You have recently installed a second Routing Engine (RE) in your Junos device and implemented Graceful Routing Engine Switchover (GRES).
Which two statements correctly describe the expected behavior if the primary RE fails? (Choose two.)
Click on the arrows to vote for the correct answer
A. B. C. D.BC
Once the RE's are synchronized, they exchange keepalives. If the backup RE does not receive a keepalive from the master RE after a specified timeout (typically
2 seconds), it determines that the master RE has failed and takes mastership. When a mastership change occurs, the PFE seamlessly disconnects from the old master RE and reconnects to the new master RE. The PFE does not reboot and continues forwarding traffic based on the existing forwarding table entries.
Sure, I'd be happy to explain the expected behavior of a Junos device when using Graceful Routing Engine Switchover (GRES) and a primary Routing Engine (RE) fails.
First, it's important to understand what GRES does. GRES is a feature that allows for a more seamless switchover between Routing Engines in a Junos device in the event of a failure. When GRES is enabled, the backup RE continuously maintains a copy of the primary RE's routing protocol and forwarding tables. This allows for a faster switchover to the backup RE should the primary RE fail.
Now, let's look at the statements and determine which two are correct:
A. The backup RE will assume the master role once the packet forwarding engine (PFE) restarts. This statement is incorrect. The backup RE will assume the master role immediately after detecting that the primary RE has failed. The PFE restarts are not related to the switchover process.
B. The backup RE will immediately assume the master role. This statement is correct. When the primary RE fails, the backup RE will take over as the master RE without any delay. This ensures that there is minimal disruption to network operations.
C. The new master RE restarts the routing protocol process (rpd) and establishes any required adjacencies based on the configuration. This statement is partially correct. When the new master RE takes over, it will indeed restart the routing protocol process (rpd) and establish any required adjacencies. However, this is not based on the configuration, but rather on the information that it has been maintaining in memory.
D. The new master RE maintains the existing protocol adjacencies initially established by the previous master RE. This statement is correct. When the new master RE takes over, it will maintain the existing protocol adjacencies that were established by the previous master RE. This ensures that there is no disruption to the network.
In summary, the correct statements are B and D. When the primary RE fails, the backup RE will immediately assume the master role and maintain the existing protocol adjacencies established by the previous master RE. The new master RE will also restart the routing protocol process (rpd) and establish any required adjacencies based on the information that it has been maintaining in memory.