What are the fields of a routing table entry and what does each field represent?

• A. Destination network; Next hop; Metric; Administrative distance; Exit interface/source.
• B. Destination host; Gateway; Bandwidth; Hop count; Cost.
• C. Path length; Route type; Source interface; Identity.
• D. Network mask; Router ID; Time to live; Interface name.

Answer: (A)

The main idea being tested is what information a routing table stores to determine how to forward packets. A typical routing table entry includes five key pieces:

• Destination network: the specific network or prefix the route applies to. This is used to match the destination address of an incoming packet. The more specific (longer) the prefix, the higher its priority in the lookup.

• Next hop: the address of the next device to forward the packet to on the way toward its destination. If the destination is directly reachable on the local network, this may be the destination itself or may be implied by the exit interface.

• Metric: the cost associated with the route, used to compare multiple possible paths. Lower costs are generally preferred, and the metric helps the router choose the best route when several options exist.

• Administrative distance: a value that indicates how trustworthy the route source is (for example, static routes, connected routes, or routes learned from different routing protocols). The route with the lower administrative distance is favored when multiple routes to the same destination exist.

• Exit interface: the local interface used to forward the packet toward the next hop. This tells the router which physical or logical path to send the packet out on, and it can be used even when there isn’t a specific next-hop IP.

The other options mix in fields that aren’t standard parts of a routing table entry (like bandwidth, hop count as separate fields, TTL, or router identity), or pair concepts that aren’t stored together as the core fields of a route.