[j-nsp] Conditional advertisting to an upstream

Phil Mayers p.mayers at imperial.ac.uk
Sun Apr 15 07:39:03 EDT 2007

Apologies if this is a basic question - I feel that I should be able to 
figure this out, but have only confused myself more.

We have the following topo:

       |                    |
  <ext-m7i-1>          <ext-m7i-2>
       |                    |
   <core-1> ------------ <core-2>
       |                    |
      (the rest of the network)--

The upstreams provide us a default and we route as appropriate. What I 
want now is for the M7is to conditionally advertise the various site 
route aggregates based on the adjacency to the neighbouring core being up.

Specifically I'd rather not "generate" an aggregate based on the 
presence of a contributing route, since a significant portion of the 
routes are not subnetted, so I'd have to have two types of configuration 
and would like to maintain the simplicity. At the moment we're single 
connected and I'm using static nulls, but obviously I need these to be 
withdrawn if the link into the core goes down.


Additionally I have a question related to the multicast AF for M-BGP. In 
the above example traffic from will go *out* via core2, 
7i-2 and upstream2 but return traffic will flow in via upstream1, 7i-2, 
core1 then across to core2.

How must I advertise the multicast routes such that traffic from doesn't fail the RPF? Is it sufficient to advertise to both upstreams? These are GSRs and our upstream seems 
(ahem) unfamiliar with the possible issues.


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