BGP Next-Hop (in Brackets)

Answered Question
Feb 20th, 2007

Hi all, Hope every is well :)

In the output below, the ip address (y.y.y.y) in brackets? What is this? It is not the BGP next hop for my external peer that I peer with so I am assuming it is an IP address from where the external peer received the prefix from? Either that or the external peers BGP RID?

router>sh ip bgp 1.1.1.0

BGP routing table entry for 1.1.1.0/24, version 477158

Paths: (1 available, best #1, table Default-IP-Routing-Table)

Advertised to peer-groups:

x.x.x.x

100 200

x.x.x.x from x.x.x.x (y.y.y.y)

Origin incomplete, localpref 100, valid, external, best

Community: xxxxx:xxxxx

Can anyone please clarify and tell me two things :-

1. Where can I find documentation on this output (I mean in the detailed format "show ip bgp <network>"

2. There must be a field in the BGP update packet to carry this address to my BGP table. What is it?

Many thx indeed for your help,

Ken

I have this problem too.
0 votes
Correct Answer by mheusinger about 9 years 7 months ago

Good morning!

Grab a coffee and read slowly ;-)

Yes, exactly, the BGP RID of the peer.

Regards, Martin

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mheusinger Tue, 02/20/2007 - 00:48

Hi,

there are 3 IP addresses, which have the following meaning:

from ()

: inserted as next hop into the IP routing table, sent in the BGP update "next hop" field

: the IP from the "neighbor remote-as" command, source IP for the TCP session

: learned through BGP setup messages

The latter is usually a loopback IP on the neighboring BGP peer. All 3 IPs can be the same or different depending on the setup.

With eBGP usually IPs 1 and 2 are identical and IP no. 3 is different, as peering in eBGP is normally not using Loopbacks.

Hope this helps!

Regards, Martin

kfarrington Tue, 02/20/2007 - 00:59

Hi Martin, Many thx for the speed of the response.

Sorry to ask, but I was just a little confused, so the address in the brackets (y.y.y.y), are you saying this is a BGP RID of the external peer?

Sorry, I have not woken up here in London yet :)

Many thx indeed,

Ken

Correct Answer
mheusinger Tue, 02/20/2007 - 01:32

Good morning!

Grab a coffee and read slowly ;-)

Yes, exactly, the BGP RID of the peer.

Regards, Martin

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