  The availability of end-hosts and their assigned routable IP addresses has
impact on the ability to fight spammers and attackers, and on peer-to-peer
application performance. Previous works study the availability of hosts mostly
by using either active pinging or by studying access to a mail service, both
approaches suffer from inherent inaccuracies. We take a different approach by
measuring the IP addresses periodically reported by a uniquely identified group
of the hosts running the DIMES agent. This fresh approach provides a chance to
measure the true availability of end-hosts and the dynamics of their assigned
routable IP addresses. Using a two month study of 1804 hosts, we find that over
60% of the hosts have a fixed IP address and 90% median availability, while
some of the remaining hosts have more than 30 different IPs. For those that
have periodically changing IP addresses, we find that the median average period
per AS is roughly 24 hours, with a strong relation between the offline time and
the probability of altering IP address.
