Monday, 30 September 2013

Windows 7 DHCP Inform/Discover packet HLen=0

Windows 7 DHCP Inform/Discover packet HLen=0

After introducing a Windows 7 machine onto my network, my DHCP server
began to complain about receiving DHCP packets with an invalid mac length.
It did not take very long to figure out that once Windows 7 got it's DHCP
address, it would start to look for NTP servers or other time servers
using DHCP inform/discover packets where the hardware address length was
set to zero. For the most part this is just noise in the logs, but I'm
looking to avoid having anyone above me claiming the end is nigh when they
browse the logs.
So far my Google-fu has failed me and I have been unable to find anything
stating that this is expected, seen elsewhere or how to deal with it on
the client side. It would not be hard to handle these specific packets
differently on the server side without loosing logging for packets that
are actually broken, but I would like a little more information about
what/why Windows is doing what it's doing.
Help is greatly appreciated.

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