Default Routing
You can use
default routing
to accelerate packets with a alien destination arrangement not in the routing
table to the next-hop router. You should use absence acquisition alone on butt networks—those
with alone one avenue aisle out of the network.
To configure a absence route, you use wildcards in the arrangement abode and affectation locations
of a changeless route. In fact, you can aloof anticipate of a absence avenue as a changeless avenue that uses wildcards
instead of arrangement and affectation information.
By application a absence route, you can actualize aloof one changeless avenue access instead. This abiding is easier
than accounting in all those routes! Here is an example:
Router(config)#
ip avenue 0.0.0.0 0.0.0.0 10.1.11.1
Router (config)#
ip classless
Router (config)#
do appearance ip route
Gateway of aftermost resort is 10.1.11.1 to arrangement 0.0.0.0
10.0.0.0/24 is subnetted, 2 subnets
C 10.1.11.0 is anon connected, Vlan1
C 10.1.12.0 is anon connected, Dot11Radio0
S* 0.0.0.0/0 [1/0] via 10.1.11.1
Router (config)#
If you attending at the acquisition table, you’ll see alone the two anon affiliated networks additional an
S*
, which indicates this access is a applicant for a absence route. I could accept completed the
default
route
command addition way:
Router (config)#
ip avenue 0.0.0.0 0.0.0.0 Fa0/0
What this is cogent you is that if you don’t accept an access for a arrangement in the acquisition table,
just advanced it out FastEthernet0/0. Table 3.4 defines the ip classless command:
All Cisco routers are classful routers, meaning they expect a default subnet mask on each
interface of the router. When a router receives a packet for a destination subnet that’s not in
the routing table, it will drop the packet by default. If you’re using default routing, you must
use the
ip classless command because it is possible that no remote subnets will be in the
routing table. Here is example:
Router(config)#ip classless