| Rfc | 6413 |
|---|
| Title | Benchmarking Methodology for Link-State IGP Data-Plane Route
Convergence |
|---|
| Author | S. Poretsky, B. Imhoff, K. Michielsen |
|---|
| Date | November 2011 |
|---|
| Format: | TXT, HTML |
|---|
| Status: | INFORMATIONAL |
|---|
|
Internet Engineering Task Force (IETF) S. Poretsky
Request for Comments: 6413 Allot Communications
Category: Informational B. Imhoff
ISSN: 2070-1721 Juniper Networks
K. Michielsen
Cisco Systems
November 2011
Benchmarking Methodology for Link-State IGP Data-Plane Route Convergence
Abstract
This document describes the methodology for benchmarking Link-State
Interior Gateway Protocol (IGP) Route Convergence. The methodology
is to be used for benchmarking IGP convergence time through
externally observable (black-box) data-plane measurements. The
methodology can be applied to any link-state IGP, such as IS-IS and
OSPF.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6413.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Motivation . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Factors for IGP Route Convergence Time . . . . . . . . . . 4
1.3. Use of Data Plane for IGP Route Convergence
Benchmarking . . . . . . . . . . . . . . . . . . . . . . . 5
1.4. Applicability and Scope . . . . . . . . . . . . . . . . . 6
2. Existing Definitions . . . . . . . . . . . . . . . . . . . . . 6
3. Test Topologies . . . . . . . . . . . . . . . . . . . . . . . 7
3.1. Test Topology for Local Changes . . . . . . . . . . . . . 7
3.2. Test Topology for Remote Changes . . . . . . . . . . . . . 8
3.3. Test Topology for Local ECMP Changes . . . . . . . . . . . 10
3.4. Test Topology for Remote ECMP Changes . . . . . . . . . . 11
3.5. Test topology for Parallel Link Changes . . . . . . . . . 11
4. Convergence Time and Loss of Connectivity Period . . . . . . . 12
4.1. Convergence Events without Instant Traffic Loss . . . . . 13
4.2. Loss of Connectivity (LoC) . . . . . . . . . . . . . . . . 16
5. Test Considerations . . . . . . . . . . . . . . . . . . . . . 17
5.1. IGP Selection . . . . . . . . . . . . . . . . . . . . . . 17
5.2. Routing Protocol Configuration . . . . . . . . . . . . . . 17
5.3. IGP Topology . . . . . . . . . . . . . . . . . . . . . . . 17
5.4. Timers . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.5. Interface Types . . . . . . . . . . . . . . . . . . . . . 18
5.6. Offered Load . . . . . . . . . . . . . . . . . . . . . . . 18
5.7. Measurement Accuracy . . . . . . . . . . . . . . . . . . . 19
5.8. Measurement Statistics . . . . . . . . . . . . . . . . . . 20
5.9. Tester Capabilities . . . . . . . . . . . . . . . . . . . 20
6. Selection of Convergence Time Benchmark Metrics and Methods . 20
6.1. Loss-Derived Method . . . . . . . . . . . . . . . . . . . 21
6.1.1. Tester Capabilities . . . . . . . . . . . . . . . . . 21
6.1.2. Benchmark Metrics . . . . . . . . . . . . . . . . . . 21
6.1.3. Measurement Accuracy . . . . . . . . . . . . . . . . . 21
6.2. Rate-Derived Method . . . . . . . . . . . . . . . . . . . 22
6.2.1. Tester Capabilities . . . . . . . . . . . . . . . . . 22
6.2.2. Benchmark Metrics . . . . . . . . . . . . . . . . . . 23
6.2.3. Measurement Accuracy . . . . . . . . . . . . . . . . . 23
6.3. Route-Specific Loss-Derived Method . . . . . . . . . . . . 24
6.3.1. Tester Capabilities . . . . . . . . . . . . . . . . . 24
6.3.2. Benchmark Metrics . . . . . . . . . . . . . . . . . . 24
6.3.3. Measurement Accuracy . . . . . . . . . . . . . . . . . 24
7. Reporting Format . . . . . . . . . . . . . . . . . . . . . . . 25
8. Test Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 26
8.1. Interface Failure and Recovery . . . . . . . . . . . . . . 27
8.1.1. Convergence Due to Local Interface Failure and
Recovery . . . . . . . . . . . . . . . . . . . . . . . 27
8.1.2. Convergence Due to Remote Interface Failure and
Recovery . . . . . . . . . . . . . . . . . . . . . . . 28
8.1.3. Convergence Due to ECMP Member Local Interface
Failure and Recovery . . . . . . . . . . . . . . . . . 30
8.1.4. Convergence Due to ECMP Member Remote Interface
Failure and Recovery . . . . . . . . . . . . . . . . . 31
8.1.5. Convergence Due to Parallel Link Interface Failure
and Recovery . . . . . . . . . . . . . . . . . . . . . 32
8.2. Other Failures and Recoveries . . . . . . . . . . . . . . 33
8.2.1. Convergence Due to Layer 2 Session Loss and
Recovery . . . . . . . . . . . . . . . . . . . . . . . 33
8.2.2. Convergence Due to Loss and Recovery of IGP
Adjacency . . . . . . . . . . . . . . . . . . . . . . 34
8.2.3. Convergence Due to Route Withdrawal and
Re-Advertisement . . . . . . . . . . . . . . . . . . . 35
8.3. Administrative Changes . . . . . . . . . . . . . . . . . . 37
8.3.1. Convergence Due to Local Interface Administrative
Changes . . . . . . . . . . . . . . . . . . . . . . . 37
8.3.2. Convergence Due to Cost Change . . . . . . . . . . . . 38
9. Security Considerations . . . . . . . . . . . . . . . . . . . 39
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 40
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 40
11.1. Normative References . . . . . . . . . . . . . . . . . . . 40
11.2. Informative References . . . . . . . . . . . . . . . . . . 41
1. Introduction
1.1. Motivation
Convergence time is a critical performance parameter. Service
Providers use IGP convergence time as a key metric of router design
and architecture. Fast network convergence can be optimally achieved
through deployment of fast converging routers. Customers of Service
Providers use packet loss due to Interior Gateway Protocol (IGP)
convergence as a key metric of their network service quality. IGP
route convergence is a Direct Measure of Quality (DMOQ) when
benchmarking the data plane. The fundamental basis by which network
users and operators benchmark convergence is packet loss and other
packet impairments, which are externally observable events having
direct impact on their application performance. For this reason, it
is important to develop a standard methodology for benchmarking link-
state IGP convergence time through externally observable (black-box)
data-plane measurements. All factors contributing to convergence
time are accounted for by measuring on the data plane.
1.2. Factors for IGP Route Convergence Time
There are four major categories of factors contributing to the
measured IGP convergence time. As discussed in [Vi02], [Ka02],
[Fi02], [Al00], [Al02], and [Fr05], these categories are Event
Detection, Shortest Path First (SPF) Processing, Link State
Advertisement (LSA) / Link State Packet (LSP) Advertisement, and
Forwarding Information Base (FIB) Update. These have numerous
components that influence the convergence time, including but not
limited to the list below:
o Event Detection
* Physical-Layer Failure/Recovery Indication Time
* Layer 2 Failure/Recovery Indication Time
* IGP Hello Dead Interval
o SPF Processing
* SPF Delay Time
* SPF Hold Time
* SPF Execution Time
o LSA/LSP Advertisement
* LSA/LSP Generation Time
* LSA/LSP Flood Packet Pacing
* LSA/LSP Retransmission Packet Pacing
o FIB Update
* Tree Build Time
* Hardware Update Time
o Increased Forwarding Delay due to Queueing
The contribution of each of the factors listed above will vary with
each router vendor's architecture and IGP implementation. Routers
may have a centralized forwarding architecture, in which one
forwarding table is calculated and referenced for all arriving
packets, or a distributed forwarding architecture, in which the
central forwarding table is calculated and distributed to the
interfaces for local look-up as packets arrive. The distributed
forwarding tables are typically maintained (loaded and changed) in
software.
