Networking issue - IP conflicts...

J

jaypeezee

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Jun 11, 2003
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I am running a small server for my dads company... just recently we started encountering tons of issues with IP conflicts. No new systems were hooked up, all workstations running win xp prof w/ sp2. Before anyone thrashes and says get a new o/s, blah blah blah... this is what we need to stick to.

The server is an IBM xseries x226
we are using a Sonicwall TZ170 firewall... lately i've been noticing the diagnostic LED lighting up (AMBER WRENCH) mind you we've had the same setup for the past 6 months with no problems just recently we are starting to see them. Could this be a sign that the firewall is the prob ? I dont want to start taking everything apart piece by piece - im looking for possibly a more narrowed down approach.
 
have other mahcines do a...
ping <the ip address of the server>
arp -a

look at the mac address
when you start seeing conflicts, clear arp cachce and look again to see if it is reoprting back with a diff mac,
you will then know if another machine (and what machine) has the same ip
 
are you perhaps running 2 dhcp servers on the network without knowing it? perhaps monitor network traffic to determine this.

what does the amber light actually mean? what kind of fault? disconnect the firewall for a while and see if the ip conflicts go away.... makes sense, i guess?
 
I've narrowed the conflict down to two machines... Sorry for the lack of info on my orig post. Total of 6 workstations w/ Access + 2 additional stations just used for inet, one server, and the firewall. I got frustrated and tired so I left early - I'm back home. But hopefully tomorrow I'll try your suggestions thanks !
 
Only 8x machines? Easy as cake to walk around and determine.

Are you running DHCP from the server? The Sonicwall? Or static LAN IPs on the workstations?

Is the IBM server running Windows server that's actually been promoted to a DC and running active directory?
 
DHCP from the sonicwall
Server running Active Directory - will confirm tomorrow 95% certain
 
jaypeezee said:
DHCP from the sonicwall
Server running Active Directory - will confirm tomorrow 95% certain
Click to expand...

I'd recommend using the server for DHCP instead of a router, IMO let your domain controller do its job..."Run your network".

At the very least, you intend to keep the router running DHCP for some reason, edit the properties so that the router is handing out your DCs IP address as the one and only DNS server for your workstations...DNS is very important for 2K and higher domains for internal functions.
 
Ok... Thanks for the input. I've narrowed it down to one workstation. All stations are up and running with no conflicts. Everytime I turn on this one specific station I get a "Limited / No Connectivity icon" I've tried renewing the ip (no luck), uninstalling the adapter (no luck).... any other ideas ?
 
A few easy checks to eliminate hardware failure:

swap NICs with a known good
use a known good cable (one from the machines not causeing a problem)
try different port on the switch
 
PROBLEM SOLVED. didnt feel like really trouble shooting the problem. I just assigned a static ip for the workstation and viola!
 
YeOldeStonecat said:
I'd recommend using the server for DHCP instead of a router, IMO let your domain controller do its job..."Run your network".
Click to expand...
I second this. While it's possible to use an external dhcp/dns server for an AD server ( and let the DC update it ), it introduces more complexity into the system than required. KISS ( keep it simple stupid ), I live by it.

And as stonecat mentioned, AD is highly dependant ( and very very touchy ) about DNS. More reason to leave it on the DC.
 
This could be a cached arp entry issue. When windows boots up it does a DHCP request. When the DHCP server responds, the PC will then do a gratuitous arp on that address, before it actually configures the network adapter with that address. If anything/something on the network responds to that arp with a different MAC address for that IP address, the machine will then not configure it's IP address and give you the "Duplicate Ip address" error

Things to try. NOTE these may or may not be solutions. They are JUST things to try>

Change the PC's MAC address. Most network adapters let you change their MAC address. Look for "locally administered address" in the configuration for the card. If this works then most likely something is responding with a different address.

Do a ipconfig /renew until it get's a new address. I have actually had this work. Up arrow for last command in a CMD prompt and then enter as fast as you can.

Find out what is responding to the arp with the other address and clear it's ARP table. NOTE this may not be the machine with the IP address in the ARP request.

This may not be your problem, but I have run across this. I am still not 100% sure what has caused it, but I think it was one of our routers responding back with a old or incorrect ARP entry. Clearing the ARP tables on the router and CAM tables on the switch seems to have fixed it. Since there are only 8 PC's on the network I suspect you are not running devices where you can clear these tables. (Unmanaged). I have some sniffer traces on this.. I should go back and look at them again. That's the problem when you find something that works you don’t actually go back and find out exactly why, because you are too busy. :( :)
 
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