IP Address Conflicts: Causes and Fixes

What Is an IP Address Conflict?

An IP address conflict occurs when two or more devices on the same network are assigned the same IP address. When this happens, the network cannot reliably deliver packets to either device, causing intermittent connectivity, dropped connections, or complete network failure for the affected devices.

Operating systems typically detect conflicts and display warnings like "Another device on the network is using your IP address" (macOS) or "There is an IP address conflict" (Windows).

Common Causes

• Static IP overlap -- An administrator manually assigns an IP that is already in use by another device or falls within the DHCP pool range.
• DHCP misconfiguration -- Two DHCP servers on the same network assign overlapping address ranges.
• Stale DHCP leases -- A device reconnects and receives a new IP, but its old lease has not expired and another device now holds that address.
• VM or container cloning -- Cloned virtual machines may retain the same static IP configuration as the original.
• Rogue devices -- An unauthorized device with a static IP configuration joins the network.

Diagnosing Conflicts

# On Windows: check for conflicts
ipconfig /all
# Look for "Duplicate IP address" events in Event Viewer

# On Linux/macOS: scan for duplicate MACs on the same IP
arp -a | sort
# Two different MAC addresses for the same IP = conflict

# Network-wide scan with arping
arping -D -I eth0 192.168.1.100
# If you get a reply, someone else has that IP

Resolving Conflicts

1. Release and renew DHCP -- On the affected device, release the current lease and request a new one: bash # Windows ipconfig /release && ipconfig /renew # Linux sudo dhclient -r && sudo dhclient
2. Change the static IP -- If one device uses a static IP, assign it a different address outside the DHCP pool.
3. Restart the DHCP server -- If the DHCP server's lease table is corrupted, restarting it forces fresh allocations.
4. Identify the conflicting device -- Use the MAC address from the ARP table to find which device holds the duplicate IP.

Prevention Strategies

• Use DHCP for all client devices -- Avoid static IPs on workstations and phones.
• Reserve static IPs via DHCP reservations -- Assign fixed IPs through the DHCP server (tied to MAC addresses) rather than configuring them on the device.
• Separate DHCP pool from static range -- If your subnet is 192.168.1.0/24, reserve .1-.49 for static devices and set the DHCP pool to .50-.254.
• Enable DHCP snooping -- On managed switches, DHCP snooping prevents rogue DHCP servers and tracks legitimate leases.