3Com WX3000 IP Routing Protocol Overview, Introduction to IP Route and Routing Table

1 IP Routing Protocol Overview

Go to these sections for information you are interested in:

z

z

z

Introduction to IP Route and Routing Table Routing Protocol Overview

Displaying and Maintaining a Routing Table

The term router in this chapter refers to a router in a generic sense or a WX3000 series device running a routing protocol.

Introduction to IP Route and Routing Table

IP Route

Routers are used for route selection on the Internet. As a router receives a packet, it selects an appropriate route (through a network) according to the destination address of the packet and forwards the packet to the next router. The last router on the route is responsible for delivering the packet to the destination host.

Routing Table

Function

The key for a router to forward packets is the routing table. Each router maintains a routing table. Each entry in this table contains an IP address that represents a host/subnet and specifies which physical port on the router should be used to forward the packets destined for the host/subnet. And the router forwards those packets through this port to the next router or directly to the destination host if the host is on a network directly connected to the router.

Routes in a routing table can be divided into three categories by origin:

z

z

z

Direct routes: Routes discovered by data link protocols, also known as interface routes.

Static routes: Routes that are manually configured.

Dynamic routes: Routes that are discovered dynamically by routing protocols.

Routing entry

Each routing entry in a routing table contains:

z

z

Destination: It identifies the address of the destination host or network of an IP packet.

Mask: Along with the destination address, it identifies the address of the network segment where the destination host or router resides. By performing a logical AND operation between destination address and network mask, you can get the address of the network segment where the destination

1-1