As per Relevance of the word forwarding, we have this rfc below:
Network Working Group G.
Request for Comments: 3222 Agilent
Category: Informational December 2001
Terminology for Forwarding Information Base (FIB) based
Status of this
This memo provides information for the Internet community. It
not specify an Internet standard of any kind. Distribution of
memo is unlimited
Copyright
Copyright (C) The Internet Society (2001). All Rights Reserved
This document describes the terms to be used in a methodology
determines the IP packet forwarding performance of IP routers as
function of the forwarding information base installed within
router. The forwarding performance of an IP router may be
upon or may be linked to the composition and size of the
information base installed within a router
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RFC 3222 FIB based Router Performance December 2001
Table of
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.
This document defines terms that are to be used in a methodology
determines the IP packet forwarding performance of IP routers as
function of the forwarding information base installed within
router
The objective of this methodology is to evaluate the
levels of IP routers as forwarding information bases continue to
in size and complexity of structure
This methodology utilizes the packet forwarding
measurements described in [2]; reference will also be made to
associated terminology document [3] for these terms
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2.
In order to measure the forwarding information base-based
performance, different forwarding information bases (5.3)
installed in the router. The two key elements describing the FIB
the FIB size (5.5) and FIB prefix distribution (5.7). The
performance of a router may be dependent upon these two
factors, particularly if FIB prefix distributions tend towards
network prefixes (5.1). The FIB-dependent throughput, latency
frame loss rate (6.3, 6.4, 6.5), measured with fully meshed
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
to be manually entered into the router, or advertised via a
protocol. It may take some period of time (the FIB learning
(6.2)) before the router learns all the routes
When routes are advertised into the router, the routes should
advertised in such a way so that route aggregation (5.10) does
occur. Also, the effect of a per-interface FIB cache (5.9) needs
be taken into account
3. Existing
[3] should be consulted before attempting to make use of
document. [2] contains discussions of a number of terms relevant
the benchmarking of network interconnect devices and should also
consulted
4. Definition
The definition format is the equivalent to that defined in [3],
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
restrictions on measurement procedures
Measurement units
The units used to report measurements of this term, if applicable
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Issues
List of issues or conditions that effect this term
See Also
List of other terms that are relevant to the discussion of
term
5. Definitions -
This section defines parameters that would dictate the execution
methodology to determine the FIB based forwarding performance of
router
5.1 Network
Definition
"A network prefix is . . . a contiguous set of bits at the
significant end of the address that defines a set of systems;
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
of an IP address. A common alternative to using a bitwise mask
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
network component of this IPv4 address is 17 bits wide
Measurement units
Issues
See Also
Network Prefix Length (5.2)
5.2 Network Prefix
Definition
The number of bits used to define the network prefix.
prefixes, using CIDR terminology, are typically referred to
15.35.128.0 /17, indicating that the network prefix is 17
long
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Discussion
When referring to groups of addresses, the network prefix
is often used as a means of describing groups of addresses as
equivalence class. For example, 100 /16 addresses refers to 100
addresses whose network prefix length is 16 bits
Measurement units
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
Datagrams, in this document, is called the Forwarding
Base. At minimum, this contains the interface identifier and
hop information for each reachable destination network prefix."
Discussion
The forwarding information base describes a database
network prefixes versus router port identifiers
A forwarding information base consists of [FIB size (5.5)]
entries (5.4).
The forwarding information base is distinct from the "
table" (or, the Routing Information Base), which holds all
information received from routing peers
The forwarding information base contains unique paths only (i.e
does not contain secondary paths).
Measurement units
Issues
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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
Definition
A single entry within a forwarding information base. This
consists of the minimum amount of information necessary to make
forwarding decision on a particular packet. The
components within a forwarding information base entry are
network prefix, a router port identifier and next hop information
This is an entry that the router can and does use to
packets
Discussion
See (5.3).
Measurement units
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
Definition
Refers to the number of forwarding information base entries
a forwarding information base
Discussion
The number of entries within a forwarding information base is
of the key elements that may influence the forwarding
of a router. Generally, the more entries within the
information base, the longer it could take to find the
matching network prefix within the forwarding information base
Measurement units
Number of
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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
Definition
An algorithm that a router uses to quickly match
addresses within received IP packets to exit interfaces on
router
Discussion
Measurement Units
Issues
See Also
5.7 Forwarding Information Base Prefix
Definition
The distribution of network prefix lengths within the
information base
Discussion
Network prefixes within the forwarding information base could
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
populated with the same network prefix length, as well as
FIBs with some distribution of network prefix lengths
The distribution of network prefix lengths may have an impact
the forwarding performance of a router. The longer the
prefix length, the longer it will take for a router to perform
longest length prefix match algorithm, and potentially the
the performance of the router
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Measurement units
The forwarding information base prefix distribution is
by a list of network prefix lengths and the percentage of
within the forwarding information base with a particular
prefix length. For example, a forwarding information base
distribution is represented as
{[/16, 100], [/20, 360], [/24, 540]}
This indicates that 100 of the entries within the
information base have a 16 bit network prefix length, 360 have
20 bit network prefix length, and 540 have a 24 bit network
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
Definition
A complete copy of the forwarding information base, installed on
router's card or individual physical interface to speed
destination address to network prefix lookup process
Discussion
Router manufacturers have developed many optimizations
routers, of which one optimization is to copy the
information base to every interface or interface card on
router. By doing this, destination address / network
lookups can be performed on the interface or card, unloading
router's CPU
Measurement units
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
Definition
A subset of a forwarding information base, installed on a router'
interface card to speed the destination address / network
lookup process
Discussion
Prior to installing a complete copy of the forwarding
base on each interface of a router, a popular technique
speeding destination address lookups is to install a cache
frequently used routes on a router's interface
The most frequently used routes are placed in the
information base cache. IP packets whose destination address
not match a network prefix within the per-interface
information base cache are forwarded to a router's
processor for lookup in the complete forwarding information base
The implication for benchmarking the performance of a router as
function of the forwarding information base is significant.
