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Network Working Group M. Schwartz Request for Comments: 1273 University of Colorado

                                                         November 1991
                 A Measurement Study of Changes in
              Service-Level Reachability in the Global
            TCP/IP Internet: Goals, Experimental Design,
             Implementation, and Policy Considerations

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

 In this report we discuss plans to carry out a longitudinal
 measurement study of changes in service-level reachability in the
 global TCP/IP Internet.  We overview our experimental design,
 considerations of network and remote site load, mechanisms used to
 control the measurement collection process, and network appropriate
 use and privacy issues, including our efforts to inform sites
 measured by this study.  A list of references and information on how
 to contact the Principal Investigator are included.

Introduction

 The global TCP/IP Internet interconnects millions of individuals at
 thousands of institutions worldwide, offering the potential for
 significant collaboration through network services and electronic
 information exchange.  At the same time, such powerful connectivity
 offers many avenues for security violations, as evidenced by a number
 of well publicized events over the past few years.  In response, many
 sites have imposed mechanisms to limit their exposure to security
 intrusions, ranging from disabling certain inter-site services, to
 using external gateways that only allow electronic mail delivery, to
 gateways that limit remote interactions via access control lists, to
 disconnection from the Internet.  While these measures are preferable
 to the damage that could occur from security violations, taken to an
 extreme they could eventually reduce the Internet to little more than
 a means of supporting certain pre-approved point-to-point data
 transfers.  Such diminished functionality could hinder or prevent the
 deployment of important new types of network services, impeding both
 research and commercial advancement.
 To understand the evolution of this situation, we have designed a

Schwartz [Page 1] RFC 1273 A Measurement Study November 1991

 study to measure changes in Internet service-level reachability over
 a period of one year.  The study considers upper layer service
 reachability instead of basic IP connectivity because the former
 indicates the willingness of organizations to participate in inter-
 organizational computing, which will be an important component of
 future wide area distributed applications.
 The data we gather will contribute to Internet research and
 engineering planning activities in a number of ways.  The data will
 indicate the mechanisms sites use to distance themselves from
 Internet connectivity, the types of services that sites are willing
 to run (and hence the type of distributed collaboration they are
 willing to support), and variations in these characteristics as a
 function of geographic location and type of institution (commercial,
 educational, etc.).  Understanding these trends will allow
 application designers and network builders to more realistically plan
 for how to support future wide area distributed applications such as
 digital library systems, information services, wide area distributed
 file systems, and conferencing and other collaboration-support
 systems.  The measurements will also be of general interest, as they
 represent direct measurements of the evolution of a global electronic
 society.
 Clearly, a study of this nature and magnitude raises a number of
 potential concerns.  In this note we overview our experimental
 design, considerations of network and remote site load, mechanisms
 used to control the measurement collection process, and our efforts
 to inform sites measured by this study, along with concomitant
 network appropriate use and privacy issues.
 A point we wish to stress from the outset is that this is not a study
 of network security.  The experiments do not attempt to probe the
 security mechanisms of any machine on the network.  The study is
 concerned solely with the evolution of network connectivity and
 service reachability.

Experimental Design

 The study consists of a set of runs of a program over the span of one
 to two days each month, repeated bimonthly for a period of one year
 (in January 1992, March 1992, May 1992, July 1992, September 1992,
 and November 1992).  Each program run attempts to connect to 13
 different TCP services at each of approximately 12,700 Internet
 domains worldwide, recording the failure/success status of each
 attempt.  The program will attempt no data transfers in either
 direction.  If a connection is successful, it is simply closed and
 counted.  (Note in particular that this means that the security
 mechanism behind individual network services will not be tested.)

Schwartz [Page 2] RFC 1273 A Measurement Study November 1991

 The machines on which connections are attempted will be selected at
 random from a large list of machines in the Internet, constrained
 such that at most 1 to 3 machines is contacted in any particular
 domain.
 The services to which connections will be attempted are:
  __________________________________________________________________
    Port Number   Service                Port Number   Service
  ------------------------------------------------------------------
        13        daytime                    111       Sun portmap
        15        netstat                    513       rlogin
        21        FTP                        514       rsh
        23        telnet                     540       UUCP
        25        SMTP                       543       klogin
        53        Domain Naming System       544       krcmd, kshell
        79        finger
   _________________________________________________________________
 This list was chosen to span a representative range of  service
 types, each of which can be expected to be found on any machine in a
 site (so that probing random machines is meaningful).  The one
 exception  is  the  Domain  Naming  System,  for which the machines
 to probe are selected from information  obtained  from the  Domain
 system itself.  Only TCP services are tested, since the TCP
 connection mechanism  allows  one  to  determine  if  a server is
 running in an application-independent fashion.
 As an aside, it would be possible  to  retrieve  "Well  Known
 Service"  records  from the Domain Naming System, as a somewhat less
 "invasive" measurement approach.  However,  these  records are  not
 required  for proper network operation, and hence are far from
 complete or consistent in the  Domain  Naming  System.  The  only way
 to collect the data we want is to measure them in the fashion
 described above.

