e links between Routers E, F, and G are all direct fiber links running at 1 Gbps. That means that the path through Routers E, F, and G Chapter 10: Routing Protocols 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. 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 in excess of this number are considered to be unreachable. In RIP, the maxi- mum 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 unreach- able. 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 proto- cols 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. The cost of a link is determined as 100,000,000 divided by the bandwidth of the link in bits per second (bps). The costs of some common links are therefore: 100 Mbps (100,000,000 / 100,000,000 bps) = 10 Mbps (100,000,000 / 10,000,000 bps) = 10 1.5 Mbps (100,000,000 / 1,540,000 bps) = 64 (results are rounded) Metrics and P