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Versions: 00 01 02 03 04 rfc3222                                        
Benchmarking Methodology Working Group                       G. Trotter
Internet Draft                                     Agilent Technologies
Document: draft-ietf-bmwg-fib-term-03.txt                September 2001
Category: Informational


      Terminology for Forwarding Information Base (FIB) based Router
                                Performance

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-
   Drafts.

   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
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

Abstract

   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 terms to be used in a methodology that determines the IP packet
   forwarding performance of IP routers as a function of the forwarding
   information base installed within a router.

Table of Contents

   1. Introduction....................................................2
   2. Overview........................................................2
   3. Existing Definitions............................................3
   4. Definition Format...............................................3
   5. Definitions - parameters........................................3
   5.1 Network Prefix.................................................3
   5.2 Network Prefix Length..........................................4
   5.3 Forwarding Information Base (FIB)..............................4
   5.4 Forwarding Information Base Entry..............................5
   5.5 Forwarding Information Base Size...............................5
   5.6 Longest Length Prefix Match Algorithm..........................6
   5.7 Forwarding Information Base Prefix Distribution................6
   5.8 Per-Interface or Per-Card Forwarding Information Base..........7

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             Terminology for FIB based Router Performance  Sept., 2001


   5.9 Per-Interface Forwarding Information Base Cache................8
   5.10 Route Aggregation.............................................9
   6. Definitions - metrics...........................................9
   6.1 Maximum Forwarding Information Base Size.......................9
   6.2 Forwarding Information Base Learning Time.....................10
   6.3 Forwarding Information Base-dependent Throughput..............11
   6.4 Forwarding Information Base-dependent Latency.................11
   6.5 Forwarding Information Base-dependent Frame Loss Rate.........11
   7. Security Considerations........................................12
   8. References.....................................................12
   9. Acknowledgments................................................12
   10. Author's Addresses............................................12


1. Introduction

   This document defines terms that are to be used in a methodology
   that determines the IP packet forwarding performance of IP routers
   as a function of the forwarding information base installed within
   the router.

   This document is restricted to IPv4 routers.

   The objective of this methodology is to evaluate the performance
   levels of IP routers as forwarding information bases continue to
   grow in size and complexity of structure.

   This methodology utilizes the packet forwarding performance
   measurements described in [2]; reference will also be made to the
   associated terminology document [3] for these terms.

2. Overview

   In order to measure the forwarding information base-based router
   performance, different forwarding information bases (5.3) are
   installed in the router.  The two key elements describing the FIB
   are the FIB size (5.5) and FIB prefix distribution (5.6).  The
   forwarding performance of a router may be dependent upon these two
   primary factors, particularly if FIB prefix distributions tend
   towards longer network prefixes (3).  The FIB-dependent throughput,
   latency and frame loss rate (6.3, 6.4, 6.5), measured with fully
   meshed traffic flows [2], will reflect the change in performance of
   the router.  Tests may need to be performed up to the maximum FIB
   size (6.1).

   When configuring the router for these measurements, the routes need
   to be manually entered into the router, or advertised via a routing
   protocol.  It may take some period of time (the FIB learning time
   (6.2)) before the router learns all the routes.

   When routes are advertised into the router, the routes should be
   advertised in such a way so that route aggregation (5.10) does not


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             Terminology for FIB based Router Performance  Sept., 2001


   occur.  Also, the effect of a per-interface FIB cache (5.9) needs to
   be taken into account.

3. Existing Definitions

   [3] should be consulted before attempting to make use of this
   document.  [2] contains discussions of a number of terms relevant to
   the benchmarking of network interconnect devices and should also be
   consulted.

4. Definition Format

   The definition format is the equivalent to that defined in [3], and
   is repeated here for convenience:

   X.x Term to be defined. (e.g., Latency)

   Definition:
          The specific definition for the term.

   Discussion:
          A brief discussion about the term, it's application and any
          restrictions on measurement procedures.

   Measurement units:
          The units used to report measurements of this term, if
          applicable.

   Issues:
          List of issues or conditions that effect this term.

   See Also:
          List of other terms that are relevant to the discussion of
          this term.

5. Definitions - parameters

   This section defines parameters that would dictate the execution of
   methodology to determine the FIB based forwarding performance of a
   router.

