DHCP Auto Image Update support
DHCP includes support for Auto Image Update which is a mechanism that allows for the automatic upgrading and updating of network devices. For this purpose, DHCP uses the vendor-specific option of 125.
This is a feature that allows network devices, such as switches, routers, access points, and others, to be able to download an image or firmware upgrade accompanied by an automatically from a server on the network.
Option 125 indicates to the client the IP address of primary and backup TFTP or SCP servers from which a new firmware image and a new configuration file can be downloaded. It is a method by which you can achieve mass deployment and configuration of many devices with automatic upgrading without the need to individually upgrade each individual device.
If this option is not set, the Syslog message will appear to inform you of that like so:
*Jun 15 01:31:38.582: DHCPD: No option 125
Links:
https://forum.networklessons.com/t/cisco-ios-dhcp-relay-agent/1121/69?u=lagapides