z-Tree and also z-Leaf have a funny way to determine their IP
address. They try to get their hostname and then look up reversely
the corresponding IP address with the help of the DNS mechanism.
Thus, your hostname must have a corresponding DNS entry, or an entry
If this reverse looking up of IP addresses fails, z-Tree and z-Leaf
will self-diagnose a missing IP address (which is misleading, since
the machine usually has an IP address and a working connection to