The operation of BGP combined with routing policy

Hi there,

I have been trying to figure a concept about the operation of BGP when configured with policy, then deleted, and then configured again:

Let say I have 1 BGP RR which learn routes via eBGP to some ISP.
those routes are filtered using route-map which sets the community for those incoming routes lets say for example - 11:11.

the RR will advertise those route to his iBGP neighbors and his other eBGP neighbors as expected from BGP.

the process steps that the router perform are as below:

  1. bgp adjacency is done
  2. neighbor advertise routes
  3. RR receive routes and filter them with the route-map and taging them with the community of 11:11.
  4. the RR advertise those routes along with that community to his other neighbors.

now my question is - how would the router operate if the route-map would be deleted and then inserted right back again?

my assumption for the process is the following:

after delete:

  1. RR would ask the neighbor to advertise the routes again so he could make new filtering
  2. the router will not delete its already known routes that he learned before the route-map got deleted
  3. after receiving back the whole NLRI, now the router doesn’t set the community so it will advertise his neighbors the whole routes he learned in a FIFO way which means that even if we will configure right away the route-map again then this advertising process will not stop in the middle and the operation would keep advertising the whole routes to the other neighbors

after configuring the route-map again as before:

  1. RR would ask the neighbor to send the routing table again , lets assume that it is FULL ROUTE table which already is being advertised and we configured the route-map again before that process ended - would the new configuration will stop that advertisement and send a new request for the same advertisement because we applied a new route-map for the neighborship policy?

  2. now the RR would tag those routes with community 11:11 and advertise all of them again to his neighbors because those routes are different NLRI then the previous which doesn’t contain community?

this operation is some example of a problem we had last week in work which causes some big BGP advertisement that took the whole bandwidth for 20 long minutes and I would like to understand what exactly happend as much as possible since it is pretty tricky and advanced question which I couldn’t figure it out.

And for last - if my explenation of the pocess is not half bad , would that same process still be the same in case I wouldn’t tag those routes with any community but instead would filter some Private address network like RFC 1918?

Thanks you very much