0 Prefixes exchanged even when EBGP session is Established

[amitkumar.777]

Guys,

Can anyone help me out about the cases when a EBGP session which is in established state with it's neighbor but 0 prefixes are exchanged between them as per the output of bgp summary command.

Also how can I solve this issue?

Regards

Amit

[Abzal]

Hi,

In order to exchange routes they need to be in routing table. And check If there is any filter configured on BGP neighbor.

Little more info would be helpful though.

Example:

router bgp 100

network 1.1.1.0 0.0.0.255

neighbor 2.2.2.2 remote-as 200

ip route 1.1.1.0 255.255.255.0 null0

Hope it will help.

[Giuseppe Larosa]

Hello Amit,

to advertise an IP prefix you need to provide specific commands like:

under router bgp

network command

OR

redistribute other-protocol

It is quite possible to setup an eBGP session with neighbor related commands and to have 0 prefixes to advertise or 0 prefixes learned.

Another possibility is that some form of route filtering is blocking the routes learned/advertised.

We cannot say anything more precise without seeing the configuration. If you like to be helped post the BGP configuration of your two routers just avoid to expose public IP addresses for safety

Hope to help

Giuseppe

[Raju Sekharan]

Hi Amit,

This is genertic question

You can look at the below  cisco doc to start your troubleshooting

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a00800945ff.shtml

Thanks

Raju

[Richard Burts]

Amit

I would suggest that you check these factors:

- is there an appropriate network statement under router BGP?

- does the network statement need to specify a mask?

- is there an entry in the routing table that matches the network statement? (it needs to be the correct subnet/network and the correct mask)

- is there any filtering on the sending router that would impact what is advertised?

- is there any filtering on the receiving router that would impact what is advertised?

If these suggestions do not lead to a solution then I would suggest that you post some details so that we can help you find why it is not working. It would be good to start with the configuration of BGP (preferably from both routers) and also the output of show ip route (or at least the output of show ip route that matches the network statement).

HTH

Rick

[milan.kulik]

Hi,

show ip bgp nei ... adv

should show you if you are advertising any prefixes to your neighbor.

If yes, then you can start investigating why the neighbor is not receiving them (inbound fiters on his side?).

If not, you need to have a look why you are not advertising anything (outbound filters on your side?).

You can apply both directions.

HTH,

Milan