Benchmarking Terminology for LAN Switching Devices
RFC 2285

Network Working Group R. Mandeville
Request for Comments: 2285 European Network Laboratories
Category: Informational February 1998
 Benchmarking Terminology for LAN Switching Devices
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.
Table of Contents
 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 2
 2. Existing definitions . . . . . . . . . . . . . . . . . . . . . . 2
 3. Term definitions . . . . . . . . . . . . . . . . . . . . . . . . 3
 3.1 Devices. . . . . . . . . . . . . . . . . . . . . . . . . . . 3
 3.1.1 Device under test (DUT) . . . . . . . . . . . . . . . . 3
 3.1.2 System under test (SUT) . . . . . . . . . . . . . . . . 3
 3.2 Traffic orientation. . . . . . . . . . . . . . . . . . . . . 4
 3.2.1 Unidirectional traffic. . . . . . . . . . . . . . . . . 4
 3.2.2 Bidirectional traffic . . . . . . . . . . . . . . . . . 5
 3.3 Traffic distribution . . . . . . . . . . . . . . . . . . . . 6
 3.3.1 Non-meshed traffic. . . . . . . . . . . . . . . . . . . 6
 3.3.2 Partially meshed traffic. . . . . . . . . . . . . . . . 7
 3.3.3 Fully meshed traffic. . . . . . . . . . . . . . . . . . 8
 3.4 Bursts . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
 3.4.1 Burst . . . . . . . . . . . . . . . . . . . . . . . . . 9
 3.4.2 Burst size . . . . . . . . . . . . . . . . . . . . . . 10
 3.4.3 Inter-burst gap (IBG). . . . . . . . . . . . . . . . . 10
 3.5 Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
 3.5.1 Intended load (Iload) . . . . . . . . . . . . . . . . 11
 3.5.2 Offered load (Oload) . . . . . . . . . . . . . . . . . 12
 3.5.3 Maximum offered load (MOL) . . . . . . . . . . . . . . 13
 3.5.4 Overloading . . . . . . . . . . . . . . . . . . . . . 14
 3.6 Forwarding rates . . . . . . . . . . . . . . . . . . . . . 15
 3.6.1 Forwarding rate (FR) . . . . . . . . . . . . . . . . . 15
 3.6.2 Forwarding rate at maximum offered load (FRMOL). . . . 16
 3.6.3 Maximum forwarding rate (MFR). . . . . . . . . . . . . 16
 3.7 Congestion control . . . . . . . . . . . . . . . . . . . . 17
 3.7.1 Backpressure . . . . . . . . . . . . . . . . . . . . . 17
 3.7.2 Forward pressure . . . . . . . . . . . . . . . . . . . 18
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 3.7.3 Head of line blocking . . . . . . . . . . . . . . . . 19
 3.8 Address handling . . . . . . . . . . . . . . . . . . . . . 20
 3.8.1 Address caching capacity . . . . . . . . . . . . . . . 20
 3.8.2 Address learning rate . . . . . . . . . . . . . . . . 20
 3.8.3 Flood count . . . . . . . . . . . . . . . . . . . . . 21
 3.9 Errored frame filtering . . . . . . . . . . . . . . . . . . 21
 3.9.1 Errored frames . . . . . . . . . . . . . . . . . . . . 22
 3.10 Broadcasts . . . . . . . . . . . . . . . . . . . . . . . . 22
 3.10.1 Broadcast forwarding rate at maximum load . . . . . . 22
 3.10.2 Broadcast latency . . . . . . . . . . . . . . . . . . 23
 4. Security Considerations . . . . . . . . . . . . . . . . . . . . 24
 5. References. . . . . . . . . . . . . . . . . . . . . . . . . . . 24
 6. Acknowledgements. . . . . . . . . . . . . . . . . . . . . . . . 24
 7. Author's Address. . . . . . . . . . . . . . . . . . . . . . . . 24
 8. Full Copyright Statement. . . . . . . . . . . . . . . . . . . . 25
1. Introduction
 This document is intended to provide terminology for the benchmarking
 of local area network (LAN) switching devices. It extends the
 terminology already defined for benchmarking network interconnect
 devices in RFCs 1242 and 1944 to switching devices.
