Network Working Group S. Poretsky
Internet Draft Allot Communications
Expires: September 08, 2009
Intended Status: Informational March 08, 2009
Considerations for Benchmarking
Link-State IGP Data Plane Route Convergence
<draft-ietf-bmwg-igp-dataplane-conv-app-17.txt>
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ABSTRACT
This document discusses considerations for benchmarking Interior
Gateway Protocol (IGP) Route Convergence for any link-state IGP, such
as Intermediate System-Intermediate System (ISIS) and Open-Shorted
Path first (OSPF). A companion methodology document is to
be used for benchmarking IGP convergence time through externally
observable (black box) data plane measurements. A companion
terminology document is to be referenced to support the benchmarking.
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Table of Contents
1. Introduction ...............................................2
2. Existing definitions .......................................2
3. Factors for IGP Route Convergence Time......................2
4. Network Events that Cause Route Convergence.................3
5. Use of Data Plane for IGP Route Convergence Benchmarking....4
6. IANA Considerations.........................................4
7. Security Considerations.....................................4
8. Acknowledgements............................................5
9. Normative References........................................5
10. Author's Address...........................................6
1. Introduction
Convergence Time is a critical performance parameter. Customers
of Service Providers use convergence packet loss [Po07t] due to
Interior Gateway Protocol (IGP) convergence as a key metric of
their network service quality. Service Providers use IGP
Convergence time as a key metric of router design and architecture
for any IGP such as Intermediate System - Intermediate System
(ISIS) [Ca90] and Open-Shorted Path first (OSPF) [Mo98]. Fast
network convergence can be optimally achieved through deployment
of fast converging routers. The fundamental basis by which network
users and operators benchmark convergence is packet loss, which is
an externally observable event having direct impact on their
application performance.
IGP Route Convergence is a Direct Measure of Quality (DMOQ) when
benchmarking the data plane. For this reason it is important to
develop a standard router benchmarking methodology and terminology
for measuring IGP convergence that uses the data plane as described
in [Po07m] and [Po07t]. This document describes all of the factors
that influence a convergence measurement and how a purely black box
test can be designed to account for all of these factors. This
enables accurate benchmarking and evaluation for route convergence
time.
2. Existing definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in BCP 14, RFC
2119 [Br97]. RFC 2119 defines the use of these key words to help
make the intent of standards track documents as clear as possible.
While this document uses these keywords, this document is not a
standards track document.
3. Factors for IGP Route Convergence Time
There are four major categories of factors contributing to the
measured Router IGP Convergence Time. As discussed in [Vi02],
[Ka02], [Fi02], [Al02] and [Al00], these categories are Event
Detection, Shortest Path First (SPF) Processing, IGP Advertisement,
and Forwarding Information Base (FIB) Update. These have numerous
components that influence the convergence time, as listed below:
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-Event Detection-
Physical Layer failure/recovery indication time
Layer 2 failure/recovery indication time
IGP Hello Dead Interval
-SPF Processing-
SPF Delay Time
SPF Hold time
SPF Execution time
-IGP Advertisement-
LSA/LSP Flood Packet Pacing
LSA/LSP Retransmission Packet Pacing
LSA/LSP Generation time
-FIB Update-
Tree Build time
Hardware Update time
-Increased Forwarding Delay due to Queueing
The contribution of each of these factors listed above will vary
with each router vendors' architecture and IGP implementation.
Routers may have a centralized forwarding architecture, in which
one route table is calculated and referenced for all arriving
packets, or a distributed forwarding architecture, in which the
central route table is calculated and distributed to the
interfaces for local look-up as packets arrive. The distributed
route tables are typically maintained in hardware.
It is therefore necessary to design a convergence test that
considers all of these components contributing to convergence time
and is independent of the Device Under Test (DUT) architecture,
The benefit of designing a test for these considerations is that
it enables black-box testing in which knowledge of the routers'
internal implementations is not required. It is then possible
to make valid use of the convergence benchmarking metrics when
comparing routers from different vendors.
