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Network Working Group                                          M. LottorRequest for Comments: 1296                             SRI International                                      Network Information Systems Center                                                            January 1992Internet Growth (1981-1991)Status of this Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard.  Distribution of this memo is   unlimited.Abstract   This document illustrates the growth of the Internet by examination   of entries in the Domain Name System (DNS) and pre-DNS host tables.   DNS entries are collected by a program called ZONE, which searches   the Internet and retrieves data from all known domains.  Pre-DNS host   table data were retrieved from system archive tapes.  Various   statistics are presented on the number of hosts and domains.Table of Contents   Introduction....................................................1   How ZONE Works..................................................2   Problems with Data Collection...................................3   Scope of the Study..............................................3N. Results......................................................4N.1 Number of Internet Hosts....................................4N.2 Number of Domains...........................................6N.3 Distribution of IP Addresses per Host.......................7N.4 Distribution of Hosts by Top-level Domain...................7N.5 Distribution of Hosts by Host Name..........................8   Future Issues...................................................8   RFC References..................................................9   Security Considerations.........................................9   Author's Address................................................9Introduction   This document provides statistics on the growth of the Internet by   examining the number of Internet hosts and domains over a 10-year   period.  Before the Domain Name System was established, practically   all hosts on the Internet were registered with the Network   Information Center (SRI-NIC) and entries were placed in the Official   Host Table for each one.  Data on the number of hosts for pre-DNSLottor                                                          [Page 1]

RFC 1296              Internet Growth (1981-1991)           January 1992   years comes from copies of the host table at selected times.  The DNS   system was introduced around 1984 but took almost 4 years before it   was fully implemented on the Internet.  However, by this time many   hosts were no longer registered in the Host Table.   In 1986, the ZONE (Zealot Of Name Edification) program was written.   ZONE was originally intended to be used during the host-table-to-DNS   transition period.  ZONE would "walk" the DNS tree and build a host   table of all the information it collected.  This host table could   then be used by sites that had not yet made the DNS transition.   However, ZONE was never used for this purpose.  Instead, it was found   to be useful for collecting statistics on the size of the domain   system and the Internet.   ZONE could not collect complete data on the DNS until around 1988,   because early versions of BIND (the popular Unix DNS implementation)   had major problems with the zone transfer function of the DNS   protocol.  ZONE has been used in varying ways ever since to collect   this information.  In the first few years, it was used to produce a   wall-size chart of the domain tree.  However, the number of domains   quickly outgrew the size of the wall and the charts were abandoned.   In later years, statistics on the number of hosts and domains were   extracted from the resulting host table, sometimes categorizing data   based on top-level domain names or on computer system type or   manufacturer.   The time to gather the data also grew from hours to a week, and the   size of the host table produced soon reached 50 megabytes.  In order   to reduce the amount of data collected, ZONE is now run in a mode   collecting only host names and IP addresses, ignoring protocol, host   information and MX record data.  The host table is then groveled over   by some utilities (such as sort, uniq and grep) to produce the   statistics required.  ZONE is currently run every 3 months at SRI.How ZONE Works   ZONE maintains a list of domains and their servers and a flag   indicating whether information for a domain has been successfully   loaded from one of the servers. Because of another bug in BIND, ZONE   must be primed with a list of all the top-level domains and their   name servers.  It then cycles through the domain list, attempting to   contact one of the servers for each domain not yet transferred.  When   a server is contacted (via TCP), a Start of Authority (SOA) query is   first sent to make sure the server is authoritative for the domain   being requested.  If so, then a zone transfer query (AXFR) is sent to   request all the resource records for the domain to be retrieved.   When a name server record (NS) is received, the referenced domain andLottor                                                          [Page 2]

RFC 1296              Internet Growth (1981-1991)           January 1992   server are added to the list of domains to process.  When host   records (A, CNAME, HINFO, MX) are received, they are added to an in-   core table of host information.  The program ends when it has cycled   through the entire list of domains without receiving any new   information.  It then dumps the table of host information to a   HOSTS.TXT format file.Problems with Data Collection   For various reasons, some Internet sites do not allow zone transfers   of their domain servers.  ZONE also eventually gives up trying to   transfer a domain after too many failures.  The number of domains   that could not be zone transferred during the 1-Jan-92 ZONE run was   around 800 out of 17,000.  Additionally, it is assumed that not all   hosts on the Internet are registered in a domain server.  These   problems cause the statistics gathered by ZONE to be lower than the   actual amounts.   Manual review of some of the data collected by ZONE also shows a lot   of random entries in the DNS.  Misformatted entries may cause bogus   server or host records to appear.  Many times a server is found to   not be authoritative for the domain listed.  Sometimes entire domains   are renamed and their old entries left in place for a transition   period, thus causing each host within that domain to be counted   twice.  These problems cause the results of ZONE to be higher than   the actual amounts.   Manual scanning of the data indicates that the additional entries are   insignificant compared to the missing entries discussed earlier.   ZONE data can thus be viewed as the minimum number of Internet hosts,   and not the actual figures.   A final problem with data collection is that of expense.  Downloading   domain information from every domain on the Internet generates a   large amount of network traffic.  It also puts an extra CPU load on   each domain server it must contact.  An organized effort might be   considered to have only one such program doing this on the Internet   at regularly scheduled intervals to keep the problem of multiple data   collectors from occurring.Scope of the Study   A problem with counting hosts and domains on the Internet is defining   what the Internet really is.  Finding host entries in the DNS does   not necessarily indicate that the host is reachable from the   Internet.  Many companies have mail gateways between the Internet and   their local nets, thus disallowing direct access.  However, some of   these companies advertise all their hosts, and some advertise onlyLottor                                                          [Page 3]

