How to give IP (DHCP) by mac address?

I want to give IP 172.168.100.241 to MAC Address XX-XX-XX-XX-XX-XX how to do that?

thank you

/ip dhcp-server leases add address=x.x.x.x mac-address=xx:xx:xx:xx:xx:xx

where to specify the gateway, subnet mask and dns?

thank you

in the DHCP server settings