document how to do split-horizon setups with mpw

this is needed^Wuseful since the kernel doesn't implicitly implement
split horizon in bridge for mpw anymore. it does allow the joining
of different VPLS meshes on the same bridge now though.

based on discussion with Lee Nelson and Mitchell Krome

1 files changed, 25 insertions, 2 deletions

diff --git a/share/man/man4/mpw.4 b/share/man/man4/mpw.4
index 731206981f5..36e164982e1 100644
--- a/share/man/man4/mpw.4
+++ b/share/man/man4/mpw.4
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: mpw.4,v 1.5 2019/03/11 18:55:29 jmc Exp $
+.\"	$OpenBSD: mpw.4,v 1.6 2019/04/02 23:50:14 dlg Exp $
 .\"
 .\" Copyright (C) 2015 Rafael Zalamena <rzalamena@openbsd.org>
 .\"
@@ -14,7 +14,7 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: March 11 2019 $
+.Dd $Mdocdate: April 2 2019 $
 .Dt MPW 4
 .Os
 .Sh NAME
@@ -60,6 +60,29 @@ Transport of Pseudowires:
 .Bd -literal -offset indent
 # ifconfig mpw5 pwecw -pwefat
 .Ed
+.Pp
+.Nm mpw
+interfaces may be used to build a Virtual Private LAN Service
+(VPLS) with
+.Xr bridge 4 .
+A VPLS is constructed with a full mesh of MPLS pseudowire tunnels
+between all peers, but this introduces loops in the topology.
+To prevent broadcast packets received from the VPLS being forwarded
+it's peers, all the pseudowire interfaces can be configured as a
+set of protected bridge members.
+Different VPLS meshes can be joined together on the same bridge
+using different identifiers for their protected domains.
+.Bd -literal -offset indent
+# ifconfig mpw10 create up
+# ifconfig mpw11 create up
+# ifconfig mpw12 create up
+# ifconfig bridge0 create
+# ifconfig bridge0 add em2
+# ifconfig bridge0 add mpw10 add mpw11 add mpw12
+# ifconfig bridge0 protected mpw10 1
+# ifconfig bridge0 protected mpw11 1
+# ifconfig bridge0 protected mpw12 1
+.Ed
 .Sh SEE ALSO
 .Xr hostname.if 5 ,
 .Xr ifconfig 8 ,