Load balancing multiple bgp full feeds + some backups


I'm facing the following problem: we have two border routers (let's call them bdr1 and bdr2). We receive 3 full BGP feeds from 3 different providers (A,B,C), for providers A and C we have backup links (capacity equal to primary links) with BGP on them, but we can't use them (due to commercial reasons) unless the primary link for given provider is down. To make things more complicated links are of different capacity (A - 400Mb, B and C - 100Mb). Our traffic is about 60% in/ 40% out.

So the whole picture looks like this:

A B Cb Ab C | | | | | | | | | |

++-+-+--+ ++--+---+ | bdr1 +-----+ bdr2 | +-------+ +-------+

b - backup

Currently we simply shut down BGP on the backup links manually to prevent any traffic on them (we got both backup links quite recently). But we would like to get it going in an automated manner. So far traffic is being load-balanced by prepending on outbound and inbound. I made a few experiments - I set up MED on outbound to attract traffic only onto primary links - that works well, but how do I prevent the outbound traffic from choosing the backup links (for example Ab on bdr2)? If I set the local preference for backup links (Ab,Cb) to a lower value then A,B,C then if the primary A goes down outbound traffic won't choose Ab as the local preference of B and C is still higher (even though they don't have enough capacity to handle outbound), inbound traffic will come through Ab as our provider honours the MED. Any ideas or pointers are welcome.

kind regards pshemko

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Have your tried prepending your local AS to the backup ISP? That way the AS path is lengthen on this ISP circuit.

pshemko wrote:

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