Message-ID: <1999Dec2119.38.47.7242@koobera.math.uic.edu>
Date: 21 Dec 1999 19:38:47 GMT
Newsgroups: comp.protocols.tcp-ip.domains,comp.dcom.net-analysis
Subject: Over 80 million IP addresses have PTR records
Organization: IR

My latest DNS survey started from a random set of 1000000 IP addresses,
excluded 31645 of them (e.g., 10.*) for policy reasons, and looked up
*.*.*.*.in-addr.arpa PTR records for the rest.

The survey found PTR records for 19543 of the 1000000 IP addresses. This
means that roughly 83.9 million of the Internet's 4.3 billion IP
addresses have PTR records.

Internet survey results are often misreported in the press. Let me
emphasize that a count of PTR records is not a count of computers. The
number of live computers on the Internet during the survey period might
have been smaller or larger than 83.9 million, for several reasons:

   * One computer may have several names and several IP addresses. One
     corporation has a firewall with several thousand addresses.

   * Dead computers may have names and IP addresses. Some companies have
     assigned huge blocks of addresses to nonexistent computers.

   * Computers may be on the Internet without being listed in any PTR
     records, although they are cut off from some Internet services.

   * All the DNS servers for a computer may be temporarily unreachable
     or misconfigured, even when the computer itself is alive and well.

The survey took 4.5 hours this morning on a Pentium-133, using several
new pieces of DNS software: an asynchronous resolver library, a parallel
address-resolution filter, and a robust DNS cache. In theory, the filter
can use BIND as a cache; in practice, BIND is too fragile to support a
large survey.

---Dan