[nsp] eBGP routes not balancing

Steve Francis steve at expertcity.com
Mon Nov 17 17:59:02 EST 2003

Jeff Chan wrote:

>After enabling "bgp bestpath compare-routerid" and resetting the
>sessions, most of the traffic went to the peer with the lower
>numerical address (ID), which again is unbalanced.  So I've
>disabled compare-routerid and will probably reset all the
>sessions late at night with "clear ip bgp all" in the hopes
>that the ages of the routes will then be close enough, since
>they're all cleared and re-learned at the same time, to
>result in traffic that is closer to balanced.
>Both providers are large, our pipes to them and routing tables
>learned similar sized, so balanced traffic should be a
>reasonable goal.  Any other suggestions are welcomed.  Aside
>from external route servers, how is anyone else dealing with
>this?  Balancing fully multi-homed traffic must be an issue
>for lots of folks....    Why can't IOS just do the right thing?
If both providers are presenting you with the same number of AS hops to 
the destination networks, then oldest path will win.  (subject to usual 
caveats about other selection mechanims: origin type, etc)

One way I've made the load balancing more equal in such situations is to 
apply a route map to one of the peers, that says if the route learned is 
for an IP in the range through, it has a 
local_pref of 90; everything else from that peer has a local_pref of 110.

The local_pref of the other peer will have the default of 100.

Thus everything for the top half of the Internet will prefer the peer 
with the route map; everything else will prefer the peer w/o it (for 

You can tweak the IP where the route map changes its local_pref to get 
the traffic as balanced as you like.

>Jeff C.

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