[c-nsp] BGP neighbor with more specific prefixes

[Jon Lewis]

On Tue, 13 Sep 2011, Justin Krejci wrote:

> Cisco Folks,
>
> Internet Transit Providers
> Provider 1
> Provider 2
> Provider 3
> Provider 4
>
> We have aggregated prefixes (/19's, /18's etc) currently advertised to
> providers 1-3 on a single router. We are bringing on provider 4 but want
> to advertise only a few individual /24's within those aggregated
> prefixes to provider 4 and then tag them no-export. No other
> advertisements to provider 4.

Tag them no-export where?  Are you saying you don't want P4 to propagate 
those /24s outside their AS, or are you saying you want to announce those 
/24s only to P4 and not to P1-3?  Either way, it should be trivial.  You 
should have output route-maps for each provider.  In those route-maps, you 
can do whatever selective process you want for controlling what's 
advertised to that provider.  My recommendation would be use of community 
strings and "match community <community-list name>" in the route-maps.

> Can it just be done with the network command to include the more
> specific /24's and the filter out the more specific /24's with a
> prefix-list on our bgp sessions with providers 1-3 and filter out the
> aggregated /18's and /19's on our session with provider 4?

That'd work too.  Doing it with communities is just a whole lot more 
flexible and easier to manage down the road.

----------------------------------------------------------------------
  Jon Lewis, MCP :)           |  I route
  Senior Network Engineer     |  therefore you are
  Atlantic Net                |
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