Network Working Group S. Poretsky
InternetDraft Allot Communications
Intended status: Informational B. Imhoff
Expires: May 12, 2011 Juniper Networks
K. Michielsen
Cisco Systems
November 8, 2010
Terminology for Benchmarking LinkState IGP Data Plane Route Convergence
draftietfbmwgigpdataplaneconvterm22
Abstract
This document describes the terminology for benchmarking Interior
Gateway Protocol (IGP) Route Convergence. The terminology is to be
used for benchmarking IGP convergence time through externally
observable (black box) data plane measurements. The terminology can
be applied to any linkstate IGP, such as ISIS and OSPF.
Status of this Memo
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Table of Contents
1. Introduction and Scope . . . . . . . . . . . . . . . . . . . . 4
2. Existing Definitions . . . . . . . . . . . . . . . . . . . . . 4
3. Term Definitions . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Convergence Types . . . . . . . . . . . . . . . . . . . . 5
3.1.1. Route Convergence . . . . . . . . . . . . . . . . . . 5
3.1.2. Full Convergence . . . . . . . . . . . . . . . . . . . 5
3.1.3. Network Convergence . . . . . . . . . . . . . . . . . 6
3.2. Instants . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.2.1. Traffic Start Instant . . . . . . . . . . . . . . . . 6
3.2.2. Convergence Event Instant . . . . . . . . . . . . . . 7
3.2.3. Convergence Recovery Instant . . . . . . . . . . . . . 7
3.2.4. First Route Convergence Instant . . . . . . . . . . . 8
3.3. Transitions . . . . . . . . . . . . . . . . . . . . . . . 8
3.3.1. Convergence Event Transition . . . . . . . . . . . . . 8
3.3.2. Convergence Recovery Transition . . . . . . . . . . . 9
3.4. Interfaces . . . . . . . . . . . . . . . . . . . . . . . . 10
3.4.1. Local Interface . . . . . . . . . . . . . . . . . . . 10
3.4.2. Remote Interface . . . . . . . . . . . . . . . . . . . 10
3.4.3. Preferred Egress Interface . . . . . . . . . . . . . . 10
3.4.4. NextBest Egress Interface . . . . . . . . . . . . . . 11
3.5. Benchmarking Methods . . . . . . . . . . . . . . . . . . . 11
3.5.1. RateDerived Method . . . . . . . . . . . . . . . . . 11
3.5.2. LossDerived Method . . . . . . . . . . . . . . . . . 14
3.5.3. RouteSpecific LossDerived Method . . . . . . . . . . 15
3.6. Benchmarks . . . . . . . . . . . . . . . . . . . . . . . . 16
3.6.1. Full Convergence Time . . . . . . . . . . . . . . . . 16
3.6.2. First Route Convergence Time . . . . . . . . . . . . . 17
3.6.3. RouteSpecific Convergence Time . . . . . . . . . . . 18
3.6.4. LossDerived Convergence Time . . . . . . . . . . . . 19
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3.6.5. Route Loss of Connectivity Period . . . . . . . . . . 20
3.6.6. LossDerived Loss of Connectivity Period . . . . . . . 21
3.7. Measurement Terms . . . . . . . . . . . . . . . . . . . . 22
3.7.1. Convergence Event . . . . . . . . . . . . . . . . . . 22
3.7.2. Packet Loss . . . . . . . . . . . . . . . . . . . . . 22
3.7.3. Convergence Packet Loss . . . . . . . . . . . . . . . 23
3.7.4. Connectivity Packet Loss . . . . . . . . . . . . . . . 23
3.7.5. Packet Sampling Interval . . . . . . . . . . . . . . . 24
3.7.6. Sustained Convergence Validation Time . . . . . . . . 25
3.7.7. Forwarding Delay Threshold . . . . . . . . . . . . . . 25
3.8. Miscellaneous Terms . . . . . . . . . . . . . . . . . . . 26
3.8.1. Stale Forwarding . . . . . . . . . . . . . . . . . . . 26
3.8.2. Nested Convergence Event . . . . . . . . . . . . . . . 26
4. Security Considerations . . . . . . . . . . . . . . . . . . . 27
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 27
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 27
7.1. Normative References . . . . . . . . . . . . . . . . . . . 27
7.2. Informative References . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 28
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1. Introduction and Scope
This draft describes the terminology for benchmarking LinkState
Interior Gateway Protocol (IGP) Convergence. The motivation and
applicability for this benchmarking is provided in [Po09a]. The
methodology to be used for this benchmarking is described in [Po10m].
The purpose of this document is to introduce new terms required to
complete execution of the IGP Route Methodology [Po10m].
