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

Matthew Melbourne matt at melbourne.org.uk
Mon Feb 8 14:59:36 EST 2010

Thanks for the pointers towards eBGP Multipath. Can I check that this still
works if two links are terminated on different edge routers (though with
iBGP between the edge routers). I assume this will use additional TCAM
resources (Sup720-3BXL) in maintaining two routes per prefix, which could be
significant for a full BGP feed?



-----Original Message-----
From: Erik Cuevas [mailto:ecuevas at fxcm.com] 
Sent: 05 February 2010 12:33
To: Matthew Melbourne
Subject: RE: [c-nsp] Load-sharing with two links to the same ISP

Did you check out BGP multipath?


or is the AS Path is different try...

bgp bestpath as-path multipath-relax(its hidden)

-----Original Message-----
From: cisco-nsp-bounces at puck.nether.net
[mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of Matthew Melbourne
Sent: Friday, February 05, 2010 6:33 AM
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] Load-sharing with two links to the same ISP


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?



Matthew Melbourne
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