RE: [PLUG] What is the best way to create a tunnel or a forward?iptables?

[Marc Zucchelli <marcz908@yahoo.com>]

I tried the iptables command that Chad provided me with on my test server:

iptables -A FORWARD -i eth0 -p tcp --sport 2525 --dport 25 -d mailserver_IP -j ACCEPT

I set the ip address correctly, tried several variations, and I'm not getting a port forward.  I get refused connections when I try to connect to 2525.  I have seen several sites on the internet do it with NAT, but I'm not trying to send these packets to a different server, same one.  Do I have to use NAT?  Any other suggestions?  My iptables skills are weak!

Chad Vogelsong <chad@vogelsong.net> wrote:

Marc,

Can't you just SSH or VPN into the server that you are hosting their e-mail on?

If they have a business level internet package, port 25 should no be blocked.  Talk to their ISP about that.  If they have a consumer level package, tough luck.

It would be trivial to create an iptables forward rule to forward mailserver:2525 to mailserver:25.  Make the rule on the router/firewall something like this:

iptables -A FORWARD -i eth0 -p tcp --sport 2525 --dport 25 -d mailserver_IP -j ACCEPT

Assuming that eth0 is the router/fw external interface.  YMMV.

Chad

I'm hosting a clients email on my server.  Something went wrong with their router and it's blocking port 25.  I won't have the time to make the long trip up to fix it for them for a while, so I was thinking about maybe openning up a higher port on the same server, and just tunneling that to port 25, and it will be easy enough for me to walk them through changing their outgoing port in their email software.  What is the best way to pull this off?  This is just a temporary solution so I don't lose them! Get your own web address. Have a HUGE year through Yahoo! Small Business.

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Philadelphia Linux Users Group         --        http://www.phillylinux.org
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