 the better path. This router will be added to the routing table with a metric of 3. Using hop count as a metric has a limitation that can cause suboptimal paths to be chosen. Looking at Figure 10-5, you can see that the link between Routers B and C is a T1 running at 1.54 Mbps, while the links between Routers E, F, and G are all direct fiber links running at 1 Gbps. That means the path through Routers E, F, and G will be substantially faster than the link between Routers B and C, even though that link has fewer hops. However, RIP doesn't know about the bandwidth of the links in use, and takes into account only the number of hops. Metrics and Protocol Types Three hops RIP prefers this route 1.5 Mbps Gig fiber 1,000 Mbps Four hops Figure 10-5. RIP uses hops to determine the best routes A protocol such as RIP is called a distance-vector routing protocol, as it relies on the distance to the destination network to determine the best path. Distance-vector pro- tocols suffer from another problem, called counting to infinity. Protocols such as RIP place an upper limit on the number of hops allowed to reach a destination. Hop counts that exceed this number are considered to be unreachable. In RIP, the maximum hop count is 15, with a hop count of 16 being unreachable. As you might imagine, this does not scale well in modern environments, where there may easily be more than 16 routers in a given path. A more modern version of RIP, called RIP version 2 (RIPv2 or RIP2), raises the limit to 255 hops, with 256 being unreachable. However, since RIPv2 still doesn't understand the states and capabilities of the links that join the hops together, most networks employ newer, more robust routing protocols instead. Routing protocols such as OSPF are called link-state routing protocols. These protocols include information about the links between the source router and destination network, as opposed to simply counting the number of routers between them. OSPF adds up the cost of each link. You determine the cost of a link by dividing 10