The default hierarchical node-id consists of 3 levels with 8 bits
assigned to each level. The hierarchical configuration may be invoked as
follows:
$ns set-address-format hierarchical
This sets :
* 8 bits for port-id,
* 24 bits for node-id assigned in
- 3 levels of hierarchy
- 8 bits for each level
- looks like 8 8 8
- or 7 8 8, if multicast is enabled.
