nat — Shorewall one-to-one NAT file




This file is used to define one-to-one Network Address Translation (NAT).


If all you want to do is simple port forwarding, do NOT use this file. See Also, in many cases, Proxy ARP (shorewall-proxyarp(5)) is a better solution that one-to-one NAT.

The columns in the file are as follows.


External IP Address - this should NOT be the primary IP address of the interface named in the next column and must not be a DNS Name.

If you put COMMENT in this column, the rest of the line will be attached as a comment to the Netfilter rule(s) generated by the following entries in the file. The comment will appear delimited by "/* ... */" in the output of "shorewall show nat"

To stop the comment from being attached to further rules, simply include COMMENT on a line by itself.

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.

INTERFACE - interfacelist[:[digit]]

Interfacees that have the EXTERNAL address. If ADD_IP_ALIASES=Yes in shorewall.conf(5), Shorewall will automatically add the EXTERNAL address to this interface. Also if ADD_IP_ALIASES=Yes, you may follow the interface name with ":" and a digit to indicate that you want Shorewall to add the alias with this name (e.g., "eth0:0"). That allows you to see the alias with ifconfig. That is the only thing that this name is good for -- you cannot use it anwhere else in your Shorewall configuration.

Each interface must match an entry in shorewall-interfaces(5). Shorewall allows loose matches to wildcard entries in shorewall-interfaces(5). For example, ppp0 in this file will match a shorewall-interfaces(5) entry that defines ppp+.

If you want to override ADD_IP_ALIASES=Yes for a particular entry, follow the interface name with ":" and no digit (e.g., "eth0:").

INTERNAL - address

Internal Address (must not be a DNS Name).


If Yes or yes, NAT will be effective from all hosts. If No or no (or left empty) then NAT will be effective only through the interface named in the INTERFACE column.

LOCAL - [Yes|No]

If Yes or yes, NAT will be effective from the firewall system




shorewall(8), shorewall-accounting(5), shorewall-actions(5), shorewall-blacklist(5), shorewall-hosts(5), shorewall-interfaces(5), shorewall-maclist(5), shorewall-masq(5), shorewall-netmap(5), shorewall-params(5), shorewall-policy(5), shorewall-providers(5), shorewall-proxyarp(5), shorewall-route_rules(5), shorewall-routestopped(5), shorewall-rules(5), shorewall.conf(5), shorewall-tcclasses(5), shorewall-tcdevices(5), shorewall-tcrules(5), shorewall-tos(5), shorewall-tunnels(5), shorewall-zones(5)