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Network Working Group S. Parker Request for Comments: 2398 C. Schmechel FYI: 33 Sun Microsystems, Inc. Category: Informational August 1998 Some Testing Tools for TCP Implementors Status of this Memo This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited. Copyright Notice Copyright (C) The Internet Society (1998). All Rights Reserved.

1. Introduction

Available tools for testing TCP implementations are catalogued by this memo. Hopefully disseminating this information will encourage those responsible for building and maintaining TCP to make the best use of available tests. The type of testing the tool provides, the type of tests it is capable of doing, and its availability is enumerated. This document lists only tools which can evaluate one or more TCP implementations, or which can privde some specific results which describe or evaluate the TCP being tested. A number of these tools produce time-sequence plots, see Tim Shepard's thesis [She91] for a general discussion of these plots. Each tools is defined as follows: Name The name associated with the testing tool. Category One or more categories of tests which the tools are capable of providing. Categories used are: functional correctness, performance, stress. Functional correctness tests how stringent a TCP implementation is to the RFC specifications. Performance tests how Parker & Schmechel Informational [Page 1]
RFC 2398 Some Testing Tools for TCP Implementors August 1998 quickly a TCP implementation can send and receive data, etc. Stress tests how a TCP implementation is effected under high load conditions. Description A description of the tools construction, and the implementation methodology of the tests. Automation What steps are required to complete the test? What human intervention is required? Availability How do you retrieve this tool and get more information about it? Required Environment Compilers, OS version, etc. required to build and/or run the associated tool. References A list of publications relating to the tool, if any.

2. Tools

2.1. Dbs

Author Yukio Murayama Category Performance / Stress Description Dbs is a tool which allows multiple data transfers to be coordinated, and the resulting TCP behavior to be reviewed. Results are presented as ASCII log files. Automation Command of execution is driven by a script file. Parker & Schmechel Informational [Page 2]
RFC 2398 Some Testing Tools for TCP Implementors August 1998 Availability See for details of precise OS versions supported, and for download of the source code. Current implementation supports BSDI BSD/OS, Linux, mkLinux, SunOS, IRIX, Ultrix, NEWS OS, HP-UX. Other environments are likely easy to add. Required Environment C language compiler, UNIX-style socket API support.

2.2. Dummynet

Author Luigi Rizzo Category Functional Correctness / Performance Description Dummynet is a tool which simulates the presence of finite size queues, bandwidth limitations, and communication delays. Dummynet inserts between two layers of the protocol stack (in the current implementation between TCP and IP), simulating the above effects in an operational system. This way experiments can be done using real protocol implementations and real applications, even running on the same host (dummynet also intercepts communications on the loopback interface). Reconfiguration of dummynet parameters (delay, queue size, bandwidth) can be done on the fly by using a sysctl call. The overhead of dummynet is extremely low. Automation Requires merging diff files with kernel source code. Command-line driven through the sysctl command to modify kernel variables. Availability See or e-mail Luigi Rizzo ( Source code is available for FreeBSD 2.1 and FreeBSD 2.2 (easily adaptable to other BSD-derived systems). Required Environment C language compiler, BSD-derived system, kernel source code. References [Riz97] Parker & Schmechel Informational [Page 3]
RFC 2398 Some Testing Tools for TCP Implementors August 1998

2.3. Netperf

Author Rick Jones Category Performance Description Single connection bandwidth or latency tests for TCP, UDP, and DLPI. Includes provisions for CPU utilization measurement. Automation Requires compilation (K&R C sufficient for all but-DHISTOGRAM, may require ANSI C in the future) if starting from source. Execution as child of inetd requires editing of /etc/services and /etc/inetd.conf. Scripts are provided for a quick look (snapshot_script), bulk throughput of TCP and UDP, and latency for TCP and UDP. It is command-line driven. Availability See or e-mail Rick Jones ( Binaries are available here for HP/UX Irix, Solaris, and Win32. Required Environment C language compiler, POSIX.1, sockets.

