IP address conflict

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brockalee

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So here's one that should be easy but has me scratching my head.

I'm troubleshooting a server (2003 Small Business Server) that is giving a TCPIP error that another system on the network has its same address. Its IP is 192.168.0.6 and is also used as a DNS server.

The error shows a MAC address, but I can't find another system on the network that has that same MAC address or an assigned IP address of 192.168.0.6, besides the server. I did look up the MAC address and found the vendor is Dell, but that's all that I know.

All of the other devices I checked on the network are on "Assign IP" and the DHCP is handled by the router. The range of addresses it hands out start at 192.168.0.7, so it should not be screwing things up.

The server is a Dell and has 3 NIC cards, 2 of which are disabled (but I checked the MAC addresses just to be safe and they're not the same.)

I did use a tool to scan the MAC addresses on the network, but still did not come up with one matching the offending MAC address. (But then I wonder if this tool would even work properly if two machines have the same IP address.)

This site complains about connectivity every few days and the event logs do show that TCPIP error. I'm just confused about what to do with the information I have.

Any suggestions?
 
From what I read I am assuming that the network is fairly small. If it's practical, why not go around and do an ipconfig /all on each machine to see if you can find an address conflict. If you can, shut the server down (again, I am assuming that this is a small network) for just a few minutes and try to ping 192.168.0.6 to see if you get a response. If you get a response and the server is offline, then you know for sure that you have an address conflict.
 
cyabro said:
The users aren't bringing in any other devices? Perhaps that has a static ip set.
Click to expand...
No, the only other networked device is a printer and it has been checked. The confusing part is that the MAC is supposedly vendored by Dell.
 
Trusted IT Solutions said:
From what I read I am assuming that the network is fairly small. If it's practical, why not go around and do an ipconfig /all on each machine to see if you can find an address conflict. If you can, shut the server down (again, I am assuming that this is a small network) for just a few minutes and try to ping 192.168.0.6 to see if you get a response. If you get a response and the server is offline, then you know for sure that you have an address conflict.
Click to expand...
I did the ipconfig/all on all the machines already.

I haven't tried shutting the server down and can't do it immediately because I'm doing this remotely. When I do go back on site I can try unplugging network cable from the server and pinging the address to see if I get a response - that's a good suggestion!
 
On servers....any network with DHCP for that matter, I usually set the lease range to be from .100 on up. Leaving .2 to .99 for static stuff.

Not the cause of your problem however.

3x NICs on the server.....has anything changed recently? Did the server get moved from another IP range? SBS can be very lazy in letting go of old IP addresses that it had...when you re-do its IP address (like changing your network)...it should be done from the CIECW (Configure E-Mail and Internet Connection Wizard)...found in your Server Manager top of the list. Else..you'll get the old address acting as a ghost now 'n then.

Another possibility....DHCP database got corrupted on the server. I see this happen when any/both of the following were done....
1 - DHCP database directory was not put in the antivirus real time protection exclusion list (along with the LOOOOOOOOOOONG list of other directories which should be done with installing antivirus on SBS).
2 - SBS was installed on a SATA drive based server. SBS is typically "too demanding" for desktop hard drives...should be installed on SCSI/SAS.

I've got a lot of SBS installs under my belt, the couple of times I've seen issues with SBS...99% of the time it's been due to one of the above two things being done.
 
YeOldeStonecat said:
Another possibility....DHCP database got corrupted on the server. I see this happen when any/both of the following were done....
1 - DHCP database directory was not put in the antivirus real time protection exclusion list (along with the LOOOOOOOOOOONG list of other directories which should be done with installing antivirus on SBS).
Click to expand...

I went to the email/internet wizard and it said "Cannot set the DHCP scope options. Ensure that the DHCP server service is running and a scope is defined. Alternately, disable the DHCP service and configure you client computer address properties."

