DHCP, Skype for Business

Calculating DHCP Hex for time Offset

DHCP Option 2 (Time Offset) is a pain in the butt.  I always have to re-invent the wheel because I always forget how to do it, so now I will write it down.  I need this information for provision desk phones in Skype for Business, well actually any kind of phone.

  1. Open Calc (or any calculator that can convert Decimal to Hex)
  2. Switch the Programmer view (if using Windows Calc)
  3. Calculate the hours offset.  This is done by taking the GMT offset *60 *60.  So for example Pacific Standard Time is -8 *60 *60 = -28800
  4. Then convert that to hex which will return this for the above example: FFFF FFFF FFFF 8F80
  5. What you care about is the last 8 characters: FFFF8F80
  6. You would then add a 0x before that, and that is your Hex Value so it would not be 0xFFFF8F80.

If you where in PST +8 hours you would have the following

8*60*60=2800

In hex that is 7080, so here your DHCP value would be 0x7080

So negative time zones will always have FFFF while Positive Time Zones will not.

 

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