[Search] [txt|pdfized|bibtex] [Tracker] [WG] [Email] [Diff1] [Diff2] [Nits]
Versions: 00 01 02 03                                                   
INTERNET-DRAFT                                               G. Trotter
Benchmarking Methodology Working Group             Agilent Technologies
Expires: August 2003                                      February 2003

       Methodology for Forwarding Information Base (FIB) based Router

Status of this Memo

    This document is an Internet-Draft and is in full conformance with
    all provisions of Section 10 of RFC2026 [1].

    Internet-Drafts are working documents of the Internet Engineering
    Task Force (IETF), its areas, and its working groups. Note that
    other groups may also distribute working documents as Internet-

    Internet-Drafts are draft documents valid for a maximum of six
    months and may be updated, replaced, or obsoleted by other documents
    at any time. It is inappropriate to use Internet- Drafts as
    reference material or to cite them other than as "work in progress."

    The list of current Internet-Drafts can be accessed at

    The list of Internet-Draft Shadow Directories can be accessed at


    The forwarding performance of an IP router may be dependent upon or
    may be linked to the composition and size of the forwarding
    information base installed within a router.  This document describes
    the methodology to be used to determine the IP packet forwarding
    performance of an IP router as a function of the forwarding
    information base installed within a router.

Table of Contents

    1. Introduction....................................................2
    2. Terms Of Reference..............................................2
    3. Overview........................................................2
    4. Router Setup....................................................3
    5. Test Setup......................................................3
    6. Methodology Of Route Advertisements.............................3
    7. Table Size......................................................4
    8. Table Composition...............................................5
    9. Offered Packet Load.............................................5
    10. Packet Format/Size.............................................6
    11. Determining The Maximum Fib Size...............................6
    12. Methodology....................................................7
    12.1 Baseline Measurements.........................................7

Trotter                                                       [Page 1]

                      FIB-based Router Performance       February, 2003

    12.2 Maximum Fib Size Test.........................................7
    12.3 Fib Size Impact On Packet Forwarding Performance..............8
    13. Security Considerations........................................9
    14. References.....................................................9
    15. Acknowledgments................................................9
    16. Author's Addresses.............................................9

1. Introduction

    This document covers the measurement of the IP packet forwarding
    performance of IP routers on the basis of the forwarding information
    base (FIB) installed within a router.  [2] describes the terminology
    associated with this document.

    The purpose of this document is to describe a methodology for
    measuring the impact of a FIB of a particular size and composition
    on the forwarding performance of a router.  The objective is to
    determine whether a router can maintain performance levels as FIBs
    continue to grow in size.

    This document utilizes the methodology described in [3] for
    measuring the FIB-dependent throughput, FIB-dependent latency and
    FIB-dependent frame loss rate of IP packets as they traverse the
    router under test.  The forwarding performance of a router should be
    observed under different FIB sizes and compositions.

    In this document, the FIB is modified only when traffic is not
    traversing the router.  The effect of dynamic changes on the
    forwarding performance of a router is outside the scope of this

2. Terms Of Reference

    This document utilizes the methodologies for packet throughput,
    latency and loss measurements described in [3].

    Definitions unique to this test methodology are covered in [2].

    This document covers only IPv4 packets traversing an IP router.
    Applicability of this document to other packet types (such as MPLS-
    prefixed packets or non-IP packets) is not appropriate.

3. Overview

    This methodology takes into account two key features of a FIB - the
    FIB size and the FIB prefix distribution.

    This methodology does not specify a particular means of populating a
    FIB - a routing protocol should be used, although a FIB could be
    manually entered into a router.  One implication of this is that
    there needs to be protocol-independent means for determining when a
    router's FIB has been fully populated (described in 12.2).

Trotter                                                       [Page 2]

                      FIB-based Router Performance       February, 2003

    Once a FIB of a particular size and prefix distribution is entered
    into the router, [3] style measurements are performed in order to
    gauge the effect of the FIB on packet FIB-dependent throughput, FIB-
    dependent latency and FIB-dependent frame loss rate.

4. Router Setup

    This is an out-of-service methodology.  The router should be
    configured realistically.  That is, it should be configured with
    physical interface cards, switching fabrics, and route processors
    providing the basis for realistic product comparisons.

