Using BGP to multihome on links of different bandwidth

[Alex Thurlow]

New to the list, and with a question I can't seem to find an answer to 
anywhere else.  A little preface - I have recently switched jobs, so I 
am in a new network situation.  There are some upcoming changes, and I 
wish to switch from our current Linux router to OpenBSD-pf. 

We currently have 2 links that are shared via BGP.  One is an OC-12, and 
the other is 100Mb ethernet.  The reason we have lines of unmatched 
speed is that we could get the 100Mb cheap and are wanting to test the 
usefulness of multihoming. 

Under just a normal BGP setup, our 100Mb line would be saturated as it 
attempted to send traffic there based on routing distance.  Because of 
this, there are IPtables rules that count how many pps are going on the 
100Mb line, and if there are over a certain amount, they mangle the 
packets and send them over the OC-12 instead.  In this way, we are able 
to share these 2 lines of differing bandwidth. 

My previous OpenBSD/pf experience was limited mainly to bridging 
firewalls, but I would like to use it for a new router.  My question is, 
is there a way to share these 2 lines and not saturate the smaller one?  
I have looked around, and it doesn't seem to be a very common question, 
so I come here to the experts.  I was not able to actually find any 
other way to do it besides iptables, so any other product (juniper, 
xorp, cisco, etc.) that might be able to do this would be interesting to 
me as well.

Thanks,
Alex Thurlow