Routing Engine Failure | JN0-360 Exam Answer
Question
You have recently installed a second Routing Engine (RE) in your router
Which two statements correctly describe the expected behavior if the primary RE fails?
(Choose two.)
Answers
Explanations
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A. B. C. D.AC
When a router has multiple Routing Engines (REs), one of the REs is designated as the master, and the others are backup. The primary purpose of having a backup RE is to provide redundancy and to take over the master role in case the primary RE fails.
The expected behavior when the primary RE fails depends on the specific type of redundancy configuration being used, such as Nonstop Routing (NSR) or Graceful Routing Engine Switchover (GRES).
Assuming that NSR is configured, two statements that correctly describe the expected behavior if the primary RE fails are:
A. The backup RE will assume the master role once the packet forwarding engine restarts. D. The new master RE maintains the existing protocol adjacencies initially established by the previous master RE.
Here's why:
A. When the primary RE fails, the backup RE will assume the master role once the packet forwarding engine restarts. This means that the backup RE will take over packet forwarding responsibilities and will become the new master RE. The time it takes for the packet forwarding engine to restart depends on the size of the forwarding table, but it is typically a matter of seconds. Once the forwarding engine is up and running, the backup RE will take over the master role.
D. When the new master RE takes over, it maintains the existing protocol adjacencies that were initially established by the previous master RE. This means that the routing protocol process (rpd) does not need to be restarted, and the established adjacencies with other routers will not be disrupted. This is possible because of the NSR feature, which allows the backup RE to keep a copy of the routing table and forwarding state synchronized with the primary RE. When the backup RE takes over, it uses the synchronized state to seamlessly continue routing traffic without disrupting established connections.
In summary, when a router has multiple REs and NSR is configured, the backup RE will take over as the master once the packet forwarding engine restarts, and it will maintain the existing protocol adjacencies without disrupting established connections.