Network and Remote Site Load

 The measurement software is quite careful to avoid generating
 unnecessary internet packets, and to avoid congesting the internet
 with too much concurrent activity.  Once it has successfully
 connected to a particular service in a domain, the software never
 attempts to connect to that service on any machine in that domain
 again, for the duration of the current measurement run (i.e., the
 current 60 days).  Once it has recorded 3 connection refusals at any
 machines in that domain for a service, it does not try that service
 at that domain again during the current measurement run.  If it
 experiences 3 timeouts on any machine in a domain, it gives up on the

Schwartz [Page 3] RFC 1273 A Measurement Study November 1991

 domain, possibly to be retried again a day later (to overcome
 transient network problems).  In the worst case there will be 3
 connection failures for each service at 3 different machines, which
 amounts to 37 connection requests per domain (3 for each of the 12
 services other than the Domain Naming System, and one for the Domain
 Naming System).  However, the average will be much less than this.
 To quantify the actual Internet load, we now present some
 measurements from test runs of the measurement software that were
 performed in August 1991.  In total, 50,549 Domain Naming System
 lookups were performed, and 73,760 connections were attempted.  This
 measurement run completed in approximately 10 hours, never initiating
 more than 20 network operations (name lookups or connection attempts)
 concurrently.  The total NSFNET backbone load from all traffic
 sources that month was approximately 5 billion packets.  Therefore,
 the traffic from our measurement study amounted to less than .5% of
 this volume on the day that the measurements were collected.  Since
 the Internet contains several other backbones besides NSFNET, the
 proportionate increase in total Internet traffic was significantly
 less than .5%.
 The cost to a remote site being measured is effectively zero.  From
 the above measurements, on average we attempted 5.7 connections per
 remote domain.  The cost of a connection open/close sequence is quite
 small, particularly when compared to the cost of the many electronic
 mail and news transmissions that most sites experience on a given
 day.

Control Over Measurement Collection Process

 The measurement software evolved from an earlier set of experiments
 used to measure the reach of an experimental Internet white pages
 tool called netfind [Schwartz & Tsirigotis 1991b], and has been
 evolved and tested extensively over a period of two years.  During
 this time it has been used in a number of experiments of increasing
 scale.  The software uses several redundant checks and other
 mechanisms to ensure that careful control is maintained over the
 network operations that are performed [Schwartz & Tsirigotis 1991a].
 In addition, we monitor the progress and network loading of the
 measurements during the measurement runs, observing the log of
 connection requests in progress as well as physical and transport
 level network status (which indicate the amount of concurrent network
 activity in progress).  Finally, because the measurements are
 controlled from a single centralized location, it is quite easy to
 stop the measurements at any time.

Schwartz [Page 4] RFC 1273 A Measurement Study November 1991

Network Appropriate Use and Privacy Issues

 When we performed our initial test runs of this study, we attempted
 to inform site administrators at each study site about this study, by
 posting a message on the USENET newsgroup "alt.security" and by
 sending individual electronic mail messages to site administrators.
 We also informed the Computer Emergency Response Team (CERT) at CMU
 of the study.  As a practical matter, informing all sites turned out
 to be quite difficult.  Part of the problem was that no channels
 exist to allow such information to be easily disseminated.
 Approximately half of the messages we sent to site administrators
 were returned by remote mail systems as undeliverable.  Moreover, the
 network traffic and remote site administrative load caused by the
 study announcement messages far outstripped the network and
 administrative load required by the study itself.  Some sites felt
 that the announcement was an unnecessary imposition of their time.
 In addition to these practical problems, a broad announcement of this
 study could affect the measurements it attempts to gather.  Some
 sites would likely react to the announcement by changing the
 reachability of their services.  Asking for explicit permission from
 sites would yield even worse methodological problems, as this would
 have provided a self-selected study group consisting of sites that
 are less likely to disconnect from the Internet.
 In contrast with our attempts to announce the study, running the
 study without announcing it caused only a small number of site
 administrators to notice the traffic and inquire about it to either
 the CERT or to one of the responsible network contacts at the
 University of Colorado.  The remote site administrator and network
 overhead of announcing the the study, coupled with the practical and
 methodological problems of announcing the study, lead us to prefer to
 run the study without further broad announcements.  Yet, to avoid
 causing alarm at a site detecting our network measurement activity,
 it makes sense to announce the study.
 To resolve this problem, we discussed the study with the Internet
 Activities Board, Internet Engineering Steering Group, National
 Science Foundation, representatives of several U.S.  regional
 networks, and a number of individuals involved with network security,
 including the Computer Emergency Response Team, members of the
 Internet Engineering Task Force Security and Advisory Group, and a
 member of the Lawrence Livermore National Laboratory Computer
 Incident Advisory Capability.  The first part of our efforts resulted
 in the production of Internet Request For Comments (RFC) number 1262
 [Cerf 1991].  Beyond this, we have agreed that the appropriate action
 at this point is to announce the study well ahead of running it via
 the current RFC, augmented with an electronic posting that briefly

