-Open vSwitch supports Linux 2.6.15 and up, with testing focused on
-2.6.18 with Centos and Xen patches and version 2.6.26 from kernel.org.
-Open vSwitch also has special support for Citrix XenServer hosts.
+The included Linux kernel module supports Linux 2.6.15 and up, with
+testing focused on 2.6.18 with Centos and Xen patches and version
+2.6.26 from kernel.org. Open vSwitch also has special support for
+Citrix XenServer hosts.
+
+Open vSwitch can also operate, at a cost in performance, entirely in
+userspace, without assistance from a kernel module. This userspace
+implementation should be easier to port than the kernel-based switch.
+It is considered experimental.