BGP multihomed different link speed

Unanswered Question

I know load balancing is a huge issue with BGP, however I figure there has got to be a solution to this 'real world' situation that I am seeing.

We run BGP both to advertise our networks and to provide redundancy over our multi-homed network (Call it carrier "X" "Y" and "Z"). Carriers X & Y are dual T1 Bonded (3Mb) and carrier Z is T3 (32Mb).

Unfortunately carrier Y has the best path for 70% of our incoming data, carrier X 10% and our T3 line (Z) is sitting idle all day while our 3Mb pipes are slammed to 100% on the incoming data (we don't send out very much info).

I know you can use MED to try and influence the direct neighbor, but that dosn't seem to to me like it will do anything in terms of the global internet sending us data (other people will always see Carrier X as the best path to us).

Is there any way to make our small providers more of a backup, and force our incoming data to use the T3 unless it goes down while still maintaining our BGP peering?

Can this be done w/o buying a special "load balancing" box?

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Overall Rating: 5 (1 ratings)
gaurav_thapar79 Tue, 10/16/2007 - 08:18
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You can nt use MED since most of the Transit AS donot propogate MED. You can use local preference and use policy based route-maps to force the traffic on all ISPs.

Now, if you want lower capacity peering as backup to T3 peering, then please use AS-PATH PREPEND attribute in route-map inbound to force the downlink via T3 peering all the time till it goes down.

For eg.

router bgp

neighbour x.x.x.x remote-as X

neighbour x.x.x.x Route-Map-Xin in

neighbour y.y.y.y remote-as Y

neighbour y.y.y.y Route-Map-Yin in

neighbour z.z.z.z remote-as Z

neighbour z.z.z.z Route-Map-Zin in

route-map Route-Map-X permit 10

{ match ip address

set as-path prepend Y Y Y Y Y Y


route-map Route-Map-Y permit 10

{ match ip address

set as-path prepend Z Z Z Z Z Z Z


Try this and share your feedback.


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