 Although it might be found useful to apply some of the terms defined
 here to a broader range of network interconnect devices, this RFC
 primarily deals with devices which switch frames at the Medium Access
 Control (MAC) layer. It defines terms in relation to the traffic put
 to use when benchmarking switching devices, forwarding performance,
 congestion control, latency, address handling and filtering.
2. Existing definitions
 RFC 1242 "Benchmarking Terminology for Network Interconnect Devices"
 should be consulted before attempting to make use of this document.
 RFC 1944 "Benchmarking Methodology for Network Interconnect Devices"
 contains discussions of a number of terms relevant to the
 benchmarking of switching devices and should also be consulted.
 For the sake of clarity and continuity this RFC adopts the template
 for definitions set out in Section 2 of RFC 1242. Definitions are
 indexed and grouped together in sections for ease of reference.
 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
 "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
 document are to be interpreted as described in RFC 2119.
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3. Term definitions
3.1 Devices
 This group of definitions applies to all types of networking devices.
3.1.1 Device under test (DUT)
 Definition:
 The network forwarding device to which stimulus is offered and
 response measured.
 Discussion:
 A single stand-alone or modular unit which receives frames on one
 or more of its interfaces and then forwards them to one or more
 interfaces according to the addressing information contained in
 the frame.
 Measurement units:
 n/a
 Issues:
 See Also:
 system under test (SUT) (3.1.2)
3.1.2 System Under Test (SUT)
 Definition:
 The collective set of network devices to which stimulus is offered
 as a single entity and response measured.
 Discussion:
 A system under test may be comprised of a variety of networking
 devices. Some devices may be active in the forwarding decision-
 making process, such as routers or switches; other devices may be
 passive such as a CSU/DSU. Regardless of constituent components,
 the system is treated as a singular entity to which stimulus is
 offered and response measured.
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 Measurement units:
 n/a
 Issues:
 See Also:
 device under test (DUT) (3.1.1)
3.2 Traffic orientation
 This group of definitions applies to the traffic presented to the
 interfaces of a DUT/SUT and indicates whether the interfaces are
 receiving only, transmitting only, or both receiving and
 transmitting.
3.2.1 Unidirectional traffic
 Definition:
 When all frames presented to the input interfaces of a DUT/SUT are
 addressed to output interfaces which do not themselves receive any
 frames.
 Discussion:
 This definition conforms to the discussion in section 16 of RFC
 1944 which describes how unidirectional traffic can be offered to
 a DUT/SUT to measure throughput. Unidirectional traffic is also
 appropriate for:
 -the measurement of the minimum inter-frame gap -the creation of
 many-to-one or one-to-many interface overload -the detection of
 head of line blocking -the measurement of forwarding rates and
 throughput when congestion control mechanisms are active.
 When a tester offers unidirectional traffic to a DUT/SUT reception
 and transmission are handled by different interfaces or sets of
 interfaces of the DUT/SUT. All frames received from the tester by
 the DUT/SUT are transmitted back to the tester from interfaces
 which do not themselves receive any frames.
 It is useful to distinguish traffic orientation and traffic
 distribution when considering traffic patterns used in device
 testing. Unidirectional traffic, for example, is traffic
 orientated in a single direction between mutually exclusive sets
 of source and destination interfaces of a DUT/SUT. Such traffic,
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 however, can be distributed between interfaces in different ways.
 When traffic is sent to two or more interfaces from an external
 source and then forwarded by the DUT/SUT to a single output
 interface the traffic orientation is unidirectional and the
 traffic distribution between interfaces is many-to-one. Traffic
 can also be sent to a single input interface and forwarded by the
 DUT/SUT to two or more output interfaces to achieve a one-to-many
 distribution of traffic.
 Such traffic distributions can also be combined to test for head
 of line blocking or to measure forwarding rates and throughput
 when congestion control mechanisms are active.
 When a DUT/SUT is equipped with interfaces running at different
 media rates the number of input interfaces required to load or
 overload an output interface or interfaces will vary.
