Enabling Routing Between VLANs on a Multilayer Switch
Layer 3 switch virtual interface – SVI

A switched virtual interface (SVI) is a virtual Layer 3 interface that can be configured for any VLAN that exists on a Layer 3 switch. It is virtual in that there is no physical interface for the VLAN and yet it can accept configuration parameters applied to any Layer 3 router interface. The SVI for the VLAN provides Layer 3 processing for packets from all switch ports associated with that VLAN. Only one SVI can be associated with a VLAN. You configure an SVI for a VLAN for these reasons:

  • To provide a default gateway for a VLAN so traffic can be routed between VLANs
  • To provide fallback bridging if it is required for nonroutable protocols
  • To provide Layer 3 IP connectivity to the switch

By default, an SVI is created for the default VLAN (VLAN1) to permit remote switch administration. You must explicitly configure additional SVIs.

SVIs are created the first time interface configuration mode is entered for a particular VLAN SVI interface. The VLAN corresponds to the VLAN tag associated with data frames on an ISL or 802.1Q encapsulated trunk or to the VLAN ID configured for an access port. Configure and assign an IP address to each VLAN SVI that is to route traffic off of and onto the local VLAN.

SVIs support routing protocol and bridging configurations.