Serve different types of .efi boot files

[george1421]

@dureal99d Oh man, I spent 4 hours writing that and its still confusing?

Actually it is a hard subject to master.

Basically what you need is a new match test.

I want you to go look at any of the pcaps you took yesterday and in the initial “hello I’m here” (probably frame 1 or 2) from the target computer to the world, look at the options, specifically option #97 and post the answer here.

[Wayne Workman]

@dureal99d It might help to look at this, it’s a collection of george’s posts about dnsmasq basically, but links to other resources as well.

https://wiki.fogproject.org/wiki/index.php?title=ProxyDHCP_with_dnsmasq

[dureal99d]

@george1421 thats weird it says 00000000-0000-0000-0000-000000000000

[george1421]

@dureal99d Well that is a unique pattern too. But I would expect something like 44454c4c45440-038-3610-804ec4-c04f4a5831 the numbers are not important just the uniqueness of the UUID field.

Did that uuid (dhcp option 97) come from a vm or a real computer?

[dureal99d]

@george1421 real computer a Samsung np300e5c

[george1421]

@dureal99d nuts, can you try another?

You can capture this with wireshark on a computer and not have to go the tcpdump route and then copy the file, etc. Any computer on the same subnet as the booting computer can detect these broadcast messages if you are running wireshark.

[dureal99d]

@george1421 said in Serve different types of .efi boot files:

can capture this with wireshark on a computer

sure

[dureal99d]

@george1421 wire shark capture. here ip address 192.168.1.121

[dureal99d]

@george1421 tcdump here of another machine Asus R503U

[george1421]

@dureal99d well on the first one I didn’t see any systems that transmitted their uuid in dhcp option 97. That sux a bit.

You might also want to learn about capture filters in wireshark. They are similar to the capture filters for tcpdump.

‘udp.port == 67 or udp.port == 68 or udp.port == 69 or udp.port == 4011’ this one is equiv to the tcpdump one we were using. Let me look at the ASUS computer.

[dureal99d]

@george1421 said in Serve different types of .efi boot files:

might also want to learn about capture filters in wireshark

for asus 00000011-0000-0000-0000-50465d986f3c / udp.port == 68

[george1421]

@dureal99d The asus one has something we can work with. That dhcp option 97 is ‘00000011-0000-0000-0000-50465d986f3c’

I can tell you if you boot this computer in bios mode (just for this test) you will probably see this listed on the initial pxe boot screen as GUID.

This number should also be visible in the /var/log/syslog or where ever dnsmasq is writing its log. In my testing the value from wireshark did not match up exactly with what was found in the dnsmasq log. You need the value that looks similar from the dnsmasq log. But with that information we can take the next step to create a match test.

[george1421]

@dureal99d said in Serve different types of .efi boot files:

@george1421 said in Serve different types of .efi boot files:

might also want to learn about capture filters in wireshark

for asus 00000011-0000-0000-0000-50465d986f3c / udp.port == 68

Bonus points for you!!

[dureal99d]

@george1421 said in Serve different types of .efi boot files:

You need the value that looks

ok

[george1421]

@dureal99d Which computer needs the special kernel the ASUS or Lenovo?

[dureal99d]

@george1421 they both like that intel1756.efi kernel

[george1421]

@dureal99d Like it enough to make that your default kernel and then the ones that don’t like it you make exceptions for? Use the 80/20 rule what do you have the most of on your campus and then make that your default kernel and the others be the exception.

[dureal99d]

@george1421 I have a lot of mixed clients, a good amount don’t mind the standard ipxe.efi. some are just a bit more diva like these 2

[dureal99d]

@george1421 this is what i see 00:11:00:00:00:00:00:00:00:00:00:50:46:5d...

[dureal99d]

@george1421 the entire readout

Oct 12 12:59:32 dureal99d-Precision-WorkStation-T5400 dnsmasq-dhcp[1280]: 3272245650 available DHCP subnet: 192.168.1.109/255.255.255.0
Oct 12 12:59:32 dureal99d-Precision-WorkStation-T5400 dnsmasq-dhcp[1280]: 3272245650 vendor class: PXEClient:Arch:00007:UNDI:003016
Oct 12 12:59:32 dureal99d-Precision-WorkStation-T5400 dnsmasq-dhcp[1280]: 3272245650 PXE(enp8s0) 50:46:5d:98:6f:3c proxy
Oct 12 12:59:32 dureal99d-Precision-WorkStation-T5400 dnsmasq-dhcp[1280]: 3272245650 tags: BC_UEFI, enp8s0
Oct 12 12:59:32 dureal99d-Precision-WorkStation-T5400 dnsmasq-dhcp[1280]: 3272245650 next server: 192.168.1.109
Oct 12 12:59:32 dureal99d-Precision-WorkStation-T5400 dnsmasq-dhcp[1280]: 3272245650 broadcast response
Oct 12 12:59:32 dureal99d-Precision-WorkStation-T5400 dnsmasq-dhcp[1280]: 3272245650 sent size:  1 option: 53 message-type  2
Oct 12 12:59:32 dureal99d-Precision-WorkStation-T5400 dnsmasq-dhcp[1280]: 3272245650 sent size:  4 option: 54 server-identifier  192.168.1.109
Oct 12 12:59:32 dureal99d-Precision-WorkStation-T5400 dnsmasq-dhcp[1280]: 3272245650 sent size:  9 option: 60 vendor-class  50:58:45:43:6c:69:65:6e:74
Oct 12 12:59:32 dureal99d-Precision-WorkStation-T5400 dnsmasq-dhcp[1280]: 3272245650 sent size: 17 option: 97 client-machine-id  00:11:00:00:00:00:00:00:00:00:00:50:46:5d...```