[EMAIL PROTECTED] 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.
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?

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.


Use BGP communities. Tag your announcement with a community that will set the localpref for your route within Cogent as low as possible, that should do the trick and you shouldn't see any traffic from them unless your other announcements are withdrawn. (Do the same internally for routes learned via your backup link.) This works better than trying to announce a /25 that the rest of the internet is unlikely to honor, and without weird BGP tricks. Internally, you'll have to add route maps or something to bump the localpref to prefer links to your backup offices.

As for peers closer to Cogent, if you localpref it extremely low to Cogent and the ATT routes are higher, these peers (even within Cogent's network) will no longer see Cogent as preferred. I do this with my neighbors when I'm about to perform maintenance on one of the border routers.

I haven't read the rest of the thread, so this advice is just based on the preceding message. You'll probably have to mix and match this advice with others. ;)

~Seth
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