Switch virtual interface

A switched 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. By default, 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.

SVIs advantages include:

• Much faster than router-on-a-stick, because everything is hardware-switched and routed.
• No need for external links from the switch to the router for routing.
• Not limited to one link. Layer 2 EtherChannels can be used between the switches to get more bandwidth.
• Latency is much lower, because it does not need to leave the switch

An SVI can also be known as a Routed VLAN Interface (RVI) by some vendors.

References

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

• Data Centre Networking Module (COMH9003) | Cork Institute of Technology