 It should be noted that measurement of the minimum inter-frame gap
 serves to detect violations of the IEEE 802.3 standard.
 Issues:
 half duplex / full duplex
 Measurement units:
 n/a
 See Also:
 bidirectional traffic (3.2.2)
 non-meshed traffic (3.3.1)
 partially meshed traffic (3.3.2)
 fully meshed traffic (3.3.3)
 congestion control (3.7)
 head of line blocking (3.7.3)
3.2.2 Bidirectional traffic
 Definition:
 Frames presented to a DUT/SUT such that every receiving interface
 also transmits.
 Discussion:
 This definition conforms to the discussion in section 14 of RFC
 1944.
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 When a tester offers bidirectional traffic to a DUT/SUT all the
 interfaces which receive frames from the tester also transmit
 frames back to the tester.
 Bidirectional traffic MUST be offered when measuring the
 throughput or forwarding rate of full duplex interfaces of a
 switching device.
 Issues:
 truncated binary exponential back-off algorithm
 Measurement units:
 n/a
 See Also:
 unidirectional traffic (3.2.1)
 non-meshed traffic (3.3.1)
 partially meshed traffic (3.3.2)
 fully meshed traffic (3.3.3)
3.3 Traffic distribution
 This group of definitions applies to the distribution of frames
 forwarded by a DUT/SUT.
3.3.1 Non-meshed traffic
 Definition:
 Frames offered to a single input interface and addressed to a
 single output interface of a DUT/SUT where input and output
 interfaces are grouped in mutually exclusive pairs.
 Discussion:
 In the simplest instance of non-meshed traffic all frames are
 offered to a single input interface and addressed to a single
 output interface. The one-to-one mapping of input to output
 interfaces required by non-meshed traffic can be extended to
 multiple mutually exclusive pairs of input and output interfaces.
 Measurement units:
 n/a
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 Issues:
 half duplex / full duplex
 See Also:
 unidirectional traffic (3.2.1)
 bidirectional traffic (3.2.2)
 partially meshed traffic (3.3.2.)
 fully meshed traffic (3.3.3)
 burst (3.4.1)
3.3.2 Partially meshed traffic
 Definition:
 Frames offered to one or more input interfaces of a DUT/SUT and
 addressed to one or more output interfaces where input and output
 interfaces are mutually exclusive and mapped one-to-many, many-
 to-one or many-to-many.
 Discussion:
 This definition follows from the discussion in section 16 of RFC
 1944 on multi-port testing. Partially meshed traffic allows for
 one-to-many, many-to-one or many-to-many mappings of input to
 output interfaces and readily extends to configurations with
 multiple switching devices linked together over backbone
 connections.
 It should be noted that partially meshed traffic can load backbone
 connections linking together two switching devices or systems more
 than fully meshed traffic. When offered partially meshed traffic
 devices or systems can be set up to forward all of the frames they
 receive to the opposite side of the backbone connection whereas
 fully meshed traffic requires at least some of the offered frames
 to be forwarded locally, that is to the interfaces of the DUT/SUT
 receiving them. Such frames will not traverse the backbone
 connection.
 Measurement units:
 n/a
 Issues:
 half duplex / full duplex
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 See Also:
 unidirectional traffic (3.2.1)
 bidirectional traffic (3.2.2)
 non-meshed traffic (3.3.1)
 fully meshed traffic (3.3.3)
 burst (3.4.1)
3.3.3 Fully meshed traffic
 Definition:
 Frames offered to a designated number of interfaces of a DUT/SUT
 such that each one of the interfaces under test receives frames
 addressed to all of the other interfaces under test.
 Discussion:
 As with bidirectional partially meshed traffic, fully meshed
 traffic requires each one the interfaces of a DUT/SUT to both
 receive and transmit frames. But since the interfaces are not
 divided into groups as with partially meshed traffic every
 interface forwards frames to and receives frames from every other
 interface. The total number of individual input/output interface
 pairs when traffic is fully meshed over n switched interfaces
 equals n x (n - 1). This compares with n x (n / 2) such interface
 pairs when traffic is partially meshed.
