A network administrator configures a static route on a router: the destination network is 172.16.30.0/24 and the next hop is set to 10.1.1.1, an address that is not on a directly connected interface but is reachable through an existing route in the routing table. Before the router can forward packets toward 172.16.30.0/24, what must it first perform?
- AA recursive lookup to determine the exit interface associated with reaching 10.1.1.1
- BAutomatic summarization of the static route
- CRedistribution of the static route into OSPF
- DARP resolution for 172.16.30.0 directly
Show answer & explanationAnswer & explanation
Correct answer: A. A recursive lookup to determine the exit interface associated with reaching 10.1.1.1
When a static route's next-hop address is not directly connected, the router must perform a recursive lookup in its routing table to find the route that leads to that next-hop address, ultimately determining the correct outgoing interface. Only after this recursive resolution can the router forward traffic and perform ARP for the actual next-hop on the local segment.
Why the other options are wrong
- B. Automatic summarization consolidates routes and has nothing to do with resolving next-hop reachability.
- C. Redistribution is unrelated to resolving how to reach a next-hop address; it's about sharing routes between protocols.
- D. ARP resolves Layer 2 addresses for directly connected next hops, not the remote destination network itself.
Recursive Route Lookup
The process a router performs when a static route's next hop is not a directly connected interface, requiring the router to look up another route in its table to determine how to reach that next-hop address.
- Occurs when next-hop is an IP address rather than an exit interface
- Adds a small processing overhead compared to directly connected next-hop routes
- Can be avoided by specifying the exit interface directly in the static route
Memory trick: Recursive lookup: the router asks 'how do I get to the next hop?' before it can even start the trip.