Tài liệu IP Routing ppt

IP Routing

I have alluded to routing repeatedly in this chapter but have not really explained the

routing process in detail and why it is important to us. Routing is nothing more than

taking the data from a host and transmitting it across the network to a host on a different

subnet. To do this, routers (and firewalls) need to be able to determine what network the

data needs to be delivered to. We have already established how an IP address can be

configured with different network IDs, which is what routers use to determine what

specific subnets exist.

Routers collect this information regarding the subnets that exist and store it in what is

known as a routing table. The routing table consists of the following information:

• Network IDs (and thus subnets) that the router is aware of.

• IP address of the gateway or router that can be used to deliver data to the

corresponding subnet. This is the actual route to the subnet, and the router may

have multiple routes to a given subnet.

Routers can build and maintain this routing table information in one of two methods. The

first is for the data to be manually updated and maintained by an administrator. The

second is to use routing protocols to actively interrogate the network and determine all

subnets, routers, and the routes that exist so that the protocol can use that information to

successfully transmit data to the appropriate subnet.

As you would expect, in large networks the process of manually updating and

maintaining this routing information is practically impossible. Therefore, in large or

complex networks it is recommended to implement routing protocols to automatically

take care of all the processes related to the building of the routing table, the maintenance

of the routing table, the verification of the routing table, and the determination of which

route is the best route to take.

Types of Routing

Fundamentally, there are three types of routing:

• Static routing

• Default routing

• Dynamic routing

Static routing is the process of an administrator manually entering, maintaining, updating,