SVI Port Configuration
On a multilayer switch, you also can enable Layer 3 functionality for an entire VLAN on the switch. This allows a network address to be assigned to a logical interface—that of the VLAN itself. This is useful when the switch has many ports assigned to a common VLAN, and routing is needed in and out of that VLAN.
In Figure 11-2, you can see how an IP address is applied to the switched virtual interface called VLAN 10. Notice that the SVI itself has no physical connection to the outside world; to reach the outside, VLAN 10 must extend through a Layer 2 port or trunk to the outside.
The logical Layer 3 interface is known as an SVI. However, when it is configured, it uses the much more intuitive interface name vlan vlan-id, as if the VLAN itself is a physical interface.
First, define or identify the VLAN interface; then assign any Layer 3 functionality to it with the following configuration commands:
Switch(config)# interface vlan vlan-id
Switch(config-if)# ip address ip-address mask [secondary]
The VLAN must be defined and active on the switch before the SVI can be used. Make sure that the new VLAN interface also is enabled with the no shutdown interface configuration command.
Note: The VLAN and the SVI are configured separately, even though they interoperate. Creating or configuring the SVI doesn’t create or configure the VLAN; you still must define each one independently.
As an example, the following commands show how VLAN 100 is created and then defined as a Layer 3 SVI:
Switch(config)# vlan 100
Switch(config-vlan)# name Example_VLAN
Switch(config-vlan)# exit
Switch(config)# interface vlan 100
Switch(config-if)# ip address 192.168.100.1 255.255.255.0
Switch(config-if)# no shutdown
In Figure 11-2, you can see how an IP address is applied to the switched virtual interface called VLAN 10. Notice that the SVI itself has no physical connection to the outside world; to reach the outside, VLAN 10 must extend through a Layer 2 port or trunk to the outside.
The logical Layer 3 interface is known as an SVI. However, when it is configured, it uses the much more intuitive interface name vlan vlan-id, as if the VLAN itself is a physical interface.
First, define or identify the VLAN interface; then assign any Layer 3 functionality to it with the following configuration commands:
Switch(config)# interface vlan vlan-id
Switch(config-if)# ip address ip-address mask [secondary]
The VLAN must be defined and active on the switch before the SVI can be used. Make sure that the new VLAN interface also is enabled with the no shutdown interface configuration command.
Note: The VLAN and the SVI are configured separately, even though they interoperate. Creating or configuring the SVI doesn’t create or configure the VLAN; you still must define each one independently.
As an example, the following commands show how VLAN 100 is created and then defined as a Layer 3 SVI:
Switch(config)# vlan 100
Switch(config-vlan)# name Example_VLAN
Switch(config-vlan)# exit
Switch(config)# interface vlan 100
Switch(config-if)# ip address 192.168.100.1 255.255.255.0
Switch(config-if)# no shutdown
