can we change the bgp route reflector path without any impact on client

[harpal singh]

hi

i need help

i have a question Is there ia a way to change the bgp route-reflector path without changing its client path.

[Giuseppe Larosa]

Hello Harpal,

the history of reflections is stored in the Cluster list BGP attribute that is added by BGP RR and it is available /visible to clients.

A change in the BGP RR path means a new Cluster list attribute and means a new BGP advertisement that reaches the client.

So this cannot be done unnoticed.

What you can do is to deploy the new BGP RR devices in addition to existing ones, to configure the iBGP sessions with all the clients as intended and you need also to full mesh the new BGP RR devices to the existing ones

At the end of the process you can check on selected clients that new versions of BGP advertisements are present in addition to old ones ( differentiated by cluster list and other details).

At this point you can start to unconfigure / remove the old BGP RR servers as needed and this should cause BGP best path recalculations on all clients but with new BGP advertisements already present on them ( this is the key point to minimize impact).

Hope to help

Giuseppe

[harpal singh]

Gluseppe Larosa

thanks for the answer. i really appreciate that.

Are you talking about diverse path.

does i have to remove new RR route-reflector client command from Old RR, for this or it can remain there as before.

[Giuseppe Larosa]

Hello Harpal,

the idea is to develope  the new RR devices in parallel with the old RR servers, so you will remove route-reflector-client commands from the old RR servers only at the end when you have already deployed all the iBGP sessions on the new RR servers and between the RR servers themselves.

There is no problem on having a set of clients served at the same time by old RR servers and new RR servers.

Each client will perform a BGP best path selection using the known hierarchy of criteria, but it can receive multiple copies of the same advertisement from the old RR infrastructure and from the new RR infrastructure.

Hope to help

Giuseppe