IGP convergence time is measured on the data plane at the Tester by
observing packet loss through the DUT. The methodology and
terminology to be used for benchmarking IGP Convergence can be
applied to IPv4 and IPv6 traffic and linkstate IGPs such as ISIS
[Ca90][Ho08], OSPF [Mo98][Co08], and others.
2. Existing Definitions
This document uses existing terminology defined in other BMWG work.
Examples include, but are not limited to:
Frame Loss Rate [Ref.[Br91], section 3.6]
Throughput [Ref.[Br91], section 3.17]
Offered Load [Ref.[Ma98], section 3.5.2]
Forwarding Rate [Ref.[Ma98], section 3.6.1]
Device Under Test (DUT) [Ref.[Ma98], section 3.1.1]
System Under Test (SUT) [Ref.[Ma98], section 3.1.2]
OutofOrder Packet [Ref.[Po06], section 3.3.4]
Duplicate Packet [Ref.[Po06], section 3.3.5]
Packet Reordering [Ref.[Mo06], section 3.3]
Stream [Ref.[Po06], section 3.3.2]
Forwarding Delay [Ref.[Po06], section 3.2.4]
IP Packet Delay Variation (IPDV) [Ref.[De02], section 1.2]
Loss Period [Ref.[Ko02], section 4]
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
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3.1. Convergence Types
3.1.1. Route Convergence
Definition:
The process of updating all components of the router, including the
Routing Information Base (RIB) and Forwarding Information Base (FIB),
along with software and hardware tables, with the most recent route
change(s) such that forwarding for a route entry is successful on the
NextBest Egress Interface.
Discussion:
Route Convergence MUST occur after a Convergence Event. Route
Convergence can be observed externally by the rerouting of data
traffic for a destination matching a route entry to the Nextbest
Egress Interface. Completion of Route Convergence may or may not be
sustained over time.
Measurement Units: N/A
Issues: None
See Also:
Network Convergence, Full Convergence, Convergence Event
3.1.2. Full Convergence
Definition:
Route Convergence for all routes in the FIB.
Discussion:
Full Convergence MUST occur after a Convergence Event. Full
Convergence can be observed externally by the rerouting of data
traffic to destinations matching all route entries to the Nextbest
Egress Interface. Completion of Full Convergence is externally
observable from the data plane when the Forwarding Rate of the data
plane traffic on the NextBest Egress Interface equals the Offered
Load.
Completion of Full Convergence may or may not be sustained over time.
Measurement Units: N/A
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Issues: None
See Also:
Network Convergence, Route Convergence, Convergence Event, Full
Convergence Time, Convergence Recovery Instant
3.1.3. Network Convergence
Definition:
Full Convergence in all routers throughout the network.
Discussion:
Network Convergence includes all Route Convergence operations for all
routers in the network following a Convergence Event.
Completion of Network Convergence can be observed by recovery of the
network Forwarding Rate to equal the Offered Load, with no Stale
Forwarding, and no Blenders [Ca01][Ci03].
Completion of Network Convergence may or may not be sustained over
time.
Measurement Units: N/A
Issues: None
See Also:
Route Convergence, Full Convergence, Stale Forwarding
3.2. Instants
3.2.1. Traffic Start Instant
Definition:
The time instant the Tester sends out the first data packet to the
DUT.
Discussion:
If using the LossDerived Method or the RouteSpecific LossDerived
Method to benchmark IGP convergence time, and the applied Convergence
Event does not cause instantaneous traffic loss for all routes at the
Convergence Event Instant then the Tester SHOULD collect a timestamp
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on the Traffic Start Instant in order to measure the period of time
between the Traffic Start Instant and Convergence Event Instant.
Measurement Units:
hh:mm:ss:nnn:uuu, where 'nnn' is milliseconds and 'uuu' is
microseconds.
Issues: None
See Also:
Convergence Event Instant, RouteSpecific Convergence Time, Loss
Derived Convergence Time.
3.2.2. Convergence Event Instant
Definition:
The time instant that a Convergence Event occurs.
Discussion:
If the Convergence Event causes instantaneous traffic loss on the
Preferred Egress Interface, the Convergence Event Instant is
observable from the data plane as the instant that the DUT begins to
exhibit packet loss.
The Tester SHOULD collect a timestamp on the Convergence Event
Instant if it is not observable from the data plane.
Measurement Units:
hh:mm:ss:nnn:uuu, where 'nnn' is milliseconds and 'uuu' is
microseconds.
Issues: None
See Also: Convergence Event
3.2.3. Convergence Recovery Instant
Definition:
The time instant that Full Convergence has completed.
Discussion:
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The Full Convergence completed state MUST be maintained for an
interval of duration equal to the Sustained Convergence Validation
Time in order to validate the Convergence Recovery Instant.
The Convergence Recovery Instant is observable from the data plane as
the instant the DUT forwards traffic to all destinations over the
NextBest Egress Interface.
