Updated: May 06, 2022

AutoIP negotiation utility for link-local addresses


autoipd [-dfv] [-a num] -i iface_name [-p num] [-s initial_llip]
        [-t timeout] [-w num]

Runs on:

QNX Neutrino


-a num
Specify the number of ARP announcements to make to announce that an IP address is now in use. The default is 2 (ANNOUNCE_NUM).
Disable “defend” mode (enabled by default).
Force an auto-ip, even if a routable IP already exists for that interface.
-i iface_name
The name of the interface.
-p num
Specify the number of ARP probes to make to determine whether an IP address is already in use. The default is 3 (PROBE_NUM).
-s initial_llip
Specify an initial ip address.
-t timeout
Wait timeout seconds after bringing link up before starting auto-ip.
Be verbose.
-w num
Set the time between the last probe and the announcement (ANNOUNCE_WAIT), and the time between announcement packets (ANNOUNCE_INTERVAL), to num seconds. The default is 2 seconds.


The autoipd utility 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 utility has chosen, the interface is configured with the chosen address.

The AutoIP utility 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 utility 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.

When the AutoIP utility 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 primary or first IP address; the interface is assigned with both addresses (and potentially more if needed). This allows the utility to coexist with other modules or applications that configure TCP/IP stack interfaces, such as dhclient (when used with the -a option).

When more than one IP address is assigned to an interface, it's considered an alias, and must be referenced directly if it needs to be deleted; otherwise you may delete the first IP address in the list of addresses, instead of the address you intended to delete. For example, if you're manually configuring an interface in combination with AutoIP, type something like this:

ifconfig en0 alias

This way, you won't replace an IP address that may already be configured for the interface.

To unconfigure the interface, type:

ifconfig en0 delete

This way, you specifically delete the configuration you previously set. If you execute:

ifconfig en0 delete

you'll delete the first IP address in the list (whatever this is), instead of the IP address you previously configured above, which may be what the AutoIP utility configured.

Based on:

RFC 3927