Rip technology Overview (1)

Rip works on UDP port 520-that is, the source port and destination port of all RIP packets are 520.

1 initialization-during RIP initialization, request packets are sent from each interface involved in the work. The request packet requests a complete route table from all RIP routers. The request is sent to the LAN through broadcast on the LAN or to the next hop address through the point-to-point link. This is a special request that requests complete route updates from neighboring devices.
2. receive a request. RIP has two types of messages: Response and message receipt. Each route entry in the request packet is processed to create a measurement and path for the route. RIP uses the hop count measurement. If the value is 1, it indicates a directly connected network. If the value is 16, the network is inaccessible. The router returns the entire route table as a response to receive messages.
3. Receive the response. The router receives and processes the response. It adds, deletes, or modifies the route table and updates it.
4. Regular route update and timing-the router sends the entire route table to the neighbor router in the form of a reply message once every 30 seconds. When the vro receives information about a new route entry or an update of an existing route entry, a 180-second timeout is set. If there is no update information in 180 seconds, the route hop count is set to 16. The router declares the route with the measurement value 16 until the refresh timer deletes the route from the route table. Set the timer refresh time to 240 seconds or 60 seconds longer than the expiration time. Cisco also uses the third timer called the suppression timer. The 180 second time after receiving a route with a higher measurement is the time to suppress the timer. During this period, the router will not use the new information it receives to update the route table, this provides an additional period of time for network convergence.
5. Trigger route update-when a route metric changes, the router only sends the route related to the change and does not send the complete route table.

Note:
RIP-1 is a classless routing protocol. Therefore, the route declaration does not contain a subnet mask. RIP-1 uses the subnet mask of the interface that receives the route to determine the subnet mask of the destination network. This method is only effective when the received route and direct connection network are in the same master network. If the received route is not the same master network, the router will try to match the master network mask of the route, which may be A, B, and C. Therefore, it is important to keep the length of each master netmask consistent throughout the RIP route domain. When re-publishing, if the redi subnet does not match the local interface, the network will not be sent. ip sum-add should be used to adjust the network.

Vroa A is on the master network 128. 200. 0. 0 has two interfaces, each of which has the same 24-bit mask. Therefore, the router will only receive route update information for the 24-bit mask of the main network 128.200.0.0. When the router receives a route update for another primary network, such as 192.16.1.4/30), it adds a summary route of the primary network mask or the class boundary mask of the address to its routing table, this address is summarized at 192.16.1.0/24

Vrob B also has two interfaces. One is in the main network 128.200.0.0/16, and the other is in the network 192.16.1.0/24. When B receives the 128.200.2.0 subnet, he will try to send them out. Because the interface mask is 30 bits), only the summarized route 128.200.0.0/16 can be sent.

RIP-2
Supports VLSM. The router includes a subnet mask in the route update so that the router can handle VLSM addressing.
Each route entry carries the next hop address.
Support for external routing labels
Multicast Route update
Support for MD5 authentication
RIP-2 becomes the classless routing protocol, so you do not need to maintain mask consistency throughout the route domain.
The multicast address used by RIP-2 to send route updates is 224.0.0.9, while RIP-1 uses the broadcast address to be accepted, including all hosts.
RIP-2 is completely backward compatible with RIP-1, which is achieved through the compatibility switching mechanism and the receiving control switch mechanism. You can use ip rip [send | receive] version [1 | 2 | 1 2] to manually configure the switching mechanism.