The variation in router architecture and implementation necessitates
the design of a convergence test that considers all of these
components contributing to convergence time and is independent of the
Device Under Test (DUT) architecture and implementation. The benefit
of designing a test for these considerations is that it enables
black-box testing in which knowledge of the routers' internal
implementation is not required. It is then possible to make valid
use of the convergence benchmarking metrics when comparing routers
from different vendors.
Convergence performance is tightly linked to the number of tasks a
router has to deal with. As the most important tasks are mainly
related to the control plane and the data plane, the more the DUT is
stressed as in a live production environment, the closer performance
measurement results match the ones that would be observed in a live
production environment.
1.3. Use of Data Plane for IGP Route Convergence Benchmarking
Customers of Service Providers use packet loss and other packet
impairments as metrics to calculate convergence time. Packet loss
and other packet impairments are externally observable events having
direct impact on customers' application performance. For this
reason, it is important to develop a standard router benchmarking
methodology that is a Direct Measure of Quality (DMOQ) for measuring
IGP convergence. An additional benefit of using packet loss for
calculation of IGP Route Convergence time is that it enables black-
box tests to be designed. Data traffic can be offered to the Device
Under Test (DUT), an emulated network event can be forced to occur,
and packet loss and other impaired packets can be externally measured
to calculate the convergence time. Knowledge of the DUT architecture
and IGP implementation is not required. There is no need to rely on
the DUT to produce the test results. There is no need to build
intrusive test harnesses for the DUT. All factors contributing to
convergence time are accounted for by measuring on the data plane.
Other work of the Benchmarking Methodology Working Group (BMWG)
focuses on characterizing single router control-plane convergence.
See [Ma05], [Ma05t], and [Ma05c].
1.4. Applicability and Scope
The methodology described in this document can be applied to IPv4 and
IPv6 traffic and link-state IGPs such as IS-IS [Ca90][Ho08], OSPF
[Mo98][Co08], and others. IGP adjacencies established over any kind
of tunnel (such as Traffic Engineering tunnels) are outside the scope
of this document. Convergence time benchmarking in topologies with
IGP adjacencies that are not point-to-point will be covered in a
later document. Convergence from Bidirectional Forwarding Detection
(BFD) is outside the scope of this document. Non-Stop Forwarding
(NSF), Non-Stop Routing (NSR), Graceful Restart (GR), and any other
High Availability mechanism are outside the scope of this document.
Fast reroute mechanisms such as IP Fast-Reroute [Sh10i] or MPLS Fast-
Reroute [Pa05] are outside the scope of this document.
2. Existing Definitions
The keywords "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 keywords 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.
This document uses much of the terminology defined in [Po11t]. For
any conflicting content, this document supersedes [Po11t]. This
document uses existing terminology defined in other documents issued
by the Benchmarking Methodology Working Group (BMWG). Examples
include, but are not limited to:
Throughput [Br91], Section 3.17
Offered Load [Ma98], Section 3.5.2
Forwarding Rate [Ma98], Section 3.6.1
Device Under Test (DUT) [Ma98], Section 3.1.1
System Under Test (SUT) [Ma98], Section 3.1.2
Out-of-Order Packet [Po06], Section 3.3.4
Duplicate Packet [Po06], Section 3.3.5
Stream [Po06], Section 3.3.2
Forwarding Delay [Po06], Section 3.2.4
IP Packet Delay Variation (IPDV) [De02], Section 1.2
Loss Period [Ko02], Section 4
3. Test Topologies
3.1. Test Topology for Local Changes
Figure 1 shows the test topology to measure IGP convergence time due
to local Convergence Events such as Local Interface failure and
recovery (Section 8.1.1), Layer 2 session failure and recovery
(Section 8.2.1), and IGP adjacency failure and recovery
(Section 8.2.2). This topology is also used to measure IGP
convergence time due to route withdrawal and re-advertisement
(Section 8.2.3) and to measure IGP convergence time due to route cost
change (Section 8.3.2) Convergence Events. IGP adjacencies MUST be
established between Tester and DUT: one on the Ingress Interface, one
on the Preferred Egress Interface, and one on the Next-Best Egress
Interface. For this purpose, the Tester emulates three routers (RTa,
RTb, and RTc), each establishing one adjacency with the DUT.
-------
| | Preferred .......
| |------------------. RTb .
....... Ingress | | Egress Interface .......
. RTa .------------| DUT |
....... Interface | | Next-Best .......
| |------------------. RTc .
| | Egress Interface .......
-------
Figure 1: IGP convergence test topology for local changes
Figure 2 shows the test topology to measure IGP convergence time due
to local Convergence Events with a non-Equal Cost Multipath (ECMP)
Preferred Egress Interface and ECMP Next-Best Egress Interfaces
(Section 8.1.1). In this topology, the DUT is configured with each
Next-Best Egress Interface as a member of a single ECMP set. The
Preferred Egress Interface is not a member of an ECMP set. The
Tester emulates N+2 neighbor routers (N>0): one router for the
Ingress Interface (RTa), one router for the Preferred Egress
Interface (RTb), and N routers for the members of the ECMP set
(RTc1...RTcN). IGP adjacencies MUST be established between Tester
and DUT: one on the Ingress Interface, one on the Preferred Egress
Interface, and one on each member of the ECMP set. When the test
specifies to observe the Next-Best Egress Interface statistics, the
combined statistics for all ECMP members should be observed.
-------
| | Preferred .......
| |------------------. RTb .
| | Egress Interface .......
| |
| | ECMP Set ........
....... Ingress | |------------------. RTc1 .
. RTa .------------| DUT | Interface 1 ........
....... Interface | | .
| | .
| | .
| | ECMP Set ........
| |------------------. RTcN .
| | Interface N ........
-------
Figure 2: IGP convergence test topology for local changes with non-
ECMP to ECMP convergence
3.2. Test Topology for Remote Changes
Figure 3 shows the test topology to measure IGP convergence time due
to Remote Interface failure and recovery (Section 8.1.2). In this
topology, the two routers DUT1 and DUT2 are considered the System
Under Test (SUT) and SHOULD be identically configured devices of the
same model. IGP adjacencies MUST be established between Tester and
SUT, one on the Ingress Interface, one on the Preferred Egress
Interface, and one on the Next-Best Egress Interface. For this
purpose, the Tester emulates three routers (RTa, RTb, and RTc). In
this topology, a packet forwarding loop, also known as micro-loop
(see [Sh10]), may occur transiently between DUT1 and DUT2 during
convergence.
--------
| | -------- Preferred .......
| |--| DUT2 |------------------. RTb .
....... Ingress | | -------- Egress Interface .......
. RTa .------------| DUT1 |
....... Interface | | Next-Best .......
| |----------------------------. RTc .
| | Egress Interface .......
--------
Figure 3: IGP convergence test topology for remote changes
Figure 4 shows the test topology to measure IGP convergence time due
to remote Convergence Events with a non-ECMP Preferred Egress
Interface and ECMP Next-Best Egress Interfaces (Section 8.1.2). In
this topology the two routers DUT1 and DUT2 are considered System
Under Test (SUT) and MUST be identically configured devices of the
same model. Router DUT1 is configured with the Next-Best Egress
Interface an ECMP set of interfaces. The Preferred Egress Interface
of DUT1 is not a member of an ECMP set. The Tester emulates N+2
neighbor routers (N>0), one for the Ingress Interface (RTa), one for
DUT2 (RTb) and one for each member of the ECMP set (RTc1...RTcN).
IGP adjacencies MUST be established between Tester and SUT, one on
each interface of the SUT. For this purpose each of the N+2 routers
emulated by the Tester establishes one adjacency with the SUT. In
this topology, there is a possibility of a packet-forwarding loop
that may occur transiently between DUT1 and DUT2 during convergence
(micro-loop, see [Sh10]). When the test specifies to observe the
Next-Best Egress Interface statistics, the combined statistics for
all members of the ECMP set should be observed.
--------
| | -------- Preferred .......
| |--| DUT2 |------------------. RTb .
| | -------- Egress Interface .......
| |
| | ECMP Set ........
....... Ingress | |----------------------------. RTc1 .
. RTa .------------| DUT1 | Interface 1 ........
....... Interface | | .
| | .
| | .
| | ECMP Set ........
| |----------------------------. RTcN .
| | Interface N ........