2.4. NIST Net

Author Mark Carson Category Functional Correctness / Performance Description NIST Net is a network emulator. The tool is packaged as a Linux kernel patch, a kernel module, a set of programming APIs, and command-line and X-based user interfaces. NIST Net works by turning the system into a "selectively bad" router - incoming packets may be delayed, dropped, duplicated, bandwidth- constrained, etc. Packet delays may be fixed or randomly distributed, with loadable probability distributions. Packet loss may be uniformly distributed (constant loss probability) or congestion-dependent (probability of loss increases with packet queue lengths). Explicit congestion notifications may optionally be sent Parker & Schmechel Informational [Page 4]
RFC 2398 Some Testing Tools for TCP Implementors August 1998 in place of congestion-dependent loss. Automation To control the operation of the emulator, there is an interactive user interface, a non-interactive command-line interface, and a set of APIs. Any or all of these may be used in concert. The interactive interface is suitable for simple, spur-of-the-moment testing, while the command-line or APIs may be used to create scripted, non-interactive tests. Availability NIST Net is available for public download from the NIST Net web site, The web site also has installation instructions and documentation. Required Environment NIST Net requires a Linux installtion, with kernel version 2.0.27 - 2.0.33. A kernel source tree and build tools are required to build and install the NIST Net components. Building the X interface requires a version of XFree86 (Current Version is 3.3.2). An Athena-replacement widget set such as neXtaw ( is also desirable for an improved user interface. NIST Net should run on any i386-compatible machine capable of running Linux, with one or more interfaces.

2.5. Orchestra

Author Scott Dawson, Farnam Jahanian, and Todd Mitton Category Functional Correctness / Performance Description This tool is a library which provides the user with an ability to build a protocol layer capable of performing fault injection on protocols. Several fault injection layers have been built using this library, one of which has been used to test different vendor implementations of TCP. This is accomplished by probing the vendor implementation from one machine containing a protocol stack that has been instrumented with Orchestra. A connection is opened from the vendor TCP implementation to the machine which has been instrumented. Faults may then be injected at the Orchestra side of the connection and the vendor TCP's response may be monitored. The most recent version of Orchestra runs inside the X-kernel protocol stack on the OSF MK operating system. Parker & Schmechel Informational [Page 5]
RFC 2398 Some Testing Tools for TCP Implementors August 1998 When using Orchestra to test a protocol, the fault injection layer is placed below the target protocol in the protocol stack. This can either be done on one machine on the network, if protocol stacks on the other machines cannot be modified (as in the case of testing TCP), or can be done on all machines on the network (as in the case of testing a protocol under development). Once the fault injection layer is in the protocol stack, all messages sent by and destined for the target protocol pass through it on their way to/from the network. The Orchestra fault injection layer can manipulate these messages. In particular, it can drop, delay, re-order, duplicate, or modify messages. It can also introduce new messages into the system if desired. The actions of the Orchestra fault injection layer on each message are determined by a script, written in Tcl. This script is interpreted by the fault injection layer when the message enters the layer. The script has access to the header information about the message, and can make decisions based on header values. It can also keep information about previous messages, counters, or any other data which the script writer deems useful. Users of Orchestra may also define their own actions to be taken on messages, written in C, that may be called from the fault injection scripts. Automation Scripts can be specified either using a graphical user interface which generates Tcl, or by writing Tcl directly. At this time, post-analysis of the results of the test must also be performed by the user. Essentially this consists of looking at a packet trace that Orchestra generates for (in)correct behavior. Must compile and link fault generated layer with the protocol stack. Availability See or e-mail Scott Dawson ( Required Environment OSF MK operating system, or X-kernel like network architecture, or adapted to network stack. References [DJ94], [DJM96a], [DJM96b] Parker & Schmechel Informational [Page 6]
RFC 2398 Some Testing Tools for TCP Implementors August 1998

