-.\" $OpenBSD: gre.4,v 1.65 2018/02/23 03:03:36 dlg Exp $
+.\" $OpenBSD: gre.4,v 1.66 2018/02/23 09:50:30 jmc Exp $
.\" $NetBSD: gre.4,v 1.10 1999/12/22 14:55:49 kleink Exp $
.\"
.\" Copyright 1998 (c) The NetBSD Foundation, Inc.
.Nm nvgre
interface is set to 1500, and the Don't Fragment flag is set.
The MTU on the network interfaces carrying underlay network traffic
-must be raised to accomodate this and the overhead of the NVGRE
+must be raised to accommodate this and the overhead of the NVGRE
encapsulation, or the
.Nm nvgre
interface must be reconfigured for less capable underlays.
communication.
.\" bridge(4) ioctls should go here too.
.El
+.Ss Security Considerations
+The GRE protocol in all its flavours does not provide any integrated
+security features.
+GRE should only be deployed on trusted private networks,
+or protected with IPsec to add authentication and encryption for
+confidentiality.
+IPsec is especially recommended when transporting GRE over the
+public internet.
+.Pp
+The Packet Filter
+.Xr pf 4
+can be used to filter tunnel traffic with endpoint policies
+.Xr pf.conf 5 .
+.Pp
+The Time-to-Live (TTL) value of a tunnel can be set to 1 or a low
+value to restrict the traffic to the local network:
+.Bd -literal -offset indent
+# ifconfig gre0 tunnelttl 1
+.Ed
.Sh EXAMPLES
.Ss Point-to-Point Layer 3 GRE tunnel interfaces (gre)
-.Nm gre
Configuration example:
.Bd -literal
Host X ---- Host A ------------ tunnel ------------ Cisco D ---- Host E
interfaces or the bridging of VLAN tagged traffic across the tunnel.
These non-restrictions allow non-compliant tunnels to be configured
which may not interoperate with other vendors.
-.Sh SECURITY CONSIDERATIONS
-The GRE protocol in all its flavours does not provide any integrated
-security features.
-GRE should only be deployed on trusted private networks,
-or protected with IPsec to add authentication and encryption for
-confidentiality.
-IPsec is especially recommended when transporting GRE over the
-public internet.
-.Pp
-The Packet Filter
-.Xr pf 4
-can be used to filter tunnel traffic with endpoint policies
-.Xr pf.conf 5 .
-.Pp
-The Time-to-Live (TTL) value of a tunnel can be set to 1 or a low
-value to restrict the traffic to the local network:
-.Bd -literal -offset indent
-# ifconfig gre0 tunnelttl 1
-.Ed