rfc3222.txt

来自「RFC 的详细文档！」· 文本 代码 · 共 844 行 · 第 1/2 页

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