Measurement Units:
hh:mm:ss:nnn:uuu, where 'nnn' is milliseconds and 'uuu' is
microseconds.
Issues: None
See Also:
Sustained Convergence Validation Time, Full Convergence
3.2.4. First Route Convergence Instant
Definition:
The time instant the first route entry completes Route Convergence
following a Convergence Event
Discussion:
Any route may be the first to complete Route Convergence. The First
Route Convergence Instant is observable from the data plane as the
instant that the first packet is received from the NextBest Egress
Interface.
Measurement Units:
hh:mm:ss:nnn:uuu, where 'nnn' is milliseconds and 'uuu' is
microseconds.
Issues: None
See Also: Route Convergence
3.3. Transitions
3.3.1. Convergence Event Transition
Definition:
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A time interval following a Convergence Event in which Forwarding
Rate on the Preferred Egress Interface gradually reduces to zero.
Discussion:
The Forwarding Rate during a Convergence Event Transition may not
decrease linearly.
The Forwarding Rate observed on all DUT egress interfaces may or may
not decrease to zero.
The Offered Load, the number of routes, and the Packet Sampling
Interval influence the observations of the Convergence Event
Transition using the RateDerived Method. This is further discussed
with the term "RateDerived Method".
Measurement Units: seconds
Issues: None
See Also:
Convergence Event, RateDerived Method
3.3.2. Convergence Recovery Transition
Definition:
A time interval following the First Route Convergence Instant in
which Forwarding Rate on the NextBest Egress Interface gradually
increases to equal the Offered Load.
Discussion:
The Forwarding Rate observed during a Convergence Recovery Transition
may not increase linearly.
The Offered Load, the number of routes, and the Packet Sampling
Interval influence the observations of the Convergence Recovery
Transition using the RateDerived Method. This is further discussed
with the term "RateDerived Method".
Measurement Units: seconds
Issues: None
See Also:
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Full Convergence,First Route Convergence Instant, RateDerived Method
3.4. Interfaces
3.4.1. Local Interface
Definition:
An interface on the DUT.
Discussion:
A failure of the Local Interface indicates that the failure occurred
directly on the DUT.
Measurement Units: N/A
Issues: None
See Also: Remote Interface
3.4.2. Remote Interface
Definition:
An interface on a neighboring router that is not directly connected
to any interface on the DUT.
Discussion:
A failure of a Remote Interface indicates that the failure occurred
on a neighbor router's interface that is not directly connected to
the DUT.
Measurement Units: N/A
Issues: None
See Also: Local Interface
3.4.3. Preferred Egress Interface
Definition:
The outbound interface from the DUT for traffic routed to the
preferred nexthop.
Discussion:
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The Preferred Egress Interface is the egress interface prior to a
Convergence Event.
Measurement Units: N/A
Issues: None
See Also: NextBest Egress Interface
3.4.4. NextBest Egress Interface
Definition:
The outbound interface from the DUT for traffic routed to the second
best nexthop.
Discussion:
The NextBest Egress Interface becomes the egress interface after a
Convergence Event.
Measurement Units: N/A
Issues: None
See Also: Preferred Egress Interface
3.5. Benchmarking Methods
3.5.1. RateDerived Method
Definition:
The method to calculate convergence time benchmarks from observing
Forwarding Rate each Packet Sampling Interval.
Discussion:
Figure 1 shows an example of the Forwarding Rate change in time
during convergence as observed when using the RateDerived Method.
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^ Traffic Convergence
Fwd  Start Recovery
Rate  Instant Instant
 Offered ^ ^
 Load > \ /
 \ /< Convergence
 \ Packet / Recovery
 Convergence >\ Loss / Transition
 Event \ /
 Transition \/ < Max Packet Loss

+>
^ ^ time
Convergence First Route
Event Instant Convergence Instant
Figure 1: RateDerived Convergence Graph
The Offered Load SHOULD consist of a single Stream [Po06]. If
sending multiple Streams, the measured traffic rate statistics for
all Streams MUST be added together.
The destination addresses for the Offered Load MUST be distributed
such that all routes or a statistically representative subset of all
routes are matched and each of these routes is offered an equal share
of the Offered Load. It is RECOMMENDED to send traffic to all
routes, but a statistically representative subset of all routes can
be used if required.
At least one packet per route for all routes matched in the Offered
Load MUST be offered to the DUT within each Packet Sampling Interval.
For maximum accuracy the value for the Packet Sampling Interval
SHOULD be as small as possible, but the presence of IP Packet Delay
Variation (IPDV) [De02] may enforce using a larger Packet Sampling
Interval.
