[Search] [txt|pdf|bibtex] [Tracker] [WG] [Email] [Nits]

Versions: 00 01 02 03 04 rfc3222                                        
Benchmarking Methodology Working Group                       G. Trotter
Internet-Draft                                     Agilent Technologies
Expires: January 2001                                         July 2000

      Terminology for Forwarding Information Base (FIB) based Router
                        Performance Benchmarking
                    <draft-ietf-bmwg-fib-term-00.txt>

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.

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.

   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).  As FIB
   sizes increase, and as FIB prefix distributions tend towards longer
   network prefixes (5.1), then it will take more time to match the
   destination address within an IP packet and its corresponding entry

Trotter                                                       [Page 1]


             Terminology for FIB based Router Performance   July, 2000


   within the FIB.  The FIB-dependent throughput, latency and frame
   loss rate (5.11, 5.12, 5.13), measured with fully meshed traffic
   flows (5.15), will reflect the change in performance of the router.
   Tests may need to be performed up to the maximum FIB size (5.7).

   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
   (5.8)) 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 (5.14) does not
   occur.  Also, the effect of a per-interface FIB cache (5.10) 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 switching 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

5.1 Network Prefix

   Definition:
          See section 2.2.5, "Addressing Architecture", in [4].


Trotter                                                       [Page 2]


             Terminology for FIB based Router Performance   July, 2000


          A network prefix refers to the high-order 'n' bits of an IP
          address, identifying a particular network within which an IP
          host is located.

   Discussion:
          Network prefixes are represented as a 32 bit IP address with
          a mask indicating the number of bits representing the network
          prefix.  I.e. 141.184.128 /17 indicates that the network
          prefix is 17 bits long.

   Measurement units:
          <n/a>

   Issues:

   See Also:
          Network Prefix Length (5.2)

5.2 Network Prefix Length

   Definition:
          Refers to the length in bits of a network prefix.  Network
          prefixes, using CIDR terminology, are typically referred to
          as 15.35.128 /17, indicating that the network prefix is 17
          bits long.

   Discussion:

   Measurement units:
          length in 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."

          A forwarding information base consists of [FIB size (5.7)]
          FIB entries (5.4).

   Discussion:


Trotter                                                       [Page 3]


             Terminology for FIB based Router Performance   July, 2000


          The forwarding information base is an abstract concept used
          to describe a database indexing network prefixes versus
          router port identifiers.  This database may, in reality, be
          constructed in any fashion that optimizes the execution of
          the longest prefix length match algorithm, which maps the
          destination addresses within received IP packets against the
          entries in the forwarding information base.

   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 (5.7)

5.4 Forwarding Information Base Entry

   Definition:
          A single entry within a forwarding information base,
          consisting of a network prefix and a router port identifier.

   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 (5.7)

5.5 Forwarding Information Base Size

   Definition:
          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.


Trotter                                                       [Page 4]


             Terminology for FIB based Router Performance   July, 2000


   Measurement units:
          positive integer

   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 (5.7)

5.6 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
          against FIBs with some distribution of network prefix
          lengths.

          The distribution of network prefix lengths will 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, 10%], [/20, 36%], [/24, 54%]}

          This indicates that 10% of the entries within the forwarding
          information base have a 16 bit network prefix length, 36%
          have a 20 bit network prefix length, and 54% have a 24 bit
          network prefix length.

   Issues:

   See Also:
          forwarding information base (5.3)

Trotter                                                       [Page 5]


             Terminology for FIB based Router Performance   July, 2000


          forwarding information base entry (5.4)
          forwarding information base size (5.5)
          maximum forwarding information base size (5.7)

5.7 Maximum Forwarding Information Base Size

   Definition:
          The maximum number of forwarding information base entries
          that can be supported within the forwarding information base.

   Discussion:
          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:
          Positive integer.

   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)

5.8 Forwarding Information Base Learning Time

   Definition:
          The forwarding information base learning time is the time
          taken for a router to receive and process received routing
          messages, and to construct (and, possibly to distribute
          amongst the interface cards in the router) 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.


Trotter                                                       [Page 6]


             Terminology for FIB based Router Performance   July, 2000


          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:

   Issues:

   See Also:
          forwarding information base (5.3)

5.9 Per-Interface Forwarding Information Base

   Definition:
          A complete copy of the forwarding information base, installed
          on a router's interface card 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 card on the router.  By
          doing this, destination address / network prefix lookups can
          be performed on the interface, unloading a router's CPU.

   Measurement units:
          <n/a>

   Issues:

   See Also:
          forwarding information base (5.3)
          per-interface forwarding information base cache (5.10)

5.10 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

Trotter                                                       [Page 7]


             Terminology for FIB based Router Performance   July, 2000


          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 (5.9)

5.11 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 (5.12)
          forwarding information base-dependent frame loss rate (5.13)



Trotter                                                       [Page 8]


             Terminology for FIB based Router Performance   July, 2000


5.12 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 (5.11)
          forwarding information base-dependent frame loss rate (5.13)

5.13 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:
          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 (5.11)
          forwarding information base-dependent latency (5.12)

5.14 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


Trotter                                                       [Page 9]


             Terminology for FIB based Router Performance   July, 2000


          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.

   Measurement units:
          <none>

   Issues:

   See Also:

5.15 Fully Meshed Traffic Flows

   Definition:
          A traffic mesh that fully exercises the forwarding table
          continuously in the router under test.

   Discussion:
          In order to stress the forwarding information base lookup
          mechanisms within the router, packets need to be delivered on
          every interface such that every entry within the forwarding
          information base is accessed.

          This implies that the set of destination addresses used by IP
          packets delivered to each interface of the router matches the
          set of all network prefixes advertised into the router.  That
          is, IP packets are sent into every interface such that IP
          packets are directed through to every network advertised on
          every other interface on the router.

          Fully meshed traffic flows ensure that the forwarding
          information base or per-interface forwarding information
          bases are fully and continuously exercised.

   Measurement units:
          <n/a>

   Issues:

   See Also:
          fully meshed traffic (section 3.3.3 in [5])

Trotter                                                      [Page 10]


             Terminology for FIB based Router Performance   July, 2000



6. 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.

7. 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
   5  Mandeville, R., "Benchmarking Terminology for LAN Switching
      Devices", RFC 2285, February 1998

8. Acknowledgments

9. 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 (2000). 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.




Trotter                                                      [Page 11]


             Terminology for FIB based Router Performance   July, 2000


   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.














































Trotter                                                      [Page 12]