--------
Figure 4: IGP convergence test topology for remote changes with
non-ECMP to ECMP convergence
3.3. Test Topology for Local ECMP Changes
Figure 5 shows the test topology to measure IGP convergence time due
to local Convergence Events of a member of an Equal Cost Multipath
(ECMP) set (Section 8.1.3). In this topology, the DUT is configured
with each egress interface as a member of a single ECMP set and the
Tester emulates N+1 next-hop routers, one for the Ingress Interface
(RTa) and one for each member of the ECMP set (RTb1...RTbN). IGP
adjacencies MUST be established between Tester and DUT, one on the
Ingress Interface and one on each member of the ECMP set. For this
purpose, each of the N+1 routers emulated by the Tester establishes
one adjacency with the DUT. When the test specifies to observe the
Next-Best Egress Interface statistics, the combined statistics for
all ECMP members except the one affected by the Convergence Event
should be observed.
-------
| | ECMP Set ........
| |-------------. RTb1 .
| | Interface 1 ........
....... Ingress | | .
. RTa .------------| DUT | .
....... Interface | | .
| | ECMP Set ........
| |-------------. RTbN .
| | Interface N ........
-------
Figure 5: IGP convergence test topology for local ECMP changes
3.4. Test Topology for Remote ECMP Changes
Figure 6 shows the test topology to measure IGP convergence time due
to remote Convergence Events of a member of an Equal Cost Multipath
(ECMP) set (Section 8.1.4). In this topology, the two routers DUT1
and DUT2 are considered the System Under Test (SUT) and MUST be
identically configured devices of the same model. Router DUT1 is
configured with each egress interface as a member of a single ECMP
set, and the Tester emulates N+1 neighbor routers (N>0), one for the
Ingress Interface (RTa) and one for each member of the ECMP set
(RTb1...RTbN). IGP adjacencies MUST be established between Tester
and SUT, one on each interface of the SUT. For this purpose, each of
the N+1 routers emulated by the Tester establishes one adjacency with
the SUT (N-1 emulated routers are adjacent to DUT1 egress interfaces,
one emulated router is adjacent to DUT1 Ingress Interface, and one
emulated router is adjacent to DUT2). In this topology, there is a
possibility of a packet-forwarding loop that may occur transiently
between DUT1 and DUT2 during convergence (micro-loop, see [Sh10]).
When the test specifies to observe the Next-Best Egress Interface
statistics, the combined statistics for all ECMP members except the
one affected by the Convergence Event should be observed.
--------
| | ECMP Set -------- ........
| |-------------| DUT2 |---. RTb1 .
| | Interface 1 -------- ........
| |
| | ECMP Set ........
....... Ingress | |------------------------. RTb2 .
. RTa .------------| DUT1 | Interface 2 ........
....... Interface | | .
| | .
| | .
| | ECMP Set ........
| |------------------------. RTbN .
| | Interface N ........
--------
Figure 6: IGP convergence test topology for remote ECMP changes
3.5. Test topology for Parallel Link Changes
Figure 7 shows the test topology to measure IGP convergence time due
to local Convergence Events with members of a Parallel Link
(Section 8.1.5). In this topology, the DUT is configured with each
egress interface as a member of a Parallel Link and the Tester
emulates two neighbor routers, one for the Ingress Interface (RTa)
and one for the Parallel Link members (RTb). IGP adjacencies MUST be
established on the Ingress Interface and on all N members of the
Parallel Link between Tester and DUT (N>0). For this purpose, the
routers emulated by the Tester establishes N+1 adjacencies with the
DUT. When the test specifies to observe the Next-Best Egress
Interface statistics, the combined statistics for all Parallel Link
members except the one affected by the Convergence Event should be
observed.
------- .......
| | Parallel Link . .
| |----------------. .
| | Interface 1 . .
....... Ingress | | . . .
. RTa .------------| DUT | . . RTb .
....... Interface | | . . .
| | Parallel Link . .
| |----------------. .
| | Interface N . .
------- .......
Figure 7: IGP convergence test topology for Parallel Link changes
4. Convergence Time and Loss of Connectivity Period
Two concepts will be highlighted in this section: convergence time
and loss of connectivity period.
The Route Convergence [Po11t] time indicates the period in time
between the Convergence Event Instant [Po11t] and the instant in time
the DUT is ready to forward traffic for a specific route on its Next-
Best Egress Interface and maintains this state for the duration of
the Sustained Convergence Validation Time [Po11t]. To measure Route
Convergence time, the Convergence Event Instant and the traffic
received from the Next-Best Egress Interface need to be observed.
The Route Loss of Connectivity Period [Po11t] indicates the time
during which traffic to a specific route is lost following a
Convergence Event until Full Convergence [Po11t] completes. This
Route Loss of Connectivity Period can consist of one or more Loss
Periods [Ko02]. For the test cases described in this document, it is
expected to have a single Loss Period. To measure the Route Loss of
Connectivity Period, the traffic received from the Preferred Egress
Interface and the traffic received from the Next-Best Egress
Interface need to be observed.
The Route Loss of Connectivity Period is most important since that
has a direct impact on the network user's application performance.
In general, the Route Convergence time is larger than or equal to the
Route Loss of Connectivity Period. Depending on which Convergence
Event occurs and how this Convergence Event is applied, traffic for a
route may still be forwarded over the Preferred Egress Interface
after the Convergence Event Instant, before converging to the Next-
Best Egress Interface. In that case, the Route Loss of Connectivity
Period is shorter than the Route Convergence time.
At least one condition needs to be fulfilled for Route Convergence
time to be equal to Route Loss of Connectivity Period. The condition
is that the Convergence Event causes an instantaneous traffic loss
for the measured route. A fiber cut on the Preferred Egress
Interface is an example of such a Convergence Event.
A second condition applies to Route Convergence time measurements
based on Connectivity Packet Loss [Po11t]. This second condition is
that there is only a single Loss Period during Route Convergence.
For the test cases described in this document, the second condition
is expected to apply.
4.1. Convergence Events without Instant Traffic Loss
To measure convergence time benchmarks for Convergence Events caused
by a Tester, such as an IGP cost change, the Tester MAY start to
discard all traffic received from the Preferred Egress Interface at
the Convergence Event Instant, or MAY separately observe packets
received from the Preferred Egress Interface prior to the Convergence
Event Instant. This way, these Convergence Events can be treated the
same as Convergence Events that cause instantaneous traffic loss.
To measure convergence time benchmarks without instantaneous traffic
loss (either real or induced by the Tester) at the Convergence Event
Instant, such as a reversion of a link failure Convergence Event, the
Tester SHALL only observe packet statistics on the Next-Best Egress
Interface. If using the Rate-Derived method to benchmark convergence
times for such Convergence Events, the Tester MUST collect a
timestamp at the Convergence Event Instant. If using a loss-derived
method to benchmark convergence times for such Convergence Events,
the Tester MUST measure the period in time between the Start Traffic
Instant and the Convergence Event Instant. To measure this period in
time, the Tester can collect timestamps at the Start Traffic Instant
and the Convergence Event Instant.
The Convergence Event Instant together with the receive rate
observations on the Next-Best Egress Interface allow the derivation
of the convergence time benchmarks using the Rate-Derived Method
[Po11t].
By observing packets on the Next-Best Egress Interface only, the
observed Impaired Packet count is the number of Impaired Packets
between Traffic Start Instant and Convergence Recovery Instant. To
measure convergence times using a loss-derived method, the Impaired
Packet count between the Convergence Event Instant and the
Convergence Recovery Instant is needed. The time between Traffic
Start Instant and Convergence Event Instant must be accounted for.
An example may clarify this.
Figure 8 illustrates a Convergence Event without instantaneous
traffic loss for all routes. The top graph shows the Forwarding Rate
over all routes, the bottom graph shows the Forwarding Rate for a
single route Rta. Some time after the Convergence Event Instant, the
Forwarding Rate observed on the Preferred Egress Interface starts to
decrease. In the example, route Rta is the first route to experience
packet loss at time Ta. Some time later, the Forwarding Rate
observed on the Next-Best Egress Interface starts to increase. In
the example, route Rta is the first route to complete convergence at
time Ta'.
