The default settings allocates 31 lower bits for port-id, 1 higher bit for mcast and the rest 30 higher bits for node-id. The procedure to set the address format in default mode is called during initialisation of the simulator as:
# The preamble set ns [new Simulator] # initialise the simulation;
It can also be called explicitly set as:
\$ns set-address-format def
Note that this is the default and users do not typically need to configure an address format.