Network Working Group
INTERNET-DRAFT
Expires in: October 2005
Scott Poretsky
Quarry Technologies
Brent Imhoff
LightCore
February 2005
Terminology for Benchmarking
IGP Data Plane Route Convergence
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ABSTRACT
This draft describes the terminology for benchmarking IGP Route
Convergence as described in Applicability document [1] and
Methodology document [2]. The methodology and terminology is to
be used for benchmarking Route Convergence and can be applied to
any link-state IGP such as ISIS [3] and OSPF [4]. The data plane
is measured to obtain the convergence benchmarking metrics
described in [2].
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Table of Contents
1. Introduction .................................................2
2. Existing definitions .........................................3
3. Term definitions..............................................3
3.1 Convergence Event.........................................3
3.2 Route Convergence.........................................4
3.3 Network Convergence.......................................4
3.4 Full Convergence..........................................5
3.5 Convergence Packet Loss...................................5
3.6 Convergence Event Instant.................................6
3.7 Convergence Recovery Instant..............................6
3.8 Rate-Derived Convergence Time.............................7
3.9 Convergence Event Transition..............................7
3.10 Convergence Recovery Transition..........................8
3.11 Loss-Derived Convergence Time............................8
3.12 Sustained Forwarding Convergence Time....................9
3.13 Restoration Convergence Time.............................9
3.14 Packet Sampling Interval.................................10
3.15 Local Interface..........................................11
3.16 Neighbor Interface.......................................11
3.17 Remote Interface.........................................11
3.18 Preferred Egress Interface...............................12
3.19 Next-Best Egress Interface...............................12
3.20 Stale Forwarding.........................................13
3.21 Nested Convergence Events................................13
4. Security Considerations.......................................13
5. Normative References..........................................14
6. Author's Address..............................................14
1. Introduction
This draft describes the terminology for benchmarking IGP Route
Convergence. The motivation and applicability for this
benchmarking is provided in [1]. The methodology to be used for
this benchmarking is described in [2]. The methodology and
terminology to be used for benchmarking Route Convergence can be
applied to any link-state IGP such as ISIS [3] and OSPF [4]. The
data plane is measured to obtain black-box (externally observable)
convergence benchmarking metrics. The purpose of this document is
to introduce new terms required to complete execution of the IGP
Route Convergence Methodology [2]. These terms apply to IPv4 and
IPv6 traffic as well as IPv4 and IPv6 IGPs.
An example of Route Convergence as observed and measured from the
data plane is shown in Figure 1. The graph in Figure 1 shows
Forwarding Rate versus Time. Time 0 on the X-axis is on the far
right of the graph. The components of the graph and metrics are
defined in the Term Definitions section.
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Convergence Convergence
Recovery Event
Instant Instant Time = 0sec
Maximum ^ ^ ^
Forwarding Rate--> ----\ Packet /---------------
\ Loss /<----Convergence
Convergence------->\ / Event Transition
Recovery Transition \ /
\_____/<------Packet Loss
X-axis = Time
Y-axis = Forwarding Rate
Figure 1. Convergence Graph
2. Existing definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14, RFC 2119
[Br97]. RFC 2119 defines the use of these key words to help make the
intent of standards track documents as clear as possible. While this
document uses these keywords, this document is not a standards track
document.
3. Term Definitions
3.1 Convergence Event
Definition:
The occurrence of a planned or unplanned action in the network
that results in a change in the egress interface of the DUT for
routed packets.
Discussion:
Convergence Events include link loss, routing protocol session
loss, router failure, configuration change, and better next-hop
learned via a routing protocol.
Measurement Units:
N/A
Issues:
None
See Also:
Convergence Packet Loss
Convergence Event Instant
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3.2 Route Convergence
Definition:
Recovery from a Convergence Event indicated by the DUT
forwarding rate equal to the offered load.
Discussion:
Route Convergence is the action of all components of the router
being updated with the most recent route change(s) including the
RIB and FIB, along with software and hardware tables. Route
Convergence can be observed externally by the rerouting of data
Traffic to a new egress interface.
Measurement Units:
N/A
Issues:
None
See Also:
Network Convergence
Full Convergence
Convergence Event
3.3 Network Convergence
Definition:
The completion of updating of all routing tables, including the
FIB, in all routers throughout the network.
Discussion:
Network Convergence is bounded by the sum of Route Convergence
for all routers in the network. Network Convergence can be
determined by recovery of the forwarding rate to equal the offered
load, no Stale Forwarding, and no blenders[5][6].
Measurement Units:
N/A
Issues:
None
See Also:
Route Convergence
Stale Forwarding
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3.4 Full Convergence
Definition:
Route Convergence for an entire FIB.
Discussion:
When benchmarking convergence it is useful to measure
the time to converge an entire FIB. For example,
a Convergence Event can be produced for an OSPF table of
5000 routes so that the time to converge routes 1 through
5000 is measured. Full Convergence is externally observable
from the data plane when the forwarding rate on the Next-Best
Egress Interface equals the offered load.
