Hash and Stuffing: Overlooked Factors in Network Device Benchmarking
RFC 4814

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Network Working Group                                          D. Newman
Request for Comments: 4814                                  Network Test
Category: Informational                                        T. Player
                                                  Spirent Communications
                                                              March 2007

  Hash and Stuffing: Overlooked Factors in Network Device Benchmarking

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 IETF Trust (2007).

Abstract

   Test engineers take pains to declare all factors that affect a given
   measurement, including intended load, packet length, test duration,
   and traffic orientation.  However, current benchmarking practice
   overlooks two factors that have a profound impact on test results.
   First, existing methodologies do not require the reporting of
   addresses or other test traffic contents, even though these fields
   can affect test results.  Second, "stuff" bits and bytes inserted in
   test traffic by some link-layer technologies add significant and
   variable overhead, which in turn affects test results.  This document
   describes the effects of these factors; recommends guidelines for
   test traffic contents; and offers formulas for determining the
   probability of bit- and byte-stuffing in test traffic.

Newman & Player              Informational                      [Page 1]
RFC 4814                   Hash and Stuffing                  March 2007

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Requirements . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  General Considerations . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Repeatability  . . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Randomness . . . . . . . . . . . . . . . . . . . . . . . .  4
   4.  Packet Content Variations  . . . . . . . . . . . . . . . . . .  5
     4.1.  Problem Statement  . . . . . . . . . . . . . . . . . . . .  5
     4.2.  IEEE 802 MAC Addresses . . . . . . . . . . . . . . . . . .  7
       4.2.1.  Randomized Sets of MAC Addresses . . . . . . . . . . .  8
     4.3.  MPLS Addressing  . . . . . . . . . . . . . . . . . . . . .  9
     4.4.  Network-layer Addressing . . . . . . . . . . . . . . . . .  9
     4.5.  Transport-Layer Addressing . . . . . . . . . . . . . . . . 10
     4.6.  Application-Layer Patterns . . . . . . . . . . . . . . . . 10
   5.  Control Character Stuffing . . . . . . . . . . . . . . . . . . 11
     5.1.  Problem Statement  . . . . . . . . . . . . . . . . . . . . 11
     5.2.  PPP Bit-Stuffing . . . . . . . . . . . . . . . . . . . . . 12
       5.2.1.  Calculating Bit-Stuffing Probability . . . . . . . . . 14
       5.2.2.  Bit-Stuffing for Finite Strings  . . . . . . . . . . . 15
       5.2.3.  Applied Bit-Stuffing . . . . . . . . . . . . . . . . . 16
     5.3.  POS Byte-Stuffing  . . . . . . . . . . . . . . . . . . . . 16
       5.3.1.  Nullifying ACCM  . . . . . . . . . . . . . . . . . . . 17
       5.3.2.  Other Stuffed Characters . . . . . . . . . . . . . . . 17
       5.3.3.  Applied Byte-Stuffing  . . . . . . . . . . . . . . . . 17
   6.  Security Considerations  . . . . . . . . . . . . . . . . . . . 18
   7.  Normative References . . . . . . . . . . . . . . . . . . . . . 19
   Appendix A.  Acknowledgements  . . . . . . . . . . . . . . . . . . 20
   Appendix B.  Proof of Formula for Finite Bit-Stuffing  . . . . . . 20
   Appendix C.  Explicit Calculation of Bit-Stuffing Overhead for
                IPv4  . . . . . . . . . . . . . . . . . . . . . . . . 21
   Appendix D.  Explicit Calculation of Bit-Stuffing Overhead for
                IPv6  . . . . . . . . . . . . . . . . . . . . . . . . 23
   Appendix E.  Terminology . . . . . . . . . . . . . . . . . . . . . 24

Newman & Player              Informational                      [Page 2]
RFC 4814                   Hash and Stuffing                  March 2007

1.  Introduction

   Experience in benchmarking networking devices suggests that the
   contents of test traffic can have a profound impact on test results.
   For example, some devices may forward randomly addressed traffic
   without loss, but drop significant numbers of packets when offered
   packets containing nonrandom addresses.

   Methodologies such as [RFC2544] and [RFC2889] do not require any
   declaration of packet contents.  These methodologies do require the
   declaration of test parameters such as traffic distribution and
   traffic orientation, and yet packet contents can have at least as
   great an impact on test results as the other factors.  Variations in
   packet contents also can lead to non-repeatability of test results:
   Two individuals may follow methodology procedures to the letter, and