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+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.
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+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.
+
+
+
+
+
+
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+
+Trotter Informational [Page 2]
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+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]
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+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]
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+RFC 3222 FIB based Router Performance December 2001
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+ 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]
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+RFC 3222 FIB based Router Performance December 2001
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+
+ 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]
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+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.
+
+
+
+
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+Trotter Informational [Page 7]
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+RFC 3222 FIB based Router Performance December 2001
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+ 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]
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+RFC 3222 FIB based Router Performance December 2001
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+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]
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+RFC 3222 FIB based Router Performance December 2001
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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.
+
+
+
+
+
+
+
+
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+Trotter Informational [Page 10]
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+RFC 3222 FIB based Router Performance December 2001
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+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]
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+RFC 3222 FIB based Router Performance December 2001
+
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+ 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]
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+RFC 3222 FIB based Router Performance December 2001
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+
+ 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]
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+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
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+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.
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