Configuring VLANs on an Internal Route Processor

Configuring VLANs on an Internal Route Processor
First, it would be common practice to set up the internal gigabit interfaces to act as Gigabit
EtherChannel trunks. This needs to be done at both the L3SM and switch parts of the internal
link. On the L3SM, the configuration looks like this:
Terry_L3SM#configure terminal
Terry_L3SM(config)#interface GigabitEthernet3
Terry_L3SM(config-if)#channel-group 1
Terry_L3SM(config)#interface GigabitEthernet4
Terry_L3SM(config-if)#channel-group 1
And on the Catalyst, it looks like this:
Terry_4000> (enable)set port channel 3/1-2 mode on
Terry_4000> (enable)set trunk 3/1 nonegotiate dot1q 1-1005
Terry_4000> (enable)set trunk 3/2 nonegotiate dot1q 1-1005
Next, instead of creating subinterfaces as you would with an external router, you need to
configure each VLAN with the interface vlan # command. This establishes a direct virtual
connection between the switch backplane and the routing module, and what you are actually
doing is associating each VLAN with a virtual interface. Here is an example of how to configure
the processor to route between three VLANs:
Terry_L3SM#configure terminal
Terry_L3SM(config)#interface vlan 1
Terry_L3SM(config-if)#ip address 172.16.1.1 255.255.255.0
Terry_L3SM(config-if)#interface vlan 2
Using ISL and 802.1Q Routing 547
Terry_L3SM(config-if)#ip address 172.16.2.1 255.255.255.0
Terry_L3SM(config-if)#interface vlan 3
Terry_L3SM(config-if)#ip address 172.16.3.1 255.255.255.0
Terry_L3SM(config-if)#no shutdown
The interesting part of the configuration is the necessary no shutdown command for each
VLAN interface. Notice in the preceding configuration that we performed a no shutdown only
on interface VLAN 3. Take a look at the output of interface VLAN 2:
Terry_L3SM#show interface vlan 2
Vlan2 is administratively down, line protocol is down
It is important to think of each VLAN interface as a separate interface that needs an ip
address and a no shutdown performed, just as with any other router interface.
You can then verify your configuration with the show running-config command:
Terry_L3SM#show running-config
Current configuration:
!

version 12.0
service timestamps debug uptime
service timestamps log uptime
no service password-encryption
!
hostname Terry_L3SM
!
interface Vlan1
ip address 172.16.1.1 255.255.255.0
!
interface Vlan2
ip address 172.16.2.1 255.255.255.0
!
interface Vlan3
ip address 172.16.3.1 255.255.255.0
!
router eigrp 10
network 172.16.0.0
To view the routing table on the internal processor, use the show ip route command:
Terry_L3SM#show ip route
Codes: C - connected, S - static, I - IGRP, R - RIP, M �" [output cut]
Gateway of last resort is not set
548 Chapter 17  Inter-VLAN Routing
172.16.0.0/24 is subnetted, 3 subnets
C 172.16.3.0 is directly connected, Vlan3
C 172.16.2.0 is directly connected, Vlan2
C 172.16.1.0 is directly connected, Vlan1
Terry_L3SM#