RE: [nsp] Load-balancing outbound traffic -- or -- Setting MED on inboundupdates...

From: Gavin Malette (gmalette@rivien.com)
Date: Tue Nov 14 2000 - 11:25:02 EST


Hrrrmmm,

Why don't you just use localpref instead?

--gavin

-----Original Message-----
From: elijah@netvision.net.il [mailto:elijah@netvision.net.il]
Sent: Tuesday, November 14, 2000 5:48 AM
To: cisco-nsp@puck.nether.net
Subject: [nsp] Load-balancing outbound traffic -- or -- Setting MED on
inboundupdates...

Dear All

I am peering with two different ISPs, ISP A and ISP B, and receive a full
routing table from both of them. Let's assume they are both connected
to the same router.

There is obviously a need to load-balance outgoing traffic between these
two ISPs. I would like the deciding factor to be AS_PATH length, i.e.
prefixes advertised with a shorter AS_PATH by ISP A than by ISP B would
be reachable through ISP A (and vice versa), while prefixes with an equal
AS_PATH length would be always preferred through ISP B.

To achieve this I set the MED on updates coming from ISP A to 20 and from
ISP B to 10 and configured 'bgp always-compare-med' on the router.

Now to my questions:
1. Is there something wrong with the above scheme?
2. What are possible caveats in using 'bgp always-compare-med'?
3. Are there other ways to implement this?
4. What other ways to load-balance outbound traffic are there?
    The ones I know about are:
    - do nothing
    - partial table from A, full from B
    - A and A's customers through A, rest to B
    - ...and similar ones...

I appreciate your comments on this subject.

Regards,
Elijah Kagan



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