^
Fwd |
Rate |------------- ............
| \ .
| \ .
| \ .
| \ .
|.................-.-.-.-.-.-.----------------
+----+-------+---------------+----------------->
^ ^ ^ ^ time
T0 CEI Ta Ta'
^
Fwd |
Rate |------------- .................
Rta | | .
| | .
|.............-.-.-.-.-.-.-.-.----------------
+----+-------+---------------+----------------->
^ ^ ^ ^ time
T0 CEI Ta Ta'
Preferred Egress Interface: ---
Next-Best Egress Interface: ...
T0 : Start Traffic Instant
CEI : Convergence Event Instant
Ta : the time instant packet loss for route Rta starts
Ta' : the time instant packet impairment for route Rta ends
Figure 8
If only packets received on the Next-Best Egress Interface are
observed, the duration of the loss period for route Rta can be
calculated from the received packets as in Equation 1. Since the
Convergence Event Instant is the start time for convergence time
measurement, the period in time between T0 and CEI needs to be
subtracted from the calculated result to become the convergence time,
as in Equation 2.
Next-Best Egress Interface loss period
= (packets transmitted
- packets received from Next-Best Egress Interface) / tx rate
= Ta' - T0
Equation 1
convergence time
= Next-Best Egress Interface loss period - (CEI - T0)
= Ta' - CEI
Equation 2
4.2. Loss of Connectivity (LoC)
Route Loss of Connectivity Period SHOULD be measured using the Route-
Specific Loss-Derived Method. Since the start instant and end
instant of the Route Loss of Connectivity Period can be different for
each route, these cannot be accurately derived by only observing
global statistics over all routes. An example may clarify this.
Following a Convergence Event, route Rta is the first route for which
packet impairment starts; the Route Loss of Connectivity Period for
route Rta starts at time Ta. Route Rtb is the last route for which
packet impairment starts; the Route Loss of Connectivity Period for
route Rtb starts at time Tb with Tb>Ta.
^
Fwd |
Rate |-------- -----------
| \ /
| \ /
| \ /
| \ /
| ---------------
+------------------------------------------>
^ ^ ^ ^ time
Ta Tb Ta' Tb'
Tb'' Ta''
Figure 9: Example Route Loss Of Connectivity Period
If the DUT implementation were such that route Rta would be the first
route for which traffic loss ends at time Ta' (with Ta'>Tb), and
route Rtb would be the last route for which traffic loss ends at time
Tb' (with Tb'>Ta'). By only observing global traffic statistics over
all routes, the minimum Route Loss of Connectivity Period would be
measured as Ta'-Ta. The maximum calculated Route Loss of
Connectivity Period would be Tb'-Ta. The real minimum and maximum
Route Loss of Connectivity Periods are Ta'-Ta and Tb'-Tb.
Illustrating this with the numbers Ta=0, Tb=1, Ta'=3, and Tb'=5 would
give a Loss of Connectivity Period between 3 and 5 derived from the
global traffic statistics, versus the real Loss of Connectivity
Period between 3 and 4.
If the DUT implementation were such that route Rtb would be the first
for which packet loss ends at time Tb'' and route Rta would be the
last for which packet impairment ends at time Ta'', then the minimum
and maximum Route Loss of Connectivity Periods derived by observing
only global traffic statistics would be Tb''-Ta and Ta''-Ta. The
real minimum and maximum Route Loss of Connectivity Periods are
Tb''-Tb and Ta''-Ta. Illustrating this with the numbers Ta=0, Tb=1,
Ta''=5, Tb''=3 would give a Loss of Connectivity Period between 3 and
5 derived from the global traffic statistics, versus the real Loss of
Connectivity Period between 2 and 5.
The two implementation variations in the above example would result
in the same derived minimum and maximum Route Loss of Connectivity
Periods when only observing the global packet statistics, while the
real Route Loss of Connectivity Periods are different.
5. Test Considerations
5.1. IGP Selection
The test cases described in Section 8 can be used for link-state
IGPs, such as IS-IS or OSPF. The IGP convergence time test
methodology is identical.
5.2. Routing Protocol Configuration
The obtained results for IGP convergence time may vary if other
routing protocols are enabled and routes learned via those protocols
are installed. IGP convergence times SHOULD be benchmarked without
routes installed from other protocols. Any enabled IGP routing
protocol extension (such as extensions for Traffic Engineering) and
any enabled IGP routing protocol security mechanism must be reported
with the results.
5.3. IGP Topology
The Tester emulates a single IGP topology. The DUT establishes IGP
adjacencies with one or more of the emulated routers in this single
IGP topology emulated by the Tester. See test topology details in
Section 3. The emulated topology SHOULD only be advertised on the
DUT egress interfaces.
The number of IGP routes and number of nodes in the topology, and the
type of topology will impact the measured IGP convergence time. To
obtain results similar to those that would be observed in an
operational network, it is RECOMMENDED that the number of installed
routes and nodes closely approximate that of the network (e.g.,
thousands of routes with tens or hundreds of nodes).
The number of areas (for OSPF) and levels (for IS-IS) can impact the
benchmark results.
5.4. Timers
There are timers that may impact the measured IGP convergence times.
The benchmark metrics MAY be measured at any fixed values for these
timers. To obtain results similar to those that would be observed in
an operational network, it is RECOMMENDED to configure the timers
with the values as configured in the operational network.
Examples of timers that may impact measured IGP convergence time
include, but are not limited to:
Interface failure indication
IGP hello timer
IGP dead-interval or hold-timer
Link State Advertisement (LSA) or Link State Packet (LSP)
generation delay
LSA or LSP flood packet pacing
Route calculation delay
5.5. Interface Types
All test cases in this methodology document can be executed with any
interface type. The type of media may dictate which test cases may
be executed. Each interface type has a unique mechanism for
detecting link failures, and the speed at which that mechanism
operates will influence the measurement results. All interfaces MUST
be the same media and Throughput [Br91][Br99] for each test case.
All interfaces SHOULD be configured as point-to-point.
5.6. Offered Load
The Throughput of the device, as defined in [Br91] and benchmarked in
[Br99] at a fixed packet size, needs to be determined over the
preferred path and over the next-best path. The Offered Load SHOULD
be the minimum of the measured Throughput of the device over the
primary path and over the backup path. The packet size is selectable
and MUST be recorded. Packet size is measured in bytes and includes
the IP header and payload.
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 matching all
routes, but a statistically representative subset of all routes can
be used if required.
Splitting traffic flows across multiple paths (as with ECMP or
Parallel Link sets) is in general done by hashing on various fields
on the IP or contained headers. The hashing is typically based on
the IP source and destination addresses, the protocol ID, and higher-
layer flow-dependent fields such as TCP/UDP ports. In practice,
within a network core, the hashing is based mainly or exclusively on
the IP source and destination addresses. Knowledge of the hashing
algorithm used by the DUT is not always possible beforehand and would
violate the black-box spirit of this document. Therefore, it is
RECOMMENDED to use a randomly distributed range of source and
destination IP addresses, protocol IDs, and higher-layer flow-
dependent fields for the packets of the Offered Load (see also
[Ne07]). The content of the Offered Load MUST remain the same during
the test. It is RECOMMENDED to repeat a test multiple times with
different random ranges of the header fields such that convergence
time benchmarks are measured for different distributions of traffic
over the available paths.
In the Remote Interface failure test cases using topologies 3, 4, and
6, there is a possibility of a packet-forwarding loop that may occur
transiently between DUT1 and DUT2 during convergence (micro-loop, see
[Sh10]). The Time To Live (TTL) or Hop Limit value of the packets
sent by the Tester may influence the benchmark measurements since it
determines which device in the topology may send an ICMP Time
Exceeded Message for looped packets.
The duration of the Offered Load MUST be greater than the convergence
time plus the Sustained Convergence Validation Time.
Offered load should send a packet to each destination before sending
another packet to the same destination. It is RECOMMENDED that the
packets be transmitted in a round-robin fashion with a uniform
interpacket delay.
5.7. Measurement Accuracy
Since Impaired Packet count is observed to measure the Route
Convergence Time, the time between two successive packets offered to
each individual route is the highest possible accuracy of any
Impaired-Packet-based measurement. The higher the traffic rate
offered to each route, the higher the possible measurement accuracy.
