PS: I checked, and my server has DHCP, which automatically
^^^^^^^^^^^^^^^^^^^^^^ Router ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
selects an address. It is not generally permanent, and
eventually "times out". This is the likely explanation of why
AIBO became invisible overnight.

Most routers give a fixed time 'lease' to an IP address. Typically
24 hours on the models I've used. Hard wired tend to automatically
renew their 'lease', even in standby.

That I didn't know.

"Lease" is the term used in books on the subject, but I couldn't find a
value for the interval in the router's setup.