3Com CoreBuilder 2500 User Manual - page 124

10-8

C

HAPTER

 10: A

DMINISTERING

 IP R

OUTING

Administering 

Routes

Each system maintains a table of routes to other IP networks, 

subnetworks, and hosts. You either make static entries in this table using 

the Administration Console, or you configure the system to use RIP to 

automatically exchange routing information. 

Each routing table entry contains the following information:

■

Destination IP Address and Subnet Mask

 — The elements that 

define the address of the destination network, subnetwork, or host. 

An incoming packet matches a route entry in the router table when 

the packet’s destination address matches the destination address in 

the routing table entry. (The system only compares bits that 

correspond to the subnet mask in the routing table entry.) 

When routing a packet, if the system finds more than one routing 

table entry that matches an address (for example, a route to the 

destination network and a route to the specific subnetwork within 

that network), the system uses the most specific route, that is, the 

route with the most bits set in its subnet mask.

■

Routing Metric

 — The number of networks or subnetworks through 

which a packet must pass to reach its destination. This metric is 

included in RIP updates to allow routers to compare routing 

information that is received from different sources.

■

Gateway IP Address

 — Tells the router where to forward packets 

whose destination address matches the route’s IP address and subnet 

mask. The system forwards such packets to the indicated gateway.

■

Status

 — The route descriptions, as listed in Table 10-1.

Default route

In addition to the routes to specific destinations, the routing table can 

contain an additional entry called the 

default route

. The system uses the 

default route to forward packets that do not match any other routing 

table entry. You can use a default route in place of routes to numerous 

destinations that all have the same gateway IP address.

Table 10-1   

Route Status

Status 

Description

Direct

The route went to a directly connected network.

Static

The route was statically configured.

Learned

The route was learned using the indicated protocol.

Timing out

The route was learned but is partially timed out.

Timed out

The route has timed out and is no longer valid.