5. Test Setup

    The router is connected to test equipment capable of advertising
    network prefixes into the router under test and generating IP
    packets to these advertised networks.  In the absence of test gear
    capable of advertising network prefixes into the router under test,
    the network prefixes could be manually entered into the router.

    This methodology does not specify or require a particular physical
    interface type: all measurements are performed exclusively on IP

6. Methodology Of Route Advertisements

    It is recommended that routes be advertised into the router under
    test by using a routing protocol to speed the advertisement of
    routes.  Routes may be entered into the FIB manually, but this is
    both tedious, and makes the correlation between entered routes and
    offered traffic awkward (see section 9).

    Routes may be advertised into the router on a single interface, or
    over multiple interfaces.  This methodology does not distinguish
    between either method.

6.1 Order of Route Advertisements

    Routes can be advertised into the router in any order - a router may
    organize its FIB to maximize its performance - the impact of order
    of advertisement cannot be presupposed to have an impact on the
    structure of the FIB.

6.2 Prevention of Route Aggregation

    Routes should be advertised into the router in such a manner as to
    prevent route aggregation.  Routes may be aggregated as follows.  If
    100 routes are advertised on a single interface within a common
    prefix of, and no other advertisements on any other
    interface have a prefix of, then the router may enter a
    single /16 entry into the FIB, directing all traffic with a prefix to a particular interface.  Care must be taken to

Trotter                                                       [Page 3]

                      FIB-based Router Performance       February, 2003

    prevent this from occurring, as it will result in smaller than
    intended FIBs being entered within the router under test.

    As an example of a means of router advertisement designed to prevent
    route aggregation, consider the advertisement of 16 /16 prefixes
    into a 4-port router in the diagram below:

    1.1,2.1,3.1,4.1 -----|               |----- 1.3,2.3,3.3,4.3
                         |               |
                         |               |
                         |               |
    1.2,2.2,3.2,4.2 -----|               |----- 1.4,2.4,3.4,4.4

    In this example, the router will not be able to aggregate the
    entries from 1.0, since an entry exists on every port - the same
    applies for the entries from 2.0, 3.0 and 4.0.  This method of route
    advertisement into the router must be used.

6.3 Learning time

    A router takes time to "learn" routes.  The overhead associated with
    learning a route may include processing the routing protocol message
    containing a new FIB entry, placing the entry into the FIB, and
    then, in some modern routers, distributing the updated FIB to each
    interface in the router.

    This methodology does not measure or dictate the time that a router
    takes to build a complete FIB.  However, it is vital to the
    execution of this methodology to ensure that a router has completed
    learning routes and building the forwarding information base before
    tests proceed.

    There are two methods that can be taken to ensure that a router has
    learned all routes.  For the first method, the router can be queried
    via an attached console to reveal the current FIB size.  If access
    to the console is not available, then test packets can be sent
    through the router at such rate that packet loss does not ordinarily
    occur.  Test packets should test each entry in the FIB.  No packet
    loss can indicate that the router has learned all routes, and is
    forwarding packets to all advertised destinations.  However, this
    method is not foolproof - a router may instead have filled its FIB,
    and lost packets may indicate that the FIB is full, and not that the
    router is still learning routes.

7. Table Size

    This methodology does not specify FIB sizes to be installed within
    the router under test.  However, it is expected that this
    methodology will be used through to the maximum possible FIB size
    purported to be supported by the router under test.

Trotter                                                       [Page 4]

                      FIB-based Router Performance       February, 2003

    This methodology recommends starting with a small FIB size - a
    single network per physical interface - in order to perform a basic
    performance benchmark on the router under test.  Subsequent tests
    will increase the FIB by size 'N'.  The FIB will be increased
    through to the maximum size possible (see section 11 for a
    discussion of determining the maximum possible FIB size).

