IPTABLES port forwarding woes

[Erich Weiler <weiler@soe.ucsc.edu>]

Hi All,

I'm having trouble setting up port forwarding on a linux host I have... 
Basically I have 2 machines. One has a public and a private IP address, 
the other just has a private address:


Machine 1:
public IP: 120.1.1.10
private IP: 10.1.1.50

Machine 2:
private IP: 10.1.1.133

I want to ssh to port 2222 on machine 1 from the internet, on the public 
IP, and have it forward to port 22 on machine 2 on the private network. 
  I can't seem to open an SSH socket however when SSHing to port 2222 on 
machine 1's public IP address...  Note that I only want port 2222 routed 
to machine 2, all other ports should connect to machine 1 as normal. 
This is my current IP tables file on machine 1:


# Generated by iptables-save v1.3.5 on Wed May 28 20:56:31 2008
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [66:7948]
-A FORWARD -d 10.1.3.133 -i eth0 -o eth1 -p tcp -m tcp --dport 22 -m 
state --state NEW -j ACCEPT
-A FORWARD -o eth0 -m state --state NEW,RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -i eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -i eth0 -p all -j ACCEPT
-A INPUT -i eth1 -p all -j ACCEPT
-A OUTPUT -o eth0 -p all -j ACCEPT
-A OUTPUT -o eth1 -p all -j ACCEPT
COMMIT
# Completed on Wed May 28 20:56:31 2008
# Generated by iptables-save v1.3.5 on Wed May 28 20:56:31 2008
*nat
:PREROUTING ACCEPT [451:32699]
:POSTROUTING ACCEPT [2:236]
:OUTPUT ACCEPT [2:236]
-A PREROUTING -d 120.1.1.10 -i eth0 -p tcp -m tcp --dport 2222 -j DNAT 
--to-destination 10.1.3.133:22
-A POSTROUTING -s 10.1.3.133 -o eth0 -j SNAT --to-source 120.1.1.10
COMMIT
# Completed on Wed May 28 20:56:31 2008

This just doesn't seem to work - can anyone see where I'm going wrong? I 
guess I want machine 2 to see connections coming from machine 1 to be 
coming from machine 1's private IP, but I'm not sure the 'source IP' is 
being re-written when it's being forwarded to machine 2... Not sure... 
Anyway, if anyone can see what's wrong here please let me know!!

Thanks so much,
erich