Also see Section 6 for method-specific measurement accuracy.
5.8. Measurement Statistics
The benchmark measurements may vary for each trial, due to the
statistical nature of timer expirations, CPU scheduling, etc.
Evaluation of the test data must be done with an understanding of
generally accepted testing practices regarding repeatability,
variance, and statistical significance of a small number of trials.
5.9. Tester Capabilities
It is RECOMMENDED that the Tester used to execute each test case have
the following capabilities:
1. Ability to establish IGP adjacencies and advertise a single IGP
topology to one or more peers.
2. Ability to measure Forwarding Delay, Duplicate Packets, and Out-
of-Order Packets.
3. An internal time clock to control timestamping, time
measurements, and time calculations.
4. Ability to distinguish traffic load received on the Preferred and
Next-Best Interfaces [Po11t].
5. Ability to disable or tune specific Layer 2 and Layer 3 protocol
functions on any interface(s).
The Tester MAY be capable of making non-data-plane convergence
observations and using those observations for measurements. The
Tester MAY be capable of sending and receiving multiple traffic
Streams [Po06].
Also see Section 6 for method-specific capabilities.
6. Selection of Convergence Time Benchmark Metrics and Methods
Different convergence time benchmark methods MAY be used to measure
convergence time benchmark metrics. The Tester capabilities are
important criteria to select a specific convergence time benchmark
method. The criteria to select a specific benchmark method include,
but are not limited to:
Tester capabilities: Sampling Interval, number of
Stream statistics to collect
Measurement accuracy: Sampling Interval, Offered Load,
number of routes
Test specification: number of routes
DUT capabilities: Throughput, IP Packet Delay
Variation
6.1. Loss-Derived Method
6.1.1. Tester Capabilities
To enable collecting statistics of Out-of-Order Packets per flow (see
[Th00], Section 3), the Offered Load SHOULD consist of multiple
Streams [Po06], and each Stream SHOULD consist of a single flow. If
sending multiple Streams, the measured traffic statistics for all
Streams MUST be added together.
In order to verify Full Convergence completion and the Sustained
Convergence Validation Time, the Tester MUST measure Forwarding Rate
each Packet Sampling Interval.
The total number of Impaired Packets between the start of the traffic
and the end of the Sustained Convergence Validation Time is used to
calculate the Loss-Derived Convergence Time.
6.1.2. Benchmark Metrics
The Loss-Derived Method can be used to measure the Loss-Derived
Convergence Time, which is the average convergence time over all
routes, and to measure the Loss-Derived Loss of Connectivity Period,
which is the average Route Loss of Connectivity Period over all
routes.
6.1.3. Measurement Accuracy
The actual value falls within the accuracy interval [-(number of
destinations/Offered Load), +(number of destinations/Offered Load)]
around the value as measured using the Loss-Derived Method.
6.2. Rate-Derived Method
6.2.1. Tester Capabilities
To enable collecting statistics of Out-of-Order Packets per flow (see
[Th00], Section 3), the Offered Load SHOULD consist of multiple
Streams [Po06], and each Stream SHOULD consist of a single flow. If
sending multiple Streams, the measured traffic statistics for all
Streams MUST be added together.
The Tester measures Forwarding Rate each Sampling Interval. The
Packet Sampling Interval influences the observation of the different
convergence time instants. If the Packet Sampling Interval is large
compared to the time between the convergence time instants, then the
different time instants may not be easily identifiable from the
Forwarding Rate observation. The presence of IP Packet Delay
Variation (IPDV) [De02] may cause fluctuations of the Forwarding Rate
observation and can prevent correct observation of the different
convergence time instants.
The Packet Sampling Interval MUST be larger than or equal to the time
between two consecutive packets to the same destination. For maximum
accuracy, the value for the Packet Sampling Interval SHOULD be as
small as possible, but the presence of IPDV may require the use of a
larger Packet Sampling Interval. The Packet Sampling Interval MUST
be reported.
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
minimum and maximum number of packets expected in a Packet Sampling
Interval in presence of IPDV can be calculated with Equation 3.
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)
where minDelay and maxDelay indicate (respectively) the minimum and
maximum Forwarding Delay of packets received during the Packet
Sampling Interval
Equation 3
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 3.
6.2.2. Benchmark Metrics
The Rate-Derived Method SHOULD be used to measure First Route
Convergence Time and Full Convergence Time. It SHOULD NOT be used to
measure Loss of Connectivity Period (see Section 4).
6.2.3. Measurement Accuracy
The measurement accuracy interval of the Rate-Derived Method depends
on the metric being measured or calculated and the characteristics of
the related transition. IP Packet Delay Variation (IPDV) [De02] adds
uncertainty to the amount of packets received in a Packet Sampling
Interval, and this uncertainty adds to the measurement error. The
effect of IPDV is not accounted for in the calculation of the
accuracy intervals below. IPDV is of importance for the convergence
instants where a variation in Forwarding Rate needs to be observed.
This is applicable to the Convergence Recovery Instant for all
topologies, and for topologies with ECMP it also applies to the
Convergence Event Instant and the First Route Convergence Instant.
and for topologies with ECMP also Convergence Event Instant and First
Route Convergence Instant).
If the Convergence Event Instant is observed on the data plane using
the Rate Derived Method, it needs to be instantaneous for all routes
(see Section 4.1). The actual value of the Convergence Event Instant
falls within the accuracy interval [-(Packet Sampling Interval +
1/Offered Load), +0] around the value as measured using the Rate-
Derived Method.
If the Convergence Recovery Transition is non-instantaneous for all
routes, then the actual value of the First Route Convergence Instant
falls within the accuracy interval [-(Packet Sampling Interval + time
between two consecutive packets to the same destination), +0] around
the value as measured using the Rate-Derived Method, and the actual
value of the Convergence Recovery Instant falls within the accuracy
interval [-(2 * Packet Sampling Interval), -(Packet Sampling Interval
- time between two consecutive packets to the same destination)]
around the value as measured using the Rate-Derived Method.
The term "time between two consecutive packets to the same
destination" is added in the above accuracy intervals since packets
are sent in a particular order to all destinations in a stream, and
when part of the routes experience packet loss, it is unknown where
in the transmit cycle packets to these routes are sent. This
uncertainty adds to the error.
The accuracy intervals of the derived metrics First Route Convergence
Time and Rate-Derived Convergence Time are calculated from the above
convergence instants accuracy intervals. The actual value of First
Route Convergence Time falls within the accuracy interval [-(Packet
Sampling Interval + time between two consecutive packets to the same
destination), +(Packet Sampling Interval + 1/Offered Load)] around
the calculated value. The actual value of Rate-Derived Convergence
Time falls within the accuracy interval [-(2 * Packet Sampling
Interval), +(time between two consecutive packets to the same
destination + 1/Offered Load)] around the calculated value.
6.3. Route-Specific Loss-Derived Method
6.3.1. Tester Capabilities
The Offered Load consists of multiple Streams. The Tester MUST
measure Impaired Packet count for each Stream separately.
In order to verify Full Convergence completion and the Sustained
Convergence Validation Time, the Tester MUST measure Forwarding Rate
each Packet Sampling Interval. This measurement at each Packet
Sampling Interval MAY be per Stream.
Only the total number of Impaired Packets measured per Stream at the
end of the Sustained Convergence Validation Time is used to calculate
the benchmark metrics with this method.
6.3.2. Benchmark Metrics
The Route-Specific Loss-Derived Method SHOULD be used to measure
Route-Specific Convergence Times. It is the RECOMMENDED method to
measure Route Loss of Connectivity Period.
Under the conditions explained in Section 4, First Route Convergence
Time and Full Convergence Time, as benchmarked using Rate-Derived
Method, may be equal to the minimum and maximum (respectively) of the
Route-Specific Convergence Times.
6.3.3. Measurement Accuracy
The actual value falls within the accuracy interval [-(number of
destinations/Offered Load), +(number of destinations/Offered Load)]
around the value as measured using the Route-Specific Loss-Derived
Method.
