When a gateway AP detects it has the same IP address as another host on the LAN you will be alerted in 2 places...
- The AP icon will turn yellow and an alert will report, "This gateway is disabled. It is experiencing an IP address conflict with another device on its local LAN".
- The connectivity graph will turn gold. When you place your mouse over the connectivity graph on the AP detail page a warning "Gateway warning (IP address conflict on local LAN)" will appear.
You must resolve this IP address conflict for the AP to be able to operate correctly. Here are some actions you can take to remedy the issue.
Find the IP Address of the AP
- Log into Dashboard.
- Navigate to Monitor > Access points.
- Click on the gateway AP reporting an IP address conflict.
- Locate the LAN IP address value in the AP detail page.
- Notice the IP address of the AP and whether it was assigned statically or dynamically (DHCP).
Verify DHCP Service
- Locate and disconnect any unauthorized DHCP servers from your LAN.
- Verify non-overlapping address pools are being used if you LAN contains multiple DHCP servers for fault tolerance.
Resolve IP Address Conflict
- If the AP received its IP address via DHCP, try adding the IP address it received to the DHCP reservations list and then reboot the AP. This will force the AP to obtain a new IP address from the DHCP server.
- If the AP is configured with a static IP address, look in your DHCP logs to see if another host on the LAN obtained the same IP address from DHCP. If this is case exclude the IP address from the DHCP scope and reboot the host with the duplicate IP address.
- If the AP is configured with a static IP address,and you cannot locate another host using the same IP address in the DHCP logs, you may need to power off the AP and physically locate the host. In this situation ping and arp can be useful in finding the hosts MAC address.
- When the AP is powered off, ping the IP address. Once you pinged the address use ARP to locate the MAC address of the client.
- Once you have the MAC address of the client you can block it from your switch port or use the information to physically locate the port the device is connected to and subsequently remove it.
Note: Some DHCP servers have the ability to perform Conflict detection by performing a ping test of the IP address before assigning it to a DHCP client.