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rfc:rfc3222

Network Working Group G. Trotter Request for Comments: 3222 Agilent Technologies Category: Informational December 2001

  Terminology for Forwarding Information Base (FIB) based Router
                            Performance

Status of this Memo

 This memo provides information for the Internet community.  It does
 not specify an Internet standard of any kind.  Distribution of this
 memo is unlimited.

Copyright Notice

 Copyright (C) The Internet Society (2001).  All Rights Reserved.

Abstract

 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.  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.

Trotter Informational [Page 1] RFC 3222 FIB based Router Performance December 2001

Table of Contents

 1. Introduction.................................................... 2
 2. Overview........................................................ 3
 3. Existing Definitions............................................ 3
 4. Definition Format............................................... 3
 5. Definitions - parameters........................................ 4
 5.1 Network Prefix................................................. 4
 5.2 Network Prefix Length.......................................... 4
 5.3 Forwarding Information Base (FIB).............................. 5
 5.4 Forwarding Information Base Entry.............................. 6
 5.5 Forwarding Information Base Size............................... 6
 5.6 Longest Length Prefix Match Algorithm.......................... 7
 5.7 Forwarding Information Base Prefix Distribution................ 7
 5.8 Per-Interface or Per-Card Forwarding Information Base.......... 8
 5.9 Per-Interface Forwarding Information Base Cache................ 9
 5.10 Route Aggregation............................................ 10
 6. Definitions - metrics.......................................... 10
 6.1 Maximum Forwarding Information Base Size...................... 11
 6.2 Forwarding Information Base Learning Time..................... 11
 6.3 Forwarding Information Base-dependent Throughput.............. 12
 6.4 Forwarding Information Base-dependent Latency................. 12
 6.5 Forwarding Information Base-dependent Frame Loss Rate......... 13
 7. Security Considerations........................................ 13
 8. References..................................................... 13
 9. Author's Address............................................... 14
 10. Full Copyright Statement...................................... 15

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.

Trotter Informational [Page 2] RFC 3222 FIB based Router Performance December 2001

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 (5.7).  The forwarding
 performance of a router may be dependent upon these two primary
 factors, particularly if FIB prefix distributions tend towards longer
 network prefixes (5.1).  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
 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.

Trotter Informational [Page 3] RFC 3222 FIB based Router Performance December 2001

 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 2.2.5.2,
    "Classless Inter Domain Routing (CIDR)", in [4].)
 Discussion:
    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.

Trotter Informational [Page 4] RFC 3222 FIB based Router Performance December 2001

 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 (5.7)

5.3 Forwarding Information Base (FIB)

 Definition:
    As according to the definition in Appendix B of [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:
    The forwarding information base describes a database indexing
    network prefixes versus router port identifiers.
    A forwarding information base consists of [FIB size (5.5)] 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:

Trotter Informational [Page 5] RFC 3222 FIB based Router Performance December 2001

 See Also:
    forwarding information base entry (5.4)
    forwarding information base size (5.5)
    forwarding information base prefix distribution (5.7)
    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 (5.7)
    maximum forwarding information base size (6.1)

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.
 Measurement units:
    Number of routes

Trotter Informational [Page 6] RFC 3222 FIB based Router Performance December 2001

 Issues:
 See Also:
    forwarding information base (5.3)
    forwarding information base entry (5.4)
    forwarding information base prefix distribution (5.7)
    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 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.

Trotter Informational [Page 7] RFC 3222 FIB based Router Performance December 2001

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

Trotter Informational [Page 8] RFC 3222 FIB based Router Performance December 2001

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)

Trotter Informational [Page 9] RFC 3222 FIB based Router Performance December 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.

Trotter Informational [Page 10] RFC 3222 FIB based Router Performance December 2001

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:
    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 (5.7)

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

Trotter Informational [Page 11] RFC 3222 FIB based Router Performance December 2001

    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.
 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].

Trotter Informational [Page 12] RFC 3222 FIB based Router Performance December 2001

 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:
    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. and J. McQuaid, "Benchmarking Methodology for Network
     Interconnect Devices", RFC 2544, March 1999.
 [3] Bradner, S., "Benchmarking Terminology for Network
     Interconnection Devices", RFC 1242, July 1991.

Trotter Informational [Page 13] RFC 3222 FIB based Router Performance December 2001

 [4] Baker, F., "Requirements for IP Version 4 Routers", RFC 1812,
     June 1995.

9. Author's Address

 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

Trotter Informational [Page 14] RFC 3222 FIB based Router Performance December 2001

10. 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
 or assist in its implementation may be prepared, copied, published
 and distributed, in whole or in part, without restriction of any
 kind, provided that the above copyright notice and this paragraph are
 included on all such copies and derivative works.  However, this
 document itself may not be modified in any way, such as by removing
 the copyright notice or references to the Internet Society or other
 Internet organizations, except as needed for the purpose of
 developing Internet standards in which case the procedures for
 copyrights defined in the Internet Standards process must be
 followed, or as required to translate it into languages other than
 English.
 The limited permissions granted above are perpetual and will not be
 revoked by the Internet Society or its successors or assigns.
 This document and the information contained herein is provided on an
 "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
 TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
 BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
 HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
 MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Trotter Informational [Page 15]

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