The columns in the file are as follows (where the column name is followed by a different name in parentheses, the different name is used in the alternate specification syntax).

TYPE - {ipsec[:{noah|ah}]|ipsecnat|gre|l2tp|pptpclient|pptpserver|?COMMENT|{openvpn|openvpnclient|openvpnserver}[:{tcp|udp}][:port]|generic:protocol[:port]}

Types are as follows:

        ipsec         - IPv6 IPSEC
        ipsecnat      - IPv6 IPSEC with NAT Traversal (UDP port 4500 encapsulation)
        gre           - Generalized Routing Encapsulation (Protocol 47)
        l2tp          - Layer 2 Tunneling Protocol (UDP port 1701)
        openvpn       - OpenVPN in point-to-point mode
        openvpnclient - OpenVPN client runs on the firewall
        openvpnserver - OpenVPN server runs on the firewall
        generic       - Other tunnel type
        tinc          - TINC (added in Shorewall 4.6.6)

If the type is ipsec, it may be followed by :ah to indicate that the Authentication Headers protocol (51) is used by the tunnel (the default is :noah which means that protocol 51 is not used). NAT traversal is only supported with ESP (protocol 50) so ipsecnat tunnels don't allow the ah option (ipsecnat:noah may be specified but is redundant).

If type is openvpn, openvpnclient or openvpnserver it may optionally be followed by ":" and tcp or udp to specify the protocol to be used. If not specified, udp is assumed. Note: At this writing, OpenVPN does not support IPv6.

If type is openvpn, openvpnclient or openvpnserver it may optionally be followed by ":" and the port number used by the tunnel. if no ":" and port number are included, then the default port of 1194 will be used. . Where both the protocol and port are specified, the protocol must be given first (e.g., openvpn:tcp:4444).

If type is generic, it must be followed by ":" and a protocol name (from /etc/protocols) or a protocol number. If the protocol is tcp or udp (6 or 17), then it may optionally be followed by ":" and a port number.

Comments may be attached to Netfilter rules generated from entries in this file through the use of ?COMMENT lines. These lines begin with the word ?COMMENT; the remainder of the line is treated as a comment which is attached to subsequent rules until another ?COMMENT line is found or until the end of the file is reached. To stop adding comments to rules, use a line with only the word ?COMMENT.

ZONE - zone

The zone of the physical interface through which tunnel traffic passes. This is normally your internet zone.

GATEWAY(S) (gateway or gateways) - address-or-range [ , ... ]

The IP address of the remote tunnel gateway. If the remote gateway has no fixed address (Road Warrior) then specify the gateway as ::/0. May be specified as a network address and if your kernel and ip6tables include iprange match support then IP address ranges are also allowed.

Beginning with Shorewall 4.5.3, a list of addresses or ranges may be given. Exclusion (m[blue]shorewall6-exclusionm[][2] (5) ) is not supported.

GATEWAY ZONE(S) (gateway_zone or gateway_zones) - [zone[,zone]...]

Optional. If the gateway system specified in the third column is a standalone host then this column should contain a comma-separated list of the names of the zones that the host might be in. This column only applies to IPSEC tunnels where it enables ISAKMP traffic to flow through the tunnel to the remote gateway(s).