 Fully meshed traffic on half duplex interfaces is inherently
 bursty since interfaces must interrupt transmission whenever they
 receive frames. This kind of bursty meshed traffic is
 characteristic of real network traffic and can be advantageously
 used to diagnose a DUT/SUT by exercising many of its component
 parts simultaneously. Additional inspection may be warranted to
 correlate the frame forwarding capacity of a DUT/SUT when offered
 meshed traffic and the behavior of individual elements such as
 input or output buffers, buffer allocation mechanisms, aggregate
 switching capacity, processing speed or medium access control.
 The analysis of forwarding rate measurements presents a challenge
 when offering bidirectional or fully meshed traffic since the rate
 at which the tester can be observed to transmit frames to the
 DUT/SUT may be smaller than the rate at which it intends to
 transmit due to collisions on half duplex media or the action of
 congestion control mechanisms. This makes it important to take
 account of both the intended and offered loads defined in sections
 3.5.1.and 3.5.2 below when reporting the results of such
 forwarding rate measurements.
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 When offering bursty meshed traffic to a DUT/SUT a number of
 variables have to be considered. These include frame size, the
 number of frames within bursts, the interval between bursts as
 well as the distribution of load between incoming and outgoing
 traffic. Terms related to bursts are defined in section 3.4
 below.
 Measurement units:
 n/a
 Issues:
 half duplex / full duplex
 See Also:
 unidirectional traffic (3.2.1)
 bidirectional traffic (3.2.2)
 non-meshed traffic (3.3.1)
 partially meshed traffic (3.3.2)
 burst (3.4.1)
 intended load (3.5.1)
 offered load (3.5.2)
3.4 Bursts
 This group of definitions applies to the intervals between frames or
 groups of frames offered to the DUT/SUT.
3.4.1 Burst
 Definition:
 A sequence of frames transmitted with the minimum legal inter-
 frame gap.
 Discussion:
 This definition follows from discussions in section 3.16 of RFC
 1242 and section 21 of RFC 1944 which describes cases where it is
 useful to consider isolated frames as single frame bursts.
 Measurement units:
 n/a
 Issues:
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 See Also:
 burst size (3.4.2)
 inter-burst gap (IBG) (3.4.3)
3.4.2 Burst size
 Definition:
 The number of frames in a burst.
 Discussion:
 Burst size can range from one to infinity. In unidirectional
 traffic as well as in bidirectional or meshed traffic on full
 duplex interfaces there is no theoretical limit to burst length.
 When traffic is bidirectional or meshed bursts on half duplex
 media are finite since interfaces interrupt transmission
 intermittently to receive frames.
 On real networks burst size will normally increase with window
 size. This makes it desirable to test devices with small as well
 as large burst sizes.
 Measurement units:
 number of N-octet frames
 Issues:
 See Also:
 burst (3.4.1)
 inter-burst gap (IBG) (3.4.3)
3.4.3 Inter-burst gap (IBG)
 Definition:
 The interval between two bursts.
 Discussion:
 This definition conforms to the discussion in section 20 of RFC
 1944 on bursty traffic.
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 Bidirectional and meshed traffic are inherently bursty since
 interfaces share their time between receiving and transmitting
 frames. External sources offering bursty traffic for a given
 frame size and burst size must adjust the inter-burst gap to
 achieve a specified average rate of frame transmission.
 Measurement units:
 nanoseconds
 microseconds
 milliseconds
 seconds
 Issues:
 See Also:
 burst (3.4.1)
 burst size (3.4.2)
3.5 Loads
 This group of definitions applies to the rates at which traffic is
 offered to any DUT/SUT.
3.5.1 Intended load (Iload)
 Definition:
 The number of frames per second that an external source attempts
 to transmit to a DUT/SUT for forwarding to a specified output
 interface or interfaces.
 Discussion:
 Collisions on CSMA/CD links or the action of congestion control
 mechanisms can effect the rate at which an external source of
 traffic transmits frames to a DUT/SUT. This makes it useful to
 distinguish the load that an external source attempts to apply to
 a DUT/SUT and the load it is observed or measured to apply.
