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Strange Networking problem

smartcooky

Penultimate Amazing
smartcooky
Joined
Oct 26, 2012
Messages
29,036
Location
Nelson, New Zealand
At my daughter's business, they have a network of about 6 computers and other devices. They each have fixed IP adresses on the network using a hosts file (this is necessary because some of the proprietary devices on the network come with fixed/hardwired IP addresses)

Everything worked fine until recently when the motherboard of one of the computers failed. We replaced the computer and swapped the system HDD from the failed computer to the replacement. This worked fine until we tried to put it on the network.

As usual, I changed the network adapter IPV4 settings to reflect this computer's intended IP address

IP Address: 192.168.1.98
Subnet Mask: 255.255.255.0
Default Gateway: 192.168.1.1

Note. We also use Cloudflare DNS so I set this accordingly

Preferred DNS Server: 1.1.1.1
Alternate DNS Server: 1.0.0.1

However, when I do all this, the computer connects to the network fine, but will not connect to the internet. When I run the Windows 10 troubleshooter, it reports that "DHCP is not enabled for Ethernet 2". I allow the troubleshooter to apply the fix, and now the internet works, but the computer drops off the network. To summarize

When IPV4 for is set to a fixed IP address: The network is OK but no Internet.
When IPV4 is set to obtain IP address automatically: The internet is OK, but no network.

I feel this is either a configuration problem or a driver issue. The two computers involved are both HP Compaq Elite 8200 models, but the motherboards do look slightly different, so it is possible there are some minor hardware differences. I did try updating the network adapter drivers but it said it 'already has the latest drivers for this device' (I think Windows updated all the drivers when I first booted up the computer after installing the system HDD.

Anyone have any ideas why this might be happening?
 
How are the boxes networked? Switch/hub separate from gateway router or all on one device? Are there multiple network adapters in use on each system? What is 'Ethernet 2', is it a second physical connection, or a copy of the integral Ethernet connection?
 
It's a configuration issue.

ETA: More details would help. Something like, "with configuration X I opened a browser and tried to get to website Y but got error message Z instead".
 
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catsmate said:
How are the boxes networked? Switch/hub separate from gateway router or all on one device?
Click to expand...

All connected with Ethernet cables, plugged into nearby wall sockets that terminate at a patch panel. They are distributed using two HP1420 - 8 port ethernet switches which are connected to the Netgear modem for the internet connection.

catsmate said:
Are there multiple network adapters in use on each system? What is 'Ethernet 2', is it a second physical connection, or a copy of the integral Ethernet connection?
Click to expand...

As far as I can tell, there is only one network adapter on each computer. On the computer in question, at "Control Panel\All Control Panel Items\Network Connections" there is only one icon, its labelled.

Ethernet 2
Network 4
Realtek PCIe GbE Family Controller

Its almost midnight here, so I will have to go in and have a look tomorrow if you need to know about any of the other computers connected to the network
 
theprestige said:
It's a configuration issue.

ETA: More details would help. Something like, "with configuration X I opened a browser and tried to get to website Y but got error message Z instead".
Click to expand...

When IPV4 for is set to a fixed IP address: The network is OK but no Internet.

In the taskbar notification area, this icon
Net%20Connected.png
changes into this icon
Net%20Disconnected.png

I can navigate from any other computer on the network to any shared location on the replacement computer, but when I try to open a browser (Firefox) on the replacement computer and navigate to Google.com, I get

"Hmm. We’re having trouble finding that site.

We can’t connect to the server at www.google.com.

If you entered the right address, you can:

Try again later
Check your network connection
Check that Firefox has permission to access the web (you might be connected but behind a firewall)"​

When IPV4 is set to obtain IP address automatically: The internet is OK, but no network.

In the taskbar notification area, this icon
Net%20Disconnected.png
changes into this icon
Net%20Connected.png


I can open a browser (Firefox) on the replacement computer and navigate to Google.com with no problem, but when I try to navigate from any other computer on the network to the replacement computer, I get a message like "cannot locate \\Computer Name"

NOTE: I can always navigate from the replacement computer to any other computer regardless of which way I have the IPV4 settings
 
I presume the new computer retained the IP address of the old computer. The new computer will have a different MAC address to the old computer. Did you update the MAC address in the IP tables of your router?
 
Actually, that sounds like a default gateway issue or a routing table issue.

Do an “ipconfig /all” while it’s connected with DHCP, and compare those working settings with the manual ones you’re inputting.

Also, “arp -a” will show the arp table (maps MAC addresses to IPs/networks) and compare that.

If those look fine, then I’d suspect something in the switch/hub/router…it may be maintaining arp-type entries for the old MAC address. There are ways to clear/reset that, but you’d have to check your specific device for what/his to check.

Also, some devices use port security of various types which is related to all this, so one or more options intended to prevent ARP poisoning may be blocking the new device from using the same IP.


Sent from my iPhone using Tapatalk
 
Are you sure 192.168.1.1 is your modem? It's a simple mistake to make and it would fit the symptoms. Most modems assign themselves that address by default but not all do. When you allow DHCP what gateway address does it give?
 
