Re: BGP Multihoming Partial vs. Full Routes

[Anton Kapela <tkapela () gmail com>]

On Jun 14, 2010, at 12:08 PM, Fred Baker wrote:

> upstream, full routes are generally not as useful as one might expect. You're at least as well off with default 
> routes for your upstreams plus what we call "Optimized Edge Routing", which allows you to identify (dynamically, for 
> each prefix/peer you care about) which of your various ISPs gives you a route that *you* would prefer in terms of 
> reachability and RTT. In the words of a prominent hardware store in my region, "you can do it, we can help".

+1.

additionally, one could filter on reasonable RIR allocation 'boundaries' per /8, cutting the fib down substantially. 
Cisco and a host of others maintain such a list of ready-to-use examples here:

ftp://ftp-eng.cisco.com/cons/isp/security/Ingress-Prefix-Filter-Templates/

lastly,  one could do something far more crude (yet strangely effective), like so:

ip prefix-list longs permit 0.0.0.0/0 ge 23
ip prefix-list shorts permit 0.0.0.0/0 le 22

ip as-path access-list 10 permit (^_[0-9]+$|^_[0-9]+_[0-9]+$|^_[0-9]+_[0-9]+_[0-9]+$)

route-map provider-in permit 10
 match ip address prefix-list longs
 match as-path 10

route-map provider-in permit 20
 match ip address prefix-list shorts

...etc

-Tk