 In the case of Ethernet an external source of traffic MUST
 implement the truncated binary exponential back-off algorithm to
 ensure that it is accessing the medium legally
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 Measurement units:
 bits per second
 N-octets per second
 (N-octets per second / media_maximum-octets per second) x 100
 Issues:
 See Also:
 burst (3.4.1)
 inter-burst gap (3.4.3)
 offered load (3.5.2)
3.5.2 Offered load (Oload)
 Definition:
 The number of frames per second that an external source can be
 observed or measured to transmit to a DUT/SUT for forwarding to a
 specified output interface or interfaces.
 Discussion:
 The load which an external device can be observed to apply to a
 DUT/SUT may be less than the intended load due to collisions on
 half duplex media or the action of congestion control mechanisms.
 This makes it important to distinguish intended and offered load
 when analyzing the results of forwarding rate measurements using
 bidirectional or fully meshed traffic.
 Frames which are not successfully transmitted by an external
 source of traffic to a DUT/SUT MUST NOT be counted as transmitted
 frames when measuring forwarding rates.
 The frame count on an interface of a DUT/SUT may exceed the rate
 at which an external device offers frames due to the presence of
 spanning tree BPDUs (Bridge Protocol Data Units) on 802.1D-
 compliant switches or SNMP frames. Such frames should be treated
 as modifiers as described in section 11 of RFC 1944.
 Offered load MUST be indicated when reporting the results of
 forwarding rate measurements.
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 Measurement units:
 bits per second
 N-octets per second
 (N-octets per second / media_maximum-octets per second) x 100
 Issues:
 token ring
 See Also:
 bidirectional traffic (3.2.2)
 fully meshed traffic (3.3.3)
 intended load (3.5.1)
 forwarding rate (3.6.1)
3.5.3 Maximum offered load (MOL)
 Definition:
 The highest number of frames per second that an external source
 can transmit to a DUT/SUT for forwarding to a specified output
 interface or interfaces.
 Discussion:
 The maximum load that an external device can apply to a DUT/SUT
 may not equal the maximum load allowed by the medium. This
 will be the case when an external source lacks the resources
 to transmit frames at the minimum legal inter-frame gap or when
 it has sufficient resources to transmit frames below the
 minimum legal inter-frame gap. Moreover, maximum load may vary
 with respect to parameters other than a medium's maximum
 theoretical utilization. For example, on those media employing
 tokens, maximum load may vary as a function of Token Rotation
 Time, Token Holding Time, or the ability to chain multiple
 frames to a single token. The maximum load that an external
 device applies to a DUT/SUT MUST be specified when measuring
 forwarding rates.
 Measurement units:
 bits per second
 N-octets per second
 (N-octets per second / media_maximum-octets per second) x 100
 Issues:
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 See Also:
 offered load (3.5.2)
3.5.4 Overloading
 Definition:
 Attempting to load a DUT/SUT in excess of the maximum rate of
 transmission allowed by the medium.
 Discussion:
 Overloading can serve to exercise buffers and buffer allocation
 algorithms as well as congestion control mechanisms. The number
 of input interfaces required to overload one or more output
 interfaces of a DUT/SUT will vary according to the media rates of
 the interfaces involved.
 An external source can also overload an interface by transmitting
 frames below the minimum inter-frame gap. A DUT/SUT MUST forward
 such frames at intervals equal to or above the minimum gap
 specified in standards.
 A DUT/SUT using congestion control techniques such as backpressure
 or forward pressure may exhibit no frame loss when a tester
 attempts to overload one or more of its interfaces. This should
 not be exploited to suggest that the DUT/SUT supports rates of
 transmission in excess of the maximum rate allowed by the medium
 since both techniques reduce the rate at which the tester offers
 frames to prevent overloading. Backpressure achieves this purpose
 by jamming the transmission interfaces of the tester and forward
 pressure by hindering the tester from gaining fair access to the
 medium. Analysis of both cases should take the distinction
 between intended load (3.5.1) and offered load (3.5.2) into
 account.
