5-5. Virtual Interfaces

· Virtual interfaces exist for configuration where there is no single physical attachment to a broadcast domain.
· For switches with Layer 2 interfaces, VLANs define broadcast domains.
· The VLAN interface is a Layer 3 interface for any member of the given VLAN.
· For switches or routers with Layer 3 interfaces, broadcast domains are defined as bridge groups.
· To route between bridge groups and other broadcast domains, a bridged virtual interface (BVI) is used as a Layer 3 interface.
· In some instances, a physical Layer 3 interface can support traffic from multiple VLANs.
· To provide Layer 3 interfaces for each VLAN on the physical connection, a sub interface is configured as the Layer 3 interface for the members of the VLAN.