Mention keepalives here too; ok jmc@

1 files changed, 22 insertions, 2 deletions

diff --git a/share/man/man4/gre.4 b/share/man/man4/gre.4
index 2d906f68d2d..d9ef5dc0fe1 100644
--- a/share/man/man4/gre.4
+++ b/share/man/man4/gre.4
@@ -1,4 +1,4 @@
-.\" $OpenBSD: gre.4,v 1.31 2008/06/26 05:42:06 ray Exp $
+.\" $OpenBSD: gre.4,v 1.32 2010/06/29 21:43:21 sthen Exp $
 .\" $NetBSD: gre.4,v 1.10 1999/12/22 14:55:49 kleink Exp $
 .\"
 .\" Copyright 1998 (c) The NetBSD Foundation, Inc.
@@ -28,7 +28,7 @@
 .\" ARISING IN ANY WAY  OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
 .\" POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: June 26 2008 $
+.Dd $Mdocdate: June 29 2010 $
 .Dt GRE 4
 .Os
 .Sh NAME
@@ -177,6 +177,26 @@ alias on Host A for the Ethernet interface:
 and on the Cisco:
 .Pp
 .Dl ip route Y mask tunnelX
+.Pp
+Keepalive packets may optionally be sent to the remote endpoint, which
+decapsulates and returns them, allowing tunnel failure to be detected.
+Enable them like this:
+.Bd -literal -offset indent
+# ifconfig greN keepalive period count
+.Ed
+.Pp
+This will send a keepalive packet every
+.Ar period
+seconds.
+If no response is received in
+.Ar count
+*
+.Ar period
+seconds, the link is considered down.
+To return keepalives, the remote host must be configured to forward packets:
+.Bd -literal -offset indent
+# sysctl net.inet.ip.forwarding=1
+.Ed
 .Sh NOTES
 The MTU of
 .Nm