6.3 External Routers
6.3.5 Configuration example
This example illustrates inter-VLAN routing with Catalyst 5000 and 4000 Series Layer 3 switches used at the distribution layer while using a Layer 2 switch in the core.

This example is fairly straightforward and designed to illustrate all necessary commands to facilitate inter-VLAN routing. The routing protocol is EIGRP and the networks used are from the 192.168.x.x pool. The exact allocation of addresses per VLAN are shown in the top left part of the Figure.

The connections between the distribution switches and the core switch are both configured as trunk links. The Catalyst 5000 Series Switch is using ISL while the Catalyst 4000 Series Switch is using 802.1Q.

The VTP domain being used is Cisco and the VTP server is the Catalyst 5000 Series Switch, while the other switches are acting as Virtual Trunking Protocol (VTP) clients. You can verify this information by examining the configuration of CAT5505 in the #vtp section. You can also verify that CAT4000 is a vtp client by examining the #vtp section of its configuration. Remember, this must be done before you can configure VLANS.

The following outlines a configuration checklist:

CAT5505

  1. Enable interface sc0 using the set interface sc0 up command.
  2. Assign an IP address to the sc0 interface (192.168.1.3).
  3. Set any relevant passwords.
  4. Set the VTP domain and specify the switch as a VTP server.
  5. Configure the hostname (we could do this at any point).
  6. By default, VLAN 1 is enabled on all interfaces. So we created VLAN 10 on 2/4-5, VLAN 100 on 2/1 and VLAN 200 on 2/2.
  7. FastEthernet interface 2/3 was then configured as a trunk link permitting all VLANs.
  8. Now we can take a look at the RSM (Bucs) on CAT5505, we reached it by issuing the command session 3.
  9. Our first step on the RSM was to create the logical interfaces VLAN 1, VLAN 10, VLAN 100 and VLAN 200. We also gave each interface an IP address in its respective pool of addresses.
  10. The only other configuration needed here was to enable the EIGRP routing protocol and advertise the appropriate addresses.

The CAT 4000 followed the same procedure except the commands for Layer 3 services are different. The Port Channel you see configured in the #port channel section is actually representing a connection to the backplane of the switch. This is basically a port channel consisting of 2 gigabit Ethernet links.

On the Layer 3 card, you can see the difference in the command structure. While there are several ways to configure this card, channeling the internal gigabit slots is preferred. As you can see, each VLAN is represented as a subinterface of the Gigabit 3 and 4 port channel. Just like the 5000 series, we have to assign each interface an address. However, we must also specify the encapsulation type. Lastly, we enabled EIGRP again.

The other variable on the CAT4000 is the trunking protocol. In this case, the trunk link (Fast 2/3) is using the IEEE 802.1Q encapsulation. This can be verified in the switch configuration under the #vtp header.

On the Core 1 switch, which is a 2900 series layer 2 switch, there was not much to configure. As you can see we simply configured interfaces FastEthernet 0/2 and 0/3 to be trunk links. Lastly, for management purposes, we gave VLAN 1 an IP address in the VLAN 1 pool.

Interactive Lab Activity  (Flash, 295 kB)
  In this activity, you will learn how to configure the Catalyst 4000 switch and route processor to perform inter-VLAN routing.
Lab Activity
  In this lab activity, you will learn how to configure an IP helper address pointing DHCP enabled router.