Open vSwitch without Kernel Support¶
Open vSwitch can operate, at a cost in performance, entirely in userspace, without assistance from a kernel module. This file explains how to install Open vSwitch in such a mode.
This version of Open vSwitch should be built manually with
make. Debian packaging for Open vSwitch is also included, but it has not
been recently tested, and so Debian packages are not a recommended way to use
this version of Open vSwitch.
The userspace-only mode of Open vSwitch without DPDK is considered experimental. It has not been thoroughly tested.
Building and Installing¶
The requirements and procedure for building, installing, and configuring Open vSwitch are the same as those given in Open vSwitch on Linux, FreeBSD and NetBSD. You may omit configuring, building, and installing the kernel module, and the related requirements.
On Linux, the userspace switch additionally requires the kernel TUN/TAP driver
to be available, either built into the kernel or loaded as a module. If you
are not sure, check for a directory named
/sys/class/misc/tun. If it does
not exist, then attempt to load the module with
The tun device must also exist as
/dev/net/tun. If it does not exist, then
/dev/net (if necessary) with
mkdir /dev/net, then create
mknod /dev/net/tun c 10 200.
On FreeBSD and NetBSD, the userspace switch additionally requires the kernel tap(4) driver to be available, either built into the kernel or loaded as a module.
Using the Userspace Datapath with ovs-vswitchd¶
To use ovs-vswitchd in userspace mode, create a bridge with
datapath_type=netdev in the configuration database. For example:
$ ovs-vsctl add-br br0 $ ovs-vsctl set bridge br0 datapath_type=netdev $ ovs-vsctl add-port br0 eth0 $ ovs-vsctl add-port br0 eth1 $ ovs-vsctl add-port br0 eth2
ovs-vswitchd will create a TAP device as the bridge’s local interface, named the same as the bridge, as well as for each configured internal interface.
Currently, on FreeBSD, the functionality required for in-band control support is not implemented. To avoid related errors, you can disable the in-band support with the following command:
$ ovs-vsctl set bridge br0 other_config:disable-in-band=true
On Linux, when a physical interface is in use by the userspace datapath, packets received on the interface still also pass into the kernel TCP/IP stack. This can cause surprising and incorrect behavior. You can use “iptables” to avoid this behavior, by using it to drop received packets. For example, to drop packets received on eth0:
$ iptables -A INPUT -i eth0 -j DROP $ iptables -A FORWARD -i eth0 -j DROP
On NetBSD, depending on your network topology and applications, the following configuration might help. See sysctl(7).:
$ sysctl -w net.inet.ip.checkinterface=1