Cisco OTV is a way for far-flung Cisco Nexus 7000 switches to share MAC address tables. Usually,
multiple data centers has its own set of VLANs, spanning-tree, and so forth. According to SF Gate, Cisco OTV requires a switch running at each data center that has a trunked interface to the local switched LAN and plays on all VLANs relevant to the data center extension.
“When an OVF switch receives a frame destined for another data center, it encapsulates it in a normal IP packet and transmits it over the WAN to the data center where that destination MAC resides. On the receiving end, the local OVF switch strips the encapsulation and drops the frame on the appropriate VLAN as if nothing ever happened. The sending and receiving hosts never know that that they are in different datacenters, or that a WAN link was involved at all.
“The underlying table information and routing transport for this scenario is a pretty neat adaption of existing technology. Cisco is leveraging some of the capabilities of the IS-IS (Intermediate System to Intermediate System) routing protocol to make this happen, although the IS-IS configuration is completely under the covers. It really is only about five commands to add a data center to the mix, although the necessary configuration of the Nexus 7000 switches might be a bit more involved.”