[j-nsp] Conditional Advertisemet?

[Pekka Savola]

On Thu, 5 Oct 2006, Chuck Anderson wrote:

> On Thu, Oct 05, 2006 at 01:59:17PM -0400, Mellott, Eric wrote:
>> Have a BGP configuration where I learn a /16 network from one eBGP
>> neighbor and want to advertise a subset of that network, i.e. a /28, to
>> a different eBGP neighbor.  Currently, I am able to advertise the subnet
>> by configuring a static route which puts the /28 in table, however; this
>> kills anything dynamic.  Is there a way with conditional advertisements
>> or a generate route to dynamically advertise the /28 upon receipt of the
>> /16?  Also, I don't want to rely on the BGP neighbor (who is advertising
>> the /16) to give me the /28 instead.
>
> This might work:
>
> [edit routing-options]
> # show generate
> route w.x.y.z/28 policy MATCH-16;
...

Yep -- and another, hackier way to achieve the same if you don't have 
a default route (or have/want to have a routing-options - resolution 
policy) should be to create the static route with a next-hop pointing 
to an address in the superblock not covered by the more specific. 
When the superblock is revoked, the more specific is also immediately 
withdrawn, and the routing automatically follows the superblock.

-- 
Pekka Savola                 "You each name yourselves king, yet the
Netcore Oy                    kingdom bleeds."
Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings