1. Introduction to RIP
RIP is a protocol based on the Distance-Vector algorithm, which uses the Hop Count as the measurement value to measure the distance to the destination address. In the RIP network, the RIP protocol requires each router in the network to maintain routing information from itself to each destination network.
The RIP protocol uses the number of hops to measure the "distance" between networks: the hop number from a router to its directly connected network is defined as 1, and the distance from a router to its non-directly connected network is defined as the distance between each router. plus 1. "Distance" is also called "hop count". The maximum hop count allowed by RIP is the maximum number of hops. Therefore, 16 is unreachable. It can be seen that the RIP protocol is only suitable for small networks.
RIP principle:
- initialization. When RIP initializes, it sends request packets from each participating interface. The request packet will request a complete routing table from all RIP routers. This request is accomplished by sending the LAN in the form of a broadcast on the LAN or by sending it to the next-hop address on a point-to-point link. This is a special request to request complete routing updates from neighboring devices.
- Receive requests. RIP has two types of messages, response and receive messages. Each route entry in the request packet is processed to build the metric and path for the route. RIP uses the hop count measurement, a value of 1 means a directly connected network, and 16 means the network is unreachable. The router will return the entire routing table as an answer to the received message.
- Response received. The router receives and processes the response, which it updates by adding, removing, or modifying routing table entries.
- Regular routing updates and timing. The router sends the entire routing table to neighboring routers in response messages every 30 seconds. When the router receives a new route or an update of an existing route, it will set a timeout period of 180 seconds. If there is no update information for 180 seconds, the hop count of the route is set to 16. The router advertises the route with a metric of 16 &