Port Forwarding Using Incorrect IP [Business Hub 5]

[ihs_guy]

Hi there

I'm using a BT Business Hub 5 (Type A) and have a setup with a number of machines running in the local network.

I'm using the router's DHCP for all machines and have set a reserved local IP for each. Every time the machines are restarted, they are assigned the same IP according to the Business Network screen on the router's admin UI.

I set up a port forward some time ago for making RDP connections to a specific machine (let's call it Machine A). This takes all connections on port 3389 and forwards them to Machine A. This worked fine for quite a while. After restarting the machine on one occasion (not the first time it had been restarted), the remote connection ceased to work. I checked numerous things (firewall, remote setup, etc.) and determined that everything was fine on Machine A. I was able to connect to it from other machines within the network, using its IP address.

What I noticed when trying to connect from outside the network, is that the router's log is forwarding the packeds to the wrong IP (one that, in fact does not exist). Machine A is set to 192.168.1.82, but the forward is sending the connection to 192.168.1.101.

Everywhere the router lists the computer (along with name/MAC address) it is listed as 192.168.1.82 and there are no entries anywhere for 192.168.1.101. In keeping with this, the 'phantom' IP cannot be connected to or pinged.

I have attempted the following:

• Check DHCP settings (router and machine - all fine)
• Restart Machine A
• Restart Router
• Remove and replace 'application' on router
• Remove and replace port forward rule on router

Has anyone else experienced anything similar? No matter what I try, the log keeps showing my attempted connections have been forwarded to this non-extistent IP. 

Any assistance would be appreciated.

Many thanks.

[wajid]

I would check the following:

I assume you are forwarding to port 3389 on machine A too.


ISOLATE THE PROBLEM

1. check the gateway*/network mask and ip machine A, make sure they are correct
2. ping and check connectivity to the machine from within the lan
2. connect to the port from a local network machine within the lan

You can also try sniffing traffic to find issues on your lan. Usually some bad network card, duplicate ip can be the cause too. connect a hub to one of the ports on the router and move all your machines to that hub then run wireshark on your network to see if there are any issues.

If local machines and traffic is connecting fine to the machine then its time to look at the port forwarding from the router to the lan

1. use a service to check if your ports are open such as http://www.canyouseeme.org/
2. check firewall rules to make sure it is not being blocked
3. factory reset your router and setup port forwarding again
4. Get a real business class router


Would help if you gave more information about the application. but these instructions should help,.

[ihs_guy]

Hi there, thank you for your response.

As I mentioned in the first post, I can connect to Machine A from other machines in the network using the correct IP (on 3389). Obviously, I can also ping it etc. For this reason I have eliminated Machine A's own settings being the root of the issue. The IP and subnet mask seem fine on the Machine A itself.

I can connect to other machines on the network using the same configuration (though with a custom port number and a different destination IP).

When I attempt to make a connection to Machine A from outside, the router log shows it has allowed the connection *but has forwarded it to this 'phantom' IP*. The log entry is the same as successful connections to the other machines that work, only sent it to an IP that does not exist on the network.

To elaborate, it looks pretty clear that for some reason the router has 'cached' an IP that is not in use somehow. This was working fine before and simply stopped after a restart. My issue appears more about a discrepancy between the IP the Business Hub reports the machine as having (which is the one it actually has), and the completely different IP it's forwarding to based on the port forwarding rule.

I could recommend that my employer buys a 'real business class router', but it's a setup at a small satellite office and a potentially temporary operation. I'm not trying to get it to do something it's not designed to do, I've just got some anomolous behaviour which I'd like to get to the bottom of (hence my posting on the supplier's forum).

Many thanks.

[spank]

Hi there,

Yes, I've seen this before.

You could manually assign your PC's the IP's in tcp/ip and port forward to an IP rather than a netbios name.

Make sure the IP's you assign are not in the DHCP range or you might end up with conflicts.  You may need to narrow the range manually.

Thanks