 Measurement units:
 bits per second
 N-octets per second
 (N-octets per second / media_maximum-octets per second) x 100
 Issues:
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 See Also:
 unidirectional traffic (3.2.1)
 intended load (3.5.1)
 offered load (3.5.2)
 forwarding rate (3.6.1)
 backpressure (3.7.1)
 forward pressure (3.7.2)
3.6 Forwarding rates
 This group of definitions applies to the rates at which traffic is
 forwarded by any DUT/SUT in response to a stimulus.
3.6.1 Forwarding rate (FR)
 Definition:
 The number of frames per second that a device can be observed to
 successfully transmit to the correct destination interface in
 response to a specified offered load.
 Discussion:
 Unlike throughput defined in section 3.17 of RFC 1242, forwarding
 rate makes no explicit reference to frame loss. Forwarding rate
 refers to the number of frames per second observed on the output
 side of the interface under test and MUST be reported in relation
 to the offered load. Forwarding rate can be measured with
 different traffic orientations and distributions.
 It should be noted that the forwarding rate of a DUT/SUT may be
 sensitive to the action of congestion control mechanisms.
 Measurement units:
 N-octet frames per second
 Issues:
 See Also:
 offered load (3.5.2)
 forwarding rate at maximum offered load (3.6.2)
 maximum forwarding rate (3.6.3)
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3.6.2 Forwarding rate at maximum offered load (FRMOL)
 Definition:
 The number of frames per second that a device can be observed to
 successfully transmit to the correct destination interface in
 response to the maximum offered load.
 Discussion:
 Forwarding rate at maximum offered load may be less than the
 maximum rate at which a device can be observed to successfully
 forward traffic. This will be the case when the ability of a
 device to forward frames degenerates when offered traffic at
 maximum load.
 Maximum offered load MUST be cited when reporting forwarding rate
 at maximum offered load.
 Measurement units:
 N-octet frames per second
 Issues:
 See Also:
 maximum offered load (3.5.3)
 forwarding rate (3.6.1)
 maximum forwarding rate (3.6.3)
3.6.3 Maximum forwarding rate (MFR)
 Definition:
 The highest forwarding rate of a DUT/SUT taken from an iterative
 set of forwarding rate measurements.
 Discussion:
 The forwarding rate of a device may degenerate before maximum load
 is reached. The load applied to a device must be cited when
 reporting maximum forwarding rate.
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 The following example illustrates how the terms relative to
 loading and forwarding rates are meant to be used. In particular
 it shows how the distinction between forwarding rate at maximum
 offered load (FRMOL) and maximum forwarding rate (MFR) can be used
 to characterize a DUT/SUT.
 (A) (B)
 Test Device DUT/SUT
 Offered Load Forwarding Rate
 ------------ ---------------
 (1) 14,880 fps - MOL 7,400 fps - FRMOL
 (2) 13,880 fps 8,472 fps
 (3) 12,880 fps 12,880 fps - MFR
 Measurement units:
 N-octet frames per second
 Issues:
 See Also:
 offered load (3.5.2)
 forwarding rates (3.6.1)
 forwarding rate at maximum load (3.6.2)
3.7 Congestion control
 This group of definitions applies to the behavior of a DUT/SUT when
 congestion or contention is present.
3.7.1 Backpressure
 Definition:
 Any technique used by a DUT/SUT to attempt to avoid frame loss by
 impeding external sources of traffic from transmitting frames to
 congested interfaces.
 Discussion:
 Some switches send jam signals, for example preamble bits, back to
 traffic sources when their transmit and/or receive buffers start
 to overfill. Switches implementing full duplex Ethernet links may
 use IEEE 802.3x Flow Control for the same purpose. Such devices
 may incur no frame loss when external sources attempt to offer
 traffic to congested or overloaded interfaces.
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 It should be noted that jamming and other flow control methods may
 slow all traffic transmitted to congested input interfaces
 including traffic intended for uncongested output interfaces.
 A DUT/SUT applying backpressure may exhibit no frame loss when a
 tester attempts to overload one or more of its interfaces. This
 should not be interpreted to suggest that the interfaces of the
 DUT/SUT support forwarding rates above the maximum rate allowed by
 the medium. In these cases overloading is only apparent since
 through the application of backpressure the DUT/SUT avoids
 overloading by reducing the rate at which the tester can offer
 frames.