RFC 1296              Internet Growth (1981-1991)           January 1992   the gateway.  Are these hosts on the Internet or not?   Furthermore, many domains in the DNS are just mail-forwarding (MX)   entries for off-Internet (such as Usenet) sites.  Are these domains   really part of the Internet and should they be counted in an Internet   size study?   For the purposes of this study, a host has been defined as a   [name(s),IP-address(es)] grouping discovered from the DNS.  This   prevents us from counting a host with multiple names or addresses   more than once.  However, this does not consider whether the host is   directly accessible or not.  When ZONE counts the number of domains   it includes all domains referenced by an NS record in the DNS, thus   including MX-only domain sites in the final results.N. Results   This section presents data from archive tapes of SRI-NIC from 1981 to   1986, and statistics gathered by runs of ZONE from 1986 to 1992.N.1 Number of Internet Hosts   The chart below shows the number of IP hosts on the Internet.  These   are hosts with at least one IP address assigned.  Data was collected   by ZONE except where noted.  The following two sections are graphs of   the data in this chart.        Date             Hosts        08/81              213          Host table #152        05/82              235          Host table #166        08/83              562          Host table #300        10/84            1,024          Host table #392        10/85            1,961          Host table #485        02/86            2,308          Host table #515        11/86            5,089        12/87           28,174        07/88           33,000        10/88           56,000        01/89           80,000        07/89          130,000        10/89          159,000        10/90          313,000        01/91          376,000        07/91          535,000        10/91          617,000        01/92          727,000Lottor                                                          [Page 4]

RFC 1296              Internet Growth (1981-1991)           January 1992                        Number of Internet Hosts (linear)800|780|760|740|                                                                  *720|700|680|                                                                 .660|640|620|600| T                                                              *580| h560| o540| u520| s                                                             *500| a480| n                                                            .460| d440| s420|                                                             .400| o380| f360|                                                            *340| H                                                         .320| o300| s                                                        *280| t260| s                                                       .240|                                                        .220|                                                       .200|                                                      .180|                                                     .160|140|                                                    *120|                                                   *100|                                                 .. 80|                                                * 60|                                               . 40|                                              * 20|                                       ..*...*  0|...*....*......*......*.....*.*....*...    -------------------------------------------------------------------    8     8     8     8     8     8     8     8     8     9     9     9    1     2     3     4     5     6     7     8     9     0     1     2                                   Date    "*"  = data point,  "." = estimateThis graph is a linear plot of the number of Internet hosts.Lottor                                                          [Page 5]

RFC 1296              Internet Growth (1981-1991)           January 1992                        Number of Internet Hosts (logarithmic)    | 1000000    |                                                                *.*    |                                                        ..*.*..*    |                                                     ...    | 100000                                          ..**    |                                              *.*  H |                                          ...*  o |                                        .*  s | 10000                                ..  t |                                    ..  s |                               ....*    |                         ...*.*1000|                   ...*..    |                ...    |            ...*    | ..*....*... 100|.     -------------------------------------------------------------------     8     8     8     8     8     8     8     8     8     9     9     9     1     2     3     4     5     6     7     8     9     0     1     2                                    Date     "*"  = data point,  "." = estimateThis graph is a logarithmic plot of the number of Internet hosts.N.2 Number of Domains   This chart shows the number of domains existing in the Internet   Domain Name System as collected by ZONE.        Date           Domains        07/88              900        10/88            1,280        01/89            2,600        07/89            3,900        10/89            4,800        10/90            9,300        01/91           11,200        07/91           16,000        10/91           18,000        01/92           17,000Lottor                                                          [Page 6]