packets whose destination address matches an entry within
per-interface forwarding information base cache could be
more quickly than packets whose destination address does not
an entry within the per-interface forwarding information
cache
To create useful benchmarks, the role of a per-
forwarding cache needs to be considered. The nature
benchmarking tests to measure the impact of the
performance of a router requires that the destination
within IP packets transmitted into the router be
amongst the total set of network prefixes advertised into
router. This negates the role of a per-interface
information base cache, but serves to stress the
information base-based packet forwarding performance of
router
Measurement units
Issues
See Also
forwarding information base (5.3)
per-interface forwarding information base (5.8)
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5.10 Route
Definition
The ability of a router to collapse many forwarding
base entries into a single entry
Discussion
A router may aggregate routes in a forwarding information
into a single entry to conserve space
When advertising routes into a router to perform
tests as a function of the forwarding information base
within the router, it is necessary to ensure that a router
not aggregate routes
Thus, when routes are advertised to the router or
statically, care must be taken to ensure that the router does
aggregate routes
For example, if advertising a set of /24 network prefixes into
particular port on the router, 256 consecutive /24 routes,
a common leading 16 bits, should not be advertised on a
port. If this is done, then the router will install a
entry within the forwarding information base indicating that
networks matching a particular /16 network prefix are
through one particular entry
Route aggregation on a router can be turned off, but routes
still be advertised into the router in such a manner as to
route aggregation
Measurement units
Issues
See Also
6. Definitions -
This section defines the metrics, or results, that
characterized the FIB based forwarding performance of a router
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6.1 Maximum Forwarding Information Base
Definition
The maximum number of forwarding information base entries that
be supported within the forwarding information base. The
Forwarding Information Base Size is the size over which
entries can and are used to forward traffic
Discussion
It is useful to know the maximum forwarding information base
for a router as it will be an indicator of the ability of
router to function within the given application space, and
the router will be able to handle projected network growth
As a benchmarking value, it is necessary to discover this value
that performance measurements can be made up to the
possible forwarding information base size
Measurement units
Number of
Issues
Could this value vary with the forwarding information base
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
Definition
The time a router takes to process received routing messages,
to construct (and, possibly to distribute amongst the
cards in the router) the forwarding information base. This
measured from the time at which a router is presented with
first routing message, through to when it can forward
using any entry in the forwarding information base
Discussion
It takes time for a router to construct its forwarding
base. A router needs to process received routing packets,
the routing information database, select the best paths, build
forwarding information base and then possibly distribute
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forwarding information base or a subset thereof to the
cards. This entire process can take several minutes with
large forwarding information bases
When performing benchmarking tests that take the
information base into account, time must be allocated for
router to process the routing information and to install
complete forwarding information base within itself,
performance measurements are made
Measurement units
Prefixes per second
Issues
See Also
forwarding information base (5.3)
6.3 Forwarding Information Base-dependent
Definition
Throughput, as defined in [3], used in a context where
forwarding information base influences the throughput
Discussion
This definition for FIB-dependent throughput is added
distinguish the context of this measurement from that defined
[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
Definition
Latency, as defined in [3], used in a context where the
information base influences the throughput
Discussion
This definition for FIB-dependent latency is added to
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 frame loss rate (6.5)
6.5 Forwarding Information Base-dependent Frame Loss
Definition
Frame Loss Rate, as defined in [3], used in a context where
forwarding information base influences the throughput
Discussion
This definition for FIB-dependent frame loss rate is added
distinguish the context of this measurement from that defined
[3].
Measurement units
See [3].
Issues
See Also
forwarding information base-dependent throughput (6.3)
forwarding information base-dependent latency (6.4)
7. Security
As this document is solely for the purpose of providing
methodology and describes neither a protocol nor a
implementation, there are no security considerations associated
this document
8.
[1] Bradner, S., "The Internet Standards Process -- Revision 3",
9, RFC 2026, October 1996.
[2] Bradner, S. and J. McQuaid, "Benchmarking Methodology for
Interconnect Devices", RFC 2544, March 1999.
[3] Bradner, S., "Benchmarking Terminology for
Interconnection Devices", RFC 1242, July 1991.
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[4] Baker, F., "Requirements for IP Version 4 Routers", RFC 1812,
June 1995.
9. Author's
Guy
Agilent Technologies (Canada) Inc
#2500 4710
Burnaby, British
V5H 4M
Phone: +1 604 454 3516
EMail: Guy_Trotter@agilent.
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RFC 3222 FIB based Router Performance December 2001
10. Full Copyright
Copyright (C) The Internet Society (2001). All Rights Reserved
This document and translations of it may be copied and furnished
others, and derivative works that comment on or otherwise explain
or assist in its implementation may be prepared, copied,
and distributed, in whole or in part, without restriction of
kind, provided that the above copyright notice and this paragraph
included on all such copies and derivative works. However,
document itself may not be modified in any way, such as by
the copyright notice or references to the Internet Society or
Internet organizations, except as needed for the purpose
developing Internet standards in which case the procedures
copyrights defined in the Internet Standards process must
followed, or as required to translate it into languages other
English
The limited permissions granted above are perpetual and will not
revoked by the Internet Society or its successors or assigns
This document and the information contained herein is provided on
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE
Funding for the RFC Editor function is currently provided by
Internet Society
Trotter Informational [Page 15]
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