NetGear DG834G or other router Port redirection?

I just acquired an AOL branded NetGear DG834G v3 from fleabay and hooked it up to my Entanet ADSL service no problem. However, I went to configure port forwarding I found there does not seem to be an option to redirect port numbers - is this correct? I mean, for example, forward incoming port 12345 on the router to port 80 on an internal LAN address, to obfuscate services from hackers. My old D-Link DSL-500 could do this, and I just assumed that any newer router would have the same features. Do any modern routers provide this service now?

cheers, Pum.

Edited by Pum (Mon 25-Feb-08 14:10:12)

No I don't think you can do this with the DG834G (just had a look around the interface of mine). It isn't quite as easy, but could you not get the service to listen on the port you want to be open to the Internet?

Hi Pum, info for the Netgear DG834G router port forwarding instructions (here) and (here).

Cheers for the replies chaps.
E7er, thanx, but I know how to forward ports. It was redirecting ports I was enquiring about - it indeed seems that this router cannot do port redirection. I wonder if any modern routers do this?

cheers, Pum.

Actually it is possible to have the DG834G perform port redirection. However this is not available through the built in web administration interface. You have to perform this using a telnet session. For the rest of the discussion, I assume your private network is on the range 192.168.0.1 to 192.168.0.255 and the interface from the router to the internet is named ppp0 (more on this later).
First you must enable telnet on your router. In order to do so you must use the following URL in your browser : http://192.168.0.1/setup.cgi?todo=debug

Next, using a telnet session you connect to your router : telnet 192.168.0.1

You should assert the name of the internet side interface using the command : ifconfig -a
The interface of interest is the one with your public IP address.
Now comes the magic, thanks to iptables allowing for NAT (Network Address Translation). Numerous web pages details iptables. One of my favourite is at :

http://www.linif.org/~joeg/iptables/iptc.html#SESSION_3

First I suggest you create a new rules chain for your redirection. I used the following command : iptables -N MyRules

Next you can add as many rules as you which in your new chain. For example : iptables -A -i ppp0 -p tcp -m tcp --dport 100 -j DNAT --to-destination 192.168.0.87:101

This rule tells that any TCP packet coming from interface ppp0 and targeting port 100 is to be translated so as to be forwarded to port 101 on machine 192.168.0.87

Next you have to trigger this rule. I did so by inserting it in the PREROUTING chain of the translation table, using the command :

iptables -t nat -I PREROUTING 5 -i ppp0 -j MyRules

You will have to consider whether position 5 is accurate for you. In order to do so, you must list all NAT chains using the following command : iptables -t nat -L -v and figure out what each rule performs. Inserting your custom rules in first position would certainly do the case albeit opening breaches in your network defense perimeter. On the other end, appending your custom rule set at end of the PREROUTING chain would almost certainly fail because previous rules may have dropped the packets before they get a chance to reach your translation rule.

May this help

In reply to:

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Actually it is possible to have the DG834G perform port redirection. However this is not available through the built in web administration interface.

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I wish you had told me that before I did it via the GUI . We are talking port forwarding=port redirection, right?

http://www.portforward.com/english/routers/port_forwarding/Netgear/DG834G/DG834Gindex.htm