AutoIP negotiation module for link-local addresses


mount -Tio-net [-o option,option,...]

Runs on:



Specify the interface on which the AutoIP service is started. Only one interface is supported at one time. The default is "en0."
Attempt to claim address for the link-local address. If this fails, a random address is attempted until an unused IP address is found. You can use this option to force the AutoIP module to use a certain initial IP address. By default, this is a random IP address based on the MAC address of the interface. The same initial IP address would be chosen for a specific MAC address. This option is specified in dotted numeric notation.
Enable debugging in verbose mode. Debug messages are logged to slogger.
Abandon the link-local address AutoIP is using. By default, the AutoIP module attempts to defend the link-local address it's using. This means that it challenges the other host on its use of the address. If the other host persists, the AutoIP module releases its IP address, and chooses another. If you use this option, the AutoIP module releases the IP address as soon as a conflict is detected.
Set the delay before packets are transmitted. This affects the PROBE packets only. The delay is specified in milliseconds. You can set this option for a range of 8000 to 1 ms. The default is 2000 ms. You may want to set a shorter delay if your network isn't connected with Ethernet switches.


The AutoIP io-net module ( configures a specified interface with a link-local IP address by negotiating with neighboring hosts. If no host on the local network is using the IP address that the module has chosen, the interface is configured with the chosen address.

The AutoIP module chooses its address from the IANA registered IP address network of 169.254/16. Some of this network is reserved for special purposes, so the available addresses are from to

Once an IP address is chosen and configured, the AutoIP module continues to monitor the network for address conflicts, and either defends or changes the address assigned to the interface to correct conflicts.

Only one interface can be supported at one time. The io-net module can be loaded only once.

The AutoIP module begins transmitting packets as soon as it detects that the specified interface is available. If the driver that provides the interface is unmounted, the AutoIP module waits until the interface is available again, and starts the negotiation process from the beginning.

When the AutoIP module configures a TCP/IP interface with an IP address, it does so as an alias. This way, if the interface already has an IP address, it won't delete the original address; the interface is assigned both addresses. This allows the module to coexist with dhcp.client. There is no way for the AutoIP module to detect that you have unconfigured the link-local IP address on the interface, so if you don't want the AutoIP link-local IP address to be configured any longer, you must unmount the AutoIP module. Also, if you're configuring the interface manually along with a link-local address, you must pass alias argument to ifconfig so you don't delete the link-local address by accident. Also if you're deleting the manually configured address, you must specify the specific address, or ifconfig may end up deleting the link-local IP address if it was the first IP address defined.


These examples assume a manual configuration in combination with AutoIP.

Configuring the interface:

ifconfig en0 alias

Unconfiguring the interface:

ifconfig en0 delete

Don't execute the following:

ifconfig en0 delete

This following command line mounts the AutoIP module to service interface en0. The initial link-local IP address that it PROBEs for is; it has a 200 ms delay between PROBE packets. If an IP address conflict is detected after the interface has been configured, it releases the address immediately.

mount -T io-net -oif=en0,ip=,debug,delay=200,abandon

See also:

dhcp.client, ifconfig, netstat,