Meaning of the output in the "show ip bgp <prefix> <mask>" command

[rogelioalvez]

Hello team:

I have the following output in my Cisco router to the "show ip bgp 172.25.159.140 255.255.255.252" command:

LASBRUOL1001-1#show ip bgp 172.25.159.140 255.255.255.252
BGP routing table entry for 172.25.159.140/30, version 1073122
Paths: (2 available, best #2, table default)
Advertised to update-groups:
142
Refresh Epoch 1
65631, (received-only)
172.25.159.99 from 172.25.159.99 (172.25.159.81)
Origin IGP, localpref 100, valid, external
rx pathid: 0, tx pathid: 0
Refresh Epoch 1
3549 65134 65318, (received & used)
172.31.2.17 from 172.31.2.17 (172.31.2.17)
Origin incomplete, localpref 100, valid, external, best
Extended Community: RT:13835:1100035
rx pathid: 0, tx pathid: 0x0

I am interested in the "bold section", and specifically in the "red" IP address between parenthesis. It says the prefix is being learnt from AS 65631 and neighbor 172.25.159.99. ¿ Can you please explain what attribute does the IP address 172.25.159.81 between parenthesis represent? It can not be the NEXT-HOP attribute, since it is my understanding that the NEXT-HOP attribute of announcements from an external neighbor should/must be the IP address of the external neighbor..

Any hints will be greatly appreciated.

Best regards, Rogelio

[Cristian Matei · Accepted solution]

Hi,

   For all BGP prefixes, you're gonna see these 3 values, which depending on the BGP design, can have the same or different values:

A.A.A.A from B.B.B.B (C.C.C.C)

A.A.A.A is the next-hop value of the prefix

B.B.B.B is the IP address of the BGP peer over which the BGP TCP session is formed

C.C.C.C is the BGP router-ID of the BGP peer you got this route from

So that value is the BGP router-ID of your BGP peer.

Regards,

Cristian Matei.

[rogelioalvez]

Thanks for clearing this up! Best regards, Rogelio