P.J. Denyer said:
Are you sure 192.168.1.1 is your modem? It's a simple mistake to make and it would fit the symptoms. Most modems assign themselves that address by default but not all do. When you allow DHCP what gateway address does it give?
Click to expand...

Yeah, this is where I was going when I suggested checking the ipconifg info between the two. It's also common for modems to assign the 192.168.0.1 address, so maybe you've just got a bit flipped :)
 
All good suggestions which I'd try first. The other thing I'd check is the DNS server(s) on each ipconfig.

For clearing arp tables on routers, I can't remember having one that wasn't a stripped down linux variant so either you should be able to open a browser session to it where you'll get a model specific web page to manage it or you can ssh to it and from windows I use solarPutty . Then arp --help will give the syntax.
 
P.J. Denyer said:
Are you sure 192.168.1.1 is your modem? It's a simple mistake to make and it would fit the symptoms. Most modems assign themselves that address by default but not all do. When you allow DHCP what gateway address does it give?
Click to expand...

Yes.

When I type 192.168.1.1 into a browser address bar, it opens the login page for the modem. Its also the Default Gateway in the IPV4 settings on all six computers and other devices on the network. I will check using 'IP config' if it is giving a different Default Gatewat from the modem.

As for the questions asked by other posters, I will try to answer those when I get there this morning.
 
OK, I'm here now


Brett M:
1. ARP-A lists the same IP addresses as the HOSTS file.
2. The MAC address table in the router has the same entries as the physical addresses listed in ARP -A. I am presuming this is because the replacement computer is using the C: System drive from the old computer, so it will have retained the MAC address.
Note: When I first booted up this replacement computer it spent several minutes on the black boot screen bringing up a bunch of text I have never seen it do before. It has not done this on any subsequent reboots, so I am guessing this was the system working out that it was in a computer where there have been hardware changes. I have seen this sort of boot screen before on other computers when I have changed or added memory RAM sticks.

Wudang:
This is the ipconfig result from PHOTOLAB (another computer on the network)
Ethernet adapter Ethernet:

Connection-specific DNS Suffix . :
IPv6 Address. . . . . . . . . . . : 2404:440c:134d:f300:3043:8068:f30:de91
Temporary IPv6 Address. . . . . . : 2404:440c:134d:f300:18fa:39c0:6dca:3074
Link-local IPv6 Address . . . . . : fe80::4ce7:82a9:97b2:9457%13
IPv4 Address. . . . . . . . . . . : 192.168.1.55
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : fe80::1af1:45ff:fedb:ec4b%13
192.168.1.1​

This is the ipconfig result from PHOTOLAB-3 (another computer on the network)
Ethernet adapter Ethernet 4:

Connection-specific DNS Suffix . :
IPv6 Address. . . . . . . . . . . : 2404:440c:134d:f300:50ff:2fd6:fa52:8115
Temporary IPv6 Address. . . . . . : 2404:440c:134d:f300:c59e:5f08:aef5:eaa7
Link-local IPv6 Address . . . . . : fe80::d92e:13e3:1c7:1677%13
IPv4 Address. . . . . . . . . . . : 192.168.1.60
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : fe80::1af1:45ff:fedb:ec4b%13
192.168.1.1​

This is the ipconfig result from ORDERCONTROLLER (another computer on the network)

Ethernet adapter Ethernet:

Connection-specific DNS Suffix . :
IPv6 Address. . . . . . . . . . . : 2404:440c:134d:f300:503d:2db4:338:275
Temporary IPv6 Address. . . . . . : 2404:440c:134d:f300:4dcf:f365:e7fc:1f2c
Link-local IPv6 Address . . . . . : fe80::bd28:d4d:be9d:e157%12
IPv4 Address. . . . . . . . . . . : 192.168.1.98
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : fe80::1af1:45ff:fedb:ec4b%12
192.168.1.1
​
And this is the ipconfig result from PHOTOLAB-2 (the replacement computer)
This is the IP config result from Computer 2 (the replacement computer)

Ethernet adapter Ethernet 2:

Connection-specific DNS Suffix . :
IPv6 Address. . . . . . . . . . . : 2404:440c:134d:f300:b25:753b:99b0:d787
Temporary IPv6 Address. . . . . . : 2404:440c:134d:f300:3489:1d6d:ce11:abb3
Link-local IPv6 Address . . . . . : fe80::65bf:209c:2d07:d65d%5
IPv4 Address. . . . . . . . . . . : 192.168.1.65
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . : fe80::1af1:45ff:fedb:ec4b%5
192.168.1.1​

I'm not seeing anything obvious here, except that in the characters before the IPV4 address in the "Default gateway" line end with different numbers

- fe80::1af1:45ff:fedb:ec4b%13
- fe80::1af1:45ff:fedb:ec4b%13
- fe80::1af1:45ff:fedb:ec4b%12
- fe80::1af1:45ff:fedb:ec4b%5

I don't think this is significant as it probably refers to IPV6 which does not apply in this case.

