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Versions: 00 01 02 03                                                   
Benchmarking Methodology Working Group                       G. Trotter
Internet Draft                                     Agilent Technologies
Document: <draft-ietf-bmwg-fib-meth-00.txt>                January 2002
Category: Informational

      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

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                     FIB-based Router Performance      September, 2001

   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).

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                     FIB-based Router Performance      September, 2001

   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

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                     FIB-based Router Performance      September, 2001

   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.

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                     FIB-based Router Performance      September, 2001

   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:

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                     FIB-based Router Performance      September, 2001

   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.

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                     FIB-based Router Performance      September, 2001

   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

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                     FIB-based Router Performance      September, 2001

   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-

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                     FIB-based Router Performance      September, 2001

   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. 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

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                     FIB-based Router Performance      September, 2001

   The limited permissions granted above are perpetual and will not be
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Trotter                                                      [Page 10]