Measurement Units:
N/A
Issues:
None
See Also:
Network Convergence
Route Convergence
Convergence Event
3.5 Convergence Packet Loss
Definition:
The amount of packet loss produced by a Convergence Event
until Route Convergence occurs.
Discussion:
Packet loss can be observed as a reduction of forwarded traffic from
the maximum forwarding rate. Convergence Packet Loss include packets
that were lost and packets that were delayed due to buffering.
Convergence Packet Loss may or may not reach 100%.
Measurement Units:
number of packets
Issues:
None
See Also:
Route Convergence
Convergence Event
Rate-Derived Convergence Time
Loss-Derived Convergence Time
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3.6 Convergence Event Instant
Definition:
The time instant that a Convergence Event becomes observable in the
data plane.
Discussion:
Convergence Event Instant is observable from the data
plane as the precise time that the device under test begins
to exhibit packet loss.
Measurement Units:
hh:mm:ss:uuu
Issues:
None
See Also:
Convergence Event
Convergence Packet Loss
Convergence Recovery Instant
3.7 Convergence Recovery Instant
Definition:
The time instant that Full Convergence is measured
and then maintained for an interval of duration equal to
the Sustained Forwarding Convergence Time
Discussion:
Convergence Recovery Instant is measurable from the data
plane as the precise time that the device under test
achieves Full Convergence.
Measurement Units:
hh:mm:ss:uuu
Issues:
None
See Also:
Sustained Forwarding Convergence Time
Convergence Packet Loss
Convergence Event Instant
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3.8 Rate-Derived Convergence Time
Definition:
The amount of time for Convergence Packet Loss to persist upon
occurrence of a Convergence Event until occurrence of Route
Convergence.
Rate-Derived Convergence Time can be measured as the time
difference from the Convergence Event Instant to the
Convergence Recovery Instant, as shown with Equation 1.
(eq 1) Rate-Derived Convergence Time =
Convergence Recovery Instant - Convergence Event Instant.
Discussion:
Rate-Derived Convergence Time should be measured at the maximum
forwarding rate. Failure to achieve Full Convergence results in
a Rate-Derived Convergence Time benchmark of infinity.
Measurement Units:
seconds/milliseconds
Issues:
None
See Also:
Convergence Packet Loss
Convergence Recovery Instant
Convergence Event Instant
Full Convergence
3.9 Convergence Event Transition
Definition:
The characteristic of a router in which forwarding rate
gradually reduces to zero after a Convergence Event.
Discussion:
The Convergence Event Transition is best observed for
Full Convergence. The Convergence Event Transition may
not be linear.
Measurement Units:
seconds/milliseconds
Issues:
None
See Also:
Convergence Event
Rate-Derived Convergence Time
Convergence Packet Loss
Convergence Recovery Transition
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3.10 Convergence Recovery Transition
Definition:
The characteristic of a router in which forwarding rate
gradually increases to equal the offered load.
Discussion:
The Convergence Recovery Transition is best observed for
Full Convergence. The Convergence Event Transition may
not be linear.
Measurement Units:
seconds/milliseconds
Issues:
None
See Also:
Full Convergence
Rate-Derived Convergence Time
Convergence Packet Loss
Convergence Event Transition
3.11 Loss-Derived Convergence Time
Definition:
The amount of time it takes for Route Convergence to
to be achieved as calculated from the Convergence Packet
Loss. Loss-Derived Convergence Time can be calculated
from Convergence Packet Loss that occurs due to a
Convergence Event and Route Convergence.as shown with
Equation 2.
(eq 2) Loss-Derived Convergence Time =
Convergence Packets Loss / Offered Load
NOTE: Units for this measurement are
packets / packets/second = seconds
Discussion:
Loss-Derived Convergence Time gives a better than
actual result when converging many routes simultaneously.
Rate-Derived Convergence Time takes the Convergence Recovery
Transition into account, but Loss-Derived Convergence Time
ignores the Route Convergence Recovery Transition because
it is obtained from the measured Convergence Packet Loss.
Ideally, the Convergence Event Transition and Convergence
Recovery Transition are instantaneous so that the
Rate-Derived Convergence Time = Loss-Derived Convergence Time.
However, router implementations are less than ideal.
For these reasons the preferred reporting benchmark for IGP
Route Convergence is the Rate-Derived Convergence Time.
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Guidelines for reporting Loss-Derived Convergence Time are
provided in [2].
Measurement Units:
seconds/milliseconds
Issues:
None
See Also:
Route Convergence
Convergence Packet Loss
Rate-Derived Convergence Time
Convergence Event Transition
Convergence Recovery Transition
3.12 Sustained Forwarding Convergence Time
Definition:
The amount of time for which Full Convergence is maintained without
additional packet loss.
Discussion:
The purpose of the Sustained Forwarding Convergence Time is to produce
Convergence Time benchmarks protected against fluctuation in Forwarding
Rate after Full Convergence is observed. The Sustained Forwarding
Convergence Time to be used is calculated as shown in Equation 3.
(eq 3)
Sustained Forwarding Convergence Time =
5 x (# routes in FIB) / (Offered Load)
for which at least one packet per destination MUST be received at
the DUT.
