I have a Linux webserver host that has been fine for more than a year. No changes to the network configuration have been made since October, 2008 when a 2nd network card was added. I have also been able to ftp and ssh to/from this host from Internet located hosts. Suddenly yesterday, no web or Internet access to the host.

The linux host is on an office LAN with a Windows Office server connected via a separate lan card on the linux host. All LAN access works fine. I can get to the linux hosted web pages, log in, etc.

I can get out to Internet hosts FROM the local linux webserver. I can send mail, I can ftp, I can ssh; but I can't get to this machine from the Internet.

The whole building also has a Cisco router administered by a hired management group. Both the LAN administrator and the building net administrator say they haven't got a clue, so it is up to me, lowly webmaster, to figure what is going on.

Even though I can't ssh or ftp to this machine, a nslookup returns the correct IP. I can ping this host by domain name. What should I do do figure out the problem? traceroute? netstat? I'n no net guru.

Well, neither am I, but let's give this a shot. What are you using, apache? if that's your case, look at your ports.conf in /etc/apache2. Post that information. Is it possible that the ISP or the other net/router admins decided to block what port the server was listening on? You could try to change the port to something else (say, if its port 80, change it to 81) then restart your server

(depending on which distro)
/etc/init.d/apache2 force-reload
or
/etc/rc.d/init.d/apache2 force-reload

(conversely you could stop then restart it.)

Oh, and then try to get to the webpage like this:

www.blibbityblah.com:81

I found the problem! We actually powered down the linux host, but were still able to ping the IP and domain. That told me that someone else was using the same IP address as our host. We has the building lan administrator track down the router port and found the culprit. Some other tenant in the building had simply usurped our IP address. So, there were two hosts with the same IP. We disconnected the usurper and voila! back in action.