Benchmarking Methodology Working Group G. Trotter
Internet Draft Agilent Technologies
Document: draft-ietf-bmwg-fib-term-04.txt October 2001
Category: Informational
Terminology for Forwarding Information Base (FIB) based Router
Performance
Status of this Memo
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Abstract
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. 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.
Table of Contents
1. Introduction....................................................2
2. Overview........................................................2
3. Existing Definitions............................................3
4. Definition Format...............................................3
5. Definitions - parameters........................................3
5.1 Network Prefix.................................................3
5.2 Network Prefix Length..........................................4
5.3 Forwarding Information Base (FIB)..............................4
5.4 Forwarding Information Base Entry..............................5
5.5 Forwarding Information Base Size...............................5
5.6 Longest Length Prefix Match Algorithm..........................6
5.7 Forwarding Information Base Prefix Distribution................6
5.8 Per-Interface or Per-Card Forwarding Information Base..........7
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5.9 Per-Interface Forwarding Information Base Cache................8
5.10 Route Aggregation.............................................8
6. Definitions - metrics...........................................9
6.1 Maximum Forwarding Information Base Size.......................9
6.2 Forwarding Information Base Learning Time.....................10
6.3 Forwarding Information Base-dependent Throughput..............11
6.4 Forwarding Information Base-dependent Latency.................11
6.5 Forwarding Information Base-dependent Frame Loss Rate.........11
7. Security Considerations........................................12
8. References.....................................................12
9. Acknowledgments................................................12
10. Author's Addresses............................................12
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). The
forwarding performance of a router may be dependent upon these two
primary factors, particularly if FIB prefix distributions tend
towards longer network prefixes (3). 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.
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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
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,
"Addressing Architecture", 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
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"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.
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 (5.6)
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."
Discussion:
The forwarding information base describes a database indexing
network prefixes versus router port identifiers.
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A forwarding information base consists of [FIB size (6.1)]
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:
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. 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 (5.6)
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:
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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
against FIBs with some distribution of network prefix
lengths.
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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:
forwarding information base (5.3)
per-interface forwarding information base cache (5.9)
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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)
5.10 Route Aggregation
Definition:
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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:
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,
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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.
Issues:
See Also:
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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:
This definition for FIB-dependent frame loss rate is added to
distinguish the context of this measurement from that defined
in [3].
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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: Guy_Trotter@agilent.com
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