2.6. Packet Shell

Author Steve Parker and Chris Schmechel Category Functional Correctness / Performance Description An extensible Tcl/Tk based software toolset for protocol development and testing. Tcl (Tool Command Language) is an embeddable scripting language and Tk is a graphical user interface toolkit based on Tcl. The Packet Shell creates Tcl commands that allow you to create, modify, send, and receive packets on networks. The operations for each protocol are supplied by a dynamic linked library called a protocol library. These libraries are silently linked in from a special directory when the Packet Shell begins execution. The current protocol libraries are: IP, IPv6, IPv6 extensions, ICMP, ICMPv6, Ethernet layer, data layer, file layer (snoop and tcpdump support), socket layer, TCP, TLI. It includes harness, which is a Tk based graphical user interface for creating test scripts within the Packet Shell. It includes tests for no initial slow start, and retain out of sequence data as TCP test cases mentioned in [PADHV98]. It includes tcpgraph, which is used with a snoop or tcpdump capture file to produce a TCP time-sequence plot using xplot. Automation Command-line driven through Tcl commands, or graphical user interface models are available through the harness format. Availability See or e-mail owner-packet- Required Environment Solaris 2.4 or higher. Porting required for other operating systems. Parker & Schmechel Informational [Page 7]
RFC 2398 Some Testing Tools for TCP Implementors August 1998

2.7. Tcpanaly

Author Vern Paxson Category Functional Correctness / Performance Description This is a tool for automatically analyzing a TCP implementation's behavior by inspecting packet traces of the TCP's activity. It does so through packet filter traces produced by tcpdump. It has coded within it knowledge of a large number of TCP implementations. Using this, it can determine whether a given trace appears consistent with a given implementation, and, if so, exactly why the TCP chose to transmit each packet at the time it did. If a trace is found inconsistent with a TCP, tcpanaly either diagnoses a likely measurement error present in the trace, or indicates exactly whether the activity in the trace deviates from that of the TCP, which can greatly aid in determining how the traced implementation behaves. Tcpanaly's category is somewhat difficult to classify, since it attempts to profile the behavior of an implementation, rather than to explicitly test specific correctness or performance issues. However, this profile identifies correctness and performance problems. Adding new implementations of TCP behavior is possible with tcpanaly through the use of C++ classes. Automation Command-line driven and only the traces of the TCP sending and receiving bulk data transfers are needed as input. Availability Contact Vern Paxson ( Required Environment C++ compiler. References [Pax97a] Parker & Schmechel Informational [Page 8]
RFC 2398 Some Testing Tools for TCP Implementors August 1998

2.8. Tcptrace

Author Shawn Ostermann Category Functional Correctness / Performance Description This is a TCP trace file analysis tool. It reads output trace files in the formats of : tcpdump, snoop, etherpeek, and netm. For each connection, it keeps track of elapsed time, bytes/segments sent and received, retransmissions, round trip times, window advertisements, throughput, etc from simple to very detailed output. It can also produce three different types of graphs: Time Sequence Graph (shows the segments sent and ACKs returned as a function of time) Instantaneous Throughput (shows the instantaneous, averaged over a few segments, throughput of the connection as a function of time). Round Trip Times (shows the round trip times for the ACKs as a function of time) Automation Command-line driven, and uses the xplot program to view the graphs. Availability Source code is available, and Solaris binary along with sample traces. See or e-mail Shawn Ostermann ( Required Environment C compiler, Solaris, FreeBSD, NetBSD, HPUX, Linux. Parker & Schmechel Informational [Page 9]
RFC 2398 Some Testing Tools for TCP Implementors August 1998

2.9. Tracelook

Author Greg Minshall Category Functional Correctness / Performance Description This is a Tcl/Tk program for graphically viewing the contents of tcpdump trace files. When plotting a connection, a user can select various variables to be plotted. In each direction of the connection, the user can plot the advertised window in each packet, the highest sequence number in each packet, the lowest sequence number in each packet, and the acknowledgement number in each packet. Automation Command-line driven with a graphical user interface for the graph. Availability See or e-mail Greg Minshall ( Required Environment A modern version of awk, and Tcl/Tk (Tk version 3.6 or higher). The program xgraph is required to view the graphs under X11.

2.10. TReno

Author Matt Mathis and Jamshid Mahdavi Category Performance Description This is a TCP throughput measurement tool based on sending UDP or ICMP packets in patterns that are controlled at the user-level so that their timing reflects what would be sent by a TCP that observes proper congestion control (and implements SACK). This allows it to measure throughput independent of the TCP implementation of end hosts and serve as a useful platform for prototyping TCP changes. Automation Command-line driven. No "server" is required, and it only requires a single argument of the machine to run the test to. Parker & Schmechel Informational [Page 10]
RFC 2398 Some Testing Tools for TCP Implementors August 1998 Availability See or e-mail Matt Mathis ( or Jamshid Mahdavi ( Required Environment C compiler, POSIX.1, raw sockets.

