Tip

LAN connectivity problem: Blame DNS, NIC or firewall?

ITKnowledge Exchange member "BinooDas1234" had connectivity issues with a troublesome LAN, and fellow techies jumped in to help out. But does the answer lie in the DNS configuration, the NIC drivers or elsewhere? Here is a portion of the conversation. You can read the rest of the thread

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ITKnowledge Exchange member "BinooDas1234" asked:
I have a Compaq EVO n1020v notebook with Win XP Pro (SP 1) installed in it. Sometimes it works fine in our office LAN and sometimes it does not. The office LAN is a workgroup with ICS enabled in Win2K server and uses DHCP through Win 2k server. If I check the IP of the notebook, it shows the IP of the LAN but never connects to the Internet and can't access LAN computers/printers/shared folders. If I click the repair option right clicking on the right bottom connectivity icon, it says "can't repair, please contact LAN or ISP administrator." It works fine after plugging in/out the LAN cable once or twice and restarting. I checked everything but didn't find anything. Any advice would be highly appreciated.

"NHAREL" WRITES:
If Internet access is your only problem, it might be a limitation of the firewall. Check to see if you have a limited license for the number of client connections.


"LAYER9" WRITES:
The first place I would start is to check DNS. If you can access hosts on the local subnet but not on the Internet, then I would assume you are getting a good IP from your DHCP server, but not DNS.

However, I don't like the sound of a "repair" (which is just an ipconfig /release, ipconfig /renew) not working unless you unplug the cable. That could be more of a problem, like the NIC is not releasing the address, etc. For now, I would start by doing an ipconfig /all and confirming you have DNS.

Also, check to see if you have a personal firewall running on the laptop. Such a firewall can block the DHCP request/response packets.


"DREAMSCAPE" WRITES:
We happen to use Compaq EVO laptops as well. We have found that these laptops are known for losing their network connectivity or just plain acting up as far as connections go. The network card drivers just are not stable, no matter the version used. Re-installing your network card driver usually works. Sometime we've have to replace the network card.


"KOJONES" WRITES:
I agree with Dreamscape. I have had this same issue with D-Link and other NICs. The solution was to ensure the latest service packs for Windows were installed and the latest drivers for the NIC were installed. I also ran my anti-virus software to ensure I wasn't getting traces of a virus.


"LAYER9" WRITES:
Not that every answer is not a good one, but I really would focus on DNS here. If like you say, you can access the local subnet, but cannot access the Internet, then it sounds like a DNS issue.

You're either resolving local names with a local DNS server that is not forwarding external requests, or you are resolving locally with WINS. If you can ping local hosts, then I would stop worrying about NIC problems right there. If you can ping the local hosts, and particularly if you can browse the local subnet, then you can assume either you have a bad default gateway, or bad DNS.

I assume you would know if there was some sort of restriction on your network with regards to outbound access.


"JCAN123" WRITES:
Another thought on the issue. Check your subnet masks on the Win2k server and on the client and verify that the IP address is within subnet range.


"GLENKENS" WRITES:
Can you connect to your computer from any other machine in your workgroup? If you can, then try immediately afterwards to connect from your machine to another in the workgroup; this often works.

If not, try checking the network cable. This could be bad wiring, especially as you get a connection after unplugging /replugging. Try using a different cable or using an Ethernet cable tester (check both ends of the cable). Does the cable fit tightly into the socket?

As soon as you have an Internet connection, download (or acquire by other means) SP2 (there will be around 30-35), then check for hardware updates. This quite often fixes problems of this sort.


"CHIPPY088" WRITES:
Guess what -- I have just had the same problem and errors on a private LAN. Errors were indicating connectivity problems, but it was NAT/PAT not configured properly. (Firewalls are a pain sometimes.)



This was first published in January 2006

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