[nsp] eBGP routes not balancing

[Steve Francis]

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?
>:P
>
>  
>
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 0.0.0.0 through 128.255.255.255, 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 
outbound.)

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

>Jeff C.
>  
>