[c-nsp] BGP Load Sharing

[Chris Wopat]

On Fri, Apr 2, 2010 at 6:33 AM,  <cisco-nsp-request at puck.nether.net> wrote:
> Message: 8
> Date: Fri, 2 Apr 2010 05:08:04 -0700 (PDT)
> From: Bunny Singh <jump2fly82 at yahoo.com>
> To: cisco-nsp at puck.nether.net
> Subject: [c-nsp] BGP Load Sharing
> Message-ID: <291700.32887.qm at web45009.mail.sp1.yahoo.com>
>
> Hi ,
>
> I am using multihoming for my BGP with two ISP's. I have 10 mbps from one and 4 mbps from
> other ISP connecting to my single 3660 router. I am getting default route from my both of the
> ISP's and advertising /24 Public pool towards bothof the ISP's. For load sharing i am doing path
> prepending and put a weight for outbound traffic but not getting loadshare as i want.
>
> Now i want to do the loadsharing and want to use near to 14 mbps. So is it anyway to do the
> loadsharing for outbound as well as inbound traffic. I have searched in google but didnot
> get perfect answer.

One (sort of ugly) way to do this is to is to make some larger AS's
prefer one path outbound. You would create a route-map inbound so you
can make this happen. This example shows a few ways, matching AS's or
matching communities that your ISP sends you (check with them to see
what communites they send and what they mean.

============================================
! your bgp
router bgp 9999
 neighbor 1.2.3.4 route-map ROUTEMAP-1234-IN in

! sprint (1239), level3(3356), AT&T (4181)
ip as-path access-list 7 permit ^1234 1239_
ip as-path access-list 7 permit ^1234 3356_
ip as-path access-list 7 permit ^1234 4181_

! match community 321 from your 1234 neighbor
ip community-list 60 permit 1234:321

! anything
access-list 20 permit any

! set metric of 3 for anything in as-path acl 7
route-map ROUTEMAP-1234-IN permit 10
 match as-path 7
 set metric 3

! match community 321 as sent from AS 1234
route-map ROUTEMAP-1234-IN permit 20
 match community 60
 set metric 7

! set metric 10 for the rest
route-map ROUTEMAP-1234-IN permit 30
 match ip address 20
 set metric 10

============================================

You would want to set up something similar for each of your bgp peers
even if one of them only does the 'permit ip' to keep the metric of 10
as default for both.

--Chris