RIPv2 is the newer, enhanced version of the RIP routing protocol, and is specified in RFC 1723. In many ways, this newer version is still very similar to its predecessor – it is still a distance vector protocol that uses hop count as its metric (the hop count limit is still 15), and still has a default administrative distance of 120. However, version 2 also introduces a number of features not found in the original version. Firstly, RIPv2 is classless; this means that it can be used on networks that employ variable-length subnet masking (VLSM). This is possible because RIPv2 includes the subnet mask associated with a destination network in its routing table updates. Where routing table updates were broadcast in RIP version 1, RIPv2 instead uses multicasts to send updates – specifically, a router will send updates to the multicast address 188.8.131.52.
RIPv2 is also capable of employing authentication between neighboring routers. This is another feature not found in the original version. You may be asking why authentication might be an issue when it comes to routing table updates. Remember that a RIPv1 update was no more than a broadcast, and that routers completely trust the information provided by neighbors. Now, imagine how easy it would be to anyone to set up another RIP router on a network (even versions of Windows can be configured as a RIP router), and begin broadcasting all sorts of incorrect routing table information! It certainly wouldn’t take long to really mess up those RIP routing tables. With RIP version 2, authentication can be enabled on any router interface using either plain text or MD5 authentication. If authentication is enabled, a router will only accept updates from routers whose updates contain the correct authentication string.