[olug] iptables behind router

[Daniel Linder]

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William E. Kempf said:
> However... I'd like to be able to have [comp A]
> forward some ports to [comp B].

Jeff gave one solution, here is another possible solution.

The IPTables feature has a "Destination Network Address Translation"
feature (DNAT) which re-writes the destination of each IP packet to
another address when it comes in.  When it goes back out, the IPTables
un-does the translation and replaces the (now) source address with what
the machine on the outside expects.

Example:


CompX---{internet}---{Cablemodem}-{router}--+---[CompA]
                                            +---[CompB]

On Computer A, you would use a line like this:
iptables -t nat -A PREROUTING -i eth0 -d <CompA_Addr> -dport <CompaA_port>
- -j DNAT --to-destination <CompB_Addr:CompB_port>

Just make sure that Computer B has it's route to the Internet set to point
back through CompA so CompA can un-do the DNAT...

I think this should work... :)

Dan

- - - - -
"I do not fear computer,
I fear the lack of them."
 -- Isaac Asimov

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