The default method for LQ devices out of the box to initially obtain an IP address is DHCP and this is the preferred method when setting up a Link-Group over a LAN.
Most networks allocate IP addresses using DHCP. The addresses provided are dynamic and will change from time to time.
DHCP is not recommended for the Link-Master and is not recommended for units linked to the master in some situations. An example of this is when the Link-Group has to navigate 2 or more firewalls.
In these cases you will allocate the network settings statically. To do this, navigate to: Device > Network in the Core Configuration Manager and setup a static IP address, subnet mask, gateway and external IP address if needed.  
You will use an external or public IP address when routing LQ devices over firewalls (this will almost always be the case when connecting over the Internet). A Link-Master connected to devices beyond a firewall will always use an external IP address and an external port. Link-Members will use external addressing and ports if connecting over firewalls also.