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No internet on a specific network, but still connected to that network.

Posted on 2016-10-11
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Last Modified: 2016-10-11
So I've run across a very puzzling, yet interesting issue with a customer. There is a single computer on their network that refuses to identify and connect to the internet. That's not what's puzzling, however. The computer works within the network and can communicate with other computers on said network. In the office where the computer is located is another computer (pc-server) that feeds from the same 5-port hub as the computer that doesn't connect to the internet. I've tried swapping ports, still the same. I brought the PC in question back to the shop only to find out that it works here perfectly. Had no hitches and the internet picked right up. I take it back to the customer and on their network, again it doesn't work. What would cause a computer, on a network, not to attain an internet connection when all external factors seem not to be the cause? Keeping in mind that it works elsewhere and shares connection points with other machines that also work.
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Question by:BNCAdmin
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by:Russ Suter
Russ Suter earned 251 total points
ID: 41838640
This sounds like it might be a DHCP lease issue. You could try running the following commands in a command prompt window:
C:\>ipconfig /release
C:\>ipconfig /renew

Open in new window

If those commands don't work you can try removing the network adapter in the device manager and restarting the PC. It will automatically detect the network adapter and reinstall the device.

However, before going to that extreme you might consider simply altering the network adapter's IPv4 settings to use a static IP address. Make sure the subnet mask, gateway, and DNS server entries are appropriately entered as well. Use a working computer as comparison to ensure you get the correct values.
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Assisted Solution

by:BNCAdmin
BNCAdmin earned 0 total points
ID: 41838648
Unfortunately, these are things I'd already run through the system as fixes. When I gave it a static IP that was when the computer began to communicate with other machines in the network. Before that it gets a weird IP scheme that doesn't exist within the network itself. 192.168.202.185 (Not the specific IP, but a very similar scheme). The network itself is a 173 scheme. What I've been thinking is that perhaps the IP settings are somehow "stuck" on this odd scheme. I know I could release those settings, but that was to no avail. Is there perhaps a way to make a computer forget it was ever connected to anything at all? Something else I did notice was that the computer classifies it's DHCP address as "public", while the network itself is set as "work".
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by:
Russ Suter earned 251 total points
ID: 41838671
The reason it's classifying the address as public is because any IP address starting with 173 is a public IP address. This is actually a bad setup. For any private network using NAT, which is pretty much EVERY private network, you need to be using one of the private network address ranges. They are:

Class A: 10.0.0.0 - 10.255.255.255
Class B: 172.16.0.0 - 172.31.255.255
Class C: 192.168.0.0 - 192.168.255.255

Your DHCP server is being naughty!
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Assisted Solution

by:BNCAdmin
BNCAdmin earned 0 total points
ID: 41838724
The current setup is <provider modem> --> <16 port switch> --> <network clients>. So it's basically the provider settings giving out the IPs. Would having a public scheme have any real baring on the cause for a single PC to not connect, though? Why would it only be that PC specifically rejecting the service? And why would it only be rejecting the service at the customer location and no where else? It's very confusing to me as someone who has been dealing with networks for 10+ years now.
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by:Russ Suter
Russ Suter earned 251 total points
ID: 41838735
I agree with you, it is puzzling. However the fact that the PC works correctly at other locations would point to a network configuration issue. There's something about this PC that isn't getting along with the environment. Is IPv6 also enabled? Could that be a contributing factor? My next step would be to go through the network settings of the trouble PC and compare to a good one. Other factors to consider?

Is the OS version / edition different?
Windows firewall settings?
Bad network cable? (I guess the question there is does this PC still behave oddly at another physical location on the same network?)
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Assisted Solution

by:BNCAdmin
BNCAdmin earned 0 total points
ID: 41838744
As to the question of cabling, all cables coming into the location are new or previously proven to be good. OS version is Windows 10 on the offending machine (I know, I know). Firewall completely disabled still has the same issue. Now as to the question of IPv6. It wasn't enabled initially, but enabled/disabled there is no change. What I have noticed is that there are two additional installed protocols that are different from a healthy connection next to it. I've also tried disabling those to no avail. This is a problem that has truly confused me.
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by:Russ Suter
Russ Suter earned 251 total points
ID: 41838756
I guess the next thing I might try is resetting the TCP/IP stack. These instructions don't specifically address Windows 10 but they should work the same as they do for Windows 8.1

https://support.microsoft.com/en-us/kb/299357
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by:BNCAdmin
BNCAdmin earned 0 total points
ID: 41838769
I'm about to head to the customers now. That was actually an idea that hadn't ocurred to me. I'll return with updates.
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Assisted Solution

by:Bryant Schaper
Bryant Schaper earned 83 total points
ID: 41838824
can you ping an ip on the internet 8.8.8.8 and provide a traceroute as well.

Could be firewall/routing too
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by:masnrock
masnrock earned 83 total points
ID: 41838828
I concur with what Russ has been saying. Also, you never did mention exactly how many public IP addresses the customer has, along with how many machines are connected. Also, are there any other network devices, such as printers? Some of them might be taking up some of the IP addresses.

I have seen things like this happen before. Sometimes it would be an issue like the switch for some reason is taking one of the public IP addresses (assuming it has not been set up with a static address) and there are no more available IP addresses. Other times even the ISP hadn't been able to see why and they ended up having to make small changes on their side for everything to work. But what would seem most likely in this case is that all of your DHCP leases are taken up and there wasn't a way for the machine in question to obtain a lease.

However, I'd be wondering why all of the computers have public IP addresses and why there isn't a router or firewall of any sort. That's what I find the most disturbing in the entire set up. That network is just begging to get hacked.
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by:CompProbSolv
CompProbSolv earned 83 total points
ID: 41838881
If you would provide the output of ipconfig /all from the problem computer as well as a properly-working computer it could be very useful.

The suggestion to ping 8.8.8.8 is an excellent one.  If that gives you four good replies, try pinging google.com and note whether the name gets resolved into an IP address.  This will help identify if it is a connectivity problem (if ping 8.8.8.8 works, then it is technically "connected" to the internet) or a DNS problem.
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Assisted Solution

by:BNCAdmin
BNCAdmin earned 0 total points
ID: 41839122
So it turns out the issue is a pretty simple one that I'm ashamed I didn't catch sooner. A simple power cycle of the modem got the single computer that couldn't get service, to get service. Something so easy eluded me because only one PC in the entire network had no connectivity. Further research shows to me that the modem has faulty firmware and a history of issues from multiple customers. So what had confused me so heavily was a simple networking solution that presented itself in a very complex way. Also, just to clarify on some earlier things, the system had a total of 3 PCs.
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Author Closing Comment

by:BNCAdmin
ID: 41839125
Thanks guys for the help. Sorry the issue turned out to be something it definitely was not.
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Expert Comment

by:Russ Suter
ID: 41839141
Hey, if this stuff was easy everyone would do it. Glad you got it worked out. That was a noodle scratcher for sure. There's a reason why the joke, "Have you tried turning it off and on again?" is so popular.
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