Many computers connected to the Internet have short-lived connections,
such as dial-up, or are turned off part of the time.

How many nodes on the Internet are online (connected & on) at a given
time? In particular, I'm curious about the following sub-questions:

  * of all IP addresses, including servers, routers, workstations, and
home computers, how many are online at a given time?
  * of nodes with always-on connections, how many of them are actually
online (responsive) at a given time?
  * considering only workstations/personal computers, how many are
online at a given time?
  * considering workstations and personal computers in two categories,
those with always-on connections and those with dial-up (or
not-always-on) connections, how many in each category are online at a
given time?

I'm interested in the fraction of the total rather than an absolute
count for each set.

Hi Ezrakilty-ga,

I've had a look around, and I don't think I am going to be able to
come up with any useful numbers myself. But I have seen similarly
scoped questions answered before, so maybe another researcher has all
the right sources.

What did occur to me however, even before I started looking, was that
it's going to be very very hard to get any accurate numbers for
workstations and personal computers, as most ISPs use dynamic IP
addresses, of which maybe 70% are allocated at any given time. However
that IP block maybe utilised by a dial-up pool with maybe 10x the
number of computers potentially accessing it. Then there is the matter
of Network Address Translation. While I am connected to one of my ISPs
dial-up nodes, I am also providing a shared internet connection for 3
other computers.

Also, with respect to servers. Many single devices (server, firewall
etc) may have multiple real IP addresses allocated. My own server, a
single computer with a single network card, occupies two
internet-visible IP addresses.

As only TCP/IP, a Layer-3 protocol, is available to us to map these
sorts of things, we are unable to account for occurances like that as
Layer-2 information such as a MAC address is not available to us.

I hope that helps, I will keep an eye on the question to see what
others come up with.

Regards,
Sycophant-ga