RIPv2 is a distance-vector routing protocol and uses the distance, measured in hops, to determine the best route to a destination. (A distance-vector routing protocol uses only the number of routers on a path to determine the next hop.) In RIPv2, each hop corresponds to a single router, and the number of hops to a destination is the sum of the number of routers a packet has to pass through, starting at its origin.
There is also a RIP version 1 (RIPv1). It works well for networks that have not changed since 1985, but not so well for today's networks. We recommend dealing only with RIPv2.
RIPv2 is generally used in smaller or less complex networks, partly because it's something of a simple protocol, and partly because of a design limitation. The maximum hop count that a route can have is 15. If a destination is more than 15 routers away, RIPv2 can't forward packets to that destination and simply discards (drops) the packets. The two other IGPs discussed later in this chapter, OSPF and IS-IS, don't have this limitation. For this reason, and also because OSPF and IS-IS provide more features than RIPv2, they're used more often for a network's IGP (which is why this discussion of RIPv2 is fairly short!).
You want to use RIPv2 on the Juniper router when you're connecting the router to a network that is already running RIPv2. The router configuration is very straightforward. ...