Clients getting auto ip



  • Hello

    I have fog 1.20 on a ubuntu 14.04 server . My organization provides a dhcp server with static ip for every mac. So I only provide the tftpd server to the clients. I have the default installation for this on the server. The clients are using the official published kernel 3.19.3 Tom Elliot usb x86 x64.
    My problem is:
    “Sometimes” a client gets an IP by himself using the one owned by other computer. In my organization this is a “big crime”. The reason (I think)for this can be in the client kernel but I don’t know sure .
    My network administrator send me messages like:

    The computer client.xxx.xxx.xxx with the mac xx:xx:xx:xx:xx:xx and the IP xxx.xxx.xxx.xxx is using the IP address yyy.yyy.yyy.yyy owned by veryimportantpc.yyy.yyy.yyy and the mac yy:yy:yy:yy:yy:yy

    But most of the time everything works fine. I receive two or three messages a day…

    Is there a easy solution for this?


  • Moderator

    @salginer Not a problem at all. When this happens - 99% of the time it’s due to dual DHCP or Rogue DHCP setup. That’s why I asked this first. Glad you got it going! :-)



  • Sorry to all

    The clients get the IP from the isc-dhcpd-server on the fog server . I don’t know why was this service running. Removing that software solved the problem.


  • Moderator

    @salginer said:

    Is possible that some of the clients kernel linux are using avahi or something similar to get the IP?

    I suppose it’s possible if you don’t have Bonjour or the Avahi daemon disabled. I really doubt it though. If you were to disable those, you’d probably have a few Apple users become upset that they can’t move content easily from one device to another anymore, and that printers no longer just “appear” for them on their iPads and other devices.

    I’d lean more towards something being goofed with the DHCP setup. Three DHCP servers all reading the database? How do leases work? Are you sure every computer has a unique MAC assigned, a unique IP, and that there are no duplicates? I’d also closely examine each of the three DHCP servers to ensure they were configured properly. Is the lease time set the same across all three? Perhaps there were reservations made for some reason on one of the DHCP servers themselves? Just look around, I’m almost sure you’ll find the issue lies somewhere with DHCP.

    Also - quite simply allowing Wireshark to run with a DCHP filter would capture all DHCP broadcast requests and responses. It’d be really easy to see if there was a rogue DHCP that way.



  • We have three dhcp servers. They have different clients over the network . All them provide a static IP to a given MAC. Our macs are stored on a shared database. We have a monitored network so we think we don’t have rogue DHCP servers.
    We have a suspect. Is possible that some of the clients kernel linux are using avahi or something similar to get the IP?


  • Moderator

    Do you have two DHCP servers or dual-DHCP servers or redundant DHCP servers in your environment?

    How hard have you checked for a rogue DHCP?


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