Understanding Nexus - Part 22 - OTV

One of my most favorite part from NX-OS is OTV. It’s a very beautiful technology used to extend L2 domain in your different Datacenter (DC) locations.

But the question arises “Why do you need to extend this L2 domain?” Why cannot we work with L3? Ohhh…. You should not ask this to Network Engineer …:-) because it’s an application requirement.:-D

Certain application in DC does not have the functionality to work on L3. They need to maintain the L2 connections between various servers on which that application is running… Going forward if you need to expand your application, you may need some more extra servers. Now where will you deploy these servers? Obvious answer is “In the SAME DC”… but do you have enough space in your DC to add a new server? Do you have enough power and cooling capacity?

Well if your answer is NO, then you need different location. When you add another location to your DC, you need communication between those. Again, if your application supports L3 then no problems… But what if they don’t? So you need your L2 domain to be extended.

There are many technologies which support these, but each technology has its own pro & cons. Comparing to others, OTV adds many advantages for extending L2. The best one is, its simplicity. You deploy OTV on the edge devices in each site. OTV requires no other changes to the sites or the network.

To understand OTV, there is a great video from Cisco, which explains the fundamentals of OTV. Do have a look at it.



OTV is Overlay Transport Virtualization. OTV is a MAC-in-IP method that extends Layer 2 connectivity across a network. It uses MAC address-based routing and IP-encapsulated forwarding. For MAC based routing it uses IS-IS internally. You absolutely don’t need anything to do with IS-IS.

OTV does not extend STP across sites. Each site runs its own STP.

Okk… Now this is it. We will continue discussing OTV in next few blogs too. Till that time bye and Wish you a very happy new Tech-Year.