The router selection protocols are classified and unclassified.

We have reviewed the routing protocol above. For the routing protocol, we can classify it into two categories: category and category-free. First, let's take a look at the concept of classless routing.

Classful routing) Overview

The routing selection protocol that does not send subnet mask information with each network address is called the classification selection protocol r12001 and IGRP.) When a classification routing selection protocol is used, all subnetworks must use the same subnet mask. A router running a route selection protocol with a category route selection protocol performs one of the following operations to determine the routing network section: if the route update information is about the same primary network configured on the receiving interface, the router uses the subnet mask configured on the interface; if the route update is about the networks of different primary classes configured on the receiving interface, the router uses the default subnet mask according to the address category.

Classless routing Overview

Classless routing protocols include Open Shortest Path First (OSPF), OSPF, RIPV2, intermediate system to intermediate system IS-IS), and Border Gateway Protocol version 4BGP4 ), the subnet mask VLSM with different mask lengths is called variable lengths in the same primary network ).

The classless routing (classless Routing) protocol supports VLSM. Therefore, you can set a subnet mask more effectively to meet the needs of different subnets for different numbers of hosts and make full use of host addresses, most regular and routine route Updates generated by the distance vector routing selection protocol are transmitted only to directly connected routing devices. In a pure distance vector routing environment, route updates include a complete route table. By receiving the full route table of neighboring devices, the route can check all known routes and then modify the local route table based on the received update information.

The distance vector method used to solve routing problems is sometimes called "rumor routing by rumor)" cisco ios supports several distance vector routing selection protocols, such as r1_1, r1_2, and IGRP. CISCO also directly holds the Network VPN protocol, which is an advanced distance vector routing protocol.

A route update packet is generated only when the network topology changes. When the link status changes, the device that detects this change generates a link state notice about this link route ).

Then, LSA is spread to all adjacent devices through a special multicast address. Each routing device retains the LSA copy and forwards the LSA to its adjacent devices. This process is called diffusion f looding) and then updates its topology database. This is a information table that contains all links of the network ). LSA diffusion is used to ensure that all routing devices are aware of this change, so that they can update their data and generate an updated route table that reflects the new network topology.

The routing process in each vro must have a non-circular path to the logical network of all possible destinations. When all route tables are synchronized, when each route table contains an available route entry to the destination network, the network converges. Convergence is a synchronization activity associated with a route table when the network topology structure changes, for example, when the status of a new route or existing route changes.

The convergence time is the time required for the current topology to be recognized by all routes in the network, the network size, the used route selection protocol, and many configurable timers can affect the convergence time.

There are two Detection Methods: when the physical layer or data link layer fails to receive a certain number of consecutive keepalive messages, the link is considered invalid, when the route selection Protocol fails to receive a certain number of consecutive Hello messages, route updates, or similar messages, the link is considered invalid. Most routing selection protocols have timers used to prevent the generation of topology loops during link state transition.