Index: share/man/man4/gre.4
===================================================================
--- share/man/man4/gre.4	(revision 334091)
+++ share/man/man4/gre.4	(working copy)
@@ -172,6 +172,15 @@
 .Va net.inet.ip.forwarding
 .Xr sysctl 8
 variable to non-zero.
+
+By default,
+.Nm
+tunnels may not be nested.
+This behavior may be modified at runtime by setting the
+.Xr sysctl 8
+variable
+.Va net.link.gre.max_nesting
+to the desired level of nesting.
 .Sh SEE ALSO
 .Xr gif 4 ,
 .Xr inet 4 ,