IP address conflict ...

[thecomputerguy]

I am doing some work for a small business ... 8 computers + server all in a workgroup environment, no AD, DHCP on the main router.

They initially called me out because they kept getting the little IP address conflict message on the task bar on various machines. They also have a wireless AP with DHCP turned off on it.

I assumed it was the router which was pretty old so I replaced it, then they called me out again for the same problem. This happened to me once before and I replaced the router only to be called out once again for the same problem.... basically same scenario. I ended up replacing every single piece of networking equipment they had and it seemed like the problem just eventually went away without much of an explanation.

So what all can it be?

 

[othersteve]

Hey there thecomputerguy,

I ran into this the other day at a salon where I was working actually. What did it turn out to be? Why, an Android smartphone actually. The mac address recorded in the Windows Event Logs all pointed to the same device. Cross-referencing that address with the detailed logs on the router led me to an Android phone. I checked all employee phones until I eventually came to the one causing the problems. Disconnecting it from the network immediately solved the problem!

 

[MobileTechie]

If there are only 8 computers you could try scanning the network with something like The Dude and making a note of all the IPs and Macs and then going around and checking which device has which address.

Or setting the DHCP to a smaller range of IPs and giving the all the computers, printers, routers and any other other network devices fixed IPs in a range way outside the DHCP range. Then rescan.

 

[Martyn]

If you're sure you only have one dhcp server go around and check all the devices. Typically a printer would be on a fixed ip address and if it is within the scope of the dhcp server then there will be conflicts periodically. A list should be kept of the fixed ips allocated to avoid this.

 

[Steve202]

I had a similar problem a few months ago and it turned out to be a switch. Was there a managed switch connected to the network?

 

[NETWizz]

I am doing some work for a small business ... 8 computers + server all in a workgroup environment, no AD, DHCP on the main router.

They initially called me out because they kept getting the little IP address conflict message on the task bar on various machines. They also have a wireless AP with DHCP turned off on it.

I assumed it was the router which was pretty old so I replaced it, then they called me out again for the same problem. This happened to me once before and I replaced the router only to be called out once again for the same problem.... basically same scenario. I ended up replacing every single piece of networking equipment they had and it seemed like the problem just eventually went away without much of an explanation.

So what all can it be?

If they are not running DHCP, they could have one or more improper statically configured computer(s).

 

[NETWizz]

If you're sure you only have one dhcp server go around and check all the devices. Typically a printer would be on a fixed ip address and if it is within the scope of the dhcp server then there will be conflicts periodically. A list should be kept of the fixed ips allocated to avoid this.

You can set DHCP reservations for the printers, OR you can create static IP ranges outside any DHCP scopes.

 

[Martyn]

You can set DHCP reservations for the printers, OR you can create static IP ranges outside any DHCP scopes.

I know that but if that hasn't been done that way then you get the conflicts which was my point poorly made. I've seen it plenty of times.
These network scanners that scan the network looking for devices often don't pick up on non Windows(and Windows) print servers that don't answer to ICMP packets so conflicts can still occur.

 

[NETWizz]

I know that but if that hasn't been done that way then you get the conflicts which was my point poorly made. I've seen it plenty of times.
These network scanners that scan the network looking for devices often don't pick up on non Windows(and Windows) print servers that don't answer to ICMP packets so conflicts can still occur.

Most network scanners do more than PING with ICMP to find a system. They often look for commonly open ports, etc... full knowing a lot of systems don't answer PING/ICMP.

Anyway, in a network of only 10 or so computers... it should be easier to just re-use all the old hardware and set it up properly to not have any more IP conflicts. The only PITA will be changing the IP of something like a network printer when now all 10 computers can't print to it anymore until reconfigured.

I don't see how replacing the equipment is going to fix the problem is all I am saying...

 

[teksquad]

If you have a managed switch why not just check the arp table and the CAM table? There is only a few machines. I have used Angry IP in the past and works like a charm (Macs, Linux boxes, Canon and HP printers etc)