Knowledge about router protocols

With the development of China's routing industry, it has also promoted the continuous improvement of router protocols. Here we mainly introduce the knowledge of router protocols that network engineers should have mastered. Distance Vector router protocols are designed for small network environments. In a large network environment, this type of Router Protocol will generate large traffic when learning routing and maintaining routing, occupying excessive bandwidth.

If the route selection table update is not received from the adjacent site within 9 0 seconds, the adjacent site is considered inaccessible. Every 30 seconds, the distance vector Router Protocol sends the entire route selection table to the adjacent site to update the route selection table of the adjacent site. In this way, it can be directly connected from other sites or other methods) to collect a list of networks for route selection. Distance Vector Routing uses the number of hops as the metric value to calculate the number of routers that need to pass to the destination. For example, r I p uses the B e l m a n-F o r d algorithm to determine the shortest path, that is, the line that can reach the destination as long as it passes through the smallest hop count. The maximum number of hops allowed is usually set to 1 5. Terminals that must pass through more than five vrouters are considered inaccessible. Distance Vector router protocols include ip rip, ipx rip, A p l e Talk rt m p, And I G R P.

What is the connection status Router Protocol?

The connection status Router Protocol is more suitable for large networks. However, due to its complexity, the router needs more c p u resources. It can detect broken links or new routers in a shorter period of time, so that the convergence time of the Protocol is shorter than that of the Distance Vector routing protocol. Generally, if you do not receive the he l lo packet from the neighboring station within one 0 second, it is deemed that the neighboring station is no longer reachable. A connection status router sends an update message to its neighbor to notify it of all the links it knows. It determines that the measurement value of the optimal path is a numerical cost, which is generally determined by the bandwidth of the link. Links with the minimum cost are considered optimal. In the Shortest Path priority algorithm, the maximum possible cost is almost unlimited. If the network does not change, as long as the router periodically refreshes the route selection table that has not been updated, the duration of the cycle can be from 3 0 minutes to 2 hours ). The connection status router protocols include ip ospf, ipx nlsp, And I s-I S. Can a vro use the distance vector routing protocol and the link status routing protocol? Yes. Each interface can be configured to use different router protocols, but they must be able to exchange routing information through the redistribution of routing. Route redistribution will be discussed later in this chapter .)

What is an access table?

The access table is a series of rules that the manager adds to control data packets input and output in the vro. It is not generated by the router itself. The Access Table allows or disables data packets from entering or outputting to the destination. The table items for accessing the table are executed sequentially. When the data packet arrives, the system first checks whether it is restricted by the first table item. If not, it is executed sequentially; if it matches the first table item, you do not have to perform the following table item check whether it is allowed or disabled.

Why is it important to determine the adjacent router?

Determining the adjacent router in a small network is not a major problem. When a router fails, other routers can converge within an acceptable period of time. However, in a large network, the latency of a faulty router may be high. Knowing that the adjacent router can accelerate convergence, because the router can know the faulty router more quickly, because the interval of hello messages is shorter than the interval of router information exchange. When a router using the distance vector routing protocol does not send route update information to the adjacent router, it can be found that the adjacent router is no longer reachable. This time is generally 10 ~ 90 seconds. The router that uses the link status routing protocol does not receive the hello message, it can be found that the adjacent router is not reachable, this interval is generally 10 seconds. How can I find the adjacent router through distance vector routing protocol and link status routing protocol?

A Router using the Distance Vector Routing Protocol needs to create a route table, including the network directly connected to it), and it will send the route table to the router directly connected to it. The adjacent router combines the received route table into its own route table, and also sends its route table to its adjacent router. A connection status table is created for the router that uses the connection status Router Protocol, including the list of the entire network destination site. In the UPDATE message, Each router sends its entire list. When the adjacent router receives the update packet, it copies the content and sends the information to its neighbor. It is not necessary to recalculate the content of the route table. Note that the hello message is broadcast by the routers of IGRP and VPN to discover the adjacent station and exchange route update information like OSPF. For each network layer protocol, it includes the address of the neighboring station, the number of packets waiting to be sent in the queue, and the average time required to receive or send packets to the neighboring station, and the time when no message is received from the neighboring station before the link is confirmed to be disconnected.

What is an autonomous system?

An autonomous system is a vro and network group under the control of a management organization. It can be a vro that is directly connected to a LAN and connected to the Internet. It can be a LAN that is interconnected by an enterprise backbone network. All vrouters in an autonomous system must connect to each other, run the same vro protocol, and assign the same autonomous system number. Connections between autonomous systems use external router protocols, such as B G P.

What is BGP?

Border GatewayProtocol is a router protocol that dynamically exchanges route information between autonomous systems. A classic definition of an autonomous system is a group of routers under the control of a management organization. It uses IGP and common measurement values to forward packets to other autonomous systems. The term autonomous systems are used in BGP to emphasize the fact that the management of an autonomous system provides a unified internal routing plan for other autonomous systems, it provides a consistent description for networks that can be reached through it.