Asking tftp server

[btoffolon]

Hi,
When computer start on PXE i have the messager tftp server :
you can see it on this video here

if i put my ip address there is this message.

I don’t have two dhcp the fog dhcp is disable :

root@FOG:/tftpboot# service isc-dhcp-server status
● isc-dhcp-server.service - LSB: DHCP server
   Loaded: loaded (/etc/init.d/isc-dhcp-server; generated)
   Active: inactive (dead)
     Docs: man:systemd-sysv-generator(8)

i use windows DHCP win option 66 (ip of my fog) and 67 undionly.kpxe

if y try to get my file in tftp from a client connect to the same network that’s work.

any idea ?

[george1421]

@btoffolon Well there are a few things we need to unpack here.

1. Is your fog server’s IP address 10.255.41.42?
2. Is the fog server and target computer on the same subnet?
3. The target computer is asking for tftp server address because its not being given an IP address by dhcp server. This can happen because of misconfiguration in dhcp server, or a second/possibly rogue dhcp server.

My intuition is telling me that you have a second (possibly unknown or rouge) dhcp server on the target computer subnet. We can find the answer pretty quickly. Take a witness (third computer we will use for testing) and load wireshark on it. Use this exact capture filter port 67 or port 68. Plug that computer into the same subnet as the target computer. Start scanning then pxe boot the target computer until you get the error. Now stop the wireshark scanner.

In the center panel you will see the captured packets. You should see a DISCOVER packet sent by your target computer then one or more OFFER packets sent by every dhcp server that heard the DISCOVER packets. Look into these OFFER packets to ensure they are sent by known and valid dhcp servers.

If there is only one OFFER packet from a known dhcp server (then I was wrong). In that OFFER packet look at the header section for {next-server} and {boot-file} those should match dhcp option 66 and 67 respectively. Also in the same dhcp OFFER packet down below the ethernet header should be the dhcp options section, make sure that options 66 and 67 are set correctly. Your answers will be in the wireshark capture.

If you can not find the issue and want one of us to look at it for you, post the file to a file share site with world read access. Once we look at it you can take down the file. You can either post the link here or DM me via the FOG Forum with the link.

[btoffolon]

@george1421
Hi, thanks fo your answer.
So, yes my fog server’s IP adress is 10.255.41.42/8 and the computers are on the same subnet in 1.0.0.0/8. my DHCP server is in 10.255.41.45.

So let’s go for fun ! x) i will launch wireshark and tell you the news but i will be able to do that tomorrow because this network is on an other building (i work on differents places and they are not link). thanks again for your help and i let you know the next information soon.

[btoffolon]

@george1421 Hi,
So, you were right, i have dhcp offer from an adress ip (10.139.178.1) the ip adress doesn’t tell me anything, i have fix all my ip adress on my tru DHCP so i will investigate. Thanks for your help