Sudden problem with LAN access to some of the net

[Bob Chiodini]

On Thu, 2005-09-29 at 08:53 -0400, Claude Jones wrote:
> This problem has so stumped me I don't know if I can fairly describe it, but I 
> post what I can here to see if it strikes a chord with anyone else. My 
> scenario is an FC4 machine that is right on the net - I use this as my home 
> machine and it is mostly for experimentation and email. I use FWBuilder to 
> protect it. It serves as dhcp server to several pc's in my home all running 
> Windows. All has been working well for months. Two nights ago, I was trying 
> to get bittorrent to work and was experimenting with opening various ports. 
> That same night I did some updates. That's a poor description, I realize, but 
> it is just to set the stage. The next morning, two of the pc's on my Lan had 
> lost some of their connectivity. My wife's laptop, for example, couldn't get 
> email or run messenger - just returned 'couldn't connect' messages. However, 
> she could still browse websites. Similar problems with a second pc that I 
> don't have much access to, so I can't be specific but, he couldn't get mail. 
> Two other pc's continued to function normally. I fired up an old laptop I 
> keep here for testing, and it connected and all functions worked. 
> 
> So -- dhcp is working - the problem machines are getting valid addresses - 
> they continue to have some functionality
> I suspect an issue with DNS - I had set up a DNS server on my FC4 box months 
> ago, and it has been working well - dhcp gives out 127.0.0.1 as the dns 
> server to the lan machines - what I did to fix the problem was to change that 
> entry in dhcp to my isp's DNS server - presto, things started working...
> 
> So, any ideas on what I could have broken with my DNS configuration? 
> -- 
> Claude Jones
> Bluemont, VA, USA
> 

Claude,

127.0.0.1 is the IP address the lo device on all machines in your net.
This may be some kind of special case, but I think your DHCP server
should hand out the real LAN address of your DNS server, something like
192.168.x.y.  Why it worked up until recently I don't know.

Bob...