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Chapter 6

Inter-VLAN Routing

You're not done yet. You need to tell the subinterface which VLAN it is

a member of, and you provide this information on the same line as the encap-
sulation command. Here is an example:

Router(config-subif)#encap isl ?

<1-1000> Virtual LAN Identifier.

Notice that you can configure the subinterface to be a part of any VLAN

up to 1000. The dot1q encapsulation is for the IEEE standard 802.1q trunk-
ing. ISL is for ISL encapsulation.

After you choose the interface and encapsulation type and VLAN num-

ber, configure the IP address this subinterface is a member of. The complete
configuration would look like this:

Router#config t

Enter configuration commands, one per line. End with
CNTL/Z.

Router(config)#int f0/0.1

Router(config-subif)#encap isl 1

Router(config-subif)#ip address 172.16.10.1 255.255.255.0

The above configuration is for subinterface f0/0.1 to VLAN 1. You would
create a subinterface for each VLAN. You can verify your configuration with
the show running-config command:

interface FastEthernet0/0.1

encapsulation isl 1

ip address 172.16.10.1 255.255.255.0

Internal

If you do not have an external router or if you have many VLANs, you
should use a Route Switch Module (RSM) or Route Switch Feature Card
(RSFC) to provide the layer 3 routing for your 5000 series switch.

The first thing you need to type in is the show module command so you

can see the RSM. Notice in the switch output below that the 5000 switch has

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