Puzzled

Here is a scenario I encountered and couldn't figure it out.



During almost half a day all client machine lost web access during check up
I noticed server running DNS/AD can't get out web as well.

Diagnose:

A) Checked DNS log and run DCDiag which show no error and working well.

B) Checked network cable and replaced with another one.

C) I was able to ping another host internally but not external addresses
so hardware does not appear to be an issue still updated NIC driver to make
sure it may not be software related.

D) Plugged my laptop to switch and router to make sure if the ISP or
component may be down, which appears to be blazing fast.

E) Upon assigning another address to the DNS server. BANG the server
start working and I can ping internal/external host.



No matter what I did it will work on any IP address except the initial
10.X.X.3 which was assign from the first place and functioning as an DNS
server in the past. Finally I gave up and deleted DNS zone and created new
one sticking with new IP Address of 10.X.X.4.



Any clue what might have caused this? Has any one face this?