What Prompts Forwarding Table Update for a Route?
Question
Your Junos device has a route in the inet.0 routing table with four valid physical next hops assigned to it.
Which to events prompt an update to the information in the forwarding table for this route? (Choose two.)
Answers
Explanations
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A. B. C. D.AD
Forwarding table information will be updated for this route when a fifth physical next hop is added to the route, or when one of the four physical next hops is removed from the route.
The forwarding table is used by the Junos device to quickly determine the next hop for a given packet based on the destination IP address. The information in the forwarding table is derived from the routing table, which contains all known routes and associated next hops.
When a route is added, modified, or removed from the routing table, the forwarding table must be updated to reflect these changes. The process of updating the forwarding table is known as the route resolution process.
In the scenario described, there is a route in the inet.0 routing table with four valid physical next hops assigned to it. This means that the Junos device has multiple paths to reach the destination network associated with the route. However, until a packet is forwarded towards the route destination, the forwarding table will not be updated for this route.
The two events that prompt an update to the information in the forwarding table for this route are as follows:
A configuration change is committed on the device (Answer B) When a configuration change is committed on the Junos device, the routing table is rebuilt, and all routes are reevaluated. If the route in question is affected by the configuration change, the forwarding table for that route will be updated accordingly.
One of the four physical next hops is removed from the route (Answer D) If one of the four physical next hops assigned to the route is removed, the route is no longer valid, and the forwarding table for that route must be updated to reflect this change. The route resolution process will automatically remove the affected next hop and update the forwarding table accordingly.
It is worth noting that adding a fifth physical next hop to the route (Answer A) will not prompt an update to the forwarding table unless a packet is forwarded towards the route destination. Similarly, forwarding a packet towards the route destination (Answer C) will update the forwarding table for that specific packet, but it will not necessarily update the forwarding table for the entire route.
