bgp bestpath confusion

[Jonn cos]

Hi all,

I have the following result when i do show ip bgp

R1#sh ip bgp

BGP table version is 2, local router ID is 1.1.1.1

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

              r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path

* i2.2.2.2/32       10.1.24.2                0    100      0 200 i

*>i                 10.1.23.2                0    100      0 200 i

R1#

I can see that best path is selected from 10.1.23.2 (coming from R3). Is there any debug or show command that can tell me exactly on which step does the best path was selected ? like was it selected on local pref or something else

[Giuseppe Larosa]

Hello Jonn,

to see more details of the two BGP advertisements you can use

show ip bgp 2.2.2.2

From the show that you have reported the two paths have:

same weight 0

same local preference 100 (default)

same AS path length  200

same origin code i (internal)

same MED 0

both paths are learned via an iBGP session that is given by the leftmost *i or *>i

the second path is the best ( > character) but we cannot see why.

The likely criteria involved are :

lowest IGP metric to BGP next-hop

lowest BGP router-id

You can see these missing details in the show ip bgp 2.2.2.2 including eventually cluster-list and originator-id if RR servers are in use.

Hope to help

Giuseppe

[Jonn cos]

Sorry Sir i didnt pasted the result of show ip bgp 2.2.2.2 but it's also not showing anything that can help me understand at exact which step does the decision was made. Basically i wanted to ask that is there any show/debug command that can tell me exact step of decision or there is no such thing ?

[Giuseppe Larosa]

Hello Jonn,

feel free to post the show ip bgp 2.2.2.2 and I will try to comment on it

Hope to help

Giuseppe