Network Working Group
INTERNET-DRAFT
Expires in: January 2006
Scott Poretsky
Reef Point Systems
July 2005
Considerations for Benchmarking
IGP Data Plane Route Convergence
<draft-ietf-bmwg-igp-dataplane-conv-app-07.txt>
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ABSTRACT
This draft provides considerations for IGP Route Convergence
benchmarking methodology [1] and IGP Route Convergence benchmarking
terminology [2]. The methodology and terminology is to be used
for benchmarking route convergence and can be applied to any
link-state IGP such as ISIS [3] and OSPF [4]. The data plane is
measured to obtain the convergence benchmarking metrics described
in [1].
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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....3
6. Security Considerations.....................................4
7. Acknowledgements............................................4
8. Normative References........................................5
9. Author's Address............................................5
1. Introduction
IGP Convergence is a critical performance parameter. Customers
of Service Providers use packet loss due to 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. 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 [1] and [2]. 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 [5], [6],
[7], [8] and [9], these categories are Event Detection, SPF
Processing, IGP Advertisement, and FIB Update. These have numerous
components that influence the convergence time. These are listed
as follow:
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-Event Detection-
SONET failure indication time
PPP failure 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
The contribution of each of these factors listed above will vary
with each router vendors' architecture and IGP implementation.
It is therefore necessary to design a convergence test that
considers all of these components, not just one or a few of these
components. The additional benefit of designing a test for all
components 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 administrative link
removal, unplanned link failure, line card failure, and route
changes such as withdrawal, flap, next-hop change, and cost change.
When benchmarking a router it is important to measure the
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 [1] and [2].
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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. Security Considerations
Documents of this type do not directly effect the security of
the Internet or of corporate networks as long as benchmarking
is not performed on devices or systems connected to operating
networks.
7. Acknowledgements
Thanks to Curtis Villamizar for sharing so much of his
knowledge and experience through the years. Also, special
thanks to the many Network Engineers and Network Architects
at the Service Providers who are always eager to discuss
Route Convergence benchmarking.
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8. Normative References
[1] Poretsky, S., "Benchmarking Methodology for IGP Data Plane
Route Convergence", draft-ietf-bmwg-igp-dataplane-conv-meth-07,
work in progress, July 2005.
[2] Poretsky, S., "Benchmarking Terminology for IGP Data Plane
Route Convergence", draft-ietf-bmwg-igp-dataplane-conv-term-07,
work in progress, July 2005.
[3] Callon, R., "Use of OSI IS-IS for Routing in TCP/IP and Dual
Environments", RFC 1195, December 1990.
[4] Moy, J., "OSPF Version 2", RFC 2328, IETF, April 1998.
[5] Villamizar, C., "Convergence and Restoration Techniques for
ISP Interior Routing", NANOG 25, October 2002.
[6] Katz, D., "Why are we Scared of SPF? IGP Scaling and
Stability", NANOG 25, October 2002.
[7] Filsfils, C., "Deploying Tight-SLA Services on an Internet
Backbone: ISIS Fast Convergence and Differentiated Services
Design (tutorial)", NANOG 25, October 2002.
[8] Alaettinoglu, C. and Casner, S., "ISIS Routing on the Qwest
Backbone: a Recipe for Subsecond ISIS Convergence", NANOG 24,
October 2002.
[9] Alaettinoglu, C., Jacobson, V., and Yu, H., "Towards
Millisecond IGP Convergence", NANOG 20, October 2000.
9. Author's Address
Scott Poretsky
Reef Point Systems
8 New England Executive Park
Burlington, MA 01803
USA
Phone: + 1 781 395 5090
EMail: sporetsky@quarrytech.com
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