CCIE RS Exam Blueprint One of CCIE study notes: Rip technology overview

Rip works on UDP port 520 - that is, all RIP packets have a source port and a destination port of 520.
  1. Initialize --w.net130.com/CMS/Pub/network/network_protocal/04937.htm" target="_blank">When RIP is initialized, the request packet is sent from each participating interface. The request data The packet will request a complete routing table from all RIP routers. The request is sent over the LAN as a broadcast or sent over the point-to-point link to the next hop address. This is a special request. The neighbor device requests a complete routing update.
  2. Receive Requests - RIP has two types of messages, responding to and receiving messages. Each route entry in the request packet is processed to establish metrics and paths for the route. RIP uses a hop count. A value of 1 means a directly connected network, and 16 is a network unreachable. The router will return the entire routing table as a response to the received message.
  3, received a response - the router receives and processes the response, it will be updated by adding, deleting or modifying the routing table entry.
  4. Regular Routing Update and Timing—The router sends the entire routing table to the neighboring router in the form of a reply message in 30 seconds. When the router receives a new route or an existing route update message, it sets a timeout of 180 seconds. If there is no update information for 180 seconds, the hop count of the route is set to 16. The router announces the route with a metric of 16 until the refresh timer deletes the route from the routing table. The time to refresh the timer is set to 240 seconds, or 60 seconds longer than the expiration timer. Cisco also used a third timer called a suppression timer. The 180 second time after receiving a higher-measurement route is the time to suppress the timer. During this time, the router will not update the routing table with the new information it receives, which can provide an extra layer for network convergence. time.
  5, trigger routing update - When a routing metric changes, the router only sends the routing related to the change, and does not send a complete routing table.
  Note: RIP-1 is a classful routing protocol, so the subnet mask is not carried in the route announcement. RIP-1 uses the subnet mask of the interface that receives the route to determine the subnet mask of the destination network. This practice is only effective when the received route and the directly connected network are on the same primary network. If the received route is not the same primary network, the router will try to match the primary network mask of the route, which may be A, B, and C. Therefore, it is important to keep the length of each primary mesh mask consistent throughout the RIP routing domain. When republishing, if the subdi of the redi does not match the local interface, the network will not be sent. Use ip sum-add to adjust.
  Router A has two interfaces on the primary network 128.200. 0, and the 24-bit mask on each interface is the same. Therefore, the router will only receive routing update information for the 24-bit mask belonging to the primary network 128.200.0.0. When the router receives a route update belonging to another primary network (such as 192.16.1.4/30), it adds a summary route of the primary network mask bit or the class boundary mask of the address to its routing table, the address Summary bit 192.16.1.0/24

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