5.1 Network Prefix

   Definition:

          "A network prefix is . . . a contiguous set of bits at the
          more significant end of the address that defines a set of
          systems; host numbers select among those systems."

          (This definition is taken directly from section 2.2.5,
          "Addressing Architecture", in [4].)

   Discussion:

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             Terminology for FIB based Router Performance  Sept., 2001


          In the CIDR context, the network prefix is the network
          component of an IP address. A common alternative to using a
          bitwise mask to communicate this component is the use of
          "slash (/) notation."  Slash notation binds the notion of
          network prefix length (see 5.2) in bits to an IP address.
          E.g., 141.184.128.0/17 indicates the network component of
          this IPv4 address is 17 bits wide.

   Measurement units:
          <n/a>

   Issues:

   See Also:
          Network Prefix Length (5.2)

5.2 Network Prefix Length

   Definition:
          The number of bits used to define the network prefix.
          Network prefixes, using CIDR terminology, are typically
          referred to as 15.35.128.0 /17, indicating that the network
          prefix is 17 bits long.

   Discussion:
          When referring to groups of addresses, the network prefix
          length is often used as a means of describing groups of
          addresses as an equivalence class.  For example, 100 /16
          addresses refers to 100 addresses whose network prefix length
          is 16 bits.

   Measurement units:
          bits

   Issues:

   See Also:
          network prefix (5.1)
          forwarding information base prefix distribution (5.6)

5.3 Forwarding Information Base (FIB)

   Definition:
          As according to the definition in [4]:

          "The table containing the information necessary to forward IP
          Datagrams, in this document, is called the Forwarding
          Information Base.  At minimum, this contains the interface
          identifier and next hop information for each reachable
          destination network prefix."

   Discussion:


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             Terminology for FIB based Router Performance  Sept., 2001


          The forwarding information base describes a database indexing
          network prefixes versus router port identifiers.

          A forwarding information base consists of [FIB size (6.1)]
          FIB entries (5.4).

          The forwarding information base is distinct from the "routing
          table" (or, the Routing Information Base), which holds all
          routing information received from routing peers.

          The forwarding information base contains unique paths only
          (i.e. does not contain secondary paths).

   Measurement units:
          <none>

   Issues:

   See Also:
          forwarding information base entry (5.4)
          forwarding information base size (5.5)
          forwarding information base prefix distribution (5.6)
          maximum forwarding information base size (6.1)

5.4 Forwarding Information Base Entry

   Definition:
          A single entry within a forwarding information base.  This
          entry consists of the minimum amount of information necessary
          to make a forwarding decision on a particular packet.  The
          typical components within a forwarding information base entry
          are a network prefix, a router port identifier and next hop
          information.  This is an entry that the router can and does
          use to forward packets.

   Discussion:
          See (5.3).

   Measurement units:
          <n/a>

   Issues:

   See Also:
          forwarding information base (5.3)
          forwarding information base size (5.5)
          forwarding information base prefix distribution (5.6)
          maximum forwarding information base size (6.1)

5.5 Forwarding Information Base Size

   Definition:


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             Terminology for FIB based Router Performance  Sept., 2001


          Refers to the number of forwarding information base entries
          within a forwarding information base.

   Discussion:
          The number of entries within a forwarding information base is
          one of the key elements that may influence the forwarding
          performance of a router.  Generally, the more entries within
          the forwarding information base, the longer it could take to
          find the longest matching network prefix within the
          forwarding information base.

   Measurement units:
          Number of routes

   Issues:

   See Also:
          forwarding information base (5.3)
          forwarding information base entry (5.4)
          forwarding information base prefix distribution (5.6)
          maximum forwarding information base size (6.1)

5.6 Longest Length Prefix Match Algorithm

   Definition:
          An algorithm that a router uses to quickly match destination
          addresses within received IP packets to exit interfaces on
          the router.

   Discussion:

   Measurement Units:
          <none>

   Issues:

   See Also:


5.7 Forwarding Information Base Prefix Distribution

   Definition:
          The distribution of network prefix lengths within the
          forwarding information base.

   Discussion:
          Network prefixes within the forwarding information base could
          be all of a single network prefix length, but, more
          realistically, the network prefix lengths will be distributed
          across some range.

