BGP Multihoming Partial vs. Full Routes

Anton Kapela tkapela at gmail.com
Tue Jun 15 22:20:20 CDT 2010


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



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