OTV or Overlay Transport Virtualization extends layer 2 VLANs between data centers. This allows us to maintain our layer 3 hierarchy and enable us to move the virtual machines cross data centers.
Think about it, if you are able to move your VMs from one location to another and not having to change any IP addresses or routing, how cool will it be ?
OTV to function ,we can either use Multicast or Unicast . I will talk about enabling OTV using Multicast here..
Here’s the steps to configure OTV on a Multicast Core :
- Enable PIM sparse-mode and IGMP version 3 on all core devices.
- Configure the OTV external interface for IGMP version 3 on the edge device.
- Enable the OTV feature and designate a site VLAN
- Configure the OTV overlay interface on edge device.
1. Enabling PIM Sparse Mode on Nexus 7K
Enabling PIM also has 4 steps..
- Enable the protocol independent multicast (PIM)
- Configure the rendezvous-point (RP)
- Enable PIM sparse mode on all core interfaces
- Enable IGMP version 3 on all core interfaces.
ip pim rp-address a.b.c.d
ip pim sparse-mode
ip igmp version 3
2. Configure the external Interface
ip igmp version 3
// note we ware not enabling PIM sparse mode on the external interface
3. Designate a Site VLAN
OTV uses the site VLAN to send hello messages to determine the authoritative edge devices . Ofcourse we need to enable OTV feature first in NX-OS
otv site-vlan 13
Do not extend the site VLAN accross the overlay network, because it is only used locally.
4. Configuring the OTV Overlay Interface
The overlay interface is used to encapsulate Layer 2 frames into ip packets. To configure the overlay interface specify the following:
- Control group : Multicast group used for the OTV control plane
- Data group : range of multicast SSM groups to use for multicast traffic
- Join interface: used to advertise MAC address reachability info across overlay
- Entend VLAN : VLANs to extend across the overlay network
interface overlay 1
otv control-group 126.96.36.199
otv data-group 188.8.131.52/29
otv join-interface ethernet1/41
otv extend-vlan 2000 ====> this is the vlan we want to extend
Verifying the Overlay Interface:
use the command show otv overlay <interface>
VPN state should be UP.
Do a show otv adjacency to verify one or more adjacency are present.
Do a show otv site to verify one or more site local adjacencies are present.
Do a show otv vlan to see the extended vlans .
Do a show mac address-table <vlan> will show the port and mac learned via OTV interface.