©À
Network Working Group Vishwas Manral
Internet Draft Netplane Systems
Russ White
Cisco Systems
Aman Shaikh
Expiration Date: November 2004 University of California
File Name: draft-bmwg-ospfconv-term-08.txt May 2004
OSPF Benchmarking Terminology and Concepts
draft-ietf-bmwg-ospfconv-term-08.txt
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Abstract
This draft explains the terminology and concepts used in OSPF
benchmarking. While some of these terms may be defined elsewhere, and
we will refer the reader to those definitions in some cases, we also
include discussions concerning these terms as they relate
specifically to the tasks involved in benchmarking the OSPF protocol.
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1. Specification of Requirements
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 RFC 2119 [RFC2119].
2. Motivation
This draft is a companion to [BENCHMARK], which describes basic Open
Shortest Path First [OSPF] testing methods. This draft explains
terminology and concepts used in OSPF Testing Framework Drafts, such
as [BENCHMARK].
3. Common Definitions
Definitions in this section are well known industry and benchmarking
terms which may be defined elsewhere.
o White Box (Internal) Measurements
- Definition
White Box measurements are measurements reported and col-
lected on the Device Under Test (DUT) itself.
- Discussion
These measurement rely on output and event recording, along
with the clocking and timestamping available on the DUT
itself. Taking measurements on the DUT may impact the
actual outcome of the test, since it can increase processor
loading, memory utilization, and timing factors. Some dev-
ices may not have the required output readily available for
taking internal measurements, as well.
Note: White box measurements can be influenced by the
vendor's implementation of the various timers and process-
ing models. Whenever possible, internal measurements should
be compared to external measurements to verify and validate
them.
Because of the potential for variations in collection and
presentation methods across different DUTs, white box
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measurements MUST NOT be used as a basis of comparison in
benchmarks. This has been a guiding principal of Bench-
marking Methodology Working Group.
o Black Box (External) Measurements
- Definition
Black Box measurements infer the performance of the DUT
through observation of its communications with other dev-
ices.
- Discussion
One example of a black box measurement is when a downstream
device receives complete routing information from the DUT,
it can be inferred that the DUT has transmitted all the
routing information available. External measurements of
internal operations may suffer in that they include not
just the protocol action times, but also propagation
delays, queuing delays, and other such factors.
For the purposes of [BENCHMARK], external techniques are
more readily applicable.
o Multi-device Measurements
- Measurements assessing communications (usually in combina-
tion with internal operations) between two or more DUTs.
Multi-device measurements may be internal or external.
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4. Terms Defined Elsewhere
Terms in this section are defined elsewhere, and included only to
include a discussion of those terms in reference to [BENCHMARK].
o Point-to-Point links
- Definition
See [OSPF], Section 1.2.
- Discussion
A point-to-point link can take lesser time to converge than
a broadcast link of the same speed because it does not have
the overhead of DR election. Point-to-point links can be
either numbered or unnumbered. However in the context of
[BENCHMARK] and [OSPF], the two can be regarded the same.
o Broadcast Link
- Definition
See [OSPF], Section 1.2.
- Discussion
The adjacency formation time on a broadcast link can be
more than that on a point-to-point link of the same speed,
because DR election has to take place. All routers on a
broadcast network form adjacency with the DR and BDR.
Async flooding also takes place thru the DR. In context of
convergence, it may take more time for an LSA to be flooded
from one DR-other router to another DR-other router,
because the LSA has to be first processed at the DR.
o Shortest Path First Execution Time
- Definition
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The time taken by a router to complete the SPF process, as
described in [OSPF].
- Discussion
This does not include the time taken by the router to give
routes to the forwarding engine.
Some implementations may force two intervals, the SPF hold
time and the SPF delay, between successive SPF calcula-
tions. If an SPF hold time exists, it should be subtracted
from the total SPF execution time. If an SPF delay exists,
it should be noted in the test results.
- Measurement Units
The SPF time is generally measured in milliseconds.
o Hello Interval
- Definition
See [OSPF], Section 7.1.
- Discussion
The hello interval should be the same for all routers on a
network.
