The Route Tag field, the Subnet Mask field, and the Next Hop field are RIPv2 extensions that do not exist in RIPv1 messages. The basic format of the RIP message remains unchanged between the two versions; Version 2 merely uses fields that are unused in Version 1.
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In addition to the functions that use the new fields, RIPv2 supports authentication and multicast updates.
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RIPv2 uses the multicast address 224.0.0.9. Multicasting of routing messages is better than broadcasting because hosts and non-RIPv2 routers will ignore the multicast messages.
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When another routing protocol uses the RIPv2 domain as a transit domain, the protocol external to RIPv2 can use the Route Tag field to communicate information to its peers on the other side of the RIPv2 domain.
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The Next Hop field is used to inform other routers of a next-hop address on the same multiaccess network that is metrically closer to the destination than the originating router.
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RIPv2 uses the same UDP port number as RIPv1, port number 520.
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RIPng uses the UDP port number 521.
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A classless routing protocol does not consider the major network address in its route lookups, but just looks for the longest match.
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To support VLSM, a routing protocol must be able to include the subnet mask of each destination address in its updates.
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The Cisco implementation of RIPv2 supports clear-text authentication and MD5 authentication. Only clear-text authentication is defined in RFC 2453.