8. Table Composition

    The composition of a FIB consists of a number FIB entries, with each
    FIB entry containing a network prefix.  The network prefix length of
    each FIB entry may vary.  These network prefixes typically range, in
    a typical Internet router's FIB, from 8 to 30 bits in length (/8 to
    /30) (this document does not attempt to pre-suppose the composition
    of a typical FIB within a router in the Internet, however).
    Destination address matches within FIBs consisting entirely of 8-bit
    network prefixes may be very rapid (few bits in each destination
    address/network prefix need to be matched), whereas it can be
    expected that destination address matches within a FIB populated
    entirely with 30-bit network prefixes (highly unlikely) will be

9. Offered Packets

    To gauge the impact of a FIB on the performance of a router, IP
    packets must be delivered to the router such that the FIB is fully
    exercised.  That is, packets must be delivered into the router on
    every interface directed to stations whose network prefix is
    advertised on every other interface.

    This method of traffic generation fairly exercises the FIB on the
    router.  Modern routers may maintain a cache of the most frequently
    used routes on a per-interface (or, per-line card) basis, or they
    may maintain a complete copy of the FIB on a per-interface (or per-
    line card) basis.  Generating packets from every interface to every
    advertised network ensures that each copy of the FIB is stressed, as
    well as ensuring that a router's FIB cannot be optimized (i.e. by
    installing summary routes).

    Consider the diagram below:

    1.1,2.1,3.1,4.1 -----|A             C|----- 1.3,2.3,3.3,4.3
                         |               |
                         |               |
                         |               |
    1.2,2.2,3.2,4.2 -----|B             D|----- 1.4,2.4,3.4,4.4

    In this diagram, packets sent into interface A must be directed to a
    destination address present in each network advertised on ports B, C
    and D.  That is, the "transmit packet list" for packets sent into
    port A must be:

Trotter                                                       [Page 5]

                      FIB-based Router Performance       February, 2003

    and then repeated.

    Note that packets are transmitted to destinations on each port in a
    round-robin manner.  That is, A transmits a packet to B, then a
    packet to C and then a packet to D, and then repeats, using the next
    destination advertised on port A, and so on.  This method ensures
    that all aspects of the router (switching fabric, interface cards,
    route processor, etc.) are stressed equally.

    Also note that packets are sent from all interfaces simultaneously,
    again ensuring that all router components are stressed equally.  See
    section 16 in [3].

10. Packet Format/Size

    See [3] for a discussion of packet formats and sizes.

11. Determining The Maximum Fib Size

    In order to determine the maximum FIB size, a method similar to that
    used to determine whether all routes have been learned (see section
    6.3) will be used.

    Without observing the exchange of the routing protocol, it is
    necessary to ascertain the size of the FIB from observation of
    packets sent from the router.

    The most methodical way of discovering the maximum FIB size is to
    advertise network prefixes to the FIB, test the addition of the
    entry by sending packets to the new network, ensure receipt of this
    packet and repeat until packets are no longer forwarded to the newly
    added network.  Care must be taken to ensure that packets continue
    to be forwarded to all advertised networks, even while new networks
    are added - a router may "age-out" old entries in order to ensure
    that its FIB is filled with current entries.

    The absence of packets received at a particular network is
    indicative of entries not being present within the FIB, and thus
    indicates that the FIB has filled.

Trotter                                                       [Page 6]

                      FIB-based Router Performance       February, 2003

    If the approximate FIB size is known in advance, a larger number of
    routes can be advertised into the router, then the maximum table
    size can be found incrementally from this point.

    When using IP packets to discover the maximum sized FIB supported by
    the DUT, IP packets should be sent in at a rate that is
    significantly below that of the maximum measured throughput of the
    router discovered during baseline measurements (see section 12.1).

12. Methodology

    This methodology makes use of the packet forwarding measurements
    described in RFC 2544.

12.1 Baseline Measurements

    Objective:  The objective of the baseline measurement is to
    determine the nominal packet forwarding performance of the router,
    with a minimal sized FIB.

    Procedure:  A route to a single network should be advertised on each
    port of the router under test - a router with 64 ports would thus
    have an installed FIB of 64 entries.

    As described in section 9, packets should be offered to the router
    in order to create a full mesh between all advertised networks.

    Using measurements described in [3] for the throughput, latency,and
    frame loss rates (as per sections 26.1, 26.2, 26.3 and 26.4 in [3]),
    the FIB-dependent throughput, FIB-dependent latency and FIB-
    dependent frame loss rate should be measured and the results duly

    Reporting Format:  Results should be reported as per [3].