          Individual performance measurements will be made against FIBs
          populated with the same network prefix length, as well as

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             Terminology for FIB based Router Performance  Sept., 2001


          against FIBs with some distribution of network prefix
          lengths.

          The distribution of network prefix lengths may have an impact
          on the forwarding performance of a router.  The longer the
          network prefix length, the longer it will take for a router
          to perform the longest length prefix match algorithm, and
          potentially the lower the performance of the router.

   Measurement units:
          The forwarding information base prefix distribution is
          expressed by a list of network prefix lengths and the
          percentage of entries within the forwarding information base
          with a particular network prefix length.  For example, a
          forwarding information base prefix distribution is
          represented as:

              {[/16, 100], [/20, 360], [/24, 540]}

          This indicates that 100 of the entries within the forwarding
          information base have a 16 bit network prefix length, 360
          have a 20 bit network prefix length, and 540 have a 24 bit
          network prefix length.

   Issues:

   See Also:
          forwarding information base (5.3)
          forwarding information base entry (5.4)
          forwarding information base size (5.5)
          maximum forwarding information base size (6.1)

5.8 Per-Interface or Per-Card Forwarding Information Base

   Definition:
          A complete copy of the forwarding information base, installed
          on a router's card or individual physical interface to speed
          the destination address to network prefix lookup process.

   Discussion:
          Router manufacturers have developed many optimizations for
          routers, of which one optimization is to copy the forwarding
          information base to every interface or interface card on the
          router.  By doing this, destination address / network prefix
          lookups can be performed on the interface or card, unloading
          a router's CPU.

   Measurement units:
          <n/a>

   Issues:

   See Also:

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             Terminology for FIB based Router Performance  Sept., 2001


          forwarding information base (5.3)
          per-interface forwarding information base cache (5.9)

5.9 Per-Interface Forwarding Information Base Cache

   Definition:
          A subset of a forwarding information base, installed on a
          router's interface card to speed the destination address /
          network prefix lookup process.

   Discussion:
          Prior to installing a complete copy of the forwarding
          information base on each interface of a router, a popular
          technique for speeding destination address lookups is to
          install a cache of frequently used routes on a router's
          interface.

          The most frequently used routes are placed in the forwarding
          information base cache.  IP packets whose destination address
          does not match a network prefix within the per-interface
          forwarding information base cache are forwarded to a router's
          central processor for lookup in the complete forwarding
          information base.

          The implication for benchmarking the performance of a router
          as a function of the forwarding information base is
          significant.  IP packets whose destination address matches an
          entry within the per-interface forwarding information base
          cache could be forwarded more quickly than packets whose
          destination address does not match an entry within the per-
          interface forwarding information base cache.

          To create useful benchmarks, the role of a per-interface
          forwarding cache needs to be considered.  The nature of
          benchmarking tests to measure the impact of the forwarding
          performance of a router requires that the destination
          addresses within IP packets transmitted into the router be
          distributed amongst the total set of network prefixes
          advertised into the router.  This negates the role of a per-
          interface forwarding information base cache, but serves to
          stress the forwarding information base-based packet
          forwarding performance of the router.

   Measurement units:
          <n/a>

   Issues:

   See Also:
          forwarding information base (5.3)
          per-interface forwarding information base (5.8)



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             Terminology for FIB based Router Performance  Sept., 2001


5.10 Route Aggregation

   Definition:
          The ability of a router to collapse many forwarding
          information base entries into a single entry.

   Discussion:
          A router may aggregate routes in a forwarding information
          base into a single entry to conserve space.

          When advertising routes into a router to perform benchmarking
          tests as a function of the forwarding information base
          installed within the router, it is necessary to ensure that a
          router does not aggregate routes.

          Thus, when routes are advertised to the router or installed
          statically, care must be taken to ensure that the router does
          not aggregate routes.

          For example, if advertising a set of /24 network prefixes
          into a particular port on the router, 256 consecutive /24
          routes, sharing a common leading 16 bits, should not be
          advertised on a single port.  If this is done, then the
          router will install a single entry within the forwarding
          information base indicating that all networks matching a
          particular /16 network prefix are accessible through one
          particular entry.

          Route aggregation on a router can be turned off, but routes
          should still be advertised into the router in such a manner
          as to avoid route aggregation.

