The dhcp relay source-ip agent-ip command sets the source IP address of DHCP relay requests to the IP address of the interface where DHCP relay is configured.
The undo dhcp relay source-ip agent-ip command cancels the setting.
By default, the IP address of the outbound interface of DHCP relay requests is used as the source IP address of the requests.
After you run this command, when the DHCP relay sends a request for allocating IP addresses to the DHCP server, the source IP address of the request is the IP address of the interface where DHCP relay is configured.