The columns in the file are as follows.

SOURCE (Optional) - {-|interface|address|interface:address}

An ip address (network or host) that matches the source IP address in a packet. May also be specified as an interface name optionally followed by ":" and an address. If the device lo is specified, the packet must originate from the firewall itself.

DEST (Optional) - {-|address}

An ip address (network or host) that matches the destination IP address in a packet.

If you choose to omit either SOURCE or DEST, place "-" in that column. Note that you may not omit both SOURCE and DEST.

PROVIDER - {provider-name|provider-number|main}

The provider to route the traffic through. May be expressed either as the provider name or the provider number. May also be main or 254 for the main routing table. This can be used in combination with VPN tunnels, see example 2 below.

PRIORITY - priority

The rule's numeric priority which determines the order in which the rules are processed. Rules with equal priority are applied in the order in which they appear in the file.

1000-1999

Before Shorewall-generated 'MARK' rules

11000-11999

After 'MARK' rules but before Shorewall-generated rules for ISP interfaces.

26000-26999

After ISP interface rules but before 'default' rule.