Now, here is a curiosity.

When the IPV4 settings work for the internet (when DHCP is enabled, and the computer assigns its own IP address) and I try to access the replacement computer using its computer name from any other computer on the network, it does not work, but when I try to access via its IP address, it works fine, e.g.

\\PHOTOLAB-2 brings the error "Windows cannot access PHOTOLAB-2", but
\\192.168.1.11 (the automatically assigned IP Address) connects to the computer

I know the computer name is correct, because when I assign its IP address manually (and the internet stops working) then using \\PHOTOLAB-2 works just fine. I also know I'm not making a typo, because I'm using the same desktop shortcuts in each case.

Go figure!
 
Last edited:
Norman Alexander said:
If you are using DHCP, have you tried this?
  1. On the computer having problems...
  2. Get a command prompt (Run CMD)
  3. ipconfig /release
  4. ipconfig /renew
Click to expand...

novaphile said:
And just in case...

ipconfig /flushdns

I've seen a few oddities caused by strange entries in a PC's dns cache too.
Click to expand...

Just tried tried all three of these, with the IP address both manually and automatically configured.

No change.
 
Yeah because DNS isn't wrong. Obviously.

The problem is that you don't know how your local DNS is resolving remote addresses. And you don't understand how to set up a new local client to see other local clients and also get out to internet DNS.

Has your daughter considered paying a hard working IT professional a fair rate to actually investigate and solve the problem?

Because I could totally solve this problem. At $80/hour plus travel costs. And a 4 hour minimum. But you don't want that.
 
theprestige said:
Yeah because DNS isn't wrong. Obviously.

The problem is that you don't know how your local DNS is resolving remote addresses. And you don't understand how to set up a new local client to see other local clients and also get out to internet DNS.

Has your daughter considered paying a hard working IT professional a fair rate to actually investigate and solve the problem?

Because I could totally solve this problem. At $80/hour plus travel costs. And a 4 hour minimum. But you don't want that.
Click to expand...

She asked me to have a look at it first.

This seems reasonable since I set the entire system up in the first place and updated it through all the transitions from the original Windows 2000 over 20 years ago, through Windows XP to what we have now with Windows 10. This included replacing all the Cat 5 cabling with Cat 6 to support 1000 Mbps, and replacing the 8-port Ethernet switches to support the faster networking. I also installed a Ubiquiti WiFi access point because we soon figured out that the NetGear modem's built in WiFi simply wasn't cutting the mustard with a limit of 16 connections with fixed lease times. We can have 50 or more different customer smartphones connect to our system during any given day so leases fill quickly and we kept having to flush all the connections. The Ubiquiti AP allows 150 simultaneous connections and we can make the lease times short.

This was all working fine a week ago, until we had a computer failure and it needed replacing. So yeah, having built the network system myself, and having 20+ years of familiarity with it, I have always been able to deal with most routine problems. But this is a curly one that has me beat... at the moment.

If I can't fix it, then I will get our IT guy at PC Systems Ltd to come have a look.
 
smartcooky said:
OK, I'm here now


Brett M:
1. ARP-A lists the same IP addresses as the HOSTS file.
2. The MAC address table in the router has the same entries as the physical addresses listed in ARP -A. I am presuming this is because the replacement computer is using the C: System drive from the old computer, so it will have retained the MAC address.Note: When I first booted up this replacement computer it spent several minutes on the black boot screen bringing up a bunch of text I have never seen it do before. It has not done this on any subsequent reboots, so I am guessing this was the system working out that it was in a computer where there have been hardware changes. I have seen this sort of boot screen before on other computers when I have changed or added memory RAM sticks.
Click to expand...


The highlighted doesn't seem right to me. The MAC address actually being used by the NIC to communicate on the network should be from the NIC, not from the configuration saved on the hard drive. Maybe this mismatch is causing some problem. Can you use the Device Manager to remove the ethernet adapter, search for new hardware to let it find the new adapter, then reconfigure and recheck your router?
 
JimOfAllTrades said:
The highlighted doesn't seem right to me. The MAC address actually being used by the NIC to communicate on the network should be from the NIC, not from the configuration saved on the hard drive. Maybe this mismatch is causing some problem. Can you use the Device Manager to remove the ethernet adapter, search for new hardware to let it find the new adapter, then reconfigure and recheck your router?
Click to expand...

As I said in the note, the computer spent long time on the black boot screen, with lots of text popping up that tbh, I didn't take a lot of notice of. I did check the Device Manager and there were no exclamation marks warning me about unknown hardware.

These computers don't have Network Interface Cards, they have Network Adapters built into the motherboard (I presume that's what you mean). I will try going into Device Manager, uninstalling the Realtec Network Adapter, then "Scan for hardware changes" and see what happens.

UPDATE: Ok, I did that. The Network Adapter reinstalled correctly, the physical addresses listed in ARP -A are unchanged, and it hasn't fixed the problem
 
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