ovs-sim [option]… [script]…


ovs-sim provides a convenient environment for running one or more Open vSwitch instances and related software in a sandboxed simulation environment.

To use ovs-sim, first build Open vSwitch, then invoke it directly from the build directory, e.g.:

git clone https://github.com/openvswitch/ovs.git
cd ovs

When invoked in the most ordinary way as shown above, ovs-sim does the following:

  1. Creates a directory sandbox as a subdirectory of the current directory (first destroying such a directory if it already exists) and makes it the current directory.

  2. Installs all of the Open vSwitch manpages into a man subdirectory of sandbox and adjusts the MANPATH environment variable so that man and other manpage viewers can find them.

  3. Creates a simulated Open vSwitch named main and sets it up as the default target for OVS commands, as if the following ovs-sim commands had been run:

    sim_add main
    as main
See Commands, below, for an explanation.
  1. Runs any scripts specified on the command line (see Options, below). The scripts can use arbitrary Bash syntax, plus the additional commands described under Commands, below.
  2. If no scripts were specified, or if -i or --interactive was specified, invokes an interactive Bash subshell. The user can use arbitrary Bash commands, plus the additional commands described under Commands, below.

ovs-sim and the sandbox environment that it creates does not require superuser or other special privileges. Generally, it should not be run with such privileges.


Runs script, which should be a Bash script, within a subshell after initializing. If multiple script arguments are given, then they are run in the order given. If any script exits with a nonzero exit code, then ovs-sim exits immediately with the same exit code.
-i or --interactive
By default, if any script is specified, ovs-sim exits as soon as the scripts finish executing. With this option, or if no scripts are specified, ovs-sim instead starts an interactive Bash session.


Scripts and interactive usage may use the following commands implemented by ovs-sim. They are implemented as Bash shell functions exported to subshells.

Basic Commands

These are the basic commands for working with sandboxed Open vSwitch instances.

sim_add sandbox

Starts a new simulated Open vSwitch instance named sandbox. Files related to the instance, such as logs, databases, sockets, and pidfiles, are created in a subdirectory also named sandbox. Afterward, the as command (see below) can be used to run Open vSwitch utilities in the context of the new sandbox.

The new sandbox starts out without any bridges. Use ovs-vsctl in the context of the new sandbox to create a bridge, e.g.:

sim_add hv0           # Create sandbox hv0.
as hv0                # Set hv0 as default sandbox.
ovs-vsctl add-br br0  # Add bridge br0 inside hv0.

The Open vSwitch instances that sim_add creates enable dummy devices. This means that bridges and interfaces can be created with type dummy to indicate that they should be totally simulated, without any reference to system entities. In fact, ovs-sim also configures Open vSwitch so that the default system type of bridges and interfaces are replaced by dummy devices. Other types of devices, however, retain their usual functions, which means that, e.g., vxlan tunnels still act as tunnels (refer to the documentation).

as sandbox

Sets sandbox as the default simulation target for Open vSwitch commands (e.g. ovs-vsctl, ovs-ofctl, ovs-appctl).

This command updates the beginning of the shell prompt to indicate the new default target.

as sandbox command arg
Runs the given command with sandbox as the simulation target, e.g. as hv0 ovs-vsctl add-br br0 runs ovs-vsctl add-br br0 within sandbox hv0. The default target is unchanged.

Interconnection Network Commands

When multiple sandboxed Open vSwitch instances exist, one will inevitably want to connect them together. These commands allow for that. Conceptually, an interconnection network is a switch that ovs-sim makes it easy to plug into other switches in other sandboxed Open vSwitch instances. Interconnection networks are implemented as bridges in the main switch that ovs-sim creates by default, so to use interconnection networks please avoid working with main directly.

net_add network
Creates a new interconnection network named network.
net_attach network bridge
Adds a new port to bridge in the default sandbox (as set with as) and plugs it into interconnection network network, which must already have been created by a previous invocation of net_add. The default sandbox must not be main.

OVN Commands

These commands interact with OVN, the Open Virtual Network.

ovn_start [options]

Creates and initializes the central OVN databases (both ovn-sb(5) and ovn-nb(5)) and starts an instance of ovsdb-server for each one. Also starts an instance of ovn-northd.

The following options are available:

--nbdb-model model
Uses the given database model for the northbound database. The model may be standalone (the default), backup, or clustered.
--nbdb-servers n
For a clustered northbound database, the number of servers in the cluster. The default is 3.
--sbdb-model model
Uses the given database model for the southbound database. The model may be standalone (the default), backup, or clustered.
--sbdb-servers n
For a clustered southbound database, the number of servers in the cluster. The default is 3.
ovn_attach network bridge ip [masklen]
First, this command attaches bridge to interconnection network network, just like net_attach network bridge. Second, it configures (simulated) IP address ip (with network mask length masklen, which defaults to 24) on bridge. Finally, it configures the Open vSwitch database to work with OVN and starts ovn-controller.


The following creates a pair of Open vSwitch instances hv0 and hv1, adds a port named vif0 or vif1, respectively, to each one, and then connects the two through an interconnection network n1:

net_add n1
for i in 0 1; do
    sim_add hv$i
    as hv$i ovs-vsctl add-br br0 -- add-port br0 vif$i
    as hv$i net_attach n1 br0

Here’s an extended version that also starts OVN:

ovn-nbctl ls-add lsw0
net_add n1
for i in 0 1; do
    sim_add hv$i
    as hv$i
    ovs-vsctl add-br br-phys
    ovn_attach n1 br-phys 192.168.0.`expr $i + 1`
    ovs-vsctl add-port br-int vif$i -- set Interface vif$i external-ids:iface-id=lp$i
    ovn-nbctl lsp-add lsw0 lp$i
    ovn-nbctl lsp-set-addresses lp$i f0:00:00:00:00:0$i

Here’s a primitive OVN “scale test” (adjust the scale by changing n in the first line:

n=200; export n
ovn_start --sbdb-model=clustered
net_add n1
ovn-nbctl ls-add br0
for i in `seq $n`; do
    (sim_add hv$i
    as hv$i
    ovs-vsctl add-br br-phys
    y=$(expr $i / 256)
    x=$(expr $i % 256)
    ovn_attach n1 br-phys 192.168.$y.$x
    ovs-vsctl add-port br-int vif$i -- set Interface vif$i external-ids:iface-id=lp$i) &
    case $i in
        *50|*00) echo $i; wait ;;
for i in `seq $n`; do
    yy=$(printf %02x $(expr $i / 256))
    xx=$(printf $02x $(expr $i % 256))
    ovn-nbctl lsp-add br0 lp$i
    ovn-nbctl lsp-set-addresses lp$i f0:00:00:00:$yy:$xx

When the scale test has finished initializing, you can watch the logical ports come up with a command like this:

watch 'for i in `seq $n`; do if test `ovn-nbctl lsp-get-up lp$i` != up; then echo $i; fi; done'