To force the DHCP client (dhclient) on a FreeBSD system to renew its IP address and get a new lease, you can use the dhclient command with the -r option.
For example, to renew the IP address for the em0 interface, you can use the following command:
dhclient -r em0
This will release the current IP address and request a new lease from the DHCP server.
You can also use the -f option to force the DHCP client to release the current IP address and request a new lease, even if the current lease is still valid. For example:
dhclient -f -r em0
This will force the DHCP client to release the current IP address and request a new lease, regardless of the remaining lease time.
Note that the dhclient command will only renew the IP address for the specified interface. If you want to renew the IP address for all interfaces, you can use the -a option instead of specifying a specific interface. For example:
dhclient -f -r -a