Still celebrating National IT Professionals Day with 3 months of free Premium Membership. Use Code ITDAY17

x
?
Solved

IP Conflict

Posted on 2008-10-03
7
Medium Priority
?
778 Views
Last Modified: 2013-11-09
I am going to try and explain this as best I can.  I have seen this issue before, I have applied the fix, but never really understood technicall why it occurs.  This time around, I need your help to understand why the following has occured.

I have a terminal server running Windows 2003 Server.  This server has a dual BroadCom NIC.  The primary card has been enabled since day one; the secondary card is disabled and all it's services.  Today, after running for 2 years, the primary NIC stop working.  From a workstation, if you ping the IP Address - it replies timed out and every so often it replies.  

* The server was rebooted, and nothing happened.  Same thing.  
* We unconfigured the static IP Address and disabled that card.
* Enabled the secondary card and reconfigured it with the static address from the primary.  Right away, the system responds with "Duplicate IP Address".  We rebooted the system again, and same message.  

* We checked the primary card to make sure it does not have that IP Address taken.  And it did not.  
* We reenabled the primary NIC and it got an IP address dynamically from the DHCP server... BUT, that IP would not respond from any workstations, nor could we connect to it.  

So, we decided, that NIC is dead.  On the secondary NIC, we again tried to put the orginal IP Address and we still got "IP Address Conflict".  We enabled DHCP, it received and IP Address, and we were able to connect to that server.  But we needed the original IP or we would have had to change the connection settings on all the PC's.

Once my level II tech explain the situation to me, I knew right away how to fix it...  Here's what I did, but I don't understand why it fixes it...

* Enabled the original NIC.
* Allowed it to get a DHCP address.
* Then disabled it, and renabled it and statically entered the ORINAL IP ADDRESS.
* Then renable DHCP - and at this point is where the error went away.
* I permanently disabled the primary card and configured the secondary NIC with the original IP Address.

So some how, the primary NIC was locking out the original IP Address?
0
Comment
Question by:BygRob
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
7 Comments
 
LVL 7

Expert Comment

by:Mikealcl
ID: 22636809
This almost sounds like an issue with the switch.  Like its not updating the mac table until the network card reports using a different ip address.  Once that is changed the switch mac table assigns the original ip from nic 1's port to the port for nic 2?


0
 
LVL 1

Expert Comment

by:freefromspam
ID: 22636846
Was the server part of a cluster?
0
 

Author Comment

by:BygRob
ID: 22636859
No cluster.
0
Take our survey for a chance to win!

As a valued customer of Targus, we’d like to ask you a few questions about us. As thanks, you will be automatically entered for a chance to win a $500 VISA gift card. To enter, just complete the survey by September 15, 2017.

 

Author Comment

by:BygRob
ID: 22636874
Good point Mikealcl.  I will look into that switch.
0
 
LVL 4

Accepted Solution

by:
Patrick49er earned 2000 total points
ID: 22636984
This isn't a switch issue but rather an issue with you DHCP and DNS servers.  Switches care more about MACs, which can be noted by the fact you cannot tell what the IP address is for a device connected to a switch port but you can the MAC.

Make sure that you do not have a WINs entry that is hanging up with the name of the server to the IP.  DNS will also have this listed.  If you use entries in your DHCP server for reserved IP addresses, you will have an issue since it assigns the IP according to the MAC you supply.  However, with your solution that you did, it does not sound like you use reserved addresses.

With that in mind, I would bet your DNS and/or WINs was not updating.  If you are forced into this situation, you can always go into your DNS and/or WINs servers and manually remove references to the server for that IP.  By doing the procedure you did, there was a logical removal of the IP address and MAC address from the server name.
0
 
LVL 39

Expert Comment

by:ChiefIT
ID: 22640240
When you get an IP address dynamically, the DHCP server provides a DHCPoffer. Within the offer packets, it tells the client requesting the DHCP address to send out an ARP ping to see if the IP address is taken. If the address is either reserved in DHCP or a ARP ping reply is returned, the offer is no good and the DHCP client will request again. If no reply or reservation, the offer goes through and a lease is assigned.

ARP stands for Address resolution protocol and it is used to map IP addresses to MAC addresses.

As Patrick49r was saying, a DHCP reservation will reserve an IP for a MAC address. If reserved, no other NIC can get that IP because it is reserved by MAC address, not by servername. Your DHCP server will reply to a ARP ping in the event the IP address is reserved. If it compares the two MACs and finds them to be dissimilar, you will get the error you are seeing.

So, Patrick49r had a very good analasys of the situation.

DHCP basics: (for your viewing pleasure. LOL)
http://support.microsoft.com/kb/169289

0
 
LVL 4

Expert Comment

by:Patrick49er
ID: 22678485
Is this one closed?
0

Featured Post

Take our survey for a chance to win!

As a valued customer of Targus, we’d like to ask you a few questions about us. As thanks, you will be automatically entered for a chance to win a $500 VISA gift card. To enter, just complete the survey by September 15, 2017.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Hello All, I have been training on Multicast for a while now and whenever I start the topic , I find out that my friends /  Colleagues mention that they do not know how to test Multicast Joins. As most of the multicast would be video traffic and …
Configuring network clients can be a chore, especially if there are a large number of them or a lot of itinerant users.  DHCP dynamically manages this process, much to the relief of users and administrators alike!
In this brief tutorial Pawel from AdRem Software explains how you can quickly find out which services are running on your network, or what are the IP addresses of servers responsible for each service. Software used is freeware NetCrunch Tools (https…
We’ve all felt that sense of false security before—locking down external access to a database or component and feeling like we’ve done all we need to do to secure company data. But that feeling is fleeting. Attacks these days can happen in many w…
Suggested Courses

722 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question