Ubuntu – System loses static IP address


One of my headless systems is assigned a static IP address through /etc/network/interfaces on a wired Ethernet. It is connected to a router which is also a DHCP server. After a couple of days, the static address is dropped and replaced by a DHCP address. Why would that be?

  • If I do a sudo ifdown eth0 && sudo ifup eth0 or sudo service networking restart or a reboot, the
    system takes on its static address again, but then a couple of days
    later, the IP address changes to a dynamic one.
  • There is no other
    system on the network with (accidentally) the same static address.
  • NetworkManager is not running on the system.
  • I have set up the system to email me as soon as the address changes, but the times at which that occurs seem completely random. DHCP Lease time is 24h but that doesn't seem to
    correlate, and anyway that shouldn't matter for a static address.
  • My /etc/network/interfaces is this:
    auto lo
    iface lo inet loopback
    auto eth0
    iface eth0 inet static

It's a bit of a puzzle.

What would cause a system to give up its static address and request a DHCP address instead? What to look for, in which log file?

Best Answer

Recently I stumbled on this problem and after some investigation it turned out that /etc/dhcp/dhcp.conf needed a block to be added, (or uncommented,) similar to this:

alias {   interface "eth0";   
option subnet-mask; }

Hope this helps!

Regards, Glendon Gross

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