RIP-2, like its predecessor, was specifically designed for use as an Interior Gateway Protocol (IGP) in small networks. Its capability to support subnet masks, however, meant that it would accommodate a degree of network addressing complexity that RIP couldn't.
RIP-2 uses a special message format, or packet, to collect and share information about distances to known internetworked destinations. This packet contains the following structure:
A 1-octet Command field
A 1-octet Version Number field
A 2-octet Unused field
A 2-octet Address Family Identifier (AFI) field
A 2-octet Route Tag field
A 4-octet Networking Address (that is, IP address) field
A 4-octet Subnet Mask field
A 4-octet Next Hop field
A 4-octet ...