RIP-1 Packet Format

The maximum datagram size in RIP is 512 octets. The first byte is used for commands such as rip update request and rip update response. The next byte is used for the Version field, which is set to 1 for RIP-1. The next 2 bytes must be 0. The 2-byte field after this is used for the address family identifier; the next 14 bytes are allocated for the network address, as shown in Figure 2-2. In the case of IP, only 4 bytes of those 14 are used for the IP address. The remaining 10 bytes are unused in RIP-1, although they are used in the RIP Version 2 (RIP-2) packet format. The next 4 bytes are used for the RIP metric, which can be up to 16. The portion from the address family identifier up to the Metric field can be repeated 25 times, to yield the maximum RIP packet size of 512 bytes.

Figure 2-2. RIP-1 Packet Format