2.11. Ttcp

Author Unknown Category Performance Description Originally written to move files around, ttcp became the classic throughput benchmark or load generator, with the addition of support for sourcing to/from memory. It can also be used as a traffic absorber. It has spawned many variants, recent ones include support for UDP, data pattern generation, page alignment, and even alignment offset control. Automation Command-line driven. Availability See or e-mail ARL ( which includes the most common variants available. Required Environment C compiler, BSD sockets.

2.12. Xplot

Author Tim Shepard Category Functional Correctness / Performance Description This is a fairly conventional graphing/plotting tool (xplot itself), a script to turn tcpdump output into xplot input, and some sample code to generate xplot commands to plot the TCP time-sequence graph). Automation Command-line driven with a graphical user interface for the plot. Parker & Schmechel Informational [Page 11]
RFC 2398 Some Testing Tools for TCP Implementors August 1998 Availability See or e-mail Tim Shepard ( Required Environment C compiler, X11. References [She91]

3. Summary

This memo lists all TCP tests and testing tools reported to the authors as part of TCP Implementer's working group and is not exhaustive. These tools have been verified as available by the authors.

4. Security Considerations

Network analysis tools are improving at a steady pace. The continuing improvement in these tools such as the ones described make security concerns significant. Some of the tools could be used to create rogue packets or denial- of-service attacks against other hosts. Also, some of the tools require changes to the kernel (foreign code) and might require root privileges to execute. So you are trusting code that you have fetched from some perhaps untrustworthy remote site. This code could contain malicious code that could present any kind of attack. None of the listed tools evaluate security in any way or form. There are privacy concerns when grabbing packets from the network in that you are now able to read other people's mail, files, etc. This impacts more than just the host running the tool but all traffic crossing the host's physical network.

5. References

[DJ94] Scott Dawson and Farnam Jahanian, "Probing and Fault Injection of Distributed Protocol Implementations", University of Michigan Technical Report CSE-TR-217-94, EECS Department. [DJM96a] Scott Dawson, Farnam Jahanian, and Todd Mitton, "ORCHESTRA: A Fault Injection Environment for Distributed Systems", University of Michigan Technical Report CSE-TR-318-96, EECS Department. Parker & Schmechel Informational [Page 12]
RFC 2398 Some Testing Tools for TCP Implementors August 1998 [DJM96b] Scott Dawson, Farnam Jahanian, and Todd Mitton, "Experiments on Six Commercial TCP Implementations Using a Software Fault Injection Tool", University of Michigan Technical Report CSE-TR-298-96, EECS Department. [Pax97a] Vern Paxson, "Automated Packet Trace Analysis of TCP Implementations", ACM SIGCOMM '97, September 1997, Cannes, France. [PADHV98] Paxson, V., Allman, M., Dawson, S., Heavens, I., and B. Volz, "Known TCP Implementation Problems", Work In Progress. [Riz97] Luigi Rizzo, "Dummynet: a simple approach to the evaluation of network protocols", ACM Computer Communication Review, Vol. 27, N. 1, January 1997, pp. 31-41. [She91] Tim Shepard, "TCP Packet Trace Analysis", MIT Laboratory for Computer Science MIT-LCS-TR-494, February, 1991. Parker & Schmechel Informational [Page 13]
RFC 2398 Some Testing Tools for TCP Implementors August 1998

6. Authors' Addresses

Steve Parker Sun Microsystems, Inc. 901 San Antonio Road, UMPK17-202 Palo Alto, CA 94043 USA Phone: (650) 786-5176 EMail: Chris Schmechel Sun Microsystems, Inc. 901 San Antonio Road, UMPK17-202 Palo Alto, CA, 94043 USA Phone: (650) 786-4053 EMail: Parker & Schmechel Informational [Page 14]
RFC 2398 Some Testing Tools for TCP Implementors August 1998

7. Full Copyright Statement

Copyright (C) The Internet Society (1998). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Parker & Schmechel Informational [Page 15]