BGP neighbor get reset while configuring it as RR

[Ashhad Hussain]

Hello, 

I have little bit confusion-

why BGP reset its neighbor ship while we configure neighbor as Route-reflector later ? Please enlighten it in data plane and control plane.

Thanks for your support.

[paul driver]

Hello
Enabling RR clients is performed on the RR itself not on the clients - and you are saying when you do this the peering drops between client and the RR?

Are all these rtrs are in the same ASN and are IGP peers?
Do they all have route reachability (NLRI) either statically or via an IGP between RR and Client?

res
Paul

[Ashhad Hussain]

Hi, 

Yes you are absolutely right , Enabling RR clients is performed on the RR itself not on the clients.

yes all router is in same AS, thats why I am enabling RR and OSPF is configured as IGP for reachability. 

Yes they all have route reachability as well.

-- logs--- below you can see, after enabling RR, neighbor is going down and up. Is there any reason behind this?

R1(config-router)#
R1(config-router)#
R1(config-router)#neighbor 13.0.0.3 route-reflector-client
R1(config-router)#
*Jan 27 22:51:09.607: %BGP-5-ADJCHANGE: neighbor 13.0.0.3 Down RR client config change
R1(config-router)#nei
R1(config-router)#neighbor
*Jan 27 22:51:11.675: %BGP-5-ADJCHANGE: neighbor 13.0.0.3 Up
R1(config-router)#neighbor 15.0.0.5 route-reflector-client
R1(config-router)#
*Jan 27 22:51:40.791: %BGP-5-ADJCHANGE: neighbor 15.0.0.5 Down RR client config change
R1(config-router)#
*Jan 27 22:51:42.951: %BGP-5-ADJCHANGE: neighbor 15.0.0.5 Up
R1(config-router)#do sh log | i BGP
*Jan 27 22:36:53.735: %BGP-5-ADJCHANGE: neighbor 15.0.0.5 Up
*Jan 27 22:36:55.099: %BGP-5-ADJCHANGE: neighbor 13.0.0.3 Up
*Jan 27 22:37:53.975: %BGP-5-ADJCHANGE: neighbor 13.0.0.3 Down RR client config change
*Jan 27 22:37:56.047: %BGP-5-ADJCHANGE: neighbor 13.0.0.3 Up
*Jan 27 22:51:09.607: %BGP-5-ADJCHANGE: neighbor 13.0.0.3 Down RR client config change
*Jan 27 22:51:11.675: %BGP-5-ADJCHANGE: neighbor 13.0.0.3 Up
*Jan 27 22:51:40.791: %BGP-5-ADJCHANGE: neighbor 15.0.0.5 Down RR client config change
*Jan 27 22:51:42.951: %BGP-5-ADJCHANGE: neighbor 15.0.0.5 Up
R1(config-router)#

[paul driver · Accepted solution]

Hello

Then I guess this is expected - as the RR will request a reset due to changing its ibgp peer to a client

res
Paul

[konstantinoschiotakis]

Hi,

When you configured your router as RR did you type the neighbor remote-as command for your clients?

Cheers,

[Ashhad Hussain]

Hi, Thanks for your response.

Neighbor remote-as command was configured earlier. but now i just configure route reflector only.

[konstantinoschiotakis]

This session reset is normal after BGP reconfiguration. For BGP after establishing a TCP session to a BGP peer, the BGP OPEN message is sent.  The OPEN message advertises the following information about itself:

• BGP Version
• BGP AS Number
• Hold Time
• BGP Identifier (BGP router-id)
• Optional Parameters (includes the router’s BGP capabilities, such as; authentication, multi protocol support, & route-refresh)

So configuring a BGP neighbor with an AS number means that a new OPEN message needs to be sent. To sent an OPEN message you need to tear down the connection and re-establish it, as the OPEN message is the very first message exchanged between BGP peers.

Hope this makes sense (kinda writing this in a hurry).