How Many Next Hops are Entered into the Forwarding Table?

A

By default, the Junos OS randomly selects one next hop to enter into the forwarding table. You can alter this behavior by using a policy.

In Junos OS, when a packet is forwarded, the router looks up the destination IP address in the forwarding table, which is a subset of the routing table. The forwarding table contains only those routes that have been selected as the best path to a particular destination, and these routes are called the active routes.

The active route for a particular destination in the routing table can have multiple next hops, which are the physical interfaces or IP addresses that the router can use to forward traffic to that destination. When a packet needs to be forwarded to the destination, the router selects one of the next hops from the active route, based on the configured load balancing algorithm.

Now coming back to the question, if a route in the inet.0 routing table has four valid physical next hops assigned to it, and no load balancing algorithm is configured, by default, only one next hop is entered into the forwarding table. This is because only one next hop is selected as the active route based on the preference and metric values of the route, and that next hop is entered into the forwarding table.

However, if load balancing is configured, then all valid next hops for the active route are entered into the forwarding table. The number of next hops that can be entered into the forwarding table depends on the Junos OS platform and the configuration of the router, but it can be up to 16.

Therefore, the correct answer to the question is A. 1, as by default, only one next hop is entered into the forwarding table even if the route in the inet.0 routing table has four valid physical next hops assigned to it, and no load balancing algorithm is configured.