Add an example about using the Spanning Tree Protocol (STP) to prevent

potential loops between bridges and pairs.

OK jmc@ sthen@

1 files changed, 21 insertions, 2 deletions

diff --git a/share/man/man4/pair.4 b/share/man/man4/pair.4
index 9ac07e0d68a..c720a70726f 100644
--- a/share/man/man4/pair.4
+++ b/share/man/man4/pair.4
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: pair.4,v 1.3 2015/10/24 15:46:10 reyk Exp $
+.\"	$OpenBSD: pair.4,v 1.4 2015/10/30 10:48:55 reyk Exp $
 .\"
 .\" Copyright (c) 2015 Reyk Floeter <reyk@openbsd.org>
 .\" Copyright (c) 2009 Theo de Raadt <deraadt@openbsd.org>
@@ -15,7 +15,7 @@
 .\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 .\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 .\"
-.Dd $Mdocdate: October 24 2015 $
+.Dd $Mdocdate: October 30 2015 $
 .Dt PAIR 4
 .Os
 .Sh NAME
@@ -47,6 +47,25 @@ Set up a pair of interfaces where each of them is a member of a different
 # ifconfig pair1 patch pair2
 # route -T 1 exec ping 10.1.1.2
 .Ed
+.Pp
+When adding multiple
+.Nm
+to multiple
+.Xr bridge 4
+interfaces, it is possible to create a loop;
+the system load will go up while it is busy sending packets from one
+bridge to another and back.
+By design, the driver does not prevent such loops by itself, but it is
+possible to use the Spanning Tree Protocol (STP) to detect and remove
+loops in the virtual network topology:
+.Bd -literal -offset indent
+# ifconfig pair0 up
+# ifconfig pair1 rdomain 1 patch pair0 up
+# ifconfig pair2 up
+# ifconfig pair3 rdomain 1 patch pair2 up
+# ifconfig bridge0 add pair0 add pair2 stp pair0 stp pair2 up
+# ifconfig bridge1 add pair1 add pair3 stp pair1 stp pair3 up
+.Ed
 .Sh SEE ALSO
 .Xr bridge 4 ,
 .Xr inet 4 ,