   Measurement units:
          <none>

   Issues:

   See Also:

6. Definitions - metrics

   This section defines the metrics, or results, that would
   characterized the FIB based forwarding performance of a router.

6.1 Maximum Forwarding Information Base Size

   Definition:
          The maximum number of forwarding information base entries
          that can be supported within the forwarding information base.
          The Maximum Forwarding Information Base Size is the size over
          which all entries can and are used to forward traffic.

   Discussion:

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             Terminology for FIB based Router Performance  Sept., 2001


          It is useful to know the maximum forwarding information base
          size for a router as it will be an indicator of the ability
          of the router to function within the given application space,
          and whether the router will be able to handle projected
          network growth.

          As a benchmarking value, it is necessary to discover this
          value so that performance measurements can be made up to the
          maximum possible forwarding information base size.

   Measurement units:
          Number of routes

   Issues:
          Could this value vary with the forwarding information base
          prefix distribution?

   See Also:
          forwarding information base (5.3)
          forwarding information base entry (5.4)
          forwarding information base size (5.5)
          forwarding information base prefix distribution (5.6)

6.2 Forwarding Information Base Learning Time

   Definition:
          The time a router takes to process received routing messages,
          and to construct (and, possibly to distribute amongst the
          interface cards in the router) the forwarding information
          base.  This is measured from the time at which a router is
          presented with the first routing message, through to when it
          can forward packets using any entry in the forwarding
          information base.

   Discussion:
          It takes time for a router to construct its forwarding
          information base.  A router needs to process received routing
          packets, build the routing information database, select the
          best paths, build the forwarding information base and then
          possibly distribute the forwarding information base or a
          subset thereof to the interface cards.  This entire process
          can take several minutes with very large forwarding
          information bases.

          When performing benchmarking tests that take the forwarding
          information base into account, time must be allocated for the
          router to process the routing information and to install the
          complete forwarding information base within itself, before
          performance measurements are made.

   Measurement units:
          Prefixes per second.


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             Terminology for FIB based Router Performance  Sept., 2001


   Issues:

   See Also:
          forwarding information base (5.3)

6.3 Forwarding Information Base-dependent Throughput

   Definition:
          Throughput, as defined in [3], used in a context where the
          forwarding information base influences the throughput.

   Discussion:
          This definition for FIB-dependent throughput is added to
          distinguish the context of this measurement from that defined
          in [3].

   Measurement units:
          See [3].

   Issues:

   See Also:
          forwarding information base-dependent latency (6.4)
          forwarding information base-dependent frame loss rate (6.5)

6.4 Forwarding Information Base-dependent Latency

   Definition:
          Latency, as defined in [3], used in a context where the
          forwarding information base influences the throughput.

   Discussion:
          This definition for FIB-dependent latency is added to
          distinguish the context of this measurement from that defined
          in [3].

   Measurement units:
          See [3].

   Issues:

   See Also:
          forwarding information base-dependent throughput (6.3)
          forwarding information base-dependent frame loss rate (6.5)

6.5 Forwarding Information Base-dependent Frame Loss Rate

   Definition:
          Frame Loss Rate, as defined in [3], used in a context where
          the forwarding information base influences the throughput.

   Discussion:


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             Terminology for FIB based Router Performance  Sept., 2001


          This definition for FIB-dependent frame loss rate is added to
          distinguish the context of this measurement from that defined
          in [3].

   Measurement units:
          See [3].

   Issues:

   See Also:
          forwarding information base-dependent throughput (6.3)
          forwarding information base-dependent latency (6.4)


7. Security Considerations

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

8. References


   1  Bradner, S., "The Internet Standards Process -- Revision 3", BCP
      9, RFC 2026, October 1996.
   2  Bradner, S., McQuaid, J., "Benchmarking Methodology for Network
      Interconnect Devices", RFC 2544, March 1999
   3  Bradner, S., "Benchmarking Terminology for Network
      Interconnection Devices", RFC 1242, July 1991
   4  Baker, F., "Requirements for IP Version 4 Routers", RFC 1812,
      June 1995

9. Acknowledgments

10. Author's Addresses

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

Full Copyright Statement

   "Copyright (C) The Internet Society (2001). 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


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             Terminology for FIB based Router Performance   July, 2001


   or assist in its implementation may be prepared, copied, published
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Trotter                                                      [Page 13]