[j-nsp] load balancing between multiple BGP links

[Guy Davies]

Hi Joe,

It can't with the physical layout you described.  BGP selects one next-hop as the best (and only one).  The only way to load share is to have two (or more) parallel links between just two routers.  You then create a static route on each end via each physical next-hop to the loopback on the far end router.  Then, you setup an ebgp multihop session between the loopbacks on the two routers.  That then uses IGP load sharing to balance traffic across the two parallel links.

Other than that, you're stuck with crude methods of dividing up the destination prefixes to approximate load sharing.  You could set localpref on routers based on AS path length or some other totally arbitrary parameter to ensure that you're getting something approximating 50/50.  But that's pretty horrible, pretty crude and rarely gives stable results.

Rgds,

Guy

>-----Original Message-----
>From: juniper-nsp-bounces at puck.nether.net 
>[mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of Joe Shen
>Sent: 14 September 2005 11:28
>To: juniper-nsp at puck.nether.net
>Cc: cisco-nsp at puck.nether.net
>Subject: [j-nsp] load balancing between multiple BGP links
>
>Hi,
>
>How could load on multiple BGP peer links be balanced
>automatically?
>
>The situation we are facing:
>
>             ---------------------------|
>             |  Service provider        |
>             |                          |
>             --R1--------------------R2---
>               |\                     |
>               | \       E-BGP        |
>               |  \ ----------------\ |          
>               |                     \|
>            ----R3--------------------R4-|
>            |     Our Network            |
>            |      (OSPF)                |
>            -----------------------------  
>
>The three links between our network and Service
>provider network are all 1Gbps. Now, we noticed that 
>load on link R1-R3, R1-R4 is about 50% (in/out), but
>load on R2-R4 are about 90% ( in/out).
>
>How could we balance those load on the three links
>automatically? or must we tune the route mannually? 
>
>Is there any technical guide on this?
>
>thanks  in advance.
>
>Joe  
>
>
>	
>
>	
>		
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