What is the metric and maximum routable value for RIP?

The Routing Information Protocol (RIP) is a distance-vector routing protocol that uses hop count as its sole metric. A hop count represents the number of routers a packet must pass through to reach a destination network. To prevent routing loops and the "count to infinity" problem, RIP imposes a limit on the maximum number of hops. The maximum valid, routable hop count is 15. A metric of 16 is considered "infinity" and is used to advertise that a network is unreachable.

A. A hop count of 16 is defined as an infinite metric in RIP, which marks the route as unreachable, not routable.
C. Link cost is the metric used by link-state protocols such as OSPF, not by RIP, which uses hop count.
D. RIP uses hop count, not link cost, as its metric, and a value of 16 indicates an unreachable route.

1. Nokia 7750 SR OS Router Configuration Guide, Release 22.10.R1: In the "RIP" chapter, section "RIP Overview", it states, "RIP uses a hop count metric to determine the distance between the source and a destination network... The maximum number of hops in a path is 15. If the hop count is 16, the destination network is considered unreachable."

2. RFC 2453 - RIP Version 2: Section 3.1, "Message Format", under the description of the "Metric" field, specifies: "The metric is a number from 1 to 15, inclusive, which is the current metric for the destination. A metric of 16 is used to indicate that the destination is not reachable."

3. RFC 1058 - Routing Information Protocol: Section 2.2.1, "Metrics", states: "The metric is a number from 1 to 15, inclusive... A metric of 16 is used to indicate that the destination is not reachable." This establishes the fundamental behavior that is carried over into RIPv2.