Command : 8, 1 indicates a request, a response indicating 2, 3 and 4 do not give up, 5 and 6 show informal polling command;
Version : 8, comprising a RIP and RIP RIP2,1 represented, of RIP2 represents 2;
Address Series : 16, this value for TCP / IP is fixed to 2;
The I P address, distance : These two already mentioned, should be very familiar with.
Notice : a RIP packet, routing can contain up to 25, which is to ensure that the total length is less than a RIP packet 512B. Under can be calculated, a RIP packet occupies up 4B + 25 * 20B = 504B. So each RIP packet can only carry a maximum of 25 routes (routing only is the routing entry, not a router), so, in order to send the entire routing table, RIP usually need to send multiple messages.
Every 30s all or part of the router which will complete the routing table to a neighbor router; a route whenever the distance is changed when it is updated it, does not need to send the complete routing table tables, which requires only a change in transmission item.
RIP routing protocol is based on vector selection very simple protocol, RIP packets from the above, we can clearly see, there is no concept RIP subnet address, host number if an IP address is not 0, RIP can not distinguish between non-zero section contains the subnet number, RIP2 overcomes this defect.
RIP2 protocol packets
RIP2 improvements to RIP that take advantage of a lot of all-zero field.
Routing domain : indicates the owner of the data reported, this field is a routing daemon identifier PID;
Routing tag : To support the EGP, carrying a EGP AS number and BGP;
Subnet Mask : allows RIP2 preparation and support classless CIDR.
Next stop IP Address : Indicates the next hop address. If the two autonomous systems share a network (e.g., backbone), this field is particularly useful. This message can be defined packet sent to the router, the router is the same regardless of the autonomous system or in another autonomous system. This field is 0, the address sent to the destination of the packet should be sent to the system sending RIP packets.