BVI stands for Bridge-Group Virtual Interface.
A BVI (Bridge Group Virtual Interface) is a routed interface that represents a set of interfaces that gets bridged.
So lets say for example that in your router you have two interfaces that needs to get bridged (one wireless and one wired for example) and you want them to behave as if they were part of the same layer two broadcast domain (because you want your hosts in either the wired or wireless interfaces behave as if they were in the same subnet). In this scenario, a BVI would act as the routed interface for that “merged” (really bridged) interfaces.
Any packets that wants to “escape” this merged layer two domain (wired + wireless) will have to go through this BVI.
To this BVI you could assign a layer three address, QoS policies, access-lists or any other “service” you may assign to any physical interface.
Source
================[COMMANDS]================
[Configuring a Bridge Group]
Router(config)# bridge bridge_group_number protocol {ieee |dec} #(From global configuration mode, assign a bridge group number and define a Spanning-Tree Protocol as either the IEEE 802.1D standard or DEC. Note The IEEE 802.1D Spanning-Tree Protocol is the preferred way of running the bridge)
Router(config)# bridge bridge_group_number priority number
(The bridge priority command assigns a specific priority to the bridge, assisting in the spanning tree root definition. The lower the priority, the more likely the bridge will be selected as the root.)
Router(config)# interface fa x/0/z
(Enter Ethernet interface configuration mode to configure the Fast Ethernet interface.)
Router(config-if)# bridge-group bridge_group_number
(Assign a network interface to a bridge group.)
Router(config-if)# interface fa x/0/y
(If you need to assign additional interfaces to a bridge group, then choose the next interface and assign it to a bridge group.)
Router(config-if)# Ctrl-Z
(Return to privileged EXEC mode.)
Router# copy running-config startup-config
(Save your configuration .)
[Administering Bridging]
clear bridge bridge_group_number
(Remove any learned entries from the forwarding database and clear the transmit and receive counts for any statically configured forwarding entries.)
clear vlan statistics
(Remove virtual LAN statistics from any static or system configured entries.)
show bridge bridge_group_number | interface address | mask
(show bridge bridge_group_number | interface address | mask)
show bridge bridge_group circuit-group circuit_group | src_mac_address | dest_mac_address
(Display the interfaces configured in each circuit group and show whether they are participating in load distribution.)
show bridge group verbose
(Display information about configured bridge groups.)
show bridge vlan
(Display IEEE 802.10 transparently bridged virtual LAN configuration.)
show span
(Display the spanning-tree topology known to the Catalyst 8500 campus switch router.)
how vlans
(Display a summary of virtual LAN subinterfaces.)
Brain Knowledge 