Static Routing Configuration; Introduction; Routing Table - 3Com 4200G 12-Port Configuration Manual

1

Static Routing Configuration

Introduction

Routing Table

Routing table
Routing tables play a key role in routing. Each router maintains a routing table, and each entry in the
table specifies which physical interface a packet destined for a certain destination should go out to
reach the next hop or the directly connected destination.
Routes in a routing table can be divided into three categories by origin:
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.
Contents of a routing table
A routing table includes the following key items:
Destination address: Destination IP address or destination network.
Network mask: Specifies, in company with the destination address, the address of the destination
network. A logical AND operation between the destination address and the network mask yields
the address of the destination network. For example, if the destination address is 129.102.8.10 and
the mask 255.255.0.0, the address of the destination network is 129.102.0.0. A network mask is
made of a certain number of consecutive 1s. It can be expressed in dotted decimal format or by the
number of the 1s.
Outbound interface: Specifies the interface through which the IP packets are to be forwarded.
IP address of the next hop: Specifies the address of the next router on the path.
Priority for the route. Routes to the same destination but having different nexthops may have
different priorities and be found by various routing protocols or manually configured. The optimal
route is the one with the highest priority (with the smallest metric).
Routes can be divided into two categories by destination:
Subnet routes: The destination is a subnet.
Host routes: The destination is a host.
Based on whether the destination is directly connected to a given router, routes can be divided into:
Direct routes: The destination is directly connected to the router.
Indirect routes: The destination is not directly connected to the router.
To prevent the routing table from getting too large, you can configure a default route. All packets without
matching any entry in the routing table will be forwarded through the default route.
In Figure 1-1, the IP address on each cloud represents the address of the network. Switch G is
connected to three networks and therefore has three IP addresses for its three physical interfaces. Its
routing table is shown under the network topology.
1-1