7. Reporting Format
For each test case, it is RECOMMENDED that the reporting tables below
be completed. All time values SHOULD be reported with a sufficiently
high resolution (fractions of a second sufficient to distinguish
significant differences between measured values).
Parameter Units
------------------------------------- ---------------------------
Test Case test case number
Test Topology Test Topology Figure number
IGP (IS-IS, OSPF, other)
Interface Type (GigE, POS, ATM, other)
Packet Size offered to DUT bytes
Offered Load packets per second
IGP Routes Advertised to DUT number of IGP routes
Nodes in Emulated Network number of nodes
Number of Parallel or ECMP links number of links
Number of Routes Measured number of routes
Packet Sampling Interval on Tester seconds
Forwarding Delay Threshold seconds
Timer Values configured on DUT:
Interface Failure Indication Delay seconds
IGP Hello Timer seconds
IGP Dead-Interval or Hold-Time seconds
LSA/LSP Generation Delay seconds
LSA/LSP Flood Packet Pacing seconds
LSA/LSP Retransmission Packet Pacing seconds
Route Calculation Delay seconds
Test Details:
Describe the IGP extensions and IGP security mechanisms that are
configured on the DUT.
Describe how the various fields on the IP and contained headers
for the packets for the Offered Load are generated (Section 5.6).
If the Offered Load matches a subset of routes, describe how this
subset is selected.
Describe how the Convergence Event is applied; does it cause
instantaneous traffic loss or not?
The table below should be completed for the initial Convergence Event
and the reversion Convergence Event.
Parameter Units
------------------------------------------- ----------------------
Convergence Event (initial or reversion)
Traffic Forwarding Metrics:
Total number of packets offered to DUT number of packets
Total number of packets forwarded by DUT number of packets
Connectivity Packet Loss number of packets
Convergence Packet Loss number of packets
Out-of-Order Packets number of packets
Duplicate Packets number of packets
Excessive Forwarding Delay Packets number of packets
Convergence Benchmarks:
Rate-Derived Method:
First Route Convergence Time seconds
Full Convergence Time seconds
Loss-Derived Method:
Loss-Derived Convergence Time seconds
Route-Specific Loss-Derived Method:
Route-Specific Convergence Time[n] array of seconds
Minimum Route-Specific Convergence Time seconds
Maximum Route-Specific Convergence Time seconds
Median Route-Specific Convergence Time seconds
Average Route-Specific Convergence Time seconds
Loss of Connectivity Benchmarks:
Loss-Derived Method:
Loss-Derived Loss of Connectivity Period seconds
Route-Specific Loss-Derived Method:
Route Loss of Connectivity Period[n] array of seconds
Minimum Route Loss of Connectivity Period seconds
Maximum Route Loss of Connectivity Period seconds
Median Route Loss of Connectivity Period seconds
Average Route Loss of Connectivity Period seconds
8. Test Cases
It is RECOMMENDED that all applicable test cases be performed for
best characterization of the DUT. The test cases follow a generic
procedure tailored to the specific DUT configuration and Convergence
Event [Po11t]. This generic procedure is as follows:
1. Establish DUT and Tester configurations and advertise an IGP
topology from Tester to DUT.
2. Send Offered Load from Tester to DUT on Ingress Interface.
3. Verify traffic is routed correctly. Verify if traffic is
forwarded without Impaired Packets [Po06].
4. Introduce Convergence Event [Po11t].
5. Measure First Route Convergence Time [Po11t].
6. Measure Full Convergence Time [Po11t].
7. Stop Offered Load.
8. Measure Route-Specific Convergence Times, Loss-Derived
Convergence Time, Route Loss of Connectivity Periods, and Loss-
Derived Loss of Connectivity Period [Po11t]. At the same time,
measure number of Impaired Packets [Po11t].
9. Wait sufficient time for queues to drain. The duration of this
time period MUST be larger than or equal to the Forwarding Delay
Threshold.
10. Restart Offered Load.
11. Reverse Convergence Event.
12. Measure First Route Convergence Time.
13. Measure Full Convergence Time.
14. Stop Offered Load.
15. Measure Route-Specific Convergence Times, Loss-Derived
Convergence Time, Route Loss of Connectivity Periods, and Loss-
Derived Loss of Connectivity Period. At the same time, measure
number of Impaired Packets [Po11t].
8.1. Interface Failure and Recovery
8.1.1. Convergence Due to Local Interface Failure and Recovery
Objective:
To obtain the IGP convergence measurements for Local Interface
failure and recovery events. The Next-Best Egress Interface can
be a single interface (Figure 1) or an ECMP set (Figure 2). The
test with ECMP topology (Figure 2) is OPTIONAL.
Procedure:
1. Advertise an IGP topology from Tester to DUT using the topology
shown in Figures 1 or 2.
2. Send Offered Load from Tester to DUT on Ingress Interface.
3. Verify traffic is forwarded over Preferred Egress Interface.
4. Remove link on the Preferred Egress Interface of the DUT. This
is the Convergence Event.
5. Measure First Route Convergence Time.
6. Measure Full Convergence Time.
7. Stop Offered Load.
8. Measure Route-Specific Convergence Times and Loss-Derived
Convergence Time. At the same time, measure number of Impaired
Packets.
9. Wait sufficient time for queues to drain.
10. Restart Offered Load.
11. Restore link on the Preferred Egress Interface of the DUT.
12. Measure First Route Convergence Time.
13. Measure Full Convergence Time.
14. Stop Offered Load.
15. Measure Route-Specific Convergence Times, Loss-Derived
Convergence Time, Route Loss of Connectivity Periods, and Loss-
Derived Loss of Connectivity Period. At the same time, measure
number of Impaired Packets.
8.1.2. Convergence Due to Remote Interface Failure and Recovery
Objective:
To obtain the IGP convergence measurements for Remote Interface
failure and recovery events. The Next-Best Egress Interface can
be a single interface (Figure 3) or an ECMP set (Figure 4). The
test with ECMP topology (Figure 4) is OPTIONAL.
Procedure:
1. Advertise an IGP topology from Tester to SUT using the topology
shown in Figures 3 or 4.
2. Send Offered Load from Tester to SUT on Ingress Interface.
3. Verify traffic is forwarded over Preferred Egress Interface.
4. Remove link on the interface of the Tester connected to the
Preferred Egress Interface of the SUT. This is the Convergence
Event.
5. Measure First Route Convergence Time.
6. Measure Full Convergence Time.
7. Stop Offered Load.
8. Measure Route-Specific Convergence Times and Loss-Derived
Convergence Time. At the same time, measure number of Impaired
Packets.
9. Wait sufficient time for queues to drain.
10. Restart Offered Load.
11. Restore link on the interface of the Tester connected to the
Preferred Egress Interface of the SUT.
12. Measure First Route Convergence Time.
13. Measure Full Convergence Time.
14. Stop Offered Load.
15. Measure Route-Specific Convergence Times, Loss-Derived
Convergence Time, Route Loss of Connectivity Periods, and Loss-
Derived Loss of Connectivity Period. At the same time, measure
number of Impaired Packets.
Discussion:
In this test case, there is a possibility of a packet-forwarding
loop that may occur transiently between DUT1 and DUT2 during
convergence (micro-loop, see [Sh10]), which may increase the
measured convergence times and loss of connectivity periods.
8.1.3. Convergence Due to ECMP Member Local Interface Failure and
Recovery
Objective:
To obtain the IGP convergence measurements for Local Interface
link failure and recovery events of an ECMP Member.
Procedure:
1. Advertise an IGP topology from Tester to DUT using the test
setup shown in Figure 5.
2. Send Offered Load from Tester to DUT on Ingress Interface.
3. Verify traffic is forwarded over the ECMP member interface of
the DUT that will be failed in the next step.
4. Remove link on one of the ECMP member interfaces of the DUT.
This is the Convergence Event.
5. Measure First Route Convergence Time.
6. Measure Full Convergence Time.
7. Stop Offered Load.
8. Measure Route-Specific Convergence Times and Loss-Derived
Convergence Time. At the same time, measure number of Impaired
Packets.
