[c-nsp] IOS XR BGP

[Vinny Abello]

On 11/24/2011 11:04 AM, Oliver Boehmer (oboehmer) wrote:
>  
>> I require the specific to be from IGP.
>>
>> I have a funny feeling all I need to do is redistribute OSPF into BGP
> then
>> use the aggregate-address as-set summary-only
> yes, and it looks you can limit the OSPF redistribution to a few (a
> single?) more specific as you are only interested in the core
> reachability? 
>
>> Just need confirmation if there is any other way.
> not to simulate your current solution in XR. 
>
> But have you thought about orignating the aggregates you advertise to
> the Internet (and customers) via some central routers in your core, for
> example some RRs, instead of on the edge(s)? This way you will never
> advertise them in case your edge devices become isolated (which, if I
> read you correctly, is the purpose of this exercise?).
>
> If you chose this approach, you might also want to advertise these
> aggregates with a special next-hop (like a private 10.1.1.1), and add a
> static null0 to 10.1.1.1/32 on all your BGP routers. Then every router
> seeing the aggregate will automatically create a Null0 and will drop all
> packets to unallocated address space within these aggregates as soon as
> it enters your network?
I have to agree with Oli here. I've followed this practice originating
aggregate routes from extremely well connected core routers at multiple
points in my networks. To the best of my memory, I never used network
statements at the border or edge. Once or twice when building out to a
new geographical area before having all of the redundancy in place, this
practice has saved us when a single failed backbone link isolates the
new routers in question. They stop announcing anything to their peers
and we stop seeing any announcements from them obviously when their iBGP
sessions drop with the rest of the network.

To me this always seemed like the most simple and effective approach. Is
there a reason this would not work in this situation or is there a
reason using the aggregate-address commands provides some other benefit
I'm missing?

-Vinny