Networks - Overlay Transport Virtualization (OTV)

Overlay Transport Virtualization (OTV) is a network virtualization technology developed by Cisco, designed to extend Layer 2 connectivity across different data centers over a Layer 3 network. It's particularly useful for enterprises looking to connect multiple geographically dispersed data centers. Here are some key aspects of OTV:

Key Features

  1. Layer 2 Extension Over Layer 3: OTV encapsulates Layer 2 traffic in IPv4 or IPv6 packets, allowing them to be transported over a Layer 3 network. This enables VLANs to be extended across geographically separated data centers.

  2. MAC Address Location Independence: OTV allows for the same MAC address to exist in multiple locations without causing conflicts. This is crucial for virtual machine mobility and for maintaining consistent network policies.

  3. Control Plane Separation: Unlike traditional Layer 2 extensions, OTV separates the control plane (for learning MAC address locations) from the data plane (for forwarding traffic), reducing the risk of Layer 2 loops and broadcast storms.

  4. Ease of Deployment: OTV is designed to be relatively simple to configure and deploy, often requiring minimal changes to existing network infrastructures.

  5. Traffic Isolation: OTV can isolate traffic between different data centers, preventing issues in one data center from affecting others.

  6. Efficient Use of Bandwidth: It uses multicast in the transport network for more efficient bandwidth utilization, especially useful for applications that require broadcast or multicast traffic.

Operational Principles

  • Edge Devices: OTV functions are carried out by edge devices, which encapsulate and decapsulate traffic. These devices are usually high-end Cisco routers or switches.

  • OTV Overlay Network: This is the Layer 2 extension created over the Layer 3 network. It's often referred to as the overlay, while the underlying Layer 3 network is known as the transport or underlay network.

  • OTV Control Protocol: This protocol is responsible for MAC address learning and distribution across data centers. It ensures that the edge devices have updated MAC routing information.


  • Reduced Complexity: OTV simplifies extending Layer 2 networks over long distances, compared to traditional methods.
  • Enhanced Mobility: Supports dynamic workload relocation, particularly important for cloud computing and data center consolidation.
  • Resiliency: Offers built-in mechanisms to avoid common Layer 2 problems, like loops and spanning tree issues.

Use Cases

  • Data Center Interconnect (DCI): Ideal for connecting multiple data centers for disaster recovery, load balancing, and resource sharing.
  • Workload Mobility: Facilitates the movement of virtual machines across data centers without reconfiguring the network.


  • Vendor Specific: OTV is a Cisco proprietary technology, which might limit interoperability with equipment from other vendors.
  • Network Design: Proper network design and planning are essential to prevent potential issues, like suboptimal routing or multicast configuration complexities.
  • Cost: Depending on the existing infrastructure, implementing OTV may involve additional costs for compatible hardware and software licenses.

OTV is a powerful tool for organizations needing to extend Layer 2 networks across multiple data centers, offering benefits in terms of flexibility, scalability, and ease of management, but it requires careful planning and consideration of its Cisco-specific nature.