Measurement Units:
seconds or milliseconds
Issues: None
See Also:
Full Convergence
Convergence Recovery Instant
3.13 Restoration Convergence Time
Definition:
The amount of time for the router under test to restore
traffic to the original outbound port after recovery from
a Convergence Event.
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Discussion:
Restoration Convergence Time is the amount of time to
Converge back to the original outbound port. This is achieved
by recovering from the Convergence Event, such as restoring
the failed link. Restoration Convergence Time is measured
using the Rate-Derived Convergence Time calculation technique,
as provided in Equation 1. It is possible, but not desired
to have the Restoration Convergence Time differ from the
Rate-Derived Convergence Time.
Measurement Units:
seconds or milliseconds
Issues:
None
See Also:
Convergence Event
Rate-Derived Convergence Time
3.14 Packet Sampling Interval
Definition:
The interval at which the tester (test equipment) polls to make
measurements for arriving packet flows.
Discussion:
Metrics measured at the Packet Sampling Interval may include
Forwarding Rate and Convergence Packet Loss.
Measurement Units:
seconds or milliseconds
Issues:
Packet Sampling Interval can influence the Convergence Graph.
This is particularly true as implementations achieve Full
Convergence in less than 1 second. The Convergence Event
Transition and Convergence Recovery Transition can become
exaggerated when the Packet Sampling Interval is too long.
This will produce a larger than actual Rate-Derived
Convergence Time. The recommended value for configuration
of the Packet Sampling Interval is provided in [2].
See Also:
Convergence Packet Loss
Convergence Event Transition
Convergence Recovery Transition
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3.15 Local Interface
Definition:
An interface on the DUT.
Discussion:
None
Measurement Units:
N/A
Issues:
None
See Also:
Neighbor Interface
Remote Interface
3.16 Neighbor Interface
Definition:
The interface on the neighbor router or tester that is
directly linked to the DUT's Local Interface.
Discussion:
None
Measurement Units:
N/A
Issues:
None
See Also:
Local Interface
Remote Interface
3.17 Remote Interface
Definition:
An interface on a neighboring router that is not directly
connected to any interface on the DUT.
Discussion:
None
Measurement Units:
N/A
Issues:
None
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See Also:
Local Interface
Neighbor Interface
3.18 Preferred Egress Interface
Definition:
The outbound interface from the DUT for traffic routed to the
preferred next-hop.
Discussion:
Preferred Egress Interface is the egress interface prior to
a Convergence Event
Measurement Units:
N/A
Issues:
None
See Also:
Next-Best Egress Interface
3.19 Next-Best Egress Interface
Definition:
The outbound interface from the DUT for traffic routed to the
second-best next-hop. It is the same media type and link speed
as the Preferred Egress Interface
Discussion:
Next-Best Egress Interface is the egress interface after
a Convergence Event.
Measurement Units:
N/A
Issues:
None
See Also:
Preferred Egress Interface
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3.20 Stale Forwarding
Definition:
Forwarding of traffic to route entries that no longer exist
or to route entries with next-hops that are no longer preferred.
Discussion:
Stale Forwarding can be caused by a Convergence Event and is
also known as a "black-hole" since it may produce packet loss.
Stale Forwarding exists until Network Convergence is achieved.
Measurement Units:
N/A
Issues:
None
See Also:
Network Convergence
3.21 Nested Convergence Events
Definition:
The occurence of Convergence Event while the route table
is converging from a prior Convergence Event.
Discussion:
The Convergence Events for a Nested Convergence Events
MUST occur with different neighbors. A common
observation from a Nested Convergence Event will be
the withdrawal of routes from one neighbor while the
routes of another neighbor are being installed.
Measurement Units:
N/A
Issues:
None
See Also:
Convergence Event
4. Security Considerations
Documents of this type do not directly affect the security of
Internet or corporate networks as long as benchmarking
is not performed on devices or systems connected to operating
networks.
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5. Normative References
[1] Poretsky, S., "Benchmarking Applicability for IGP Data Plane
Route Convergence", draft-ietf-bmwg-igp-dataplane-conv-app-05,
work in progress, February 2005.
[2] Poretsky, S., "Benchmarking Methodology for IGP Data Plane
Route Convergence", draft-ietf-bmwg-igp-dataplane-conv-meth-05,
work in progress, February 2005.
[3] Callon, R., "Use of OSI IS-IS for Routing in TCP/IP and Dual
Environments", RFC 1195, December 1990.
[4] Moy, J., "OSPF Version 2", RFC 2328, IETF, April 1998.
[5] S. Casner, C. Alaettinoglu, and C. Kuan, "A Fine-Grained View
of High Performance Networking", NANOG 22, May 2001.
[6] L. Ciavattone, A. Morton, and G. Ramachandran, "Standardized
Active Measurements on a Tier 1 IP Backbone", IEEE Communications
Magazine, pp90-97, June, 2003.
6. Author's Address
Scott Poretsky
Quarry Technologies
8 New England Executive Park
Burlington, MA 01803
USA
Phone: + 1 781 395 5090
EMail: sporetsky@quarrytech.com
Brent Imhoff
USA
EMail: bimhoff@planetspork.com
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