Should DHCP server service be running if DHCP is handled by the router? The server was moved a few months ago but nothing was changed IP address wise that I'm aware of. The antivirus is the same one that has been installed for a few years. (Trend-Micro Worry-Free Business)

I checked the event log and that same conflict 192.168.0.6 popped up at about 2:30AM this morning.
 
brockalee said:
I went to the email/internet wizard and it said "Cannot set the DHCP scope options. Ensure that the DHCP server service is running and a scope is defined. Alternately, disable the DHCP service and configure you client computer address properties."

Should DHCP server service be running if DHCP is handled by the router? The server was moved a few months ago but nothing was changed IP address wise that I'm aware of. The antivirus is the same one that has been installed for a few years. (Trend-Micro Worry-Free Business)

I checked the event log and that same conflict 192.168.0.6 popped up at about 2:30AM this morning.
Click to expand...

If Windows DHCP service detects another DHCP service on the network, it will shut down the Windows DHCP service.

If you have a Windows server on your network running active directory (which SBS does)...you SHOULD BE using the servers DHCP service, it keeps active directory tighter with better DNS registration and updates. You do not want to use the DHCP from some other node like a router. Disable DHCP on the router. This could well be the problem on this network.
 
YeOldeStonecat said:
If Windows DHCP service detects another DHCP service on the network, it will shut down the Windows DHCP service.

If you have a Windows server on your network running active directory (which SBS does)...you SHOULD BE using the servers DHCP service, it keeps active directory tighter with better DNS registration and updates. You do not want to use the DHCP from some other node like a router. Disable DHCP on the router. This could well be the problem on this network.
Click to expand...

This +1.
Also, you need DHCP on the server should you need to migrate to SBS2011.
 
OK so I disabled DHCP on the router and now I'm going through the CEICW. Since the machine is also a DNS server, do I put in its address for DNS (192.168.0.6) or do I need to put in the ISP's DNS?
 
brockalee said:
OK so I disabled DHCP on the router and now I'm going through the CEICW. Since the machine is also a DNS server, do I put in its address for DNS (192.168.0.6) or do I need to put in the ISP's DNS?
Click to expand...

In the CEICW...it asks for your ISPs DNS servers, in which it will plug those servers in the DNS services forwarding section. (I put in OpenDNS DNS servers on all my setups...for increased malware protection, instead of the ISPs servers).

On the servers TCP/IP settings...the CEICW will have it look at itself for DNS....which all DNS servers/domain controllers must do. So you'll see its own internal IP address in the DNS section (newer servers you'll see the standard loopback address..127.0.0.1..which is the same thing).
 
YeOldeStonecat said:
In the CEICW...it asks for your ISPs DNS servers, in which it will plug those servers in the DNS services forwarding section. (I put in OpenDNS DNS servers on all my setups...for increased malware protection, instead of the ISPs servers).

On the servers TCP/IP settings...the CEICW will have it look at itself for DNS....which all DNS servers/domain controllers must do. So you'll see its own internal IP address in the DNS section (newer servers you'll see the standard loopback address..127.0.0.1..which is the same thing).
Click to expand...
OK I disabled DHCP on the router but had not finished with the CEICW (awaiting advice about the DNS server) and the network lost connectivity again with the same IP address conflict. (192.168.0.6) It lasted about 10 minutes, as it always does.

Now I'm done with the CEICW. I guess we'll see if it stays working over the next 12-24 hours.

I'm wondering if I need a second set and more experienced eyes to help with this!
 
Well that didn't take long. It was down for about 20 minutes this time. I checked the system log and there was no IP address conflict this time, but the internet WAS down. I'm wondering now if I should be looking at the router?

That MAC address - 00:1c:23:5d:69:XX of the Dell device that always showed up as duplicated in the system event still has me confused. But I'm just trying to figure out in what direction I should be going now.
 
Last edited:
Long outside shot but there isn't a forgotten wireless point anywhere dishing out IPs or maybe set at 192.168.0.6?

I recall reading a similar post ages ago where something similar happened and they had forgot about a wireless router up above in a void that was in for a manager long gone.

Maybe worth asking them if they ever had something.

No chance that another network is interfering from a neighbour some how?
 
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