fer very good port density. The addition of switch modules, which provide a few interfaces, has improved their port densities, but nothing beats the flexibility of a multilayer switch when it comes to Ethernet. Configuring SVIs Switch virtual interfaces are configured differently depending on the switch platform and operating systems installed. Chapter 16: Multilayer Switches Native Mode (4500, 6500, 3550, 3750) Here is the output of the command show ip interface brief from a 3550: Cat-3550# sho ip int brief Interface IP-Address OK? Method Status Protocol Vlan1 192.168.134.22 YES DHCP FastEtherneto/1 unassigned YES unset down FastEtherneto/2 unassigned YES unset FastEthernet0/3 unassigned YES unset FastEtherneto/4 unassigned YES unset [-Text Removed-] FastEthernet0/23 unassigned YES unset FastEthernet0/24 unassigned YES unset down GigabitEthernet0/1 unassigned YES unset GigabitEthernet0/2 unassigned YES unset The first interface is a switched virtual interface for VLAN 1. This SVI cannot be removed on a 3550, as it is used for management. Looking at the VLAN table with the show vlan command, we can see there are five VLANs configured in addition to the default VLAN 1: Cat-3550# - sho vlan VLAN Name Status Ports default active Fa0/1, Fao/2, Fa0/3, Fao/4 Fao/5, Fao/6, Fa0/7, Fao/8 Fa0/9, Fa0/10, Fa0/11, Fao/16 Fao/17, Fa0/18, Fa0/19, Fao/21 Fa0/22, Fa0/23, Fa0/24, Gio/1 Gio/2 VLAN0002 active Fa0/12 VLAN0003 active VLAN0004 active VLAN0010 active VLAN0100 active 1002 fddi-default act/unsup 1003 token-ring-default act/unsup 1004 fddinet-default act/unsup 1005 trnet-default act/unsup [-Text Removed- These VLANs are strictly layer-2, in that the switch will not route between them. For the switch to be able to access these VLANs at higher layers, we need to create an SVI for each one. The only step required to create an SVI is to define it. Simply by entering the global configuration command interface vlan vlan#, you will create the SVI. The vlan# does not need to match an existing VLAN. For example, defining an SVI for