So, I discovered a weird issue tonight with Windows Server 2003 DHCP Services, and thus far, haven’t found it documented – but was able to reproduce it and did discover the cause. So being that is what blogging is all about in the tech community, sharing knowledge, I’m going to:

Issue

• When Windows Server 2003 DHCP Services restart (stop/start) or the equivalent (a reboot), the Router value (your Default Gateway), which is Code ‘003’, goes ‘missing’ (gone, deleted, nada, zilch, kapoot – you can put it back, but it will be gone again next time … neat!)
  • Thus, the end user result is users can’t surf the Internet – they can resolve DNS (those DHCP Values remain) but they can’t get ‘out’ – no gateway, no place to go besides the local LAN

The Cause

• Well, for starter’s this shouldn’t really be able to happen but the cause is an invalid ‘reservation’ defined in DHCP. If you create a reservation and forget to complete the final octet, it will keep the zero (“0”) which indicates the whole subnet – this shouldn’t be a valid reservation, but Windows will let you do it. For example, a reservation created of 192.168.25.0 (the zero, shouldn’t be a reservation, it should be anything from .1 to .254)

The Fix

• Well, for starters, avoidance is the key. Don’t create reservations incorrectly (.0)
• However, if your router is ‘bailing’ on you, be sure you delete the reservation, then restart the DHCP Service and then put your router value back, just one last time