How to set the time server with a DHCP server

  1. Install a DHCP server. See Step 3 Method 2. The following instructions assume you are using DHCPsrv.exe, but you can adapt them to whatever DHCP server you are using.
  2. Add the following lines to the [General] section of dhcpsrv.ini:

    OPTION_2=FF:FF:AB:A0 ;

    OPTION_42= ;

  3. Explanation of these two entries

    • Option 2 is the DHCP field for time offset, specified in RFC 2132. FF:FF:AB:A0 is a hexadecimal representation of the time offset in minutes of the local time from UTC. For US Central Standard Time the offset is -6 hours. I converted this to hexadecimal using Google. I typed into the search field:

      2^32-6*60*60 in hex

      the 2^32 is to get it to 32 bit twos complement representation, the 6 is the 6 hours, and the 60*60 gets us the number of seconds in an hour. Google came back with

      (2^32) – (6 * 60 * 60) = 0xFFFFABA0

      Note that putting OPTION_02 doesn’t work in DHCPsrv.exe; it has to be OPTION_2.

    • Option 42 is the DHCP field for the Network Time Protocol (NTP) server, specified in RFC 2132. is the address that comes back when you ping
  4. Save the updated dhcpsrv.ini, and restart DHCPsrv.exe.
  5. Unplug the phone power cord and plug it in again. The screen says Welcome, 12 seconds to reboot.
  6. A couple of minutes later the phone screen says Welcome, then with any luck shows the right date and time.

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