The set command is used to set an existing value, in contrast to
add which is used to add something to the parameter tree. For example, the
set command is used to specify the IP address for an Ethernet interface:
set network interface eth0 IP address. In contrast, new hosts need to be added with the add command before their parameters can be specified;
add network hosts IP address makes an entry for a host with the specified IP address in the
hosts list. Parameters for this new host can be changed with the set command:
set network hosts IP address name
hostname.