12.2 Maximum FIB Size Test

    Objective:  The objective of this test is to determine the maximum
    size of the FIB that can be accommodated within the DUT.  Discovery
    of the maximum limit of the size of the FIB is necessary for the
    establishment of limits in subsequent tests.

    Procedure:  Initially, advertise a single network on every port as
    per section 12.1.  Establish a traffic mesh between all advertised
    networks as per section 9.  Transmit IP packets through the DUT to
    all advertised networks at a rate well below the maximum throughput
    rate of the router, discovered in section 12.1. Ensure that packet
    loss is zero (indicating that packets are being forwarded to all
    advertised networks).

    Repeatedly advertise additional networks into the DUT and add these
    networks into the traffic mesh established through the DUT to the

Trotter                                                       [Page 7]

                      FIB-based Router Performance       February, 2003

    advertised networks.  Stop when packet loss is detected, or when an
    ICMP destination unreachable message with a code value of 0 (network
    unreachable) or 6 (destination network unknown) is received.  This
    will indicate that the FIB has filled (or, that the DUT is unable to
    add additional entries into the FIB).  The test should continue in
    order to establish increasing packet loss as a consequence of
    increasing networks advertised into the DUT.

    Reporting Format:  The results should be reported as a single number
    (the maximum FIB size).  The results should be backed up with a
    graph of the packet loss (on the y-axis) versus the networks
    advertised into the DUT (on the x-axis).

12.3 FIB Size Impact On Packet Forwarding Performance

    Objective:  The objective of this test is to evaluate the impact of
    FIB size and composition upon the packet forwarding performance of
    the DUT.

    Procedure:  This iterative test changes both the size and
    composition of the FIB, and makes performance measurements for each
    iteration.  That is, the FIB is set to a certain size and
    composition, then performance measurements are made for packet
    throughput, latency, and packet loss rate.  The FIB is incremented,
    then the tests are repeated, through to the maximum sized FIB
    supported by the DUT.

    The following code segment illustrates this methodology:

        set forward_table_compositions [List 16 22 24 realistic]

        for (forwarding_table_size = num_physical_interfaces;
             Forwarding_table_size <= maximum_forwarding_table_size;
             Forwarding_table_size += increment)
            foreach value forward_table_compositions_
                set_forwarding_table_composition $value
                measure_FIB-dependent_packet loss rate;
                measure_FIB-dependent_back-to-back frames;

    Reporting Format:  Results will be reported as a series of [3]-style
    graphs, with a separate set of graphs for each individual FIB size /
    FIB composition test.  Results could be overlaid onto a single set
    of graphs.

    It may be useful to create a set of graphs to aid in direct
    interpretation of this test.  One recommended graph would be, for a
    particular frame size, a graph of the appropriate metric on the y-

Trotter                                                       [Page 8]

                     FIB-based Router Performance       February, 2003

    axis (FIB-dependent throughput, FIB-dependent latency, FIB-dependent
    packet loss) versus the FIB size, with overlaid lines for each FIB

13. Security Considerations

    As this document is solely for the purpose of providing metric
    methodology and describes neither a protocol nor a protocol's
    implementation, there are no security considerations associated with
    this document.

14. Informative References

    1  Bradner, S., "The Internet Standards Process -- Revision 3", BCP
       9, RFC 2026, October 1996.
    2  Trotter, G., " Terminology for Forwarding Information Base (FIB)
       based Router Performance", RFC 3222, December, 2001.
    3  Bradner, S., McQuaid, J., "Benchmarking Methodology for Network
       Interconnect Devices", RFC 2544, March 1999

15. Acknowledgements

16. Author's Addresses

    Guy Trotter
    Agilent Technologies (Canada) Inc.
    #2500 4710 Kingsway
    Burnaby, British Columbia
    V5H 4M2
    Phone: +1 604 454 3516
    Email: Guy_Trotter@agilent.com

Full Copyright Statement

    "Copyright (C) The Internet Society (2002). 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

Trotter                                                       [Page 9]

                      FIB-based Router Performance       February, 2003

    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

Trotter                                                      [Page 10]