NetAlly Network Testing Solutions

Tech Tips



•  EtherScope nXG
•  AirCheck G3

Subscribe to Tech Tips

What does a Duplicate IP Address issue look like?

Within a subnet, it is important that only one station is assigned to an IP address. Otherwise, this can create problems for end-users as they try to utilize applications and network services. In this tech tip, we’ll explore how a duplicate IP can happen and what the symptoms are.

What causes duplicate IP addresses?

In most cases, duplicate IP conflicts are due to configuration mistakes. Perhaps a technician added a device to the network with a statically set IP address that is also assigned to the DHCP address pool for that subnet. At first, the device might work just fine. But sooner or later, that same address could be assigned to a machine trying to join the network with a DHCP allocated address. Most operating systems are designed for duplicate IP address detection and prevention, however, some are not, which will cause the duplicate IP problem.

Another way a duplicate IP conflict could happen is that both stations are statically set to the same address. Good IP management should help to prevent this, as well as active network discovery and IP detection with an analysis tool like the EtherScope nXG prior to deploying a new device.

What does an IP conflict look like?

Imagine the headache that your mail carrier would have if another house popped up on your street with the same house address as your own. Which house is the “correct” one? You may get some of your mail, while others are directed to the other house and vice versa. This is exactly what the two stations in conflict will experience when trying to access applications and services. Connectivity will suffer (or not work at all) because packets will not consistently be delivered to the correct device. ARP tables on all subnet devices will be constantly refreshed as the two endpoints compete for the IP address.

The EtherScope is designed to help quickly detect problems like this. Using ARP requests and analyzing the replies, it quickly detects and alerts you to duplicate IP conflicts, even pointing to the switch ports where the problem devices reside on the network.

How to fix duplicate IP addresses?

The next step is to fix the duplicate IP address detected. Here’s how you can resolve this issue:

  1. Restart your router: The simplest and first go-to method to solve the problem entails rebooting the router as it prompts a new IP address to be reassigned automatically to every device that is connected to the Wi-Fi network.
  2. Manual change of IP address: If restarting the router doesn’t resolve the issue, setting a static IP address for each device manually can resolve the conflict.
  3. Check for DHCP: Make sure that your devices are set to automatically get (DHCP) IP addresses. Sometimes, the issue could be that both devices are set to get static IP addresses.
  4. Disable and enable network adapter: This could potentially fix the problem by resetting and refreshing the network adapter’s settings, potentially clearing up any issues caused by the duplicate IP address.
  5. Update network adapter driver: If your network adapter drivers are outdated or corrupt, they can cause this problem. You might need to update your drivers to the latest version or reinstall them.

In conclusion, a duplicate IP address can be a potential pitfall in your network system, causing disruptions in connectivity and application usage. Monitoring your IP addresses for possible duplicate conflicts and taking swift corrective action highlighted above should it occur can easily resolve this issue. Keeping a close eye on the health of your network’s IP addresses are a vital process in maintaining a robust and efficient network.

Author Bio –
Product Manager – Wireless

Julio Petrovitch is a product manager at NetAlly, plus a certified CWNA/CWAP/CWDP/CWSP. He’s worked with network design, testing and validation for more than 15 years. Throughout he’s career he has had the opportunity to work with multiple networking technologies, including POTS, DSL, Copper/Fiber Ethernet, Wi-Fi, Bluetooth, and BLE.