IP Conflict

By cypher.msix ·
One of our servers has an IP Address of Every few days (and sometimes every day) the system reports an IP Address conflict with another machine.

I've traced the physical addresses down to the IP addresses and resolved the names of the machines from there. They are all laptops that are causing the issue.

My assumpion is that these users take home their laptops, and I'm guessing they are getting on their home networks and getting the same IP Address ( Then when they come to work and login to the domain, I think that's when they conflict occurs (always in the early a.m.)

The conflict is causing issues with software on the server and I need to resolve the issue as soon as I can. Is there anything I can do for the short-run to get this situation corrected? And how can I go about correcting this issue so that we can avoid this problem in the future?

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How IP Address Conflicts Happen.

Two computers can acquire conflicting IP addresses in any of several ways:

* A system administrator assigns two computers on the LAN the same static IP address

* A system administrator assigns a computer a static IP address within the local network's DHCP range (dynamic IP range), and the same address is automatically assigned by the LAN DHCP server.

* A malfunction in the network's DHCP server allows the same dynamic address to automatically be assigned to multiple computers.

* An Internet Service Provider (ISP) accidentally assigns two customers the same IP address (either statically or dynamically).

* A mobile computer is put into standby / hibernate mode and then awakened later.

Note that other forms of IP conflicts can also occur on a network. For example, one computer may experience an IP address conflict with itself if that computer is configured with multiple network adapters. System administrators may also create IP conflicts by accidentally connecting two ports of a network switch or router to each other.
Recognizing IP Address Conflicts
On most Microsoft Windows computers, if you attempt to set a fixed (static) IP address that is already active on the local network, you will receive the following pop-up error message:

The static IP address that was just configured is already in use on the network. Please reconfigure a different IP address.

On newer Microsoft Windows computers having dynamic IP conflicts, you should receive a balloon error message in the Taskbar as soon as the operating system detects the issue:

There is an IP address conflict with another system on the network.

Sometimes, especially on older Windows computers, a message similar to the following may instead appear in a pop-up window:

The system has detected a conflict for IP address...

On Mac or Linux computers, a similar message will normally appear on screen.
Resolving IP Address Conflicts
Try the following remedies for IP conflicts:

1. For networks where IP addresses are fixed (statically assigned), ensure each local host is configured with a unique IP address.

2. If your computer has a dynamically assigned address, releasing and renewing its IP address can workaround IP address conflicts. See also - How to Release / Renew IP Addresses on Windows

3. If your home router is believed to have a faulty DHCP server causing IP conflicts on the home network, upgrading the router firmware may resolve this problem.
Hope this solves your Conflict issue.

Please post back if you have any more problems or questions.

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Thanks for the reply

by cypher.msix In reply to How IP Address Conflicts ...

What seems to be happening is that certain laptops are being taken home and jacked into the home network and being assigned the IP: Then the user brings that laptop back to the office and jacks ito our network which is where the conflict occurs as we already have a server setup using that IP address. Those laptops then get leased another IP Address that is available from the DHCP. But, this conflict screws wth the communication of some software on our server which means every time this happens, we need to reboot. :-/

Our DHCP is set to exclude - from distribution so the DHCP isn't assigning it to the laptops... at least to my knowledge. :-P

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how many static

by mark In reply to Thanks for the reply

If you don't have too many statically assigned addresses, you could use a different address range which isn't so common for home users. 192.168.12.* for example.

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by cypher.msix In reply to how many static

That is definately something I want to do in the future, but it looks like I have a lot of work ahead of me in cleaning up the structure of this network as it is

In the meantime, how can I tell which IPs are static and which are dymanic? In the DHCP I noticed the range starts at and runs up to 255 with a bunch of odd exclusions. There is also one object listed under the 'Reservasions' deal, which is the server in question (a not-so-important but none-the-less needed server).

And if I were to change up the IP configuration, is that something that can be done quickly and propogated appropriately or will there need to be massive reboots?

