Subject: draft-ietf-bmwg-fib-term-01.txt

From: [email-masked]
Date: Mon, 5 Mar 2001 16:37:35 -0700

Benchmarking Methodology Working Group                       G. Trotter 
Internet Draft                                     Agilent Technologies 
Document: draft-ietf-bmwg-fib-term-01.txt                    March 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 
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   Drafts.  
    
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   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 
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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).  As FIB 
   sizes increase, and as FIB prefix distributions tend towards longer 
  
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             Terminology for FIB based Router Performance   July, 2000 

   network prefixes (5.1), then it will take more time to match the 
   destination address within an IP packet and its corresponding entry 
   within the FIB.  The FIB-dependent throughput, latency and frame 
   loss rate (6.3, 6.4, 6.5), measured with fully meshed traffic flows 
   (Error! Reference source not found.), 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. 
           
   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 

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             Terminology for FIB based Router Performance   July, 2000 

   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:  
          See section 2.2.5, "Addressing Architecture", in [4]. 
           
          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:  
          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: 
    
   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 
  
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             Terminology for FIB based Router Performance   July, 2000 

          identifier and next hop information for each reachable 
          destination network prefix." 
           
          A forwarding information base consists of [FIB size (6.1)] 
          FIB entries (5.4). 
           
   Discussion: 
          The forwarding information base describes a database indexing 
          network prefixes versus router port identifiers. 
           
          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, 
          consisting of 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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          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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          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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          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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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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          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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   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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          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: [email-masked] 
    
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             Terminology for FIB based Router Performance   July, 2000 

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