tWO ETHERNET PORTS, ONLY ONE WORKS AT A TIME

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JPSTECH

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Dec 19, 2012
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Hi,

We have a situation that comes up fairly regularly.
It is in the HVAC industry.
We have a computer, usually running Windows XP (sometimes 7) it connects to the internet via an Ethernet cable (which connects to a switch or more outside of our control) It is normally set up to use DHCP. We also need to connect via an Ethernet cable to a (HVAC) microprocessor/controller that has a (settable) static IP address.
We have a computer ( varies ) with a single Ethernet port to which we have added a second Ethernet port with a pci card (Broadcom BCM5751 Netxtreme Gigabit PCI Express Ethernet Network Adapter Card ). (We are not allowed, by the establishment, to use a hub in this particular location)
If I connect one Ethernet port to the HVAC controller (with IP address 198.168.1.150 and subnet mask 255 255 255 0)and set it to a static IP address (say 198.168.1.151) The program finds and talks to the controller. If I connect the second Ethernet port (with DHCP ) to the network source I can connect to the internet. In fact I can use either one (the original or the added one in either position) for either function . When I go to internet connections ..both ports show connected .. BUT.. I cannot do both at the same time. I need to be able to log on to the computer remotely via the internet and have its program communicate with the controller through the second port. It seems that which ever function I initiate first works the second does not … I have tried reversing the connections and addresses … no help. I also tried enabling DHCP and assigning alternate IP addresses on both ports … this seems to do the same thing but allows me to plug either into either port.
It looks as if when the computer (HVAC program) is communicating with the (HVAC) controller and we try to access the internet the other port only looks at the static address and does not look for anything else beyond that … ie it never finds the internet …at this point I do not know if it could be accessed remotely from the internet.
This is not an area that I am familiar with so reasonably detailed instructions would be much appreciated.
Thank you.
 

TerryNet

Terry
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Not sure I understand your problem exactly.

For the static connection to the HVAC you are leaving the Default Gateway and DNS Server blank, right?

Why are you using 192.168.1.x for the HVAC? Many routers (e.g., Linksys and Netgear by default) use that LAN subnet. Are you sure that you are having your problems when the router in question is using a different subnet?

I would use an unusual subnet for the HVAC to minimize the chance of matching that of a random router--something like 192.168.192.x or 10.20.30.x.
 

JPSTECH

Thread Starter
Joined
Dec 19, 2012
Messages
4
Thank you for the quick reply.

"Not sure I understand your problem exactly." Currently if I connect to the internet first (succesfully) then when the HVAC program looks for the HVAC controller it does not find it. On the other hand, if I start the HVAC program first it finds the controller but then if I try to connect to the internet at the same time the computer cannot find the internet.

"For the static connection to the HVAC you are leaving the Default Gateway and DNS Server blank, right?" Yes.

"Why are you using 192.168.1.x for the HVAC?" This happens to be the units default ... I could use any as long as I match it (close) on the computer ... will try your suggestion on Friday ... perhaps the internet router is using the same one.

Are there limits to what these "something like 192.168.192.x or 10.20.30.x." can be? say 20.30.40.x. or 40.20.20.x. ... I am sorry if it seems like a silly question but this is not my field (obviously). Perhaps I should be asking what range do these numbers have to be in?

Would a different subnet mask help as well?
ie "subnet mask 255 255 255 0" for one and say 250.250.250.0 for the other or some other combination?
Thank you again
Jim
 

TerryNet

Terry
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For simplicity, and to make sure things work, keep the subnet mask 255.255.255.0. That means that on that network all IP addresses have to be the same first three numbers and the fourth is unique for each device.

The simplest private IP addresses to remember are those beginning 10. and those beginning 192.168. Complete list here.
 

JPSTECH

Thread Starter
Joined
Dec 19, 2012
Messages
4
THANK YOU!
Sorry for the delay ... I have been very busy handling problems at various sites .... I finally tried this out and it works great.
Thanks again
 

TerryNet

Terry
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Mar 23, 2005
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You're welcome. :)

You can mark this solved using the
button at the upper left of the page or just below the last post.
 
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