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Catalyst 3550 Multilayer Switch Software Configuration Guide
78-11194-03
Chapter 22 Configuring IP Unicast Routing
Configuring IP Addressing
In
Figure 22-2
, classless routing is enabled. When the host sends a packet to 120.20.4.1, instead of
discarding the packet, the router forwards it to the best supernet route. If you disable classless routing
and a router receives packets destined for a subnet of a network with no network default route, the router
discards the packet.
Figure 22-2 IP Classless Routing
In
Figure 22-3
, the router in network 128.20.0.0 is connected to subnets 128.20.1.0, 128.20.2.0, and
128.20.3.0. If the host sends a packet to 120.20.4.1, because there is no network default route, the router
discards the packet.
Figure 22-3 No IP Classless Routing
To prevent the switch from forwarding packets destined for unrecognized subnets to the best supernet
route possible, you can disable classless routing behavior.
Host
128.20.1.0
128.20.2.0
128.20.3.0
128.20.4.1
128.0.0.0/8
128.20.4.1
IP classless
45749
128.20.0.0
Host
128.20.1.0
128.20.2.0
128.20.3.0
128.20.4.1
128.0.0.0/8
128.20.4.1
Bit bucket
45748
128.20.0.0
