Routing Question

[dspazman at epicup.com]

Hi all,

I figured you guys were a great place to ask this question, even though it's not bird specific.

If you have 2 discrete sites, both with BGP, one announces a 100.100.100.0/20, and another announcing 100.100.100.0/24, will traffic for the /24 block always go to the site announcing the /24, even if it's closer to the site announcing the /20?

I was thinking that yes, it always routes to the shortest prefix, no matter the ping or number hops.  And I was thinking that held true for ipv6, as well.  A /32 and a /28 that cover the same range of addresses (the /32 being a subset of the /28) being announced from two different BGP sessions on two different networks, even if you are originating traffic from the same network the /28 is being announced on, and the /32 is a different network, so has additional hops and latency, any traffic you have going to the addresses in the /32 will go to the other network to go to the specifically announced /32.


Thanks!