FOG IP Address Change -- PxE Problems

[tlems]

@sebastian-roth Work has slowed down a bit so I can fiddle with the FOG server again. I changed the IP’s in the Scope Options to the correct address but it still will not PxE boot. I have ipxe.efi for the filename and Bootfile name. Can you think of anything else that I am missing?

[george1421]

@tlems Do you have a third computer where you can load wireshark on it. The computer needs to be connected to the same IP subnet as the pxe booting computer. In wireshark you want to setup a capture filter of port 67 or port 68 Start wireshark then immediately pxe boot the target computer. When you get the error on the target computer stop wireshark capture.

In the capture you will see a discover packet from the target computer and one or more offer packets for each dhcp server that hears the discover.

Notable things in the discover is dhcp option 93 or 94 (can’t remember at the moment) will be the target computer saying what it is, 0 for bios and 7 or 9 for uefi.

In the offer from the dhcp server(s). In the ethernet header there will be {next-server} and {boot-file} for a uefi system the {boot-file} should be ipxe.efi and for [next-server} it should be the IP address of your fog server. If you look into the dhcp options 66 should be ip address of fog server and 67 the same as the {next-server} field. If they both look right confirm that dhcp option 60 is not being set (option should be absent in the offer).

If you can’t figure out the pcap then upload it to a file share site like google and either IM me or Sebastian the link or just post the link here and we will take a look at the pcap to see what we can see. The capture filter I mentioned above will only capture the dhcp process and no other data.

[tlems]

@george1421 I’ll have to get this to you tomorrow as I’m currently home. I’ll PXE boot a machine and see what Wireshark brings up. Thanks!

[Sebastian Roth]

@tlems said in FOG IP Address Change -- PxE Problems:

I changed the IP’s in the Scope Options to the correct address but it still will not PxE boot.

Need more information. Error message on screen? Please post a picture.

[tlems]

@george1421 So our FOG server is on a Hyper-V on CentOS within our Server Subnet. Then we have our Client subnet which is all of our associates machines. You want me to put this third computer within our server subnet and do a wireshark packet capture or on the Client network and do a packet capture?

[george1421]

@tlems That would be on the client subnet. We need to see what the dhcp server(s) are telling the target computer. Since dhcp relies on broadcast messages we should be able to see the discover, offer, request, and ack packets. Now I do have to say I’ve seen some dhcp-relay services that switch over to unicast messaging on the client end. In this case we will only see the discover and request packets. But lets not go down that path just yet.

[tlems]

@sebastian-roth The error message is the same as before that I posted earlier.
https://i.imgur.com/LrkYp1d.png

[george1421]

@tlems said in FOG IP Address Change -- PxE Problems:

I posted earlier.

Just for reference, that screen shot is of a bios computer pxe booting. We are still down to understanding what the dhcp server is telling the pxe booting computer. The dhcp server is either telling the computer the wrong pxe boot address or boot file name. Its being told something because the error message says it can’t open the file and not, nothing was given.

[tlems]

@george1421 I did a filter for both 67 and 68 and I didn’t get anything back (tcp.port eq 67) and I also did a search for the PxE booting machine’s ip address (ip.addr eq 10.0.2.217 and also did source ip.src eq 10.0.2.217 to see if I saw anything from this machine) and nothing matched my results in Wireshark. The ip address of the third machine I was using is 10.0.2.90 so they’re on the same subnet.

[george1421]

@tlems the exact capture filter is “port 67 or port 68” if you captured everything then use a display filter of “bootp”. If you have one of us look at it be sure to use the capture filter so we don’t see things we shouldn’t in your capture.

[tlems]

@george1421 Whoops, my bad. I got the capture filter set this time instead of doing a display filter. Also, when I sent the picture earlier I was replying back to Sebastian Roth’s comment. What’s the best way to send you the pcap file? I’m unable to upload it here.

[george1421]

@tlems via a file share site like google drive or such. Just make sure you share it as public with the link. You can either chat me the link or post it here. Once we review the pcap you can take down the pcap. That way you have control of where and when its shared.

[Sebastian Roth]

@tlems From what I see this is not a “we have changed IP” issue but simply the server is in a different subnet now and hosts need to communicate across subnets via router/gateway. This router has to allow TFTP traffic. Talk to your network people.

And while you have them on the line you might also mention NFS, maybe also multicasting. Using FOG across subnets can be really tricky.

[george1421]

@sebastian-roth The OP has some things inconsistent in his dhcp settings. I’m working with him on chat. Its not currently a fog server issue.

[tlems]

Thank you both for your help! George and I were messaging back and forth and my DHCP policies and scopes were pretty messed up. Looking back I have no idea how it worked before. After completely changing them the machines are booting into FOG again just fine. Appreciate the quick responses!