RIP uses hop count as its metric. Each router along the path counts as hop. The path with fewer hops is preferred.
Limitation: Hop count ignores link speed. A path through Gbps links has the same metric as a path through Mbps links. RIP would consider them equal.
Maximum hops: RIP limits hop count to . A destination hops away is considered unreachable. This limits RIP to smaller networks.
When a network becomes unreachable, RIP advertises it with metric (infinity). This tells other routers to remove that route. The hop limit is a design tradeoff between network size and convergence time.