Using the excellent iptables modules to do this for any mail server is easy
using the port forwarding capabilties. Here is some script to help you get
started for a 2.4.2-2 kernel:-
# Ensure ipchains isn't running and run iptables instead
rmmod ipchains
insmod /lib/modules/2.4.2-2/kernel/net/ipv4/netfilter/ip_tables.o
insmod /lib/modules/2.4.2-2/kernel/net/ipv4/netfilter/ip_nat_ftp.o
insmod /lib/modules/2.4.2-2/kernel/net/ipv4/netfilter/ip_conntrack_ftp.o
insmod /lib/modules/2.4.2-2/kernel/net/ipv4/netfilter/ipt_MASQUERADE.o
# Turn on anti-spoofing for all interfaces
for f in /proc/sys/net/ipv4/conf/*/rp_filter; do echo 1 > $f; done
# Set IP forwarding on
echo 1 > /proc/sys/net/ipv4/ip_forward
# Add new redirection rules
iptables -A PREROUTING -t nat -p tcp --dport 25:25 -j DNAT --to 10.0.0.2
iptables -A PREROUTING -t nat -p udp --dport 25:25 -j DNAT --to 10.0.0.2
iptables -A PREROUTING -t nat -p tcp --dport 110:110 -j DNAT --to 10.0.0.2
iptables -A PREROUTING -t nat -p udp --dport 110:110 -j DNAT --to 10.0.0.2
iptables -A PREROUTING -t nat -p tcp --dport 143:143 -j DNAT --to 10.0.0.2
iptables -A PREROUTING -t nat -p udp --dport 143:143 -j DNAT --to 10.0.0.2
Regards,
Mark.
-----Original Message-----
From: Bowie Bailey [mailto:[EMAIL PROTECTED]]
Sent: 03 October 2002 16:40
To: Dan Johansson; [EMAIL PROTECTED]
Subject: RE: [courier-users] Courier behind a Firewall
> -----Original Message-----
> From: Dan Johansson [mailto:[EMAIL PROTECTED]]
> Sent: Thursday, October 03, 2002 11:12 AM
> To: [EMAIL PROTECTED]
> Subject: [courier-users] Courier behind a Firewall
>
>
> Hi,
>
> I�m new to Courier and this list so please be kind to me.
>
> I�ve set up Courier succefull (I think) on a host in my network.
> This Network is behind a Firewall (consisting of a Router (doing NAT)
> and a hardened Linux box). Courier works fine for "internal" mail, and
> now I would like it to recieve mail from te rest of the world.
> So my qustion is what to do on the FW. Schould I only put
> some general-
> gateway on my FW that only passes TCP-connections on port 25 from
> the WAN sid to the Courier Mail-Server on the LAN side.
The Courier box will need to have a static IP to the outside (probably via a
static NAT on your router). Then just tell the firewall to allow
connections to port 25 on your Courier box. I could give you instructions
for a Cisco firewall, but I'm not familiar enough with iptables (or
ipchains).
> Or do you have
> any othe suggestion (No I don�t want to run my mailserver on the FW).
Running extra software on your firewall is generally not a good idea if you
can avoid it. If you do, then a vulnerability in your other applications
could give a hacker direct access to your firewall box.
>
> Regards,
> --Dan
Bowie
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