DHCPSD_ICMP(8)

NAME
icmp - detects an in use IP address via icmp(4).

DESCRIPTION
When an IP address is selected in response to a DHCP DISCOVER message, dhcpsd will send an ICMP ECHOREQUEST message to the IP address to discover if it is already in use or not.

All the following rules must be true for sending an ICMP ECHOREQUEST:

•   The address selected is due to a DHCP DISCOVER message.

•   The address must not have been configured by a plugin.

•   The address must not have an active lease.

Any one of the following rules must also be true for sending an ICMP ECHOREQUEST:

•   The address has not been offered to client before.

•   The address is being offered to a client different from the last.

•   The address is being offered to the same client that previously leased it and a least N seconds have elapsed.

If an ICMP ECHO is received then the address treated as it it has been DHCP DECLINEd and another one is selected, which may also be probed using the above rules. If an ICMP ECHO is not received within N seconds then dhcpsd assumes that the address is not in use and offers it to the client.

The client SHOULD do it's own address checking via arp(4) and if it's in use then the client should send a DHCP DECLINE message to dhcpsd and DHCP DISCOVER a new address.

SEE ALSO
dhcpsd(8).

AUTHORS
Roy Marples <roy@marples.name>

BUGS
Please report them to https://roy.marples.name/projects/dhcpsd