lim TS
> > > >
> > > >
> > > >
> > > > On 9/9/07, Gregory Gombas < ggombas@gmail.com> wrote:
> > > > >
> > > > > Does anyone know how to filter an ospf external route on a router
> > > > > other than the ASBR doing the redistribution?
> > > > >
> > > > > Oh and by the way, the forwarding address is set to 0.0.0.0.
> > > > >
> > > > > Good luck with this one :-)
> > > > >
> > > > >
> > > >
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>
>
>
> --
> Kindest regards,
> hm
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