Strange IP/DHCP/DNS problems

[jayc28 0]

Here's the situation. Our company for some time had been assigning static IP's to W98 workstations. As our company grew, maintaining this information became cumbersome, so we went with DHCP to assign all the network information to the workstations. We were also using hubs to share network resources and to get a better handle on network traffice we installed 3COM 3300 stackable switches.

 

The problem we are having is that some workstations cannot get out to the Internet with the DHCP settings after making the switch. When you run winipcfg on their machines, sure enough, DHCP has assigned an IP address to that workstation as well as the gateway and DNS information. But when you try to browse, you get nothing and then finally you get a DNS error.

 

Now, we installed the switches before we switched everybody over to DHCP, so we thought that since the switches retain the MAC addresses of the workstation NIC cards, that maybe that was part of the problem. But when we deleted the mac addresses for a few of the problem PC's and tried DHCP, it still would not work. What is also strange is that if you try to assign it an IP address it wont work UNLESS you give it the same exact IP that it was using previously. Anything else will not work. We have installed some new PC's since we made this change and they work like a charm right out of the box.

 

The question I have is, does the MAC address get stored anywhere else where it could be causing a conflict? We dont run DNS locally. The DNS information we are using is supplied to us from our ISP which is Sprint and trying to get any help from them is worse than going to the government. I was hoping to get a lead here. Any help will be appreciated.

[kgeissler 0]

Can you ping the DNS servers from these workstations?

 

Are you sure your subnet mask is correct?

[jayc28 0]

Ahh. I forgot to put that in there.

 

The subnet mask (255.255.255.0) is correct.

 

When you try to ping the DNS from those workstations you get an error saying back from the gateway (192.168.4.1) saying 'Destination Host Unreachable.'

[clutch 1]

Have you tried running a sniffer and monitoring a problematic workstation along with a workstation that is functioning properly?

 

Also, can these workstations browse the local network without any hassles even when they can't get outside access (I read "browse" in there but didn't know if you were limiting that to internet traffic or not)?

 

Do you have any kind of internet monitoring software like "SurfControl" that might have these workstations listed as "No Access"? Do these problems persist with all logons (would relate to monitoring software that would limit access based on logon)?

 

On the problem machines, have you tried removing and reinstalling TCP/IP?

 

Are all the machines on the same "192.168.4.x" subnet? I usually don't see anybody using a "4" as the last octet in the network ID without being involved in a more advanced subnetting/supernetting scheme.

[jayc28 0]

>> Have you tried running a sniffer and monitoring a problematic workstation along with a workstation that is functioning properly?

 

No I have not. Any ideas on one?

 

>> Also, can these workstations browse the local network without any hassles even when they can't get outside access (I read "browse" in there but didn't know if you were limiting that to internet traffic or not)?

 

Yes, they can browse the local network. They can receive e-mail through our Lotus Notes/Domino server. Cannot FTP or surf the web.

 

>> Do you have any kind of internet monitoring software like "SurfControl" that might have these workstations listed as "No Access"?

 

No.

 

>> On the problem machines, have you tried removing and reinstalling TCP/IP?

 

Yes and to no avail.

[kgeissler 0]

Are the workstation recieving a valid IP from your DHCP server?

 

Maybe your router is blocking certain IP's?