[c-nsp] BGP Multihomed Selective/Conditional Advertisement

[Nathan]

On Mon, Oct 27, 2008 at 6:41 PM,  <tkacprzynski at spencerstuart.com> wrote:
> Nathan, thanks for this idea. Your idea could work. I just need to find
> out if they will accept my 2x /25  routes if I split the /24.

Frances Albemuth refined my proposal with better knowledge of Cogent's
communities.

> As for the prepend, how could I deal with peers that might be closer to
> Cogent than ATT and not load-balance that traffic based on peer's
> peering location?

You won't be load-balancing whatever the case. But yes, packets that
happen to go through Cogent will come to you through your Cogent link.

> The usage of Cogent is primarily for point to point VPN backup from
> other offices that would be on Cogent's network. Ideally I would like to
> keep that link free of internet traffic unless the primary (ATT) link
> fails and also not have asymmetric traffic where traffic comes in on the
> Cogent circuit and leaves on ATT's circuit because of the default route
> match. I'm not sure if that's possible, but that would be my ideal
> solution.

If your IP for the point to point VPN backup has a fixed dedicated IP
you could maybe announce that to Cogent instead of the two halves of
your network, and if the range at Cogent is equally fixed you could
step up local-preference on that instead of Cogent's whole network.
That way, only those IPs are impacted by the special "use Cogent"
routing. Since you're going to have ask Cogent, ask them the whole
question, they know their network better than I :-)

Personally I'm not comfortable with conditionals. Propagation takes
time. Does it matter a lot if some small percentage of packets come in
the wrong way?

--
HTH,
Nathan