The Offered Load, IPDV, the number of routes, and the Packet Sampling
Interval influence the observations for the RateDerived Method. It
may be difficult to identify the different convergence time instants
in the RateDerived Convergence Graph. For example, it is possible
that a Convergence Event causes the Forwarding Rate to drop to zero,
while this may not be observed in the Forwarding Rate measurements if
the Packet Sampling Interval is too large.
IPDV causes fluctuations in the number of received packets during
each Packet Sampling Interval. To account for the presence of IPDV
in determining if a convergence instant has been reached, Forwarding
Delay SHOULD be observed during each Packet Sampling Interval. The
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minimum and maximum number of packets expected in a Packet Sampling
Interval in presence of IPDV can be calculated with Equation 1.
number of packets expected in a Packet Sampling Interval
in presence of IP Packet Delay Variation
= expected number of packets without IP Packet Delay Variation
+/( (maxDelay  minDelay) * Offered Load)
with minDelay and maxDelay the minimum resp. maximum Forwarding Delay
of packets received during the Packet Sampling Interval
Equation 1
To determine if a convergence instant has been reached the number of
packets received in a Packet Sampling Interval is compared with the
range of expected number of packets calculated in Equation 1.
If packets are going over multiple ECMP members and one or more of
the members has failed then the number of received packets during
each Packet Sampling Interval may vary, even excluding presence of
IPDV. To prevent fluctuation of the number of received packets
during each Packet Sampling Interval for this reason, the Packet
Sampling Interval duration SHOULD be a whole multiple of the time
between two consecutive packets sent to the same destination.
Metrics measured at the Packet Sampling Interval MUST include
Forwarding Rate and packet loss.
RateDerived Method is a RECOMMENDED method to measure convergence
time benchmarks.
To measure convergence time benchmarks for Convergence Events that do
not cause instantaneous traffic loss for all routes at the
Convergence Event Instant, the Tester SHOULD collect a timestamp of
the Convergence Event Instant and the Tester SHOULD observe
Forwarding Rate separately on the NextBest Egress Interface.
Since the RateDerived Method does not distinguish between individual
traffic destinations, it SHOULD NOT be used for any route specific
measurements. Therefor RateDerived Method SHOULD NOT be used to
benchmark Route Loss of Connectivity Period.
Measurement Units: N/A
Issues: None
See Also:
Packet Sampling Interval, Convergence Event, Convergence Event
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Instant, Full Convergence
3.5.2. LossDerived Method
Definition:
The method to calculate the LossDerived Convergence Time and Loss
Derived Loss of Connectivity Period benchmarks from the amount of
packet loss.
Discussion:
The Offered Load SHOULD consist of a single Stream [Po06]. If
sending multiple Streams, the measured traffic rate statistics for
all Streams MUST be added together.
The destination addresses for the Offered Load MUST be distributed
such that all routes or a statistically representative subset of all
routes are matched and each of these routes is offered an equal share
of the Offered Load. It is RECOMMENDED to send traffic to all
routes, but a statistically representative subset of all routes can
be used if required.
LossDerived Method SHOULD always be combined with RateDerived
Method in order to observe Full Convergence completion. The total
amount of Convergence Packet Loss is collected after Full Convergence
completion.
To measure convergence time and loss of connectivity benchmarks, the
Tester SHOULD in general observe packet loss on all DUT egress
interfaces (Connectivity Packet Loss).
To measure convergence time benchmarks for Convergence Events that do
not cause instantaneous traffic loss for all routes at the
Convergence Event Instant, the Tester SHOULD collect timestamps of
the Start Traffic Instant and of the Convergence Event Instant, and
the Tester SHOULD observe packet loss separately on the NextBest
Egress Interface (Convergence Packet Loss).
Since LossDerived Method does not distinguish between traffic
destinations and the packet loss statistics are only collected after
Full Convergence completion, this method can only be used to measure
average values over all routes. For these reasons LossDerived
Method can only be used to benchmark LossDerived Convergence Time
and LossDerived Loss of Connectivity Period.
Note that the LossDerived Method measures an average over all
routes, including the routes that may not be impacted by the
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Convergence Event, such as routes via nonimpacted members of ECMP or
parallel links.
Measurement Units: seconds
Issues: None
See Also:
LossDerived Convergence Time, LossDerived Loss of Connectivity
Period, Convergence Packet Loss
3.5.3. RouteSpecific LossDerived Method
Definition:
The method to calculate the RouteSpecific Convergence Time benchmark
from the amount of packet loss during convergence for a specific
route entry.
Discussion:
To benchmark RouteSpecific Convergence Time, the Tester provides an
Offered Load that consists of multiple Streams [Po06]. Each Stream
has a single destination address matching a different route entry,
for all routes or a statistically representative subset of all
routes. Convergence Packet Loss is measured for each Stream
separately.
