Start of new semester at the U… it seems everyone came back with more WiFi gadgets than ever, and wants them all on the network AT ONCE. So, our /20 network (4096 addresses) we already planned to supplant with another /22 (1024) but those both filled-up on day one. Drop the 1 hour DHCP lease to 30 minutes! Hey, that’s not helping!
Windows 2003 had a registry entry for “LeaseExtension” (HKLM\System\CurrentControlSet\Services\DHCPServer\ Parameters\LeaseExtension) that defaulted to FOUR (as in ONE-TWO-THREE-HOLY HECK WHEN CAN WE REUSE THIS IP-FOUR) hours. In addition, the CleanupInterval is 60 minutes (unless the scope is FULL – old/unused IPs are only cleaned once an hour). So… 30 minutes + 4 HOURS + up to 60 more minutes = 5.5 hours a client uses our Windows 2008R2 DHCP server’s address.
Drop LeaseExtension down, drop down the CleanupInterval – things are more sane (until we finish a re-IP project and take over a second and maybe third /20 for central-campus WiFi).
Thanks goes out to Mike Perth for the first+best Google answer to our issue.