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RE: Port Forwarding



Silly question, but after the packets go through your nat table, are
they still destined for port 3389 or are they now destined for port 80
on Machine2.  What would happen if your FORWARD chain had the following
rule:

 -A FORWARD -i eth0 -p tcp --dport 80 -d 209.209.209.209 -j ACCEPT

It sounds like once you've done your prerouting and DNAT, the packets
are being rejected because you don't have a rule to accept packets
destined for 209.209.209.209:80.

Maarten Broekman


-----Original Message-----
From: redhat-list-bounces redhat com
[mailto:redhat-list-bounces redhat com] On Behalf Of Troy Amburg
Sent: Wednesday, December 19, 2007 12:49 PM
To: General Red Hat Linux discussion list
Subject: Re: Port Forwarding

So you can traceroute from Machine1 to Machine2 without any problem,  
and you can telnet to the port in question, from Machine1 to  
Machine2? If that's the case, I guess I don't understand what's not  
working.



On Dec 19, 2007, at 9:43 AM, Steven Buehler wrote:

>> -----Original Message-----
>> From: redhat-list-bounces redhat com [mailto:redhat-list-
>> bounces redhat com] On Behalf Of Troy Amburg
>> Sent: Wednesday, December 19, 2007 11:34 AM
>> To: General Red Hat Linux discussion list
>> Subject: Re: Port Forwarding
>>
>> Do you have a traceroute from Machine1 to Machine2? Also, is the
>> default route set correctly on Machine1?
>>
>> On Dec 19, 2007, at 9:07 AM, Steven Buehler wrote:
>>
>>> I am trying to do port forwarding and I just can't seem to get it
>>> to work.
>>> I hope that someone can help.
>>>
>>> Machine 1 is running RHEL AS 4.4 with the 2.6.9-42.0.2.ELsmp kernel.
>>> iptables has been running as my firewall since I set it up.
>>>
>>> I am trying to get anything that comes in to port 3389 on "Machine
>>> 1" to go
>>> to "Machine2" at a different location.  Lets say for this that the
>>> IP of
>>> "Machine1" is 70.70.70.70 and the remote machine ("Machine 2") that
>>> I want
>>> to forward to is 209.209.209.209.  I am assuming that I don't have
>>> to do
>>> anything on "Machine2" except make sure the firewall for that port
>>> is opened
>>> to "Machine 1".
>>>
>>> I have done the following on "Machine 1":
>>> echo 1 > /proc/sys/net/ipv4/ip_forward
>>>
>>> Here is my /etc/sysconfig/iptables file from "Machine 1".  This is
>>> not the
>>> one that I would normally use because it is to open, but am for
>>> testing.
>>> ####################
>>> # Generated by iptables-save v1.2.11 on Wed Dec 19 10:50:11 2007
>>> *nat
>>> :PREROUTING ACCEPT [3:536]
>>> :POSTROUTING ACCEPT [9:635]
>>> :OUTPUT ACCEPT [8:583]
>>> -A PREROUTING -p tcp -m tcp --dport 3389 -j DNAT --to-destination
>>> 209.209.209.209:80
>>> COMMIT
>>> # Completed on Wed Dec 19 10:50:11 2007
>>> # Generated by iptables-save v1.2.11 on Wed Dec 19 10:50:11 2007
>>> *mangle
>>> :PREROUTING ACCEPT [318:24902]
>>> :INPUT ACCEPT [312:24214]
>>> :FORWARD ACCEPT [3:152]
>>> :OUTPUT ACCEPT [276:32613]
>>> :POSTROUTING ACCEPT [279:32765]
>>> COMMIT
>>> # Completed on Wed Dec 19 10:50:11 2007
>>> # Generated by iptables-save v1.2.11 on Wed Dec 19 10:50:11 2007
>>> *filter
>>> :INPUT ACCEPT [0:0]
>>> :FORWARD ACCEPT [0:0]
>>> :OUTPUT ACCEPT [276:32613]
>>> :RH-Firewall-1-INPUT - [0:0]
>>> -A INPUT -j RH-Firewall-1-INPUT
>>> -A FORWARD -i eth0 -p tcp -m tcp --dport 3389 -j ACCEPT
>>> -A FORWARD -j RH-Firewall-1-INPUT
>>> -A OUTPUT -o eth0 -j LOG --log-prefix "BANDWIDTH_OUT:" --log-level 7
>>> -A RH-Firewall-1-INPUT -i eth0 -j ACCEPT
>>> -A RH-Firewall-1-INPUT -i lo -j ACCEPT
>>> -A RH-Firewall-1-INPUT -p icmp -m icmp --icmp-type any -j ACCEPT
>>> -A RH-Firewall-1-INPUT -d 224.0.0.251 -p udp -m udp --dport 5353 -j
>>> ACCEPT
>>> -A RH-Firewall-1-INPUT -p udp -m udp --dport 631 -j ACCEPT
>>> -A RH-Firewall-1-INPUT -m state --state RELATED,ESTABLISHED -j  
>>> ACCEPT
>>> -A RH-Firewall-1-INPUT -j REJECT --reject-with icmp-host-prohibited
>>> COMMIT
>>> # Completed on Wed Dec 19 10:50:11 2007
>>> ####################
>>>
>>> Thanks
>>> Steve
>>>
>
> A traceroute shows no problems.  Goes to the remote machine just  
> fine.  I
> can also access the port on the remote machine with no problems.
>
> [root mymachine]# route -n
> Kernel IP routing table
> Destination     Gateway         Genmask         Flags Metric Ref     
> Use
> Iface
> 70.70.70.0     0.0.0.0         255.255.255.0   U     0       
> 0        0 eth0
> 169.254.0.0     0.0.0.0         255.255.0.0     U     0       
> 0        0 eth0
> 0.0.0.0         70.70.70.175   0.0.0.0         UG    0       
> 0        0 eth0
>
>
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