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repair connection

by mark In reply to Thanks

You should be able to change the dhcp scope and your static ip addresses without a reboot. the workstations with dynamic ips would pull new ip addresses with a reboot, but I believe they should see the icon down by the clock which would state limited or no connectivity. If you right click on that it should give you the option to repair connection. This should perform the ipconfig /release and ipconfig /renew and pull the new ip address scheme. The only other option I can think of for you which would be less work is to just change the static ip address of your server to .211 which I assume is high enough to not be assigned normally by a users home router. I'm not sure how that would affect the network and how many places your are using the .101 specific IP address.

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Do you really need a Static IP Address?

The difference between Static and Dynamic IP Addresses:

Static IP:
This means your ISP (Internet Service Provider) verbally gives you a specific, unique IP address that will not ever change. When setting up your DVR (or the router the DVR attaches to), you have to manually type this Static IP address into the DVR (or router) configuration screens. Then, when you want to connect to your DVR from across the internet, you just type your Static IP address into Internet Explorer, and you?re connected.

Dynamic IP:
This means that your ISP does not give you a specific IP address to manually enter, and always use. Instead, you configure your DVR (or router) to use DHCP (Dynamic Host Configuration Protocol). This means that whenever you turn your Modem (or router) on, your ISP will automatically send it an IP Address. However, the IP Address your ISP sends you, may not always be the same. It might send you a different IP address every time.

Dynamic DNS:

The good news, is that there is actually a free service, specifically tailored to fixing this sort of problem. This service, which is called Dynamic DNS, makes it so you don?t have to keep up with your changing IP Address. This service is tailored to home & small business users, who have DSL or Cable internet. You just go to and set up a free Dynamic DNS account. What this does, is ?map? a domain name (such as ?, to the IP Address your ISP assigns to you. So when you want to connect to your DVR, instead of typing the IP Address into Internet Explorer, you just type the domain name you registered for free at What?s so special about this service, is that when your IP Address changes, the new IP Address is automatically ?mapped? to your domain name. The end result is that you don?t need to keep up with your changing IP Address?you just need to remember your domain name, which is easy for anybody to do.

The only requirement is that you must have a Modem or Router that supports the Dynamic DNS service. Also, you will need to configure the Modem/Router to use Dynamic DNS.

I recommend the D-Link DI-604 (Costs about $35)? but any Router that supports Dynamic DNS should work fine.

Setting up Dynamic DNS is a somewhat technical process that many people require some assistance with. We can provide you with a detailed ?How-To? document, which explains the basics of how to set up Dynamic DNS. However, please understand that Dynamic DNS is an Internet based service that runs between your Router and the database at Dynamic DNS has absolutely nothing to do with the DVR you purchased from Security & More. Therefore, since we are not associated with, and we are not associated with the manufacturer of your Router?we can not offer technical support on making Dynamic DNS work.

If you require assistance with Dynamic DNS, you?ll need to contact the tech support at Dynamic DNS (, or the tech support department at the manufacturer of your Router.

Dynamic DNS can be a little tricky to configure?but that?s the trade off for not having to pay the extra cost of a Static IP Address.

Either way, your DVR will be fully network-capable. The only benefit of having a Static IP, is that when you go to connect to your DVR across the internet from a remote location?you will always know what your DVR?s IP address is. When you do not have a static IP, you need to keep up with what your current IP Address is, because it may have changed since last time you connected to the DVR.

Basically, this means that having a Static IP is much more convenient, because you don?t have to keep tabs on what your IP address is. However, your ISP is going to charge you a premium for this convenience. ISP?s charge about $40 a month for standard high speed internet service, without a Static IP. If you want to ?upgrade? to a package that includes a Static IP, your ISP may charge you as much as $80 a month.

Since all ISP?s are different, you really won?t know what the price difference is, until you call them and ask. If you find that a Static IP is too expensive for your budget?Please read the section below on Dynamic DNS, which offers a ?workaround? to the problems created by changing IP Addresses.

Please post back if you have any more problems or questions.

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