Decreasing the hello interval can allow the router dead
interval (below) to be reduced, thus reducing convergence
times in those situations where the router dead interval
timing out causes an OSPF process to notice an adjacency
failure. Further discussion on small hello intervals is
given in [OSPF-SCALING].
o Router Dead interval
- Definition
See [OSPF], Section 7.1.
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- Discussion
This is advertised in the router's Hello Packets in the Router-
DeadInterval field. The router dead interval should be some mul-
tiple of the HelloInterval (say 4 times the hello interval), and
must be the same for all routers attached to a common network.
5. Concepts
5.1. The Meaning of Single Router Control Plane Convergence
A network is termed to be converged when all of the devices within
the network have a loop free path to each possible destination. Since
we are not testing network convergence, but performance for a partic-
ular device within a network, however, this definition needs to be
narrowed somewhat to fit within a single device view.
In this case, convergence will mean the point in time when the DUT
has performed all actions needed to react to the change in topology
represented by the test condition; for instance, an OSPF device must
flood any new information it has received, rebuild its shortest path
first (SPF) tree, and install any new paths or destinations in the
local routing information base (RIB, or routing table).
Note that the word convergence has two distinct meanings; the process
of a group of individuals meeting the same place, and the process of
a single individual meeting in the same place as an existing group.
This work focuses on the second meaning of the word, so we consider
the time required for a single device to adapt to a network change to
be Single Router Convergence.
This concept does not include the time required for the control plane
of the device to transfer the information required to forward packets
to the data plane, nor the amount of time between the data plane
receiving that information and being able to actually forward
traffic.
5.2. Measuring Convergence
Obviously, there are several elements to convergence, even under the
definition given above for a single device, including (but not lim-
ited to):
o The time it takes for the DUT to pass the information about a
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network event on to its neighbors.
o The time it takes for the DUT to process information about a
network event and calculate a new Shortest Path Tree (SPT).
o The time it takes for the DUT to make changes in its local rib
reflecting the new shortest path tree.
5.3. Types of Network Events
A network event is an event which causes a change in the network
topology.
o Link or Neighbor Device Up
The time needed for an OSPF implementation to recoginize a new
link coming up on the device, build any necessarily adjacencies,
synchronize its database, and perform all other needed actions
to converge.
o Initialization
The time needed for an OSPF implementation to be initialized,
recognize any links across which OSPF must run, build any needed
adjacencies, synchronize its database, and perform other actions
needed to converge.
o Adjacency Down
The time needed for an OSPF implementation to recognize a link
down/adjacency loss based on hello timers alone, propogate any
information as necessary to its remaining adjacencies, and per-
form other actions needed to converge.
o Link Down
The time needed for an OSPF implementation to recognize a link
down based on layer 2 provided information, propogate any infor-
mation as needed to its remaining adjacencies, and perform other
actions needed to converge.
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6. Security Considerations
This doecument does not modify the underlying security considerations
in [OSPF].
7. Acknowedgements
The authors would like to thank Howard Berkowitz (hcb@clark.net),
Kevin Dubray, (kdubray@juniper.net), Scott Poretsky
(sporetsky@avici.com), and Randy Bush (randy@psg.com) for their dis-
cussion, ideas, and support.
8. Normative References
[BENCHMARK]
Manral, V., "Benchmarking Basic OSPF Single Router Control Plane
Convergence", draft-bmwg-ospfconv-intraarea-08, May 2004.
[OSPF]Moy, J., "OSPF Version 2", RFC 2328, April 1998.
9. Informative References
[OSPF-SCALING]
Choudhury, Gagan L., Editor, "Prioritized Treatment of Specific
OSPF Packets and Congestion Avoidance", draft-ietf-ospf-
scalability-06.txt, August 2003.
10. Authors' Addresses
Vishwas Manral,
Netplane Systems,
189 Prashasan Nagar,
Road number 72,
Jubilee Hills,
Hyderabad.
vmanral@netplane.com
Russ White
Cisco Systems, Inc.
7025 Kit Creek Rd.
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Research Triangle Park, NC 27709
riw@cisco.com
Aman Shaikh
University of California
School of Engineering
1156 High Street
Santa Cruz, CA 95064
aman@soe.ucsc.edu
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