[Ferm] Request for help with port forward

[András Kovács]

Dear All,


I am using FERM and I really appreciate this great tool. Makes me no headache to understand my own firewall rules. :)

I am implementing a NAT network, where packets sent to the network to a specific port are needed to be forwarded to an other internal IP and port.

Ferm version: 2.0.7-1 (as part of Debian squeeze)

I adapted the tiny example provided in FERM docs:

http://ferm.foo-projects.org/download/2.1/ferm.html#easy_port_forwarding

My function looks like this:

@def &FORWARD_LAN($dest, $proto, $port_external, $port_internal) = {
 table filter chain FORWARD interface $DEV_INTERNET outerface $DEV_LAN daddr $dest proto $proto dport $port_internal ACCEPT;
table nat chain PREROUTING interface $DEV_INTERNET daddr $NET_NAT_STATIC proto $proto dport $port_external DNAT to $dest:$port_internal;
}

($NET_NAT_STATIC would be the external global IP of the firewall)

It gives this error message:

"dport
    (
        smtp
    )
    DNAT to $ dest: <--
variable name expected - if you want to concatenate strings, try using double quotes"

I thought concatenation would help FERM to understand the syntax:

table nat chain PREROUTING interface $DEV_INTERNET daddr $NET_NAT_STATIC proto $proto dport $port_external DNAT to @CAT($dest,":",$port_internal);

"dport
    (
        smtp
    )
    DNAT to @CAT <--
unknown ferm built-in function"

Which is weird as documentation is referring to @cat function.

Could you please give me a hint to step forward with this and to be able to forward an external packet to a specific internal port? I find no clue in current docs and man pages.

Thank you very much.

Best regards,
Andras Kovacs