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File This Under Weird - PXE Stops TFTP Transmission When Display Is Disconnected

I am bringing a PXE server online (Symantec Ghost Solution Suite 3.1 Build 502) using the integrated Altiris PXE Server software.

Once I had everything up and running (hats off to Symantec to their "thorough" documentation) I was very disappointed with the transfer speeds (getting ~100-200 Kbps) to get the PE files downloaded onto the client and boot into a Windows environment.

A little bit of searching revealed "Double Your PXE Boot Speed!" written by a Symantec Employee, advising to not use Altiris PXE MTFTP Server, and instead replace it with OpenTFTP (gotta love it!).

Once I had the necessary configs down, I was able to pull down 20 Mbps! I was so excited that I went ahead and switched over to the other PC I had on my KVM and got that guy going to. This is where the weirdness started.

When I switched back to the original PC, I found that the transfer had again slowed to a crawl (forehead meet desk). And worse, when I checked on the second PC, it too went to a crawl.  I checked around the forums and everything pointed to adjusting the block size. First I went big as suggested here (, then started going small as I kept having issues with the speeds cutting out whenever I switched over to the second PC and got that going.

Now some of you might be thinking "Its the network!" Well that was where I was going, but had no desire to go down that rabbit hole. So I took a beat and said to my self, what exactly is happening here? 

1. Start PXE Boot on PC 1
2. Verify Speed on Server as 20+
3. KVM to PC 2
4. Start PXE Boot on PC 2
5. Verify Speed on Server and see in history that PC 1 dropped off

That's when I realized that it had nothing to do with turning on PC 2!

For those who do not follow, start on 1, see speed, switch to PC 2, see speed cut out. 

It was the switching of inputs/outputs!!!!!
(Audible whack of forehead into closest wall)

Sure enough, I can reliably get the transfer to slow to a crawl by removing the display port cable on the rear of the PC (USB does not seem to affect it)

What I am working with:
Dell Optiplex 3040 Micro with a Realtek PCI-E Gigabit Ethernet Controller (Driver on dell website has file name Network_Driver_9YMJF_WN64_2.43.2015.709_A00.EXE)

Does anyone have an idea as to how I can switch displays without killing the downloads???

Additional troubleshooting:

  • Tested the PXE load in with the Symantec-provided Linux PE.  Same results when DP is unplugged.  
  • Using the HDMI port (only display outs are 1 DP and 1 HDMI). Same results with the HDMI 😞

Maybe this is a firmware / UEFI issue? It seems like a really weird presentation though, especially since they are two different manufacturers (Realtek - Ethernet, Intel - On Board Video)

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RE: File This Under Weird - PXE Stops TFTP Transmission When Display Is Disconnected

When you switch over using the KVM or when you disconnect the DP cable, you're essentially running one PC "headless", eg with no monitor connected. So I wonder if that's part of this problem...?

Maybe you need to connect a "headless HDMI dongle" to one video output on each system, in addition to the KVM, so neither PC is ever totally headless.

NOTE: This is just a wild guess on my part. I don't know what will happen if you have both a monitor (via KVM) and a headless dongle connected to the same PC. I wouldn't expect it to do any harm, but what the heck do I know? So proceed with caution and at your own risk. emoticon.Wink.title


   Forum Member since 2004
   I am not a Dell employee

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