I just noticed that the majority of the machines on my home network started failing with "No Ping Response" back in November. My storage is pretty redundant for most of my network so it took me some time to get around to figuring out the issue. In my case the machine have been faithfully backed up by a linux machine running BackupPC (http://backuppc.sourceforge.net/) going on several years. On November 23rd (between 10 pm and midnight) that all changed. All of my DHCP Windows machines failed with the "no ping response". I knew the machines were up, but why was BackupPC not seeing them -or at least reporting a ping failure.
Turns out this was all caused by a change I had made to my Smoothwall 3.0 firewall. I had removed the Services > Static DNS entries from Smoothwall doing some routine maintenance -I think. I mean why would you have static DNS entries for machines that have their IP addresses dynamically assigned.
Ultimately, I found a solution to keep my Smoothwall DNS and Windows XP machines frequently updated in Smoothwall's DNS hosts file here: without manually putting entries in the smoothwall hosts file (/etc/hosts/ linked to /var/smoothwall/hosts/hosts).
The script runs about every 5 minutes (via a Cron job) and keeps my smoothwall DNS resolving my local Windows machine names when asked. This made BackupPC happy again and makes it easier to navigate from machine to machine on my network using friendly machine NetBIOS names.
Thanks to Nicholas 'Aquarion' Avenell for making my troubles a bit better.