The NTP client on the PXE follows the NTP RFC so the PXE rejects any NTP servers whose root dispersion is more than one second. An NTP server with a dispersion of more than one second is considered an inaccurate NTP server by the PXE.
Note: For information on NTP RFC, visit http://tools.ietf.org/html/rfc4330 to refer to the section 5.
Windows NTP servers may have a root dispersion of more than one second, and therefore cannot synchronize with the PXE. When the NTP synchronization issue occurs, change the dispersion settings to resolve it.
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\W32Time\Config
Note: Do NOT use 0x08 (Automatic reliable time server) because its dispersion starts at a high value and then gradually decreases to one second or lower.