[c-nsp] BGP load balancing (outbound)

[Andrew Tolstykh]

ECMP load balancing works with the hidden "bgp bestpath as-path multipath-relax" command applied (thanks Anton!)

router bgp XXX
maximum-paths 2
bgp bestpath as-path multipath-relax

sh ip route bgp
B*    0.0.0.0/0 [20/0] via 13.13.13.3, 00:05:59
                [20/0] via 12.12.12.2, 00:05:59

sho ip cef 0.0.0.0 0.0.0.0
0.0.0.0/0
  nexthop 12.12.12.2 FastEthernet1/0
  nexthop 13.13.13.3 FastEthernet1/1

If you are after the per-AS load-sharing configuration, then you should probably flip route-map TRANSIT-1-INT permit 10 and 20 statements.
Also don't forget to add blank "route-map TRANSIT-2-IN permit 20" statement.

route-map TRANSIT-1-IN permit 10
match as-path 105
set local-preference 210
route-map TRANSIT-1-IN permit 20

route-map TRANSIT-2-IN permit 10
match as-path 106
set local-preference 210
route-map TRANSIT-2-IN permit 20

HTH,
Andrew


On 18/05/2010, at 2:42 AM, amps wrote:

> Let's say I wanted to send traffic to even AS's out peer 1 and odd AS's out peer 2.
> 
> Am I crazy?  (Seems better than using metrics based solely on static IP ranges...)
> 
> Would this work?
> 
> route-map TRANSIT-1-IN permit 10
>  set as-path prepend last-as 1
> !
> route-map TRANSIT-1-IN permit 20
>  match as-path 105
>  set local-preference 210
> !
> 
> route-map TRANSIT-2-OUT permit 10
>  set as-path prepend xxxxx
> !
> 
> route-map TRANSIT-2-IN permit 10
>  match as-path 106
>  set local-preference 210
> !
> 
> route-map TRANSIT-2-OUT permit 10
> !
> 
> ip as-path access-list 105 permit [02468]$
> 
> ip as-path access-list 106 permit [13579]$
> 
> 
> On Mon, May 17, 2010 at 10:59 AM, Anton Kapela <tkapela at gmail.com> wrote:
> On Mon, May 17, 2010 at 10:42 AM, Andrew Tolstykh <andrew at atfam.com> wrote:
> > Just a shot in the dark, but I don't see load balancing enabled in your configuration snippet:
> >
> > router bgp xxxxx
> 
> This question comes up semi-often, perhaps there ought to be a FAQ? (I
> may have missed it).
> 
> For different-upstream AS's, ecmp will not normally occur. You'll need
> to adjust the bgp bestpath determination functions, else the different
> next-AS's will prevent ECMP forwarding from being pushed to the FIB.
> 
> http://puck.nether.net/pipermail/cisco-nsp/2005-November/025993.html
> 
> -Tk
>