[c-nsp] BGP neighbor with more specific prefixes

[Michael K. Smith - Adhost]

On 9/13/11 5:08 PM, "Justin Krejci" <jkrejci at usinternet.com> 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.
>
>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?
>
>It seems like inject-map on the provider 4 neighbor statement might work
>as well.
>
>Are there other more appropriate ways to accomplish this in IOS?
>

Shouldn't be a problem, as long as you have those individual /24's in your
routing table somewhere so they can be matched with the network statement
in your BGP process.

I agree with others - think about announcements as what you are sending,
rather than what you're not sending.  That is, only announce what you want
so you don't have to filter anything.  You can do it any number of ways.
I prefer prefix-lists for announcements to providers so that I can add and
remove as needed, with a deny all at the end so nothing crufty gets
through.

Mike