3com 2500 User Guide
10-8
C
HAPTER
10: A
DMINISTERING
IP R
OUTING
Administering
Routes
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.
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.)
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.
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.
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.
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.
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.