When rapid-withdrawal is configured UPDATE messages containing withdrawn NLRI are sent immediately to a peer - without waiting for the MRAI timer to expire. SR-OS provides a solution for this problem by supporting a configuration command called rapid-withdrawal. Fast re-convergence after some types of failures requires route withdrawals to propagate to other routers are quickly as possible so that they can calculate and start using new best paths and this is impeded by the effect of the MRAI timer at each router hop. In many cases the default MRAI is appropriate for all address families (or at least those not included in the above list) when it applies to UPDATE messages that advertise reachable NLRI but it is less than ideal for UPDATE messages that advertise unreachable NLRI (route withdrawals). When the helping router receives an EOR it deletes all remaining stale routes of the AFI/SAFI that were not refreshed in the most recent set of UPDATE messages there is an upper limit on the amount of time that routes can remain stale (before being deleted if they were not refreshed) and this is configurable using the stale-routes-time. The EOR is a minimal UPDATE message with no reachable or unreachable NLRI for the AFI/SAFI. When each router has advertised all its routes for a particular address family it sends an End-of-RIB marker (EOR) for the address family. If the session is re-established before the restart timer expires and the new GR capability from the restarting router indicates that forwarding state was preserved then helping continues and the peers exchange routes per the normal procedure. (The default Restart Time advertised by 7x50 routers is 300 seconds but this can be changed using the restart-time command.) When the restart timer expires helping stops if the session has not yet re-established.

(As noted above the ‘stale’ state is not factored into the BGP decision process and not made visible to other routers in the network.) The restart timer derives its initial value from the Restart Time carried in the peer’s last GR capability.

As soon as the failure is detected the helping 7x50 router marks the received IPv4, IPv6, VPN-IPv4 and VPN-IPv6 routes from the peer as ‘stale’ and starts a restart timer.

Check point route based vpn bpg