Cisco OTV

Cisco OTV – Overlay Transport Virtualization

What is Cisco Overlay Transport Virtualization?

  • Overlay Transport Virtualization (OTV) is the layer 2 technology for providing the Data Center Interconnection.
  • It provides L2 extension capabilities between different data centers.
  • With OTV the VLAN & IP Subnet can be extended across the data center. It helps in having the same IP address range across different Data center.

Data Center Design with Cisco OTV

1. What is Cisco OTV?

  • Overlay Transport Virtualization (OTV) is the layer 2 technology for providing the Data Center Interconnection.
  • It provides L2 extension capabilities between different data centers.
  •  With OTV the VLAN & IP Subnet can be extended across the data center. It helps in having the same IP address range across different Data center.
  • OTV only requires IP connectivity between remote data center sites and it does not require any changes in existing design. But currently it supports only Nexus 7000 series switches with M1-Series line cards.
  • OTV helps in achieving workload mobility.
  • Without virtualization we can add resources in other data center if the exiting data center runs out of space
  •  With the virtualization concept of the workload mobility the Virtual Machines can be moved across data center & maintain the same IP subnet & VLAN.

2. How Cisco OTV works?

  • OTV uses the concept of MAC routing, aka, ‘MAC in IP routing’.
  • OTV works on the concept of “MAC routing,” which means a control plane protocol is used to exchange MAC reachability information between network devices providing LAN extension functionality
  • The MAC-in-IP routing is done by encapsulating an Ethernet frame in an IP packet before forwarding across the transport IP network.
  • The action of encapsulating the traffic between the OTV devices is called an overlay between the data centre sites.
  • OTV is deployed on devices at the edge of the data centre sites called OTV Edge Devices.
  • These edge devices perform typical L2 learning & forwarding functions on their internal interfaces and performs IP based virtualizations functions on the outside interfaces for traffic that is destined between two DCs via Overlay Interface. It basically exchanges the MAC address learned between the DCs.

3. How OTV behaves in CoB scenario? What are the benefits of OTV for CoB?

     A. Without Virtualization

  • OTV helps to have the same IP Address segment available in the COB site.
  • It helps the servers to be available in each Data Center & maintaining the same LAN segment.
  • Physical Server Migration from 1 Data center to other Data center can be achieved without changing the IP address of the server & also no change in the application.
  • Microsoft Cluster servers which require same L2 network connectivity can be placed in different data center using the benefits of the OTV concept.

     B. With Virtualization

  • Virtualization solution with SRM functionality takes the advantage of the OTV technology to bring back the server in COB site maintaining the same IP address.
  • Virtualization solution with V Motion feature helps in live migration of the VM from 1 data center to the other by maintaining the same IP Address.

4. What are the requirements for deploying Cisco OTV?

  • Hardware – Cisco Nexus 7000 series switch.

    • At each data center to have the OTV feature enabled it requires Cisco Nexus 7000 series switch.
    • M1-Series line cards
    • IOS Requirement: NX-OS 5.0(3) & above
  • License – Transport Service Licenses for the OTV feature.

    • Enterprise License (N7K-LAN1K9) – We have this license in our existing Nexus 7010.
    • Transport Services License (N7K-TRS1K9)
    • LAN_ADVANCED_SERVICES (N7K-ADV1K9)
  • Topology – L2 Data center topology

5. What is the specs/scalability/capacity of Cisco OTV technology?

  • Cisco OTV is scalable up to 6 sites with 2 devices at each location.
  • Max 256 VLAN can be extended.
  • Distance Limitation – Distance/Latency is not a constraint for OTV.

6. What are the commands/configurations for deploying Cisco OTV?

  • To enable OTV it requires few commands on each of the Nexus 7000 series switches.
  • The below commands are required to enable the OTV on Cisco Nexus 7000 series switches. The below example is for extending the VLANs from 5 – 10 across the Data center.

! Configure the physical interface that OTV uses to reach the DCI transport infrastructure  

interface ethernet 2/1
 ip address 192.0.2.1/24
 ip igmp version 3
 no shutdown

!Configure the VLAN that will be extended on the overlay network and the site-vlan

vlan 2,5-10

 ! Configure OTV including the VLANs that will be extended.

feature otv
otv site-vlan 2
otv site-identifier 256

interface Overlay1
otv control-group 239.1.1.1
otv data-group 232.1.1.0/28
otv join-interface ethernet 2/1

!Extend the configured VLAN

otv extend-vlan 5-10
no shutdown

7. Any other benefits of Cisco OTV other than for CoB

  • OTV is designed for the data center interconnection & for the availability of the services across data center.
  • It extends the same IP segment Data center across multiple locations.