Solved

DNAT port forwards won't work from inside.

Posted on 2004-08-04
5
278 Views
Last Modified: 2010-05-18
Hi,
I have setup DNAT port forwards on my Linux box with IPtables to forward incoming web traffic (or whatever port) to an internal windows box.

It works fine from external machines (ie. other machines on the internet), but it won't work from machines on the Internal network (192.168.0.0/24) which use the linux box as a default gateway to nat out.

I have a friend who says that port forwards on his netgear router work from both internal and external.

How do I configure IPtables so that port forwards will work from inside?

Thanks,
Andrew
0
Comment
Question by:jonesy2k
  • 2
5 Comments
 
LVL 14

Expert Comment

by:pablouruguay
ID: 11722866
example of nat to go outside

iptables -t nat -A POSTROUTING -s 192.168.1.65 -d 0.0.0.0/0 -j SNAT --to-source publicipaddress

but please poste your rules in here. to clarify the situation
0
 
LVL 4

Author Comment

by:jonesy2k
ID: 11722950
Here are my iptables rules. As you can see, I'm using MASQUERADE rather that SNAT
*nat
:PREROUTING ACCEPT [41:1889]
:POSTROUTING ACCEPT [2:152]
:OUTPUT ACCEPT [2:152]
-A PREROUTING -i eth1 -p 47 -j DNAT --to-destination 192.168.0.113
-A PREROUTING -i eth1 -p tcp --dport 1723 -j DNAT --to-destination 192.168.0.113:1723
-A PREROUTING -i eth1 -p tcp --dport 80 -j DNAT --to-destination 192.168.0.121:80
-A POSTROUTING -s 192.168.0.0/255.255.255.0 -o eth1 -j MASQUERADE
COMMIT
*filter
:INPUT ACCEPT [50951:65998115]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [25947:1529635]
-A INPUT -i lo -j ACCEPT
-A INPUT -d 127.0.0.0/255.0.0.0 -j REJECT --reject-with icmp-port-unreachable
-A INPUT -s 192.168.0.0/255.255.255.0 -i eth0 -j ACCEPT
-A INPUT -s 192.168.0.0/255.255.255.0 -i eth1 -j REJECT --reject-with icmp-port-unreachable

-A INPUT -p tcp -m tcp --dport 20 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 21 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 22 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 53 -j ACCEPT
-A INPUT -p udp -m udp --dport 53 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 80 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 110 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 113 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 143 -j ACCEPT
-A INPUT -p tcp -m tcp --dport 443 -j ACCEPT
-A INPUT -p tcp -m tcp -j REJECT --reject-with tcp-reset
-A INPUT -j REJECT --reject-with icmp-port-unreachable
-A FORWARD -m unclean -j DROP
-A FORWARD -d 192.168.0.113 -j ACCEPT
-A FORWARD -d 192.168.0.121 -j ACCEPT
-A FORWARD -i eth0 -o eth1 -j ACCEPT
-A FORWARD -i eth1 -m state --state RELATED,ESTABLISHED -j ACCEPT
-A FORWARD -p tcp -m tcp -j REJECT --reject-with tcp-reset
-A FORWARD -j REJECT --reject-with icmp-port-unreachable
-A OUTPUT -j ACCEPT
COMMIT
0
 
LVL 4

Author Comment

by:jonesy2k
ID: 11723245
I've actually answered my own question, but thanks for your willingness to help.
I needed to loosen the iptables prerouting so that it could come in any any interface.
I also had to allow forwarding to internal hosts.
0
 
LVL 5

Accepted Solution

by:
Netminder earned 0 total points
ID: 11723699
User resolved; closed, 125 points refunded.

Netminder
Site Admin
0

Featured Post

Portable, direct connect server access

The ATEN CV211 connects a laptop directly to any server allowing you instant access to perform data maintenance and local operations, for quick troubleshooting, updating, service and repair.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

I have seen several blogs and forum entries elsewhere state that because NTFS volumes do not support linux ownership or permissions, they cannot be used for anonymous ftp upload through the vsftpd program.   IT can be done and here's how to get i…
Note: for this to work properly you need to use a Cross-Over network cable. 1. Connect both servers S1 and S2 on the second network slots respectively. Note that you can use the 1st slots but usually these would be occupied by the Service Provide…
Email security requires an ever evolving service that stays up to date with counter-evolving threats. The Email Laundry perform Research and Development to ensure their email security service evolves faster than cyber criminals. We apply our Threat…
Nobody understands Phishing better than an anti-spam company. That’s why we are providing Phishing Awareness Training to our customers. According to a report by Verizon, only 3% of targeted users report malicious emails to management. With compan…

821 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question