Ethernet Remote Access Headache

I'm trying to remotely access access a PLC (rather a remote laptop connected to local PLC) over the Internet via a remote desktop application. I've successfully done this already with a 3G usb "air card" and a wired connection to the PLC. So it kinda looks like this:

MY_PC <-->{INTERNET}<-->3G Stick<-->[USB]LAPTOP[WIREDPORT]<-->WIRED SWITCH<-->PLC

Now I tried this again except instead of a 3G-USB stick on the remote end, I'm using a 3G wireless HUB which uses the laptop's wireless card to connect.

MY_PC <-->{INTERNET}<-->3G WIRELESS HUB<-->[WIRELESSCARD]LAPTOP[WIREDPORT]<-->WIRED SWITCH<-->PLC

Now in this configuration, once we plug the ethernet cable into the WIREDPORT, the remote laptop loses connection to the 3G WIRELESS HUB, and my remote desktop session is ended.

I'm thinking my problem has to do with using both the laptops wired and wireless connections at the same time. Anybody have any ideas of what i can do to fix this?

I use a simple cradlepoint model: mbr900 plug my usb in and have wireless network presto!!!

Using a static address on the Wired side and a DHCP on the wireless side?

BillRobinson said:

I'm thinking my problem has to do with using both the laptops wired and wireless connections at the same time. Anybody have any ideas of what i can do to fix this?

Click to expand...

There shouldn't be a problem with using both the wired and wireless cards in the laptop at the same time. I've done it several times in the last month. The only difference was replacing you "wireless hub" with a plants wifi network. I would check to make sure that your wired port is not set to pull an IP via DHCP, and that it is not set up to try to "share" wifi connection out over its wired port.

EDIT: What version of windows are you running on the remote laptop?

-Benaiah

My first suspicion is that your Wireless card and your Wired port both share the same subnet. In Windows networking this causes a lot of issues since Windows needs each Network card to be on it's own subnet.

If the cards share a subnet, then Windows cannot determine which card to send traffic out of and it just 'picks' one. Usually the wrong one.

IE Wireless card is IP 192.168.0.1 with Subnet mask 255.255.0.0 and Wired is IP 192.168.1.1 with Subnet mask of 255.255.0.0. Both cards share a subnet.

To fix it; Wireless card is IP 192.168.0.1 with Subnet mask 255.255.255.0 and Wired is IP 192.168.1.1 with Subnet mask of 255.255.255.0. Both cards now are on individual subnets.

MORE INFO:
Wired port is static IP with subnet 255.255.255.248
Wireless port is probably using DHCP

Do you have a gateway set on the static interface?
(reason being, Windows gets confused w/ multiple gateways as well)
You CAN set static routes if you need access outside a subnet and use a gateway for that, it just can't be all-encompassing.

Default Gateway is none on the Static IP for the laptop.
OS is XP

I just went thru this issue with a PC in my lab that I use both a wired and wireless network card. The way I got around this was to set the wired lan to a static I/P address then let it connect to my devices. I then activated my Wireless and let it connect to the internet. As someone else mentioned your system is probably picking the wrong route but once you point the way one time it will remeber.

@ BillRobinson

Dude everyone is making this waaaay tooo Harrrrd.

Go to this link https://secure.logmein.com/ logmein and make a account it is 100% free no strings then just install logmein on the laptop or computers you need access to and they will appear in you're account. You can connect even without anyone on the other side after initial setup.

No need to worry about firewalls,proxys,NAT,WAN,LAn and all that stuff as logmein will even cut through the firewall with no issues because the request is coming from the inside out and not the outside in.


KISS.

Thanks for the KISS, my wife may not appreciate it though.

This IS exactly what I'm trying to do. The problem here is that the remote computer is connected to the internet via a wireless connection.

Very similar to logmein I have always used Team Viewer:
http://www.teamviewer.com/en/index.aspx

While PLC Kid's answer is the simplest I don't think it will work in this case because as soon as you connect the wired connection on the laptop the laptop is trying to route all network traffic through the PLC. So any traffic, including logmein, is rerouted on to the PLCs network and dead-ends there.

You may have to muck through setting up static routes on the laptop. It can be a pain, especially if you're unfamiliar with it.

Let's assume that the laptop has two Ethernet Connections on different subnets.

WiredPort 192.168.1.100 subnet 255.255.255.248
WirelessCard 10.0.2.200 subnet 255.255.255.0

You're trying to connect to My_PC @ 172.0.3.50

You need to tell the laptop where to send the packets when you have two possible paths, cause as icky says Windows has a tendency to always pick the wrong one.

If your wireless and wired ports are indeed on different subnets this should be fairly simple. Open a cmd window with admin privileges and type:

route add 172.0.3.50 mask 255.255.255.255 10.0.2.200

This tells windows to send all traffic destined to 172.0.3.50 (my_PC)to the 10.0.2.200 (wireless) interface. This particular command won't stick through rebooting so it's safe to try, if it doesn't help simply reboot the laptop and you will be right back to where you are.

[edit]I think the above will work if you don't have a gateway specified in either interface. The 10.0.2.200 should be replaced with the address of the gateway for the wireless card. The command should be:

route add [my_PC] mask 255.255.255.255 [wirelessCard's Gateway]

BillRobinson said:

Thanks for the KISS, my wife may not appreciate it though.

This IS exactly what I'm trying to do. The problem here is that the remote computer is connected to the internet via a wireless connection.

Click to expand...

If connected through DHCP, the wireless connection should not be a problem.

If someone local to the laptop can walk up to it get online with the PLC and surf to the internet through wireless at the same time then logmein or teamviewer should work without a problem.

Just last week had someone put teamviewer on their laptop and I was able to take control of it when they were tethered to the internet through a smart phone. We are indeed spoiled

How do you guys handle PLC that's located on private network that's not connected to the Internet?