random internet connection loss

are those users that can't connect to the internet still able to connect to local resources?
are they able to ping the default gateway?  what about a public IP address: 4.2.2.3?
Do you have a proxy that these users have to go through?
What about a firewall?  Is it licensed for that many users?  Cisco PIX 501 had a 10 user license limit unless you purchased a larger user license.

the users who are experiencing the issue can still access all local file shares, printers etc, we use a Gnat firewall, we have had the same firewall right the way through and have not increased or decreased users, I had wondered if perhaps the firewall is blocking the users for some reason, no we don't use a proxy, and they can all ping the gateway.

To rule out a DNS problem; next time the problem occurs, see if you can ping an external public IP from the problem machine and also confirm that you can ping the gateway from the problem machine. Are the pc's using DHCP or static IP's? Might also run an 'ipconfig /all' on the problem machine also.

Hi,

You should analyze your network using WireShark:


www.wireshark.org


Incase you are new to wireshark:

wiki.wireshark.org

I have installed wireshark, and captured some traffic from my machine, not really sure what it is telling me, some of the information is familiar jet direct chatter, and other recognisable information, but most of it is foreign to me.

I will try and ping the gateway and an external IP next time the situation occurs.

any information you can give me regarding wireshark will be helpful, I looked at the wiki, but it seems to be all about installing it, and setting filters, I dont see any guidelines for what you do with the info when it is captured :)

I think wireshark is going to be a bit too much information for you at this time.  Wireshark is a great network monitoring tool, and we may have to resort to it, but for now stick with the basics.

When a user can't access the internet:
1. Find the IP address of that workstation
     a. is the IP address correct  - I have seen where a rouge DHCP server is on the network that causes this same issue.
     b. is the DNS server correct?  cmd --> ipconfig /all
2. Can you ping the gateway?
3. Can you ping pass the gateway?  Public IP: 4.2.2.3
4. Can you ping www.yahoo.com?  - yahoo will respond
5. if you can ping a public IP and not a name, then you have DNS issues, if you can't ping either then you have a physical issue.

Let me know what you come up with and we can go from there.

what is your gateway device? problems like this can sometimes be caused by licensing issues with your router.  

I've definitely seen issues with sonicwalls like this.

There are limits to the number of concurrent connections and people will have no internet access while some do.  

If you reboot your router do these people then get internet access?