Hi Qazik,
The dhcp select global command needs to invoke an address pool created in global mode. The gateway and DNS are configured in the IP pool. In dhcp select interface, the IP address range of the current interface and mask is used as the IP address pool for delivery. You do not need to manually specify the IP address range. The gateway is the IP address of the current interface, and the DNS is configured on the interface.
I hope it helps.