How to Use the VTEP Emulator

This document explains how to use ovs-vtep, a VXLAN Tunnel Endpoint (VTEP) emulator that uses Open vSwitch for forwarding. VTEPs are the entities that handle VXLAN frame encapsulation and decapsulation in a network.


The VTEP emulator is a Python script that invokes calls to tools like vtep-ctl and ovs-vsctl. It is only useful when Open vSwitch daemons like ovsdb-server and ovs-vswitchd are running and installed. To do this, either:


At the end of this process, you should have the following setup:


| Host Machine                                      |
|                                                   |
|                                                   |
|       +---------+ +---------+                     |
|       |         | |         |                     |
|       |   VM1   | |   VM2   |                     |
|       |         | |         |                     |
|       +----o----+ +----o----+                     |
|            |           |                          |
| br0 +------o-----------o--------------------o--+  |
|            p0          p1                  br0    |
|                                                   |
|                                                   |
|                              +------+   +------+  |
+------------------------------| eth0 |---| eth1 |--+
                               +------+   +------+
                  MANAGEMENT      |          |
                +-----------------o----+     |
                             DATA/TUNNEL     |

Some important points.

  • We will use Open vSwitch to create our “physical” switch labeled br0

  • Our “physical” switch br0 will have one internal port also named br0 and two “physical” ports, namely p0 and p1.

  • The host machine may have two external interfaces. We will use eth0 for management traffic and eth1 for tunnel traffic (One can use a single interface to achieve both). Please take note of their IP addresses in the diagram. You do not have to use exactly the same IP addresses. Just know that the above will be used in the steps below.

  • You can optionally connect physical machines instead of virtual machines to switch br0. In that case:

    • Make sure you have two extra physical interfaces in your host machine, eth2 and eth3.

    • In the rest of this doc, replace p0 with eth2 and p1 with eth3.

  1. In addition to implementing p0 and p1 as physical interfaces, you can also optionally implement them as standalone TAP devices, or VM interfaces for simulation.

  2. Creating and attaching the VMs is outside the scope of this document and is included in the diagram for reference purposes only.


These instructions describe how to run with a single ovsdb-server instance that handles both the OVS and VTEP schema. You can skip steps 1-3 if you installed using the debian packages as mentioned in step 2 of the “Requirements” section.

  1. Create the initial OVS and VTEP schemas:

    $ ovsdb-tool create /etc/openvswitch/ovs.db vswitchd/vswitch.ovsschema
    $ ovsdb-tool create /etc/openvswitch/vtep.db vtep/vtep.ovsschema
  2. Start ovsdb-server and have it handle both databases:

    $ ovsdb-server --pidfile --detach --log-file \
        --remote punix:/var/run/openvswitch/db.sock \
        --remote=db:hardware_vtep,Global,managers \
        /etc/openvswitch/ovs.db /etc/openvswitch/vtep.db
  3. Start ovs-vswitchd as normal:

    $ ovs-vswitchd --log-file --detach --pidfile \
  4. Create a “physical” switch and its ports in OVS:

    $ ovs-vsctl add-br br0
    $ ovs-vsctl add-port br0 p0
    $ ovs-vsctl add-port br0 p1
  5. Configure the physical switch in the VTEP database:

    $ vtep-ctl add-ps br0
    $ vtep-ctl set Physical_Switch br0 tunnel_ips=
  6. Start the VTEP emulator. If you installed the components following Open vSwitch on Linux, FreeBSD and NetBSD, run the following from the vtep directory:

    $ ./ovs-vtep --log-file=/var/log/openvswitch/ovs-vtep.log \
        --pidfile=/var/run/openvswitch/ \
        --detach br0

    If the installation was done by installing the openvswitch-vtep package, you can find ovs-vtep at /usr/share/openvswitch/scripts.

  7. Configure the VTEP database’s manager to point at an NVC:

    $ vtep-ctl set-manager tcp:<CONTROLLER IP>:6640

    Where <CONTROLLER IP> is your controller’s IP address that is accessible via the Host Machine’s eth0 interface.

Simulating an NVC

A VTEP implementation expects to be driven by a Network Virtualization Controller (NVC), such as NSX. If one does not exist, it’s possible to use vtep-ctl to simulate one:

  1. Create a logical switch:

    $ vtep-ctl add-ls ls0
  2. Bind the logical switch to a port:

    $ vtep-ctl bind-ls br0 p0 0 ls0
    $ vtep-ctl set Logical_Switch ls0 tunnel_key=33
  3. Direct unknown destinations out a tunnel.

    For handling L2 broadcast, multicast and unknown unicast traffic, packets can be sent to all members of a logical switch referenced by a physical switch. The “unknown-dst” address below is used to represent these packets. There are different modes to replicate the packets. The default mode of replication is to send the traffic to a service node, which can be a hypervisor, server or appliance, and let the service node handle replication to other transport nodes (hypervisors or other VTEP physical switches). This mode is called service node replication. An alternate mode of replication, called source node replication, involves the source node sending to all other transport nodes. Hypervisors are always responsible for doing their own replication for locally attached VMs in both modes. Service node mode is the default. Service node replication mode is considered a basic requirement because it only requires sending the packet to a single transport node. The following configuration is for service node replication mode as only a single transport node destination is specified for the unknown-dst address:

    $ vtep-ctl add-mcast-remote ls0 unknown-dst
  4. Optionally, change the replication mode from a default of service_node to source_node, which can be done at the logical switch level:

    $ vtep-ctl set-replication-mode ls0 source_node
  5. Direct unicast destinations out a different tunnel:

    $ vtep-ctl add-ucast-remote ls0 00:11:22:33:44:55