Windows

I would start with just PINGing some remote sites constantly, to see if you get dropped packets during these blackout times. That is probably what the problem is, a loss of connectivity, not a DNS issue.
Now, you can't PING www.microsoft.com or www.hotmail.com, 'cause they suppress ICMP packets.
But www.symantec.com does allow you to PING it. How nice of them!
You can also PING www.yahoo.com as a control path.
So, I would fire up 2 Command Prompt windows, and run this one one:
PING -t WWW.SYMANTEC.COM

and in the other:
PING -t WWW.YAHOO.COM

Yes, the -t switch IS case-sensitive; it must be in lower case.

Anyway the -t switch will keep a constant PING going; it won't stop PINGing. Just let them keep going.
Then browse the Symantec website (and the others that drop on you) and keep an eye on the PINGs. When the websites stop registering, look at the PINGs and see if they are stopping/slowing or if the PINGs just stop. If so, then you could take that to your ISP, and tell them when the drops happened, and to where, and from where.

You could also, if you get drops in the PINGs, do a TRACERT to the domains and see at what point the drops happen. That would also be good to send to your ISP.

hope this helps

The problem kind of fixed itself this morning. I'm still monitoring it and so far so good. I also called my ISP this morning to report the problem to them and they are monitoring it on their end too.

But I'm really interested in what caused this to happened. Is it something on our end or the ISP end?

Joseph Moore - Thanks for walking me through the trouble shooting steps, I really appreciated it. You will get the points, I'm still hoping if you or someone can provide me with the probable cause of this problem. Thanks again!

It sounds as though your bandwidth is being over driven. This could be from many different sources. To isolate you need to look at your router logs and see how much info is being passed. It will show what is passing on a 5 minute average. Also you can work with your provider. Most providers can tell you how much bandwidth you are using. If you are over driving the circuit and you will need to determine if you need more bandwidth or id the problem is on the network. If you do not have software to monitor the network try islolating it to a subnet by disconnecting subnets one at a time and see if the problem goes away. If you can isolate it to a subnet scan for virus's if none found try shutting down the work stations one at a time. If you have a large network ( which it doesn't seem you do becuase you have one t-1 line ) this would be a rough way to go but on small networks it is possible to isloate the culprit doing harm. If you narrow it down to a pc and find no virus's check the NIC and connections. It would help to know more about how your network is setup and how large.

EZmoney - Our network is a pretty small network of about 40 stations and 5 servers, all running on Windows 2000. I will certainly use your suggestions the next time the problem arise.

You mentioned software to monitor network, what do you recommend I use to help me monitor and troubleshoot network problems? Thanks!

The cause is really difficult to determine without lots and lots of extra information - most of which would have to have been found at the time of failure.

I would expect that if you're losing access only to certain sites that one of the border routers at the ISP was playing up.

For that I would look into whether or not remote DNS is still returning the correct information.

Then there are a number of programs like WinMTR which would allow me to perform a recursive trace route / ping to the site and show me exactly where the failure is occuring.

The advantage of programs like that are that you can determine pretty much immediately where the problem is rather than trying to get a random first line support guy from the ISP to try and find out for you.

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