Two directly connected routers, R1 and -R2, are both configured for OSPF graceful restart. R2 is
able to switch packets in hardware, but R1 is not. If a network administrator logs on to R2 and
performs a system reload, which will be the result?
A.
Traffic forwarded from R2 to or through -R1 will continue to be forwarded based on the
forwarding table state at the time of the reload.
B.
R2 will continue to forward traffic to -R1, but -R1 will drop the traffic because its neighbor
adjacency with R2 has failed.
C.
R2 will continue forwarding traffic to and through R1, but R1 will drop this traffic because it is
not capable of maintaining its forwarding state.
D.
All the traffic R2 is forwarding to or through R1 will be dropped while OSPF rebuilds its neighbor
adjacency and forwarding tables.
Explanation:
Graceful Restart Router Operation
Graceful Restart Initiation
The restarting router becomes aware that it should start the graceful restart process when the
network administrator issues the appropriate command or when an RP reloads and forces and
Redundancy Facility (RF) switchover. The length of the grace period can be set by the network
administrator or calculated by the OSPF software of the restarting router. In order to prevent the
LSAs from the restarting router from aging out, the grace period should not exceed an LSA refresh
time of 1800 seconds. In preparation for graceful restart, the restarting router must perform the
following action before its software can be reloaded: The restarting router
must ensure that its forwarding table is updated and will remain in place during the restart. No
OSPF shutdown procedures are performed since neighbor routers must act as if the restarting
router is still in service. The OSPF software is reloaded on the router (it undergoes graceful
restart).OSPF Processes during Graceful Restart
After the router has reloaded; it must modify its OSPF processes until it reestablishes full
adjacencies with all former fully adjacent OSPF neighbors. During graceful restart, the restarting
router modifies its OSPF processes in the following ways:
The restarting router does not originate LSAs with LSA types 1, 5, or 7 so that the other routers in
the OSPF domain will use the LSAs that the restarting router had originated prior to reloading. The
router does not modify or flush any self-originated LSAs. The restarting router runs its OSPF
routing calculations in order to return any OSPF virtual links to operation. However, the restarting
router does not install OSPF routes into the system??s forwarding table, and the router relies on
the forwarding entries that it had installed prior to undergoing the graceful restart process. If the
restarting router determines that is was the Designated Router on a given
segment prior to the graceful restart, it will reelect itself.
Graceful Restart Process Exit
The restarting router exits the graceful restart process when one of the following events occurs:
The router has reestablished all adjacencies. The graceful restart was successful. The router
receives an LSA that is inconsistent with an LSA from the same router prior to the graceful restart.
The inconsistency can mean either that the router does not support the graceful restart feature or
that the router has terminated its helper mode for some reason. The graceful restart was
unsuccessful. The grace period has expired.
The graceful restart was not successful.
Once the restarting router has completed the graceful restart process, it returns to normal OSPF
operation, reoriginating LSAs based on the current state of the router and updating its forwarding
tables based on current link-state database contents. At this time, it flushes the grace-lsa’s that it
had originated during the initiation of the graceful restart process.