Unable to PXE boot on from different subnet

  • Server
    • FOG Version: 1.4.3
    • OS: 16.04 LTS
    • Service Version:
    • OS: Windows 7, Dell Optiplex 390


    I was wondering if anyone may help with resolving this? I currently have a FOG server running at the school (10.30.x.x), and it is working perfectly under that subnet. When it comes to different different VLANs, some devices can boot with PXE, and some cant. On the subnet that is 10.80.x.x the Dell computer won’t PXE boot, but when I bring the computer physically on this network it boots just fine in PXE. I did run Wireshark between the client and server, and it seems like it just keeps reading the file undionly.kpxe over and over until it times out. The firewalls are off on the FOG server to accept all traffic.



    Any ideas?

  • @Sebastian-Roth Thank you for the reply! Sorry for late response; during the summer months of school people take a lot of vacation during this time.

    I heard back from the technician over there, and she sent over screen shots, and here there are provided below.

    HP 7800 Error Screen
    alt text

    Dell Optiplex 390 Error Screen
    alt text

  • Developer

    I feel like there are some parts of the picture still missing. So first I shall mention that the packet size is not playing a role here as far as I can see. The figure 558 is just the size of the full packet (TFTP plus headers for UDP, IP and ethernet/MAC). In the TFTP RFC (page 6) it says:

    The data field is from zero to 512 bytes long.

    So this is perfectly fine I reckon.

    Second: The first transfer finishing and another one just starting right after it in the second picture of the initial post looks strange at first but there is a major time gap between those two so I think this is because it’s trying again after a reboot.

    @Defcon I am still missing the actual error here. The text you posted (ending with “Installation failed cannot continue”) seems to be copied from wireshark and is probably just the readable strings within the transfered iPXE binary. Could you please describe exactly what you see when things go wrong. Take a picture or even video of a failed PXE boot!

  • Moderator

    @Defcon ok lets focus on just a single computer on a single subnet that doesn’t pxe boot. Once that is identified, I would like to take a (dumb) unmanaged switch and place it between the building computer and the pxe booting computer to see if that ‘masks’ the issue.

  • @george1421 Hey George, apologizes on the long response. I wanted to get more information regarding this, but the employee was gone on vacation.

    The school is actually a direct connect, no VPN etc. Apparently we own that fiber as well. Regarding the random PC’s that boot, so far it’s only the GX520 desktop that’s able to boot into PXE. All of the schools that are connected to the main district are direct connect (something new I learned). Do you think this may be a switch issue?

  • Moderator

    @Defcon So just to confirm at that remote location random pc’s will pxe boot?

    How is that remote location connected to the main location? What technology is being used (mpls, dsl, vpn over internet, etc.)

  • @george1421 It’s at a remote location, and the PXE booting is random for sure. The ones that work at the moment are the Dell Optiplex GX520 desktops. I tested out the PXE at high school and the packet size is 1503. The 1503 packet size is what I am pulling here as well, where the server is at. Yikes…

  • Moderator

    @Defcon As I pointed out earlier, I find it strange that your packet size is 558. Is that consistent across your entire network or just the subnets in question?

    The case of 10.80.x.x, is that vlan connected at GbE speeds or is that vlan at a remote location (off-campus)?

    Is it correct to say every computer on that vlan can’t pxe boot or is it random?

  • @george1421 Yep, you’re right. No luck haha! Any other thoughts?

  • Moderator

    @Defcon I don’t think that is your problem here, but by all means test it out. If it fixes it I will have learned something today.

  • George,

    Don’t know why it didn’t show up earlier, but here’s the code below. I did snoop through the forums and found this and tried to change the bootfile to ipxe.kpxe instead of undionly.kpxe. Still no luck with connecting.


    PXEEBG PXENV at  PXE at  No PXE stack found
     entry point at 
             UNDI code segment  data segment  kB
             UNDI device is PCI          Unable to determine UNDI physical device type  workaround enabled         kB free base memory after PXE unload
             UNDI API call  failed status code 
    XP XPtXffP
    iXPXfQgfYfQP1gXfYfPfUfhfhfh0    jfh    jfjjffffnff
    ffFhfV  fVf ffXfQSbrffTfffffYjdPPdXfVfWfUf1f1fffffff1fQfWfVf1ffVfffffSBfYfffhsPh4hPh0fuffffffffffPfufff
    Installation failed  cannot continue```

  • Thank you for the reply! There is no firewall between the two subnets (that I know of) and it’s connected through a VLAN.

    Here’s the filtered file here of the wireshark capture.

  • Moderator

    We’re missing the preamble on this tftp dialog, but I find its strange that your block size is 558 bytes, I might expect something around 1,500 bytes. How is this subnet connected to your HQ subnet (where the fog server is located)?

  • Moderator

    I’m still trying to digest the pcap file at this moment.

    But I have to ask

    1. There are no network firewalls between the two subnets?
      I have to say
    2. I know there are some flaky pxe boot firmware that will only pxe boot from the local subnet.

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