36.1.4 Preventing Dual Distribution of IP Addresses

If the Switch is restarted after the DHCP server of the Switch has assigned addresses to DHCP clients, all of the DHCP address pools on the Switch become empty. Also, when the master switch is switched in the stacked configuration, all DHCP address pools are "free" in the same way.

When the Switch resumes assigning IP addresses to DHCP clients, the switch sends an ICMP Echo Request packet for a previously assigned IP address. The Switch checks whether a reply packet is returned and makes sure that no client is using the previously assigned IP address, avoiding a duplicate assignment of IP addresses. At the same time, if a client previously assigned a IP address extends the lease time, IP address does not change, so it does not affect client communication.

If a reply is returned for the ICMP Echo Request packet (a network terminal is using the IP address in question), the incident is displayed on the screen as a detected address conflict when the show ip dhcp conflict command is executed.