BGP Router id in nexus 7k.

[fabio.marino]

Hi,

I have a quick one.

On the config guide of the nexus 7k you can read the following

You can configure the router ID. By default, Cisco NX-OS sets the router ID to the IPv4 address of a loopback interface on the router. If no loopback interface is configured on the router, the software chooses the highest IPv4 address configured to a physical interface on the router to represent the BGP router ID.

I exeplicitely configured the router id.

Question

• I will shutdown the interface xyz that has the ip assigned to the router id. What will happen?
  • Will I have a reset of all the bgp connections?
  • The router will automatically select the new router id? If yes, then it means that the router  will ignore the command router-id until the interface is xyz  up again?

Thanks all.

[Bilal Nawaz]

The 7K should keep using the router-id it has been configured with, i.e. the interface xyz, because you have "pinned it". As long as the router-id is not used for peering with BGP neighbors you should be OK. If this is the case you should not encounter a reset of bgp connections.

[fabio.marino]

Hi,

Thank you for the reply but it is not clear.

You stated

The 7K should keep using the router-id it has been configured with, i.e. the interface xyz, because you have "pinned it".

Again, what will happen when the interface xyz is down? Which router-id will use the router?Still the interface xyz??

[Bilal Nawaz]

Fabio... My reply is precisely what I said.

If I hard code a router-id, whether the interface is down or not,

it will still be used. It should keep using the router ID it has been configured with - Because you have pinned it.

[fabio.marino]

Hi

perfect..then I have to expect a bgp reset because this ip is used for  peering with BGP neighbors.....

Thanks!!

[Richard Burts · Accepted solution]

I think there are two different issues involved here and want to be sure that we see the differences. The first part of the question is about router ID being configured. And the correct answer is that when you have configured a router ID it will continue to be the router ID whether the interface is in the UP state or is in the DOWN state.

The second issue is the impact of a DOWN state on an interface that is the address that is used as the peer address by neighbors. If the peering address interface is down then the packets from the neighbor will not be processed and the BGP session will time out and be terminated. But this is about the peering address and is separate from the function of the router ID.

HTH

Rick

[fabio.marino]

Hi Richard,

I agree, then I think I mixed up the answers and I mixed up with ospf concept as well.

In brief

• I will shutdown the interface  so of course I am exepecting the shutdown of the bgp neighboprship
• The BGP process will never reset in my specific scenario becasue
  • I am not going to change the router-id
  • I explicetely configured the router id and, as you said, it does not depend from state of the  interface xyz .

Thanks all!!!

I will now close the topic!!

[Bilal Nawaz]

Hi Rick, thats basically what I said before... no? You've just repeated what I've posted but in other words, or am I missing something here?

[Richard Burts]

I agree that your answer about the function of router ID is correct and that what I said about router ID was very similar. My main point that what had started as a question about one thing had evolved into a discussion about two things and wanted to be clear that a BGP session going down when the interface is down does not have anything to do with the choice of router ID.

HTH

Rick