As you may already know, Hyper-V does not allow you to connect physical COM ports to child virtual machines. This poses a problem for many people who want to virtualize servers with legacy devices connected via RS-232. There are different hardware and/or software solutions available, but ultimately they all require that you make your COM ports available over a network connection. Your main options are to share/redirect a COM port from a physical machine to a virtual machine, or to use a hardware adapter to connect the RS-232 device directly to the network.
For our legacy application, I chose to go with a hardware adapter. We purchased the StarTech 1 Port RS-232/422/485 Serial over IP adapter. I was very eager to get this adapter because it would allow us to virtualize an old server that was still relying on a directly connected serial device. I chose to go with an adapter so we could have flexibility and not need to rely on a single server to do some sort of sharing or redirecting of a COM port.
After we received the adapter I was a little disappointed. The documentation was sparse, and I could not get the virtual COM port software to work. The virtual COM port driver is what connects to the adapter on the network and allows the application to continue to interact with the RS-232 device as if it were still connected locally. Unfortunately, the virtual COM port drivers included with the StarTech device were very outdated and would not even run on Windows Server 2003. 
Although I was a little discouraged, I didn't give up hope just yet! After some research, I found a very similar adapter that StarTech was selling - the NETRS2321POE. It seemed to be the same exact adapter, just with Power Over Ethernet. After examining the (much better) manual for this device, I came to realize it was the same basic hardware/firmware as the device that I had. When I checked the driver download, I saw there was a newer virtual COM driver! Success! This new driver installs and works fine with my NETRS2321E. The download even has Vista drivers included, so it likely works on Windows Server 2008 as well. Our old server is now able to be virtualized!
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Add CommentDec 03, 2010
Alex
Jonathan, thanks for your post, I'm glad I found it.
"As you may already know, Hyper-V does not allow you to connect physical COM ports to child virtual machines".
You can connect COM port to the virtual machine (as well as to any machine on your network) using Fabulatech's "Network Serial Port Kit".
www.fabulatech.com
They also have the similar tool for connecting USB port ("USB over Network"). I hope other people find it useful.
Dec 03, 2010
Jonathan Briggs [SoftArtisans]
Alex,
That statement was meant to highlight the fact that you can't connect a COM port (from the physical host hardware) directly to a Hyper-V virtual machine. Hyper-V doesn't provide any mechanism for doing it, so you're forced to use a 3rd party network based solution. The Fabulatech offering you reference is just another of several options available on the market for doing this. My main motivation for the original blog post was to help others who may have issues finding the right driver for the StarTech hardware.
-Jon
Apr 18, 2011
Anonymous
Jon - this article made my week!
I've been struggling with the NETRS2321E drivers for a while... the POE version drivers are a breeze in comparison!
This helps me virtualize the last two systems I have! :D
Alex - the product you're recommending doesn't solve the issue Jon & I appear to want to solve. Fabulatech's product shares serial ports between computers - StarTech's makes a serial port from a device such as an electric meter accessible on the network.
-Shawn