9. Wait sufficient time for queues to drain.
10. Restart Offered Load.
11. Restore link on the ECMP member interface of the DUT.
12. Measure First Route Convergence Time.
13. Measure Full Convergence Time.
14. Stop Offered Load.
15. Measure Route-Specific Convergence Times, Loss-Derived
Convergence Time, Route Loss of Connectivity Periods, and Loss-
Derived Loss of Connectivity Period. At the same time, measure
number of Impaired Packets.
8.1.4. Convergence Due to ECMP Member Remote Interface Failure and
Recovery
Objective:
To obtain the IGP convergence measurements for Remote Interface
link failure and recovery events for an ECMP Member.
Procedure:
1. Advertise an IGP topology from Tester to DUT using the test
setup shown in Figure 6.
2. Send Offered Load from Tester to DUT on Ingress Interface.
3. Verify traffic is forwarded over the ECMP member interface of
the DUT that will be failed in the next step.
4. Remove link on the interface of the Tester to R2. This is the
Convergence Event Trigger.
5. Measure First Route Convergence Time.
6. Measure Full Convergence Time.
7. Stop Offered Load.
8. Measure Route-Specific Convergence Times and Loss-Derived
Convergence Time. At the same time, measure number of Impaired
Packets.
9. Wait sufficient time for queues to drain.
10. Restart Offered Load.
11. Restore link on the interface of the Tester to R2.
12. Measure First Route Convergence Time.
13. Measure Full Convergence Time.
14. Stop Offered Load.
15. Measure Route-Specific Convergence Times, Loss-Derived
Convergence Time, Route Loss of Connectivity Periods, and Loss-
Derived Loss of Connectivity Period. At the same time, measure
number of Impaired Packets.
Discussion:
In this test case, there is a possibility of a packet-forwarding
loop that may occur temporarily between DUT1 and DUT2 during
convergence (micro-loop, see [Sh10]), which may increase the
measured convergence times and loss of connectivity periods.
8.1.5. Convergence Due to Parallel Link Interface Failure and Recovery
Objective:
To obtain the IGP convergence measurements for local link failure
and recovery events for a member of a parallel link. The links
can be used for data load-balancing
Procedure:
1. Advertise an IGP topology from Tester to DUT using the test
setup shown in Figure 7.
2. Send Offered Load from Tester to DUT on Ingress Interface.
3. Verify traffic is forwarded over the parallel link member that
will be failed in the next step.
4. Remove link on one of the parallel link member interfaces of the
DUT. This is the Convergence Event.
5. Measure First Route Convergence Time.
6. Measure Full Convergence Time.
7. Stop Offered Load.
8. Measure Route-Specific Convergence Times and Loss-Derived
Convergence Time. At the same time, measure number of Impaired
Packets.
9. Wait sufficient time for queues to drain.
10. Restart Offered Load.
11. Restore link on the Parallel Link member interface of the DUT.
12. Measure First Route Convergence Time.
13. Measure Full Convergence Time.
14. Stop Offered Load.
15. Measure Route-Specific Convergence Times, Loss-Derived
Convergence Time, Route Loss of Connectivity Periods, and Loss-
Derived Loss of Connectivity Period. At the same time, measure
number of Impaired Packets.
8.2. Other Failures and Recoveries
8.2.1. Convergence Due to Layer 2 Session Loss and Recovery
Objective:
To obtain the IGP convergence measurements for a local Layer 2
loss and recovery.
Procedure:
1. Advertise an IGP topology from Tester to DUT using the topology
shown in Figure 1.
2. Send Offered Load from Tester to DUT on Ingress Interface.
3. Verify traffic is routed over Preferred Egress Interface.
4. Remove Layer 2 session from Preferred Egress Interface of the
DUT. This is the Convergence Event.
5. Measure First Route Convergence Time.
6. Measure Full Convergence Time.
7. Stop Offered Load.
8. Measure Route-Specific Convergence Times, Loss-Derived
Convergence Time, Route Loss of Connectivity Periods, and Loss-
Derived Loss of Connectivity Period. At the same time, measure
number of Impaired Packets.
9. Wait sufficient time for queues to drain.
10. Restart Offered Load.
11. Restore Layer 2 session on Preferred Egress Interface of the
DUT.
12. Measure First Route Convergence Time.
13. Measure Full Convergence Time.
14. Stop Offered Load.
15. Measure Route-Specific Convergence Times, Loss-Derived
Convergence Time, Route Loss of Connectivity Periods, and Loss-
Derived Loss of Connectivity Period. At the same time, measure
number of Impaired Packets.
Discussion:
When removing the Layer 2 session, the physical layer must stay
up. Configure IGP timers such that the IGP adjacency does not
time out before Layer 2 failure is detected.
To measure convergence time, traffic SHOULD start dropping on the
Preferred Egress Interface on the instant the Layer 2 session is
removed. Alternatively, the Tester SHOULD record the time the
instant Layer 2 session is removed, and traffic loss SHOULD only
be measured on the Next-Best Egress Interface. For loss-derived
benchmarks, the time of the Start Traffic Instant SHOULD be
recorded as well. See Section 4.1.
8.2.2. Convergence Due to Loss and Recovery of IGP Adjacency
Objective:
To obtain the IGP convergence measurements for loss and recovery
of an IGP Adjacency. The IGP adjacency is removed on the Tester
by disabling processing of IGP routing protocol packets on the
Tester.
Procedure:
1. Advertise an IGP topology from Tester to DUT using the topology
shown in Figure 1.
2. Send Offered Load from Tester to DUT on Ingress Interface.
3. Verify traffic is routed over Preferred Egress Interface.
4. Remove IGP adjacency from the Preferred Egress Interface while
the Layer 2 session MUST be maintained. This is the Convergence
Event.
5. Measure First Route Convergence Time.
6. Measure Full Convergence Time.
7. Stop Offered Load.
8. Measure Route-Specific Convergence Times, Loss-Derived
Convergence Time, Route Loss of Connectivity Periods, and Loss-
Derived Loss of Connectivity Period. At the same time, measure
number of Impaired Packets.
9. Wait sufficient time for queues to drain.
10. Restart Offered Load.
11. Restore IGP session on Preferred Egress Interface of the DUT.
12. Measure First Route Convergence Time.
13. Measure Full Convergence Time.
14. Stop Offered Load.
15. Measure Route-Specific Convergence Times, Loss-Derived
Convergence Time, Route Loss of Connectivity Periods, and Loss-
Derived Loss of Connectivity Period. At the same time, measure
number of Impaired Packets.
Discussion:
Configure Layer 2 such that Layer 2 does not time out before IGP
adjacency failure is detected.
To measure convergence time, traffic SHOULD start dropping on the
Preferred Egress Interface on the instant the IGP adjacency is
removed. Alternatively, the Tester SHOULD record the time the
instant the IGP adjacency is removed and traffic loss SHOULD only
be measured on the Next-Best Egress Interface. For loss-derived
benchmarks, the time of the Start Traffic Instant SHOULD be
recorded as well. See Section 4.1.
8.2.3. Convergence Due to Route Withdrawal and Re-Advertisement
Objective:
To obtain the IGP convergence measurements for route withdrawal
and re-advertisement.
Procedure:
1. Advertise an IGP topology from Tester to DUT using the topology
shown in Figure 1. The routes that will be withdrawn MUST be a
set of leaf routes advertised by at least two nodes in the
emulated topology. The topology SHOULD be such that before the
withdrawal the DUT prefers the leaf routes advertised by a node
"nodeA" via the Preferred Egress Interface, and after the
withdrawal the DUT prefers the leaf routes advertised by a node
"nodeB" via the Next-Best Egress Interface.
2. Send Offered Load from Tester to DUT on Ingress Interface.
3. Verify traffic is routed over Preferred Egress Interface.
4. The Tester withdraws the set of IGP leaf routes from nodeA.
This is the Convergence Event. The withdrawal update message
SHOULD be a single unfragmented packet. If the routes cannot be
withdrawn by a single packet, the messages SHOULD be sent using
the same pacing characteristics as the DUT. The Tester MAY
record the time it sends the withdrawal message(s).
5. Measure First Route Convergence Time.
6. Measure Full Convergence Time.
7. Stop Offered Load.
8. Measure Route-Specific Convergence Times, Loss-Derived
Convergence Time, Route Loss of Connectivity Periods, and Loss-
Derived Loss of Connectivity Period. At the same time, measure
number of Impaired Packets.
