Computer does not see DHCP on PXE-Boot, but it does with Windows running

[Tywyn]

Hi there,

I have a strange behaviour here trying to register some hosts.

• Assume I have Room1 and Room2 and ComputerA is in Room1.
  Trying to pxe-boot fails, because ComputerA in Room1 does not see the dhcp-server. I also do not see the MAC-Adress in the /var/log/daemon.log.
• Taking ComputerA to Room2, PXE works fine, registration also and also dhcp-log shows ComputerA.
• Taking ComputerA back to Room1: PXE-Boot still fails, but when I start Windows and configure network to use dhcp I immediately get an ip-address from the dhcp.

Same Computer on PXE boot gets an IP in Room2, but not in Room1 but it gets an ip via dhcp when windows is running in Room1.

Any ideas?

Thanx in advance
Rainer

[Wayne Workman]

@george1421 I’ve had this problem before, it was a port-fast issue on a particular switch. It could also be a vlan issue, but I think that’s less likely.

@Tywyn in the room where it doesn’t work right, put a mini-switch (a dumb switch) between the building and the computer and see if that works.

[george1421]

Let me see if I understand the truth table here.

Computer A in room 1 = no pxe boot
Computer A in room 2 = pxe boot and imaging.
Computer A back in room 1 = Windows boot + dhcp.

OK So I would have to ask this.

1. When computer A is in room 2 what is the dhcp address (specifically)?
2. When computer A is in room 1 what is the dhcp address (when booted in windows)
3. Do each rooms have their own subnet or does your whole building have the same subnet?
4. Is there a router in the mix some place between the FOG server and these two classrooms?
5. Is the dhcp server for your network a windows dhcp server or linux?

[Wayne Workman]

@george1421 I’ve had this problem before, it was a port-fast issue on a particular switch. It could also be a vlan issue, but I think that’s less likely.

@Tywyn in the room where it doesn’t work right, put a mini-switch (a dumb switch) between the building and the computer and see if that works.

[Tywyn]

@Wayne-Workman, @george1421 Thank you, gentlemen. It was indeed a portfast issue. Enabling portfast on the specific switches solved the problem.
Btw: Your hint to put a dump hub/switch between client and network dose did solve the problem as well.

[george1421]

@tywyn said in Computer does not see DHCP on PXE-Boot, but it does with Windows running:

Your hint to put a dump hub/switch between client and network dose did solve the problem as well.

FWIW: This is a quick test we can use to see if standard spanning tree is the issue. The dumb switch will keep the building switch from transitioning during the boot of FOS.