maximum-paths question

[paublo]

hi i have a router doing bgp with multiple upstreams. I'm trying to get this router to use more than one best path so i used the maximum-paths 2 command on my router bgp statement.
however it looks like the router is still only using one best path and ignoring the maximum-paths command.

I'm not an expert on bgp and im wondering what i did wrong, do i have to restart bgp clear ip bgp all? if so what is the best method to do this.

border1.prv.ri#sh run | in maximum
maximum-paths 2

border1.prv.ri#sh ip bgp 64.236.16.20
BGP routing table entry for 64.236.0.0/16, version 3311310
Paths: (2 available, best #2, table Default-IP-Routing-Table)
Multipath: eBGP
Advertised to update-groups:
1
17xx 3356 1668
199.232.xx.xx from 199.232.xx.xx (199.232.xx.xx)
Origin IGP, metric 1, localpref 100, valid, external
Community: 17xx:1002 3356:3 3356:86 3356:575 3356:666 3356:2010
70xx 1668
12.116.xx.xx from 12.116.xx.xx (12.122.xx.xx)
Origin IGP, localpref 100, valid, external, best

border1.prv.ri#sh ip route 64.236.16.20
Routing entry for 64.236.0.0/16
Known via "bgp 10xx", distance 20, metric 0
Tag 70xx, type external
Last update from 12.116.xx.xx 6w3d ago
Routing Descriptor Blocks:
* 12.116.xx.xx, from 12.116.xx.xx, 6w3d ago
Route metric is 0, traffic share count is 1
AS Hops 2
Route tag 7018

 

[leedsit]

Hi,

Just from a quick scan, I would say the MED is causing the issue. For mulitiple paths to work all BGP attributes must be the same, however 199.232.xx.xx has a metric ( med ) of 1. Your ISP or upstream router is setting that MED. You should be able to manipulate that with a route map.

Lee.

LEEroy
MCNE6,CCNP,CWNA,CCSA,Project+

 

[leedsit]

Hi,

the routes must also be learned via the same neighbor AS, looks like yours are 17xx and 70xx, so it would not work.

Quote from the cisco site

In order to be candidates for multipath, paths to the same destination need to have these characteristics equal to the best-path characteristics:

Weight

Local preference

AS-PATH length

Origin

MED

One of these:

Neighboring AS or sub-AS (before the addition of the eiBGP Multipath feature)

AS-PATH (after the addition of the eiBGP Multipath feature)



LEEroy
MCNE6,CCNP,CWNA,CCSA,Project+

 

[paublo]

thanks I did some research on cisco.com and you guys are right.

 

[bizhelp]

You may wish to consider "bgp bestpath as-path multipath-relax"

http://wiki.nil.com/Multipath_Load_Sharing_with_two_ISPs