Adjust the DHCP lease time for a computer in AirPort Utility on Mac
When you use AirPort Utility Setup Assistant to set up your new base station or to extend an existing network, it automatically configures the best settings for your network. That said, you can control how long an IP address is assigned to a device on your network by adjusting the DHCP lease time. In an environment where there are more devices connecting and disconnecting from the network than there are available IP addresses, you can use very short lease times to allow DHCP to reuse unused IP addresses faster.
Open the AirPort Utility app
on your Mac, located in the Utilities folder in the Applications folder. In the graphical overview, select the base station you want to configure, then click Edit. You may need to enter a password for the base station.
Click Network, then verify that “DHCP and NAT” or “DHCP only” is selected in the Router Mode pop-up menu.
Click the Network Options button near the bottom of the pane. In the dialogue that appears, enter a duration in the DHCP Lease field, then choose a value (minute, hour or day) from the pop-up menu on the right.
Important: During setup, AirPort Utility Setup Assistant automatically determined whether “Enable IGMP Snooping”, “Block incoming IPv6 connections”, “Allow Teredo tunnels” and “Allow incoming IPSec authentication” should be turned on or off. Don’t modify these settings unless you’re instructed to do so by your ISP or network administrator.
Click Save to save your changes and close the dialogue, then click Update to save the changes.