do not respond to DHCPINFORM requests

[Steven Carr]

I believe this is caused by the browser persistently asking for a
proxy server configuration.

You can silence this behaviour by sending back a "poison pill"
response to the DHCP client... configure the wpad variable and
configure the value to send back. I've implemented this for a couple
of clients who were getting 10's of thousands of DHCPINFORM requests a
day from Windows 7 systems.

option wpad code 252 = text;
option wpad "\n\000";