RFC 1296              Internet Growth (1981-1991)           January 1992N.3 Distribution of IP Addresses per Host   This chart shows how many hosts have how many IP addresses.  This   data was collected on 1-Jan-92 and only the first 10 entries are   shown.     Addresses           Hosts         1              715143         2                9015         3                1027         4                 556         5                 314         6                 213         7                 100         8                  85         9                  58        10                  71N.4 Distribution of Hosts by Top-level Domain   This chart shows the number of hosts per top-level domain (top 40   only) on 1-Jan-92.  The percentage listed is the increase since 1-   Oct-91.  Large variations are probably due to problems and variations   in the collection process; these figures are not meant to be   authoritative, but serve as reasonable estimates.   243020 edu 13%     13011 fr    4%     1791 dk   4%     357 be  -5%   181361 com 12%     12770 nl   21%     1662 es  15%     334 gr  14%    46463 gov 13%     12647 ch   10%     1506 kr   9%     308 br  26%    31622 au  19%     11994 fi   15%     1111 nz -16%     284 mx  -5%    31016 de  20%     10228 no    9%     1016 tw  n/a     207 is   0%    27492 mil 26%      8579 jp    6%      929 za  n/a     146 pl  97%    27052 ca  22%      4109 net -49%      784 pt  n/a     127 us  25%    19117 org 10%      3324 at   19%      484 sg 251%      25 tn   0%    18984 uk 139%      2719 it  197%      448 hk  78%      24 hu  71%    18473 se  34%      2020 il   14%      374 ie  -7%       6 arpa 0%Lottor                                                          [Page 7]

RFC 1296              Internet Growth (1981-1991)           January 1992N.5 Distribution of Hosts by Host Name   This chart shows the distribution of hosts by their host name on 1-   Jan-92.  The host name is defined to be the first part of a fully   qualified domain name.  Only the top 100 names are shown.384 venus     204 mac4       172 mac9        155 pollux     138 chaos356 pluto     201 hobbes     172 mac11       155 frodo      136 bart323 mars      201 hermes     170 mac8        153 helios     135 pc5288 jupiter   198 thor       169 phoenix     152 mac17      135 larry286 saturn    198 sirius     169 mac12       151 vega       135 cs285 pc1       196 gw         169 hal         151 mac18      133 odin282 zeus      195 calvin     168 snoopy      150 falcon     131 tiger262 iris      194 mac5       168 mac13       150 bach       131 sparky260 mercury   191 mac10      167 mac15       146 castor     131 ariel259 mac1      190 fred       167 mac14       145 sol        130 sneezy258 orion     189 titan      167 grumpy      145 dopey      128 mac254 mac2      189 pc3        163 gandalf     144 mac20      127 sun1240 newton    186 opus       162 pc4         144 mac19      127 rocky234 neptune   186 mac6       160 uranus      142 spock      126 pc6233 pc2       185 charon     159 mac16       142 euler      125 hydra224 gauss     185 apollo     158 sleepy      141 mickey     125 homer222 eagle     179 mac7       158 io          141 atlas      124 isis213 mac3      179 athena     157 earth       140 maxwell    123 moe209 merlin    177 alpha      156 europa      140 happy      123 delta207 cisco     172 mozart     155 rigel       140 doc        122 pc10Future Issues   ZONE currently runs on a DECsystem-20 and is written in assembler.   The amount of data is quickly reaching the limits of the DEC-20   section address space, and the hardware's ability to survive gets   slimmer each day.  ZONE assembles all its data in core before dumping   it to disk.  The implementation does this in order to be able to   match host nicknames with official names before dumping complete host   records.  Sometimes a nickname can be in a different domain than the   official name, complicating simpler methods.   A new version of ZONE needs to be written to run on a modern computer   system.  A completely new architecture should be designed to handle   the enormous amount of data collected and expected in the future.   Data should be kept on disk so that a system crash will not wipe out   days of collection.  Multiple zone transfers could be occurring in   parallel to reduce the time needed for data gathering.  A new ZONE   might run continuously, cycling through the domain system on a cycle   lasting weeks to a month, updating a local database with statistics   collected for each domain.  In this way, current statistics on the   size of the Internet would always be known.  The resulting databaseLottor                                                          [Page 8]

RFC 1296              Internet Growth (1981-1991)           January 1992   may also be useful for other network information services.RFC References   Libes, D., "Choosing a Name for Your Computer",RFC 1178, Integrated   Systems Group/NIST, August 1990.  (Also FYI 5.)   Mockapetris, P., "Domain Names - Implementation and Specification",RFC 1035, USC/Information Sciences Institute, November 1987.   Mockapetris, P., "Domain names - Concepts and Facilities",RFC 1034,   USC/Information Sciences Institute, November 1987.   Lazear, W., "MILNET Name Domain Transition",RFC 1031, Mitre,   November 1987.   Harrenstien, K. Stahl, M., and J. Feinler, "DoD Internet Host Table   Specification", SRI, October 1985.   Postel, J., "Domain Name System Implementation Schedule - Revised",RFC 921, USC/Information Sciences Institute, October 1984.Security Considerations   Security issues are not discussed in this memo.Author's Address   Mark K. Lottor   SRI International   Network Information Systems Center   333 Ravenswood Avenue, EJ282   Menlo Park, CA  94025   EMail: mkl@nisc.sri.comLottor                                                          [Page 9]