[c-nsp] interesting ASR 9k bgp multipath issue

[Jared Mauch]

John,

You're going to want some options like this under the main BGP policy:

 address-family ipv4 unicast
  bgp attribute-download
  maximum-paths ibgp 16
  maximum-paths ebgp 16 selective

as well as setting 'multipath' under the address-family under the bgp peering or the neighbor-group to the resolver.

- Jared

On Mar 31, 2014, at 5:44 PM, John van Oppen <jvanoppen at spectrumnet.us> wrote:

> So, to be clear, here is an example of this working right on a 6500 with IOS   (multipath on the ibgp route that is the same IGP cost and not on the one that is not):
> 
> cr1-pdx#show ip bgp 64.187.160.0
> BGP routing table entry for 64.187.160.0/20, version 562475581
> Paths: (2 available, best #1, table Default-IP-Routing-Table)
> Multipath: eBGP iBGP
> Flag: 0x1000
>  Advertised to update-groups:
>     1          3          5          6          7          8
>  54858
>    208.76.153.78 (metric 516) from 208.76.153.116 (208.76.153.116)
>      Origin IGP, metric 0, localpref 115, valid, internal, multipath, best
>      Community: 11404:993 11404:4000 11404:4010
>      Originator: 208.76.153.78, Cluster list: 208.76.153.116
>  54858
>    208.76.153.79 (metric 516) from 208.76.153.117 (208.76.153.117)
>      Origin IGP, metric 0, localpref 115, valid, internal, multipath
>      Community: 11404:993 11404:4000 11404:4010
>      Originator: 208.76.153.79, Cluster list: 208.76.153.117
> cr1-pdx#show ip bgp 208.76.152.9
> BGP routing table entry for 208.76.152.9/32, version 562275567
> Paths: (3 available, best #1, table Default-IP-Routing-Table)
> Multipath: eBGP iBGP
>  Not advertised to any peer
>  64524
>    208.76.153.79 (metric 516) from 208.76.153.116 (208.76.153.116)
>      Origin incomplete, metric 10, localpref 200, valid, internal, best
>      Community: 11404:800
>      Originator: 208.76.153.79, Cluster list: 208.76.153.116
>  64524
>    208.76.153.79 (metric 516) from 208.76.153.117 (208.76.153.117)
>      Origin incomplete, metric 10, localpref 200, valid, internal
>      Community: 11404:800
>      Originator: 208.76.153.79, Cluster list: 208.76.153.117
>  64524
>    208.76.153.118 (metric 2050) from 208.76.153.118 (208.76.153.118)
>      Origin incomplete, metric 10, localpref 200, valid, internal
>      Community: 11404:800
> cr1-pdx#
> 
> -----Original Message-----
> From: cisco-nsp [mailto:cisco-nsp-bounces at puck.nether.net] On Behalf Of John van Oppen
> Sent: Monday, March 31, 2014 2:37 PM
> To: 'Vitkovský Adam'; 'Oliver Boehmer (oboehmer)'; cisco-nsp at puck.nether.net
> Subject: Re: [c-nsp] interesting ASR 9k bgp multipath issue
> 
> It sure was not in this case, it was pretty obviously 50-50 from my traceroute testing
> 
> -----Original Message-----
> From: Vitkovský Adam [mailto:adam.vitkovsky at swan.sk]
> Sent: Monday, March 31, 2014 2:12 PM
> To: John van Oppen; 'Oliver Boehmer (oboehmer)'; cisco-nsp at puck.nether.net
> Subject: RE: [c-nsp] interesting ASR 9k bgp multipath issue
> 
> If I recall correctly the load-sharing should be proportional to the matric so in your case 254:1 in favor of the path with metric 10.
> 
> 
> adam
> 
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