RouteSpecific LossDerived Method SHOULD always be combined with
RateDerived Method in order to observe Full Convergence completion.
The total amount of Convergence Packet Loss for each Stream is
collected after Full Convergence completion.
RouteSpecific LossDerived Method is a RECOMMENDED method to measure
convergence time benchmarks.
To measure convergence time and loss of connectivity benchmarks, the
Tester SHOULD in general observe packet loss on all DUT egress
interfaces (Connectivity Packet Loss).
To measure convergence time benchmarks for Convergence Events that do
not cause instantaneous traffic loss for all routes at the
Convergence Event Instant, the Tester SHOULD collect timestamps of
the Start Traffic Instant and of the Convergence Event Instant, and
the Tester SHOULD observe packet loss separately on the NextBest
Egress Interface (Convergence Packet Loss).
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Since RouteSpecific LossDerived Method uses traffic streams to
individual routes, it measures packet loss as it would be experienced
by a network user. For this reason RouteSpecific LossDerived
Method is RECOMMENDED to measure RouteSpecific Convergence Time
benchmarks and Route Loss of Connectivity Period benchmarks.
Measurement Units: seconds
Issues: None
See Also:
RouteSpecific Convergence Time, Route Loss of Connectivity Period,
Convergence Packet Loss
3.6. Benchmarks
3.6.1. Full Convergence Time
Definition:
The time duration of the period between the Convergence Event Instant
and the Convergence Recovery Instant as observed using the Rate
Derived Method.
Discussion:
Using the RateDerived Method, Full Convergence Time can be
calculated as the time difference between the Convergence Event
Instant and the Convergence Recovery Instant, as shown in Equation 2.
Full Convergence Time =
Convergence Recovery Instant  Convergence Event Instant
Equation 2
The Convergence Event Instant can be derived from the Forwarding Rate
observation or from a timestamp collected by the Tester.
For the testcases described in [Po10m], it is expected that Full
Convergence Time equals the maximum RouteSpecific Convergence Time
when benchmarking all routes in FIB using the RouteSpecific Loss
Derived Method.
It is not possible to measure Full Convergence Time using the Loss
Derived Method.
Measurement Units: seconds
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Issues: None
See Also:
Full Convergence, RateDerived Method, RouteSpecific LossDerived
Method
3.6.2. First Route Convergence Time
Definition:
The duration of the period between the Convergence Event Instant and
the First Route Convergence Instant as observed using the Rate
Derived Method.
Discussion:
Using the RateDerived Method, First Route Convergence Time can be
calculated as the time difference between the Convergence Event
Instant and the First Route Convergence Instant, as shown with
Equation 3.
First Route Convergence Time =
First Route Convergence Instant  Convergence Event Instant
Equation 3
The Convergence Event Instant can be derived from the Forwarding Rate
observation or from a timestamp collected by the Tester.
For the testcases described in [Po10m], it is expected that First
Route Convergence Time equals the minimum RouteSpecific Convergence
Time when benchmarking all routes in FIB using the RouteSpecific
LossDerived Method.
It is not possible to measure First Route Convergence Time using the
LossDerived Method.
Measurement Units: seconds
Issues: None
See Also:
RateDerived Method, RouteSpecific LossDerived Method, First Route
Convergence Instant
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3.6.3. RouteSpecific Convergence Time
Definition:
The amount of time it takes for Route Convergence to be completed for
a specific route, as calculated from the amount of packet loss during
convergence for a single route entry.
Discussion:
RouteSpecific Convergence Time can only be measured using the Route
Specific LossDerived Method.
If the applied Convergence Event causes instantaneous traffic loss
for all routes at the Convergence Event Instant, Connectivity Packet
Loss should be observed. Connectivity Packet Loss is the combined
packet loss observed on Preferred Egress Interface and NextBest
Egress Interface. When benchmarking RouteSpecific Convergence Time,
Connectivity Packet Loss is measured and Equation 4 is applied for
each measured route. The calculation is equal to Equation 8 in
Section 3.6.5.
RouteSpecific Convergence Time =
Connectivity Packet Loss for specific route/Offered Load per route
Equation 4
If the applied Convergence Event does not cause instantaneous traffic
loss for all routes at the Convergence Event Instant, then the Tester
SHOULD collect timestamps of the Traffic Start Instant and of the
Convergence Event Instant, and the Tester SHOULD observe Convergence
Packet Loss separately on the NextBest Egress Interface. When
benchmarking RouteSpecific Convergence Time, Convergence Packet Loss
is measured and Equation 5 is applied for each measured route.
RouteSpecific Convergence Time =
Convergence Packet Loss for specific route/Offered Load per route
 (Convergence Event Instant  Traffic Start Instant)
Equation 5
The Convergence Event Instant and Traffic Start Instant SHOULD be
collected by the Tester.