 Measurement units:
 frame loss on congested interface or interfaces N-octet frames per
 second between the interface applying backpressure and an
 uncongested destination interface
 Issues:
 jamming not explicitly described in standards
 See Also:
 intended load (3.5.1)
 offered load (3.5.2)
 overloading (3.5.4)
 forwarding rate (3.6.1)
 forward pressure (3.7.2)
3.7.2 Forward pressure
 Definition:
 Methods which depart from or otherwise violate a defined
 standardized protocol in an attempt to increase the forwarding
 performance of a DUT/SUT.
 Discussion:
 A DUT/SUT may be found to inhibit or abort back-off algorithms in
 order to force access to the medium when contention occurs. It
 should be noted that the back-off algorithm should be fair whether
 the DUT/SUT is in a congested or an uncongested state.
 Transmission below the minimum inter-frame gap or the disregard of
 flow control primitives fall into this category.
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 A DUT/SUT applying forward pressure may eliminate all or most
 frame loss when a tester attempts to overload one or more of its
 interfaces. This should not be interpreted to suggest that the
 interfaces of the DUT/SUT can sustain forwarding rates above the
 maximum rate allowed by the medium. Overloading in such cases is
 only apparent since the application of forward pressure by the
 DUT/SUT enables interfaces to relieve saturated output queues by
 forcing access to the medium and concomitantly inhibiting the
 tester from transmitting frames.
 Measurement units:
 intervals between frames in microseconds
 intervals in microseconds between transmission retries during
 16 successive collisions.
 Issues:
 truncated binary exponential back-off algorithm
 See Also:
 intended load (3.5.1)
 offered load (3.5.2)
 overloading (3.5.4)
 forwarding rate (3.6.1)
 backpressure (3.7.1)
3.7.3 Head of line blocking
 Definition:
 Frame loss or added delay observed on an uncongested output
 interface whenever frames are received from an input interface
 which is also attempting to forward frames to a congested output
 interface.
 Discussion:
 It is important to verify that a switch does not slow transmission
 or drop frames on interfaces which are not congested whenever
 overloading on one of its other interfaces occurs.
 Measurement units:
 forwarding rate and frame loss recorded on an uncongested
 interface when receiving frames from an interface which is also
 forwarding frames to a congested interface.
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 Issues:
 input buffers
 See Also:
 unidirectional traffic (3.2.1)
3.8 Address handling
 This group of definitions applies to the address resolution process
 enabling a DUT/SUT to forward frames to their correct destinations.
3.8.1 Address caching capacity
 Definition:
 The number of MAC addresses per n interfaces, per module or per
 device that a DUT/SUT can cache and successfully forward frames to
 without flooding or dropping frames.
 Discussion:
 Users building networks will want to know how many nodes they can
 connect to a switch. This makes it necessary to verify the number
 of MAC addresses that can be assigned per n interfaces, per module
 and per chassis before a DUT/SUT begins flooding frames.
 Measurement units:
 number of MAC addresses per n interfaces, modules, or chassis
 Issues:
 See Also:
 address learning rate (3.8.2)
3.8.2 Address learning rate
 Definition:
 The maximum rate at which a switch can learn new MAC addresses
 without flooding or dropping frames.
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 Discussion:
 Users may want to know how long it takes a switch to build its
 address tables. This information is useful to have when
 considering how long it takes a network to come up when many users
 log on in the morning or after a network crash.
 Measurement units:
 frames with different source addresses per second
 Issues:
 See Also:
 address caching capacity (3.8.1)
3.8.3 Flood count
 Definition:
 Frames forwarded to interfaces which do not correspond to the
 destination MAC address information when traffic is offered to a
 DUT/SUT for forwarding.
 Discussion:
 When recording throughput statistics it is important to check that
 frames have been forwarded to their proper destinations. Flooded
 frames MUST NOT be counted as received frames. Both known and
 unknown unicast frames can be flooded.
 Measurement units:
 N-octet valid frames
 Issues:
 spanning tree BPDUs.
 See Also:
 address caching capacity (3.8.1)
3.9 Errored frame filtering
 This group of definitions applies to frames with errors which a
 DUT/SUT may filter.
