Switch virtual interface

A Switch Virtual Interfaces (SVI) represents a logical Layer 3 interface on a switch.

SVI or VLAN interface, is a virtual routed interface that connects a VLAN on the device to the Layer 3 router engine on the same device. Only one VLAN interface can be associated with a VLAN, but you need to configure a VLAN interface for a VLAN only when you want to route between VLANs or to provide IP host connectivity to the device through a virtual routing and forwarding (VRF) instance that is not the management VRF. When you enable VLAN interface creation, a switch creates a VLAN interface for the default VLAN (VLAN 1) 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, Configuring SVI
• Cisco Systems, 2006, "Building Cisco Multilayer Switched Networks" (Version 3.0), Cisco Systems Inc.

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