9. Wait sufficient time for queues to drain.
10. Restart Offered Load.
11. Re-advertise the set of withdrawn IGP leaf routes from nodeA
emulated by the Tester. The update message SHOULD be a single
unfragmented packet. If the routes cannot be advertised by a
single packet, the messages SHOULD be sent using the same pacing
characteristics as the DUT. The Tester MAY record the time it
sends the update message(s).
12. Measure First Route Convergence Time.
13. Measure Full Convergence Time.
14. Stop Offered Load.
15. Measure Route-Specific Convergence Times, Loss-Derived
Convergence Time, Route Loss of Connectivity Periods, and Loss-
Derived Loss of Connectivity Period. At the same time, measure
number of Impaired Packets.
Discussion:
To measure convergence time, traffic SHOULD start dropping on the
Preferred Egress Interface on the instant the routes are withdrawn
by the Tester. Alternatively, the Tester SHOULD record the time
the instant the routes are withdrawn, and traffic loss SHOULD only
be measured on the Next-Best Egress Interface. For loss-derived
benchmarks, the time of the Start Traffic Instant SHOULD be
recorded as well. See Section 4.1.
8.3. Administrative Changes
8.3.1. Convergence Due to Local Interface Administrative Changes
Objective:
To obtain the IGP convergence measurements for administratively
disabling and enabling a Local Interface.
Procedure:
1. Advertise an IGP topology from Tester to DUT using the topology
shown in Figure 1.
2. Send Offered Load from Tester to DUT on Ingress Interface.
3. Verify traffic is routed over Preferred Egress Interface.
4. Administratively disable the Preferred Egress Interface of the
DUT. This is the Convergence Event.
5. Measure First Route Convergence Time.
6. Measure Full Convergence Time.
7. Stop Offered Load.
8. Measure Route-Specific Convergence Times, Loss-Derived
Convergence Time, Route Loss of Connectivity Periods, and Loss-
Derived Loss of Connectivity Period. At the same time, measure
number of Impaired Packets.
9. Wait sufficient time for queues to drain.
10. Restart Offered Load.
11. Administratively enable the Preferred Egress Interface of the
DUT.
12. Measure First Route Convergence Time.
13. Measure Full Convergence Time.
14. Stop Offered Load.
15. Measure Route-Specific Convergence Times, Loss-Derived
Convergence Time, Route Loss of Connectivity Periods, and Loss-
Derived Loss of Connectivity Period. At the same time, measure
number of Impaired Packets.
8.3.2. Convergence Due to Cost Change
Objective:
To obtain the IGP convergence measurements for route cost change.
Procedure:
1. Advertise an IGP topology from Tester to DUT using the topology
shown in Figure 1.
2. Send Offered Load from Tester to DUT on Ingress Interface.
3. Verify traffic is routed over Preferred Egress Interface.
4. The Tester, emulating the neighbor node, increases the cost for
all IGP routes at the Preferred Egress Interface of the DUT so
that the Next-Best Egress Interface becomes the preferred path.
The update message advertising the higher cost MUST be a single
unfragmented packet. This is the Convergence Event. The Tester
MAY record the time it sends the update message advertising the
higher cost on the Preferred Egress Interface.
5. Measure First Route Convergence Time.
6. Measure Full Convergence Time.
7. Stop Offered Load.
8. Measure Route-Specific Convergence Times, Loss-Derived
Convergence Time, Route Loss of Connectivity Periods, and Loss-
Derived Loss of Connectivity Period. At the same time, measure
number of Impaired Packets.
9. Wait sufficient time for queues to drain.
10. Restart Offered Load.
11. The Tester, emulating the neighbor node, decreases the cost for
all IGP routes at the Preferred Egress Interface of the DUT so
that the Preferred Egress Interface becomes the preferred path.
The update message advertising the lower cost MUST be a single
unfragmented packet.
12. Measure First Route Convergence Time.
13. Measure Full Convergence Time.
14. Stop Offered Load.
15. Measure Route-Specific Convergence Times, Loss-Derived
Convergence Time, Route Loss of Connectivity Periods, and Loss-
Derived Loss of Connectivity Period. At the same time, measure
number of Impaired Packets.
Discussion:
To measure convergence time, traffic SHOULD start dropping on the
Preferred Egress Interface on the instant the cost is changed by
the Tester. Alternatively, the Tester SHOULD record the time the
instant the cost is changed, and traffic loss SHOULD only be
measured on the Next-Best Egress Interface. For loss-derived
benchmarks, the time of the Start Traffic Instant SHOULD be
recorded as well. See Section 4.1.
9. 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 "black-box" 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.
10. Acknowledgements
Thanks to Sue Hares, Al Morton, Kevin Dubray, Ron Bonica, David Ward,
Peter De Vriendt, Anuj Dewagan, Julien Meuric, Adrian Farrel, Stewart
Bryant, and the Benchmarking Methodology Working Group for their
contributions to this work.
11. References
11.1. 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 IS-IS for routing in TCP/IP and dual
environments", RFC 1195, December 1990.
[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 IS-IS", RFC 5308,
October 2008.
[Ko02] Koodli, R. and R. Ravikanth, "One-way Loss Pattern Sample
Metrics", RFC 3357, August 2002.
[Ma05] Manral, V., White, R., and A. Shaikh, "Benchmarking Basic
OSPF Single Router Control Plane Convergence", RFC 4061,
April 2005.
[Ma05c] Manral, V., White, R., and A. Shaikh, "Considerations When
Using Basic OSPF Convergence Benchmarks", RFC 4063,
April 2005.
[Ma05t] Manral, V., White, R., and A. Shaikh, "OSPF Benchmarking
Terminology and Concepts", RFC 4062, April 2005.
[Ma98] Mandeville, R., "Benchmarking Terminology for LAN Switching
Devices", RFC 2285, February 1998.
[Mo98] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[Ne07] Newman, D. and T. Player, "Hash and Stuffing: Overlooked
Factors in Network Device Benchmarking", RFC 4814,
March 2007.
[Pa05] Pan, P., Swallow, G., and A. Atlas, "Fast Reroute Extensions
to RSVP-TE for LSP Tunnels", RFC 4090, May 2005.
[Po06] Poretsky, S., Perser, J., Erramilli, S., and S. Khurana,
"Terminology for Benchmarking Network-layer Traffic Control
Mechanisms", RFC 4689, October 2006.
[Po11t] Poretsky, S., Imhoff, B., and K. Michielsen, "Terminology
for Benchmarking Link-State IGP Data-Plane Route
Convergence", RFC 6412, November 2011.
[Sh10] Shand, M. and S. Bryant, "A Framework for Loop-Free
Convergence", RFC 5715, January 2010.
[Sh10i] Shand, M. and S. Bryant, "IP Fast Reroute Framework",
RFC 5714, January 2010.
[Th00] Thaler, D. and C. Hopps, "Multipath Issues in Unicast and
Multicast Next-Hop Selection", RFC 2991, November 2000.
11.2. Informative References
[Al00] Alaettinoglu, C., Jacobson, V., and H. Yu, "Towards
Millisecond IGP Convergence", NANOG 20, October 2000.
[Al02] Alaettinoglu, C. and S. Casner, "ISIS Routing on the Qwest
Backbone: a Recipe for Subsecond ISIS Convergence",
NANOG 24, February 2002.
[Fi02] Filsfils, C., "Tutorial: Deploying Tight-SLA Services on an
Internet Backbone: ISIS Fast Convergence and Differentiated
Services Design", NANOG 25, June 2002.
[Fr05] Francois, P., Filsfils, C., Evans, J., and O. Bonaventure,
"Achieving SubSecond IGP Convergence in Large IP Networks",
ACM SIGCOMM Computer Communication Review v.35 n.3,
July 2005.
[Ka02] Katz, D., "Why are we scared of SPF? IGP Scaling and
Stability", NANOG 25, June 2002.
[Vi02] Villamizar, C., "Convergence and Restoration Techniques for
ISP Interior Routing", NANOG 25, June 2002.
Authors' Addresses
Scott Poretsky
Allot Communications
300 TradeCenter
Woburn, MA 01801
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