The RouteSpecific Convergence Time benchmarks enable minimum,
maximum, average, and median convergence time measurements to be
reported by comparing the results for the different route entries.
It also enables benchmarking of convergence time when configuring a
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priority value for route entry(ies). Since multiple RouteSpecific
Convergence Times can be measured it is possible to have an array of
results. The format for reporting RouteSpecific Convergence Time is
provided in [Po10m].
Measurement Units: seconds
Issues: None
See Also:
Convergence Event, Convergence Packet Loss, Connectivity Packet Loss,
Route Convergence
3.6.4. LossDerived Convergence Time
Definition:
The average Route Convergence time for all routes in FIB, as
calculated from the amount of packet loss during convergence.
Discussion:
LossDerived Convergence Time is measured using the LossDerived
Method.
If the applied Convergence Event causes instantaneous traffic loss
for all routes at the Convergence Event Instant, Connectivity Packet
Loss should be observed. Connectivity Packet Loss is the combined
packet loss observed on Preferred Egress Interface and NextBest
Egress Interface. When benchmarking LossDerived Convergence Time,
Connectivity Packet Loss is measured and Equation 6 is applied.
LossDerived Convergence Time =
Connectivity Packet Loss/Offered Load
Equation 6
If the applied Convergence Event does not cause instantaneous traffic
loss for all routes at the Convergence Event Instant, then the Tester
SHOULD collect timestamps of the Start Traffic Instant and of the
Convergence Event Instant and the Tester SHOULD observe Convergence
Packet Loss separately on the NextBest Egress Interface. When
benchmarking LossDerived Convergence Time, Convergence Packet Loss
is measured and Equation 7 is applied.
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LossDerived Convergence Time =
Convergence Packet Loss/Offered Load
 (Convergence Event Instant  Traffic Start Instant)
Equation 7
The Convergence Event Instant and Traffic Start Instant SHOULD be
collected by the Tester.
Measurement Units: seconds
Issues: None
See Also:
Convergence Packet Loss, Connectivity Packet Loss, Route Convergence
3.6.5. Route Loss of Connectivity Period
Definition:
The time duration of traffic loss for a specific route entry
following a Convergence Event until Full Convergence completion, as
observed using the RouteSpecific LossDerived Method.
Discussion:
In general the Route Loss of Connectivity Period is not equal to the
RouteSpecific Convergence Time. If the DUT continues to forward
traffic to the Preferred Egress Interface after the Convergence Event
is applied then the Route Loss of Connectivity Period will be smaller
than the RouteSpecific Convergence Time. This is also specifically
the case after reversing a failure event.
The Route Loss of Connectivity Period may be equal to the Route
Specific Convergence Time if, as a characteristic of the Convergence
Event, traffic for all routes starts dropping instantaneously on the
Convergence Event Instant. See discussion in [Po10m].
For the testcases described in [Po10m] the Route Loss of Connectivity
Period is expected to be a single Loss Period [Ko02].
When benchmarking Route Loss of Connectivity Period, Connectivity
Packet Loss is measured for each route and Equation 8 is applied for
each measured route entry. The calculation is equal to Equation 4 in
Section 3.6.3.
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Route Loss of Connectivity Period =
Connectivity Packet Loss for specific route/Offered Load per route
Equation 8
Route Loss of Connectivity Period SHOULD be measured using Route
Specific LossDerived Method.
Measurement Units: seconds
Issues: None
See Also:
RouteSpecific Convergence Time, RouteSpecific LossDerived Method,
Connectivity Packet Loss
3.6.6. LossDerived Loss of Connectivity Period
Definition:
The average time duration of traffic loss for all routes following a
Convergence Event until Full Convergence completion, as observed
using the LossDerived Method.
Discussion:
In general the LossDerived Loss of Connectivity Period is not equal
to the LossDerived Convergence Time. If the DUT continues to
forward traffic to the Preferred Egress Interface after the
Convergence Event is applied then the LossDerived Loss of
Connectivity Period will be smaller than the LossDerived Convergence
Time. This is also specifically the case after reversing a failure
event.
The LossDerived Loss of Connectivity Period may be equal to the
LossDerived Convergence Time if, as a characteristic of the
Convergence Event, traffic for all routes starts dropping
instantaneously on the Convergence Event Instant. See discussion in
[Po10m].
For the testcases described in [Po10m] each route's Route Loss of
Connectivity Period is expected to be a single Loss Period [Ko02].
When benchmarking LossDerived Loss of Connectivity Period,
Connectivity Packet Loss is measured for all routes and Equation 9 is
applied. The calculation is equal to Equation 6 in Section 3.6.4.
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LossDerived Loss of Connectivity Period =
Connectivity Packet Loss for all routes/Offered Load
Equation 9
LossDerived Loss of Connectivity Period SHOULD be measured using
LossDerived Method.