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3.9.1 Errored frames
 Definition:
 Frames which are over-sized, under-sized, misaligned or with an
 errored Frame Check Sequence.
 Discussion:
 Switches, unlike IEEE 802.1d compliant bridges, do not necessarily
 filter all types of illegal frames. Some switches, for example,
 which do not store frames before forwarding them to their
 destination interfaces may not filter over-sized frames (jabbers)
 or verify the validity of the Frame Check Sequence field. Other
 illegal frames are under-sized frames (runts) and misaligned
 frames.
 Measurement units:
 n/a
 Issues:
 See Also:
3.10 Broadcasts
 This group of definitions applies to MAC layer and network layer
 broadcast frames.
3.10.1 Broadcast forwarding rate
 Definition:
 The number of broadcast frames per second that a DUT/SUT can be
 observed to deliver to all interfaces located within a broadcast
 domain in response to a specified offered load of frames directed
 to the broadcast MAC address.
 Discussion:
 There is no standard forwarding mechanism used by switches to
 forward broadcast frames. It is useful to determine the broadcast
 forwarding rate for frames switched between interfaces on the same
 card, interfaces on different cards in the same chassis and
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 interfaces on different chassis linked together over backbone
 connections. The terms maximum broadcast forwarding rate and
 broadcast forwarding rate at maximum load follow directly from the
 terms already defined for forwarding rate measurements in section
 3.6 above.
 Measurement units:
 N-octet frames per second
 Issues:
 See Also:
 forwarding rate at maximum load (3.6.2)
 maximum forwarding rate (3.6.3)
 broadcast latency (3.10.2)
3.10.2 Broadcast latency
 Definition:
 The time required by a DUT/SUT to forward a broadcast frame to
 each interface located within a broadcast domain.
 Discussion:
 Since there is no standard way for switches to process
 broadcast frames, broadcast latency may not be the same on all
 receiving interfaces of a switching device. The latency
 measurements SHOULD be bit oriented as described in section 3.8
 of RFC 1242. It is useful to determine broadcast latency for
 frames forwarded between interfaces on the same card, on
 different cards in the same chassis and on different chassis
 linked over backbone connections.
 Measurement units:
 nanoseconds
 microseconds
 milliseconds
 seconds
 Issues:
 See Also:
 broadcast forwarding rate (3.10.1)
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4. Security Considerations
 Documents of this type do not directly effect the security of the
 Internet or of corporate networks as long as benchmarking is not
 performed on devices or systems connected to operating networks.
 The document points out that switching devices may violate the IEEE
 802.3 standard by transmitting frames below the minimum interframe
 gap or unfairly accessing the medium by inhibiting the backoff
 algorithm. Although such violations do not directly engender
 breaches in security, they may perturb the normal functioning of
 other interworking devices by obstructing their access to the medium.
 Their use on the Internet or on corporate networks should be
 discouraged.
5. References
 [1] Bradner, S., "Benchmarking Terminology for Network
 Interconnection Devices", RFC 1242, July 1991.
 [2] Bradner, S., and J. McQuaid, "Benchmarking Methodology for
 Network Interconnect Devices", RFC 1944, May 1996.
6. Acknowledgments
 The Benchmarking Methodology Working Group of the IETF and
 particularly Kevin Dubray (Bay Networks) are to be thanked for the
 many suggestions they collectively made to help complete this
 document. Ajay Shah (WG), Jean-Christophe Bestaux (ENL), Henry Hamon
 (Netcom Systems), Stan Kopek (Digital) and Doug Ruby (Prominet) all
 provided valuable input at various stages of this project.
 Special thanks go to Scott Bradner for his seminal work in the field
 of benchmarking and his many encouraging remarks.
7. Author's Address
 Robert Mandeville
 European Network Laboratories (ENL)
 2, rue Helene Boucher
 78286 Guyancourt Cedex
 France
 Phone: + 33 1 39 44 12 05
 Mobile Phone + 33 6 07 47 67 10
 Fax: + 33 1 39 44 12 06
 EMail: bob.mandeville@eunet.fr
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8. 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.
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