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Rob Nicholson
Asked: 2016-03-17 06:02:01 +0800 CST

Unknown port forwarding set-up on Netgear router

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I'm pretty familiar with firewalls, routers, port-forwarding etc after 20 years of managing networks but this one has got me flummoxed. I'm helping out a small brewery business which has a pretty simple network consisting of a Netgear WNR1000v3 router, a Windows 2003 server, couple of network printers and laptops. The Windows server has RDP configured, accessible via their single static IP address. There is also a bespoke monitoring program running on the server accessible via port 81.

So nothing particularly unusual and as with many small businesses, records of configuration are non-existent.

We're installing a new Dell server running Windows 2012 and one of my early tasks is to get remote desktop working - on a different port to 3389 because that's assigned to the existing server. Change the port via the registry, add a new rule into Windows firewall for port 3388 - check RDP works from the LAN. No problems.

Come to look at the port forwarding rules on the Netgear and hit a brick wall. Expected to see a couple of existing entries for RDP and the bespoke app on port 81. But the port forwarding lists are empty. Add the 3388 port forwarding rule anyway and that works.

But I'm flummoxed how RDP is being routed to the existing server without any rules on the Netgear router/firewall? The existing server is on 192.168.100.250. It's almost like the router is pushing all packets to this IP sort of by default but I've come across anything like that. I've scoured every single screen on the Netgear and can't find a reference to 192.168.100.250 anywhere.

I know Windows can act as a router but that's not configured plus you need two network ports and only one is in use.

So very confused...

port-forwarding

2 Answers

  1. Is the server set up as the "DMZ host" in the router? Many consumer-grade routers let you configure a DMZ host, to which all traffic from the outside will be directed.

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  2. Best Answer

    Thanks to posters who confirmed I wasn't missing anything obvious. Problem was with corrupt firmware/configuration. Upgrade to latest firmware didn't resolve the problem. Had to resort to resetting to factory settings and reconfiguring - port forwarding now working as expected, i.e. shows all the rules and doesn't hide some of them.

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