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BGP Load Sharing & Balancing - 2 AS's (ISP's) 3 links

Currently I have 2 DS3's to two different providers (ATT & Broadwing). I am turning up a third circuit which is an OC-3 to ATT (AS 7018). Right now I am using AS-Prepending on my /24's to successfully balance inbound traffic on the two DS3's. However, it doesn?t appear that I can prepend on a per neighbor (per circuit) basis, I can only prepend on an AS. How can I enforce inbound traffic ratios on the ATT DS3 and OC-3? Any configuration recommendations?

FYI: I cannot do a flash-cut so taking down the ATT DS3 is not an option at this time. I may however, make the DS3 a backup.

-JGR

1 ACCEPTED SOLUTION

Accepted Solutions
Gold

Re: BGP Load Sharing & Balancing - 2 AS's (ISP's) 3 links

You are exactly correct. I though I had responded on this post.. maybe I got distracted and didn't hit post.

You can also prepend the AS as many times as you want and prepend a different number of times on different links. You only need 1 when the neighbors are the same AS when they are different you are safer doing more. I think I normally do 3 to make sure there is not a extra AS or 2 between the 2 isps. I assume some ISP have a limit so I wouldn't go too crazy with prepend.

3 REPLIES

Re: BGP Load Sharing & Balancing - 2 AS's (ISP's) 3 links

check this URL if it gives you any clue.

http://www.cisco.com/warp/public/459/40.html#conf5

rate if it helps ....

New Member

Re: BGP Load Sharing & Balancing - 2 AS's (ISP's) 3 links

I'm gathering that the answer may be that I can prepend the AS from ATT. This can be done because I can regulate the prepending on a per neighbor basis.

router bgp 12345

neighbor A.T.T.1 remote-as 7018

neighbor A.T.T.1 route-map localonly out

neighbor A.T.T.2 remote-as 7018

neighbor A.T.T.2 route-map oc-3-local-prepend out

neighbor B.W.G.1 remote-as 6395

neighbor B.W.G.1 route-map broadwing-out out

!

route-map oc-3-local-prepend permit 10

set as-path prepend 12345

!

Gold

Re: BGP Load Sharing & Balancing - 2 AS's (ISP's) 3 links

You are exactly correct. I though I had responded on this post.. maybe I got distracted and didn't hit post.

You can also prepend the AS as many times as you want and prepend a different number of times on different links. You only need 1 when the neighbors are the same AS when they are different you are safer doing more. I think I normally do 3 to make sure there is not a extra AS or 2 between the 2 isps. I assume some ISP have a limit so I wouldn't go too crazy with prepend.

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