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Routing & Switching · Intermediate

Count to Infinity

A distance-vector routing loop problem where routers keep incrementing the metric of an unreachable route.

Definition

When a network fails, routers that rely on periodic updates may learn stale routes from each other and increment the metric indefinitely. RIP caps the problem by defining 16 hops as infinity. Split horizon, route poisoning and hold-down timers are designed to prevent it.

Example

Two RIP routers bounce a dead route between them, raising the hop count until it reaches 16.

Exam tip

The maximum valid RIP hop count is 15 precisely to bound count to infinity.

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