This happens if your computer takes an IP address that is being used by another computer. After the duplicate address is identified, one or both computers shut down their network interfaces. You may see a message explaining what happened.
This can happen in either Mac OS X or Mac OS X Server version 10.3 or later.
Tip: A switch is a more sophisticated type of Ethernet hub. This document only applies if you are using one. If you are on a large network, ask your administrator if you are using a switch.
To resolve the issue:
During startup, Mac OS X sends four ARP probes to determine whether a duplicate IP address exists on the network. Four is not enough when using certain switches. To solve the issue, increase the number of ARP probes sent at startup by editing a configuration file.
Important: The following steps describe an advanced technique using the command line in Terminal. Review the instructions before you begin. If you are not comfortable following these instructions, you should seek assistance. Inappropriate changes to the configuration file could prevent system features from working properly.
Follow these steps:
- Open Terminal (/Applications/Utilities/).
- Type: sudo pico /System/Library/SystemConfiguration/IPConfiguration.bundle/Resources/IPConfiguration.xml
- Press Return.
- Enter your administrator password when prompted, and press Return.
- Use the arrow keys to scroll to these lines:
<key>ARPProbeCount</key>
<integer>4</integer>
- Change the integer value (4) to 15 or more.
- Press Control-O to save the file, and press Return to confirm.
- Press Control-X to exit pico.
Note: Increasing the number of ARP probes at startup increases the amount of time the computer takes to start up.