Switch virtual interface

A switch virtual interface (SVI) is a VLAN of switch ports represented by one interface to a routing or bridging system. There is no physical interface for the VLAN and the SVI provides the Layer 3 processing for packets from all switch ports associated with the VLAN.

There is one-to-one mapping between a VLAN and SVI, thus only a single SVI can be mapped to a VLAN. In default setting, an SVI is created for the default VLAN (VLAN1) to permit remote switch administration. An SVI cannot be activated unless associated with a physical port.

SVIs are generally configured for a VLAN for the following reasons:
* Allow traffic to be routed between VLANs by providing a default gateway for the VLAN.
* Provide fallback bridging (if required for non-routable protocols).
* Provide Layer 3 IP connectivity to the switch.
* Support bridging configurations and routing protocol.

References

* Cisco Systems, 2006, "Building Cisco Multilayer Switched Networks" (Version 3.0), Cisco Systems Inc.