[c-nsp] Load-sharing with two links to the same ISP

Aftab Siddiqui aftab.siddiqui at gmail.com
Fri Feb 5 07:33:43 EST 2010

use "maximum-paths" in BGP peering. With this you can add multiple routes in
the routing table as long as the routes you are getting from the same AS.
BUT once this is added it is applied to all BGP peers, not possible to do it
for some selected peers. If you have many neighbors on this router than care
should be taken before making this decision.


Aftab A. Siddiqui

On Fri, Feb 5, 2010 at 4:32 PM, Matthew Melbourne <matt at melbourne.org.uk>wrote:

> Hi,
> What techniques are available to load-share traffic on two links (of
> equal bandwidth) to the same ISP  (same AS) given that BGP only enters
> the best path into the RIB? We could announce our prefixes over both
> links, but splitting the preferred path announcements over the two
> links, either using MED or ISP communities, but this only really
> addresses inbound traffic. More of an issue is trying to load-share
> outbound traffic; we assume we'll learn the same set of prefixes over
> both links from the same ISP - one technique may be to simple split
> the IPv4 address space in half and local-pref accordingly to prefer
> one link or the other depending on the destination IP prefix?
> Cheers,
> Matt
> --
> Matthew Melbourne
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