Overview

While reviewing Host logs, you may notice frequent DHCP lease requests for particular devices:

  [06/Oct/2020 14:45:45] [IPv4] 10.0.4.45 [MAC] 80-82-23-61-bf-a8 [Hostname] Sados-iPhone - IP address leased from DHCP

  [06/Oct/2020 14:45:46] [IPv4] 10.0.4.45 [MAC] 80-82-23-61-bf-a8 [Hostname] Sados-iPhone - IP address leased from DHCP

  [06/Oct/2020 14:45:56] [IPv4] 10.0.3.188 [MAC] f0-67-28-6a-92-d9 [Hostname] OPPO-Reno3 - IP address leased from DHCP

  [06/Oct/2020 14:45:56] [IPv4] 10.0.3.188 [MAC] f0-67-28-6a-92-d9 [Hostname] OPPO-Reno3 - IP address leased from DHCP

This article provides explanations about devices' common reasons for requesting DHCP leases 3-4 times straight after each other.

Information

Kerio Control sets 4 days as the default Lease timeout for DHCP clients. The configuration varies depending on the DHCP scope configuration. Unless the timeout is reached, the device won't be released from the DHCP server scope automatically. The device itself may be disconnecting from the Kerio Control network.

Screen_Shot_2020-12-18_at_10.09.23_AM.png

For more information, please refer to DHCP Lease Renewal and Rebinding Processes.

The most common reasons for the frequent DHCP lease request are the following:

The device has outdated firmware/software.
The device is losing a WiFi signal connection and reconnecting.
If you have multiple access points (APs) on-site, then the movement of the device would cause switching between APs based on perceived differences in Signal level.

Note: only applicable if WiFi Auto-join (Connect Automatically) feature is enabled for all APs.

The extended DHCP output can be displayed while DHCP messages, DHCP requested/offered options, and DHCP unsupported messages items are enabled in Debug logs.

Screen_Shot_2020-12-18_at_10.20.06_AM.png

The usual flow of DHCP server-client communication:

DHCP server receives DHCPREQUEST from the device with the prebuilt DHCP options. Some of these options might be not supported (unrecognized) by Kerio Control.
DHCP server decides whether there is an existing lease or not. If not -> assigns the new lease.
DHCP server passes the DHCP options (parameters) to the client device.

The examples of various devices behaving in a different way are shown below.

iPhone

Screen_Shot_2020-12-17_at_5.45.20_PM.png