Schwartz [Page 5] RFC 1273 A Measurement Study November 1991

 describes the study goals and methodology and points to this RFC.
 That announcement will be posted to the Internet Engineering Task
 Force mailing list, the comp.protocols.tcp-ip USENET bulletin board,
 and the Computer Emergency Response Team's cert-tools mailing list.
 Moreover, in case a site misses these announcements, we will run the
 measurement software in a fashion intended to minimize the effort a
 site administrator might expend to determine the nature of the
 activity after detecting it.  In particular, we will run the program
 from an account called "testnet" on a machine with few other users
 logged in.  "Fingering" [Zimmerman 1990] this machine will indicate
 the testnet login.  "Fingering" the testnet login will return
 information about this study.
 The data collected by this study is somewhat sensitive to privacy and
 security concerns, in the sense that it might be used as a "road map"
 of accessible network services.  We will treat the raw data as
 private information, publishing measurements only in global
 statistical terms, divorced from the actual sites that make up the
 underlying data points.  We previously carried out a study with much
 larger privacy implications than the current study [Schwartz & Wood
 1991], and successfully masked the data to protect individual
 privacy.

For Further Information

 Information about the general research program within which this
 study fit is available by anonymous FTP from latour.cs.colorado.edu,
 in pub/RD.Papers.  This directory contains a "README" file that
 describes the overall research project (which focuses on resource
 discovery), and includes a bibliography.  Particularly relevant are:
    o [Schwartz 1991b], a project overview;
    o [Schwartz 1991a], about an earlier, simpler  version  of  the
      current study;
    o [Schwartz & Tsirigotis 1991b], about the netfind white  pages
      tool;
    o [Schwartz & Tsirigotis 1991a], which considers  a  number  of
      the  techniques  used in this experiment, including those for
      controlling the progress of the measurements;
      and
    o [Schwartz & Wood 1991], about an earlier study we carried out
      that  raises  significant  potential  privacy  questions, for
      which we carefully masked the underlying data, presenting the

Schwartz [Page 6] RFC 1273 A Measurement Study November 1991

      results without sacrificing individual privacy.
      Also:
    o [Cerf  1991],  IAB  guidelines   for   Internet   measurement
      activity.
 Once the results of this study are complete, we will publish them in
 a conference or journal, as well as by anonymous FTP.

Communication With Principal Investigator

 If you would like to have your site removed from this study, or you
 would like to be added to the list of people who receive results from
 this study, or you would like to communicate with the Principal
 Investigator for some other reason, please send electronic mail to
 schwartz@cs.colorado.edu.

References

 [Cerf 1991]
           Cerf, V., Editor, "Guidelines for Internet Measurement
           Activities", RFC 1262, IAB, October 1991.
 [Schwartz & Tsirigotis 1991a]
           Schwartz M., and P. Tsirigotis, "Techniques for
           Supporting Wide Area Distributed Applications", Technical
           Report CU-CS-519-91, Department of Computer Science,
           University of Colorado, Boulder, Colorado, February 1991;
           Revised August 1991.  Submitted for publication.
 [Schwartz & Tsirigotis 1991b]
           Schwartz M., and P. Tsirigotis "Experience with a
           Semantically Cognizant Internet White Pages Directory
           Tool", Journal of Internetworking: Research and Experience,
           2(1), pp. 23-50, March 1991.
 [Schwartz 1991a]
           Schwartz, M., "The Great Disconnection?", Technical Report
           CU-CS-521-91, Department of Computer Science, University of
           Colorado, Boulder, Colorado, February 1991.
 [Schwartz & Wood 1991]
           Schwartz M., and D. Wood, "A Measurement Study of
           Organizational Properties in the Global Electronic Mail
           Community", Technical Report CU-CS- 482-90, Department of
           Computer Science, University of Colorado, Boulder, Colorado,
           August 1990; Revised July 1991.  Submitted for publication.

Schwartz [Page 7] RFC 1273 A Measurement Study November 1991

 [Schwartz 1991b]
           Schwartz, M., "Resource Discovery in the Global Internet",
           Technical Report CU-CS-555-91, Department of Computer
           Science, University of Colorado, Boulder, Colorado,
           November 1991.  Submitted for publication.
 [Zimmerman 1990]
           Zimmerman, D., "The Finger User Information Protocol",
           RFC 1194, Center for Discrete Mathematics and Theoretical
           Computer Science, November 1990.

Security Considerations

 Security issues are discussed in the "Network Appropriate Use and
 Privacy Issues" section.

Author's Address

 Michael F. Schwartz
 Department of Computer Science
 Campus Box 430
 University of Colorado
 Boulder, Colorado 80309-0430
 Phone:  (303) 492-3902
 EMail: schwartz@cs.colorado.edu

Schwartz [Page 8]

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