4. Network Events that Cause Convergence
There are different types of network events that can cause IGP
convergence. These network events are as follow:
* administrative link removal
* unplanned link failure
* line card failure
* route changes such as withdrawal, flap, next-hop change,
and cost change.
* session loss due to loss of peer or adjacency
* link recovery
* link insertion
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When benchmarking a router it is important to measure convergence
time for local and remote occurrence of these network events.
The convergence time measured will vary whether the network event
occurred locally or remotely due to varying combinations of
factors listed in the previous sections. This behavior makes it
possible to design purely black-box tests that isolate
measurements for each of the components of convergence time.
5. Use of Data Plane for IGP Route Convergence Benchmarking
Customers of service providers use packet loss as the metric to
calculate convergence time. Packet loss is an externally
observable event having direct impact on customers' application
performance. For this reason it is important to develop a
standard router benchmarking methodology and terminology that is
a Direct Measure of Quality (DMOQ) for measuring IGP convergence.
Such a methodology uses the data plane as described in [Po07m]
using the terminology provided in [Po07t].
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 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.
Use of data traffic and measurement of packet loss on the data
plane also enables Route Convergence methodology test cases that
consider the time for the Route Controller to update the FIB on
the forwarding engine of the hardware. A router is not fully
converged until all components are updated and traffic is
rerouted to the correct egress interface. As long as there is
packet loss, routes have not converged. It is possible to send
diverse traffic flows to destinations matching every route in
the FIB so that the time it takes for the router to converge an
entire route table can be benchmarked.
6. IANA Considerations
This document requires no IANA considerations.
7. Security Considerations
Documents of this type do not directly affect the security of
Internet or corporate networks as long as benchmarking is not
performed on devices or systems connected to production networks.
Security threats and how to counter these in SIP and the media
layer is discussed in RFC3261, RFC3550, and RFC3711 and various
other drafts. This document attempts to formalize a set of
common methodology for benchmarking IGP convergence performance
in a lab environment.
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8. Acknowledgements
Thanks to Curtis Villamizar for sharing so much of his knowledge
and experience through the years. Thanks to Ron Bonica, Al Morton,
David Ward, and the BMWG for their reviews and comments.
9. References
9.1 Normative References
[Br97] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997
[Ca90] Callon, R., "Use of OSI IS-IS for Routing in TCP/IP
and Dual Environments", RFC 1195, December 1990.
[Mo98] Moy, J., "OSPF Version 2", RFC 2328, IETF, April 1998.
[Po07m] Poretsky, S., "Benchmarking Methodology for
Link-State IGP Data Plane Route Convergence",
draft-ietf-bmwg-igp-dataplane-conv-meth-17, work in
progress, March 2009.
[Po07t] Poretsky, S., "Benchmarking Terminology for
Link-State IGP Data Plane Route Convergence",
draft-ietf-bmwg-igp-dataplane-conv-term-17, work in
progress, March 2009.
9.2 Informative References
[Al00] Alaettinoglu, C., Jacobson, V., and Yu, H., "Towards
Millisecond IGP Convergence", NANOG 20, March 2000.
[Al02] Alaettinoglu, C. and Casner, S., "ISIS Routing on the
Qwest Backbone: a Recipe for Subsecond ISIS Convergence",
NANOG 24, March 2002.
[Fi02] Filsfils, C., "Deploying Tight-SLA Services on an
Internet Backbone: ISIS Fast Convergence and
Differentiated Services Design (tutorial)", NANOG 25,
March 2002.
[Ka02] Katz, D., "Why are we Scared of SPF? IGP Scaling and
Stability", NANOG 25, March 2002.
[Vi02] Villamizar, C., "Convergence and Restoration Techniques
for ISP Interior Routing", NANOG 25, March 2002.
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10. Author's Address
Scott Poretsky
Allot Communications
67 South Bedford Street, Suite 400
Burlington, MA 01803
USA
Phone: + 1 508 309 2179
Email: sporetsky@allot.com
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