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New Member

Show ip bgp not showing all BGP Paths

Hi,

We've setup BGP as shown in the diagram.

Drawing2.jpg

Now Router Router A and B are peers of each other. Router A peers with ISP A and Router B peers with Router B.

The issue we have is that Router B knows how to get to router C via eBGP connection to ISP B router or via ISP A, which is advertised via iBGP from Router A.

But ....

Router A only shows in "show ip bgp" about network Router C via ISP A.

If I do a soft clear of bgp information on Router A I then see both paths to Router C via ISP A or ISPB, but once BGP is converged im only seeing best path via ISP A. Can anyone explain why the path via ISP B is not shown on Router A? we are using local preference in a route map to say prefer router A over Router B to exit the network to get to router C.

Synchronisation is disabled. Router A and B are running the same code of IOS and also have similiar configs.

My assumption is that becuase of the local preference Router A stops listing path via Router B in the BGP table. This thought doesnt make complete sense to me ???? In my test lab I always see all paths to exit the AS.

router#show ip bgp 192.168.100.0     
BGP routing table entry for 192.168.100.0/22, version 40
Paths: (2 available, best #2, table default)
  Not advertised to any peer
  65530 64514, (aggregated by 64514 10.x.x.246)
    10.x.x.30 from 10.x.x.30 (202.x.x.x)
      Origin IGP, localpref 80, valid, external, atomic-aggregate
  65530 64514, (aggregated by 64514 10.202.103.246)
    10.x.x.22 from 10.x.x.78 (10.x.x.78)
      Origin IGP, metric 0, localpref 120, valid, internal, atomic-aggregate, best

Thanks

B

2 REPLIES
New Member

Re: Show ip bgp not showing all BGP Paths

I've just lab'd this and it is the local preference.

If I remove my route map I see all paths as expected. Once I apply my route-map which matches ips and assigns the local preference then I see the shown behaviour.

Note to self - lab first before posting on cisco support forum

Re: Show ip bgp not showing all BGP Paths

Hi B,

Can you issue command to find out reasons why that route is not installed in bgp

show ip bgp rib-failure

will be helpful to know reasons

Regards

Mahesh

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