Network basics lecture 13: routing information protocol (RIP) (1)

Welcome back to the core of the Network: routing protocol. In this series of route protocol lectures, we will first introduce one of the earliest and simplest protocols: the route information protocol (RIP ).

Like all protocols, RIP is used to distribute network information related to routers. On the most basic level, the router needs to know what network can be reached and how far it is from these networks. The RIP Protocol does this. The RIP Protocol is still widely used.

Many people cursing the RIP Protocol, saying that the aggregation speed is too slow, there is no scalability and security, because the RIP Protocol only supports plaintext authentication, this protocol is also affected by the Split-horizon protocol. These situations are true. However, this protocol is still very useful. We hope this article will illustrate these issues and help you understand one of the most widely used internal gateway protocols.

There are two versions of the RIP Protocol: the first version (r1_1) and the second version (r1_2 ). R12001 has very limited functions because it does not support CIDR (classless Inter-Domain Routing) Address Resolution. This means that this Protocol is only a domain-like protocol. You cannot divide the 24-mask network into smaller units. In addition, r12001 also uses broadcast to send messages. This means that the host cannot ignore RIP broadcast. Remember that every time a broadcast is sent, every host in the broadcast domain receives an interruption and must process the packet to determine whether the packet is of interest to it. R12002 uses Multicast technology. This technology will be introduced in subsequent lectures. Now, you only need to know whether the host can ignore this multicast packet without processing this packet.

Remember, we once said that RIP is a distance vector protocol. The distance mentioned here refers to the number of hops in the RIP Protocol, and the vector refers to the destination. Other distance vector protocols may use other rules to measure vectors, such AS-PATH in BGP. Both versions of RIP send messages to UDP port 520 every 30 seconds. But what information do they send? If you guess it is "their route information", you can guess it. RIP can send specific information about the network it can reach and broadcast itself as a default gateway (Destination: 0.0.0.0, metric value/metric is 1 ).

R12002 data packets have their own headers, the same as many other protocols. Note that the RIP Protocol is based on the UDP protocol, so it is actually an application layer protocol. Each RIP packet contains a command, a version number, and a route domain. Then there is a maximum of 25 route entries in one packet ).

RIP packet instructions

A rip command can be a request or a response. When a host (either a Unix server or a router) is started for the first time, the host needs to obtain some routing information. A "request" command is sent. Broadcasts packets containing request instructions to the network. "Response" is another common RIP command. It is used to answer a request, or simply publish a broadcast every 30 seconds.

Version Number

The version number is one or two, indicating the RIP Protocol version of this packet.

Route domain

A routing domain in the RIP Protocol is an identifier used to specify a route instance. There can be more than one set of RIP instances in the same network. You can specify a specific information that is only sent to people in a specific domain.

Other parts of the RIP Packet

After the route domain, the real RIP route information starts. A data packet can contain up to 25 route entries. Each route entry must contain the following information:

• Network Address: Identify the start point of the target subnet address.

• Subnet mask: indicates the size of the network.

• Next Hop IP Address: the router that allows you to reach your destination.

• Metric value: the distance between the hops of the network.