Why do I have intermittent internet connectivity?

I have a network of approximately 30 computers all running windows XP SP2
We have Embarq ADSL for internet, and also a Sonicwall TZ170 for a firewall
We are currently having some internet connectivity issues with some of our computers.
It will happen to one computer at a time
The lan connectivity stays up all the time, but when you try to access a web page it will either give you an incomplete load or nothing at all.
Repairing the connection fixes the problem FOR A WHILE then later it will go out again.

Any other information you need just ask.
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Well if network stay up and only internet drops than first thing to check would be your Gateway. Do you have a server that all computers go to access internet? Can you draw out how your computers access internet for example

PC --> Router --> InternetModem --> Internet

When next time connection drops i would recommend to use "tracert" command in command promt to see where exactly the traffic stops.
chrisrandlemanAuthor Commented:
our network is

pc->switch->router->dsl modem -> internet

I have run tracert  but it doesn't get out of our network
"It will happen to one computer at a time"

To confirm - do you mean that while the problem is occuring it affects just one computer with the other computers still able to access the Internet?
Do You Have a Trusted Wireless Environment?

A Trusted Wireless Environment is a framework for building a complete Wi-Fi network that is fast, easy to manage, and secure.

chrisrandlemanAuthor Commented:
Yes I mean my computer will drop internet connection, but all other computers are able to get there.
But then the accountants computer will drop 4 hours later and everyone else can still use the internet.

there seems to be no ryhme or reason to why it happens. But a repair does fix the problem.
chrisrandlemanAuthor Commented:
To answer your question about the tracert it responds unable to resovle host
Can you try pinging router->dsl modem -> internet in that order. That would seem to be most logical to see where exactly connection drops. Also what acts as your DHCP server?
chrisrandlemanAuthor Commented:
I will try next time it drops.

Post tomorrow.
chrisrandlemanAuthor Commented:
Also doing an arp -d

fixes the problem
for a little while....
chrisrandlemanAuthor Commented:
I found out what the problem was....

I also had a linksys router on my network that used to be the company's firewall before i started so it was basically poisoning the arp cache

Problem is solved

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