In which two ways does the BGP graceful capability preserve prefix information during a restart?
(Choose two)

A.
The peer router immediately removes the BGP routers that it learned from the restarting router
from its BGP routing tables.

B.
The router establishes BGP sessions with other routers and relearns the BGP routes from
others that are also capable of graceful restart. The restarting router waits to receive updates from
the neighboring routers.

C.
The peer router sends an end-of-RIB message to the restarting router.

D.
The restarting router removes any stale prefixes after the timer for stale entries expires.

E.
The restarting router does not remove any stale prefixes after the timer for stale entries expires.

Explanation:
BGP Graceful Restart for NSF
When an NSF-capable router begins a BGP session with a BGP peer, it sends an OPEN message
to the peer.
Included in the message is a declaration that the NSF-capable or NSF-aware router has graceful
restart capability. Graceful restart is the mechanism by which BGP routing peers avoid a routing
flap following a switchover. If the BGP peer has received this capability, it is aware that the device
sending the message is NSF-capable. Both the NSF-capable router and its BGP peer(s) (NSFaware peers) need to exchange the graceful restart capability in their OPEN messages, at the time
of session establishment. If both the peers do not exchange the graceful restart capability, the
session will not be graceful restart capable.
If the BGP session is lost during the RP switchover, the NSF-aware BGP peer marks all the routes
associated with the NSF-capable router as stale; however, it continues to use these routes to
make forwarding decisions for a set period of time. This functionality means that no packets are
lost while the newly active RP is waiting for convergence of the routing information with the BGP
peers.
After an RP switchover occurs, the NSF-capable router reestablishes the session with the BGP
peer. In establishing the new session, it sends a new graceful restart message that identifies the
NSF-capable router as having restarted.
At this point, the routing information is exchanged between the two BGP peers. Once this
exchange is complete, the NSF-capable device uses the routing information to update the RIB and
the FIB with the new forwarding information. The NSF-aware device uses the network information
to remove stale routes from its BGP table. Following that, the BGP protocol is fully converged.
If a BGP peer does not support the graceful restart capability, it will ignore the graceful restart
capability in an
OPEN message but will establish a BGP session with the NSF-capable device. This functionality
will allow interoperability with non-NSF-aware BGP peers (and without NSF functionality), but the
BGP session with non-NSF-aware BGP peers will not be graceful restart capable.