Regarding IBGP

[sachinmhatre011]

Hello All,

I have two routers connected and running IBGP between two of them and I am able to ping each other.

But later I replace one of the router with same configuration and now I am unable to ping the other router, the replaced new router is of same vendor.

May I know why this is happening.

[Francesco Molino]

Hi,

Do you see a correct peering between them?

If your routers are directly connected to mount iBGP sessions, you can't ping the direct connected interface, is that right?

Could you explain a little bit more your issue and maybe a quick sketch would help.

[sachinmhatre011]

Hi,

Same configuration is done on the new router but unable to ping the other device.

[Francesco Molino]

I understand that point however what do you mean by unable to ping:

 - Ping connected interfaces ?

 - Is there a router in the middle or they are directly connected with a cable?

- Does iBGP session came out

Even you copied the configuration, the issue could be physical, or logical.

In order to help, I need to understand a bit more your design, configuration

[sachinmhatre011]

Actually this was the question asked to me in an interview at Infosys, so I wanna know the answer of it .

[Vinit Jain]

Refer to the Cisco live presentation:

https://www.ciscolive.com/online/connect/sessionDetail.ww?SESSION_ID=83643&backBtn=true

It shows show to troubleshoot peering down issues.

Hope this helps.

Regards

Vinit

[sachinmhatre011]

I am trying to Ping connected interfaces and they are directly connected with a cable

[Francesco Molino]

Ok if you are trying to ping the other end device from the cable and you insure that subnet is correctly configured, you have to troubleshoot from layer 1.

- Is it Ethernet cable or fiber?

- Does cable is ok?

- If SFP are used for fiber and/or ethernet, does the SFP is ok?

- Speed/Duplex configuration from interface

- If physical layer is ok then move on next steps:

- Switch in between?

- Route to null (sometimes on exam they love doing such stuff....)

- ACL,....

But if you have trust config that are exactly the same, the only issue could be physical or logical (interface missconfigured, shutdown,...)

The idea is to begin from layer 1 and going step by step.

[Vinit Jain]

The reason for the issue can be a bad port or SFP (if you are using fiber).

One way to troubleshoot would be to perform a ping test to the connected device. If the connected device is a Cisco router, then you can run "show ip traffic | in echo" and see if the ECHO received counters and echo-reply sent counter are incrementing or not.

You can verify the same command on the problematic router and see if you are seeing the Echo sent counters and Echo-reply received counter incrementing.

Hope this helps.

Regards

Vinit

[sachinmhatre011]

Thanks Vinit.

[Support07]

Hi,

iBGP is it up now ?

Each router are directly connected ? or connected to the same LAN ?

if you can show us : show ip interface brief, show ip bgp summary of the both router it will be more easy to help you

TkR07_9393