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Catalyst 3550 Multilayer Switch Software Configuration Guide
78-11194-03
Chapter22 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 be st su perne t r out e. If you di sabl e cla ssless ro uti ng
and a router receives packets destined for a subnet of a network with no network default route, the router
discards the packet.
Figure22-2 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 route r
discards the packet.
Figure22-3 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