Measurement Units: seconds
Issues: None
See Also:
LossDerived Convergence Time, LossDerived Method, Connectivity
Packet Loss
3.7. Measurement Terms
3.7.1. Convergence Event
Definition:
The occurrence of a planned or unplanned event in the network that
will result in a change in the egress interface of the Device Under
Test (DUT) for routed packets.
Discussion:
Convergence Events include but are not limited to link loss, routing
protocol session loss, router failure, configuration change, and
better nexthop learned via a routing protocol.
Measurement Units: N/A
Issues: None
See Also: Convergence Event Instant
3.7.2. Packet Loss
Definition:
The number of packets that should have been forwarded by a DUT under
a constant Offered Load that were not forwarded due to lack of
resources.
Discussion:
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Packet Loss is a modified version of the term "Frame Loss Rate" as
defined in [Br91]. The term "Frame Loss" is intended for Ethernet
Frames while "Packet Loss" is intended for IP packets.
Measurement units: Number of offered packets that are not forwarded.
Issues: None
See Also: Convergence Packet Loss
3.7.3. Convergence Packet Loss
Definition:
The number of packets lost due to a Convergence Event until Full
Convergence completes, as observed on the NextBest Egress Interface.
Discussion:
Convergence Packet Loss is observed on the NextBest Egress
Interface. It only needs to be observed for Convergence Events that
do not cause instantaneous traffic loss at Convergence Event Instant.
Convergence Packet Loss includes packets that were lost and packets
that were delayed due to buffering. The maximum acceptable
Forwarding Delay (Forwarding Delay Threshold) is a parameter of the
methodology, if it is applied it MUST be reported.
Measurement Units: number of packets
Issues: None
See Also:
Packet Loss, Full Convergence, Convergence Event, Connectivity Packet
Loss
3.7.4. Connectivity Packet Loss
Definition:
The number of packets lost due to a Convergence Event until Full
Convergence completes.
Discussion:
Connectivity Packet Loss is observed on all DUT egress interfaces.
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Connectivity Packet Loss includes packets that were lost and packets
that were delayed due to buffering. The maximum acceptable
Forwarding Delay (Forwarding Delay Threshold) is a parameter of the
methodology, if it is applied it MUST be reported.
Measurement Units: number of packets
Issues: None
See Also:
Packet Loss, Route Loss of Connectivity Period, Convergence Event,
Convergence Packet Loss
3.7.5. Packet Sampling Interval
Definition:
The interval at which the Tester (test equipment) polls to make
measurements for arriving packets.
Discussion:
At least one packet per route for all routes matched in the Offered
Load MUST be offered to the DUT within the Packet Sampling Interval.
Metrics measured at the Packet Sampling Interval MUST include
Forwarding Rate and received packets.
Packet Sampling Interval can influence the convergence graph as
observed with the RateDerived Method. This is particularly true
when implementations complete Full Convergence in less time than the
Packet Sampling Interval. The Convergence Event Instant and First
Route Convergence Instant may not be easily identifiable and the
RateDerived Method may produce a larger than actual convergence
time.
Using a small Packet Sampling Interval in the presence of IPDV [De02]
may cause fluctuations of the Forwarding Rate observation and can
prevent correct observation of the different convergence time
instants.
The value of the Packet Sampling Interval only contributes to the
measurement accuracy of the RateDerived Method. For maximum
accuracy the value for the Packet Sampling Interval SHOULD be as
small as possible, but the presence of IPDV may enforce using a
larger Packet Sampling Interval.
Measurement Units: seconds
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Issues: None
See Also: RateDerived Method
3.7.6. Sustained Convergence Validation Time
Definition:
The amount of time for which the completion of Full Convergence is
maintained without additional packet loss.
Discussion:
The purpose of the Sustained Convergence Validation Time is to
produce convergence benchmarks protected against fluctuation in
Forwarding Rate after the completion of Full Convergence is observed.
The RECOMMENDED Sustained Convergence Validation Time to be used is
the time to send 5 consecutive packets to each destination with a
minimum of 5 seconds. The BMWG selected 5 seconds based upon [Br99]
which recommends waiting 2 seconds for residual frames to arrive
(this is the Forwarding Delay Threshold for the last packet sent) and
5 seconds for DUT restabilization.
Measurement Units: seconds
Issues: None
See Also:
Full Convergence, Convergence Recovery Instant
3.7.7. Forwarding Delay Threshold
Definition:
The maximum waiting time threshold used to distinguish between
packets with very long delay and lost packets that will never arrive.
Discussion:
Applying a Forwarding Delay Threshold allows to consider packets with
a too large Forwarding Delay as being lost, as is required for some
applications (e.g. voice, video, etc.). The Forwarding Delay
Threshold is a parameter of the methodology, if it is applied it MUST
be reported.
