SBS 2011 wierd issue DHCP/Netgear router
Total chaos last week - went to a client site and they had no connectivity across their small network. Ended up removing and reinstalled DNS and DHCP, replaced the router, replaced the switch. Everything then hobbled back into life. The local IT shop only had an 8 port switch, so I ordered a 24 port netgear prosafe. Went to site yesterday to install it - as soon as I plugged the router and the server (I wanted to introduce hardware one piece at a time) The server stopped all connectivity. It could not longer see the router. I plugged it back into the 8 port switch, the server then could see the router but reported the connection as "unauthenticated". I had to run fix my network to sort it out. I then tried to daisy chain the 8 port switch with another to expand the network for all users - as soon as I introduced the other switch, connectivity stopped again. DHCP on router and access points triple checked as disabled. Had to reinstall DHCP completely yesterday as it kept stopping (I know this points to another DCHP server but there isn't one). I have swept the PCs for malware. We run Sophos anyway. So now I have the network up and running but I am short of 2 ports! I cannot understand what is happening with the switch - BTW I have tested another switch too and the same thing happens so it isn't hardware.....
I should have added "or a cable with both ends connected to the same switch" on the first question.
Once you have it up and running, I'd stop the DHCP server service (temporarily) on the server and run the following on a workstation that uses DHCP to get its address:
Start
Run
cmd
ipconfig /release
ipconfig /renew
ipconfig /all
On the last command, note if it received an IPv4 address on the appropriate adapter. If it did, then note the IP address of the DHCP server. It shouldn't get an address if you have disabled the DHCP server service. Of course, make sure you start the service after testing.
I'd be cautious about concluding that there isn't another DHCP server unless you've done the sort of test I mention above. It's not at all unheard of for someone to add a wireless access point with DHCP enabled without notifying the appropriate people.
Once you have it up and running, I'd stop the DHCP server service (temporarily) on the server and run the following on a workstation that uses DHCP to get its address:
Start
Run
cmd
ipconfig /release
ipconfig /renew
ipconfig /all
On the last command, note if it received an IPv4 address on the appropriate adapter. If it did, then note the IP address of the DHCP server. It shouldn't get an address if you have disabled the DHCP server service. Of course, make sure you start the service after testing.
I'd be cautious about concluding that there isn't another DHCP server unless you've done the sort of test I mention above. It's not at all unheard of for someone to add a wireless access point with DHCP enabled without notifying the appropriate people.
ASKER
Hi there thanks for the comment. Yes only one NIC (the other is disabled) on the server. As soon as I plug the router into the switch and the server into the switch, I have no internet connectivity. I need to return to site to test but they are obviously not keen for me to go in and disrupt their day at the mo! The connection shows on the server as OK but it won't resolve any websites. When I then go back to the 8 port switch, the connection then shows as unauthenticated. This can be resolved by running fix my network
It is important to look at the problem from a lower level. "Won't resolve any websites" involves a number of requirements. If you check the server IP address and netmask and ensure that they are compatible with the LAN address and netmask on the router, you should be able to ping the IP address of the router from the server (assuming that the router responds to pings).
Next is to confirm that the Default Gateway on the server points to the router. That should allow you to ping the internet by number (4.2.2.2 for example).
When you ping the internet by name (google.com for example) you'll test whether or not DNS is working.
By breaking it down into these pieces it will make troubleshooting much easier and likely much quicker. I would lean on these sorts of low-level tests to troubleshoot rather than how the connection is shown in Windows.
Next is to confirm that the Default Gateway on the server points to the router. That should allow you to ping the internet by number (4.2.2.2 for example).
When you ping the internet by name (google.com for example) you'll test whether or not DNS is working.
By breaking it down into these pieces it will make troubleshooting much easier and likely much quicker. I would lean on these sorts of low-level tests to troubleshoot rather than how the connection is shown in Windows.
If you unplug the router and just have the server and computers connected to the switch can they ping each other?
If that works fine, it may be the router - I've seen similar behaviour (granted this was years ago) which after days of diagnosis turned out to be a faulty port on the router itself. Also, does the router have Upnp enabled? It could be something on the server trying to change the router details/setup and causing a conflict?
The previous answers already sm up most of the stuff I would suggest - break down the diagnosis until you can pinpoint what the problem area is and focus on that.
If that works fine, it may be the router - I've seen similar behaviour (granted this was years ago) which after days of diagnosis turned out to be a faulty port on the router itself. Also, does the router have Upnp enabled? It could be something on the server trying to change the router details/setup and causing a conflict?
The previous answers already sm up most of the stuff I would suggest - break down the diagnosis until you can pinpoint what the problem area is and focus on that.
ASKER
Thanks guys - will work through your suggestions next week and update you then
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ASKER
Many thanks for all of your comments. It was the NIC - replaced this morning and everything now connects happily. Can't believe I changed everything expect the NIC (although did try onboard disabled one and that didn't work). Thanks again
When you say you lost connectivity, exactly what did you see? For example, was the server able to ping the router by IP address? If that isn't working, then you don't have to look at DNS or DHCP yet. I'm presuming that your server has a static IP address.
I think you are correct to try this one device at a time. Try running a cable from the server (only one connected NIC there?) to the router and disconnect everything else on the LAN side of the router. Ping the router by IP address, ping 4.2.2.2, and ping google.com. You may want to create a .CMD file for this as you'll run it a number of times. If all three work properly, then continue.
Connect the server to the new switch (moving the cable from the router to the switch) and connect a cable from the switch to the router. No other devices should connect to the switch. Run the same three ping tests again.
Add cables one at a time and repeat the three ping tests. At some point it will fail and you'll identify the culprit.