This read-write IP address sets the address for the local WAN port, expressed as a 4-byte dotted-decimal value, where setting it to 000.000.000.000 means no address is defined and the unit instead uses the global default IP address. An administrator assigns a per-port address when that port needs a distinct IP identity separate from the unit's default addressing. For example, leaving this at all zeros on most ports while assigning a unique address only to a port needing independent addressing keeps configuration simple while still allowing exceptions.