Measurement Units: seconds
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Issues: None
See Also:
Convergence Packet Loss, Connectivity Packet Loss
3.8. Miscellaneous Terms
3.8.1. Stale Forwarding
Definition:
Forwarding of traffic to route entries that no longer exist or to
route entries with nexthops that are no longer preferred.
Discussion:
Stale Forwarding can be caused by a Convergence Event and can
manifest as a "blackhole" or microloop that produces packet loss, or
outoforder packets, or delayed packets. Stale Forwarding can exist
until Network Convergence is completed.
Measurement Units: N/A
Issues: None
See Also: Network Convergence
3.8.2. Nested Convergence Event
Definition:
The occurrence of a Convergence Event while the route table is
converging from a prior Convergence Event.
Discussion:
The Convergence Events for a Nested Convergence Event MUST occur with
different neighbors. A possible 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
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4. Security Considerations
Benchmarking activities as described in this memo are limited to
technology characterization using controlled stimuli in a laboratory
environment, with dedicated address space and the constraints
specified in the sections above.
The benchmarking network topology will be an independent test setup
and MUST NOT be connected to devices that may forward the test
traffic into a production network, or misroute traffic to the test
management network.
Further, benchmarking is performed on a "blackbox" basis, relying
solely on measurements observable external to the DUT/SUT.
Special capabilities SHOULD NOT exist in the DUT/SUT specifically for
benchmarking purposes. Any implications for network security arising
from the DUT/SUT SHOULD be identical in the lab and in production
networks.
5. IANA Considerations
This document requires no IANA considerations.
6. Acknowledgements
Thanks to Sue Hares, Al Morton, Kevin Dubray, Ron Bonica, David Ward,
Peter De Vriendt, Anuj Dewagan and the BMWG for their contributions
to this work.
7. References
7.1. Normative References
[Br91] Bradner, S., "Benchmarking terminology for network
interconnection devices", RFC 1242, July 1991.
[Br97] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[Br99] Bradner, S. and J. McQuaid, "Benchmarking Methodology for
Network Interconnect Devices", RFC 2544, March 1999.
[Ca90] Callon, R., "Use of OSI ISIS for routing in TCP/IP and dual
environments", RFC 1195, December 1990.
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[Co08] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF for
IPv6", RFC 5340, July 2008.
[De02] Demichelis, C. and P. Chimento, "IP Packet Delay Variation
Metric for IP Performance Metrics (IPPM)", RFC 3393,
November 2002.
[Ho08] Hopps, C., "Routing IPv6 with ISIS", RFC 5308,
October 2008.
[Ko02] Koodli, R. and R. Ravikanth, "Oneway Loss Pattern Sample
Metrics", RFC 3357, August 2002.
[Ma98] Mandeville, R., "Benchmarking Terminology for LAN Switching
Devices", RFC 2285, February 1998.
[Mo06] Morton, A., Ciavattone, L., Ramachandran, G., Shalunov, S.,
and J. Perser, "Packet Reordering Metrics", RFC 4737,
November 2006.
[Mo98] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[Po06] Poretsky, S., Perser, J., Erramilli, S., and S. Khurana,
"Terminology for Benchmarking Networklayer Traffic Control
Mechanisms", RFC 4689, October 2006.
[Po09a] Poretsky, S., "Considerations for Benchmarking LinkState
IGP Data Plane Route Convergence",
draftietfbmwgigpdataplaneconvapp17 (work in
progress), March 2009.
[Po10m] Poretsky, S., Imhoff, B., and K. Michielsen, "Benchmarking
Methodology for LinkState IGP Data Plane Route
Convergence", draftietfbmwgigpdataplaneconvmeth20
(work in progress), March 2010.
7.2. Informative References
[Ca01] Casner, S., Alaettinoglu, C., and C. Kuan, "A FineGrained
View of High Performance Networking", NANOG 22, June 2001.
[Ci03] Ciavattone, L., Morton, A., and G. Ramachandran,
"Standardized Active Measurements on a Tier 1 IP Backbone",
IEEE Communications Magazine p9097, May 2003.
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Authors' Addresses
Scott Poretsky
Allot Communications
67 South Bedford Street, Suite 400
Burlington, MA 01803
USA
Phone: + 1 508 309 2179
Email: sporetsky@allot.com
Brent Imhoff
Juniper Networks
1194 North Mathilda Ave
Sunnyvale, CA 94089
USA
Phone: + 1 314 378 2571
Email: bimhoff@planetspork.com
Kris Michielsen
Cisco Systems
6A De Kleetlaan
Diegem, BRABANT 1831
Belgium
Email: kmichiel@cisco.com
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