Benchmarking Methodology Working Group G. Trotter
Internet Draft Agilent Technologies
Document: <draft-ietf-bmwg-fib-meth-00.txt> January 2002
Category: Informational
Methodology for Forwarding Information Base (FIB) based Router
Performance
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [1].
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Abstract
The forwarding performance of an IP router may be dependent upon or
may be linked to the composition and size of the forwarding
information base installed within a router. This document describes
the methodology to be used to determine the IP packet forwarding
performance of an IP router as a function of the forwarding
information base installed within a router.
Table of Contents
1. Introduction....................................................2
2. Terms Of Reference..............................................2
3. Overview........................................................2
4. Router Setup....................................................3
5. Test Setup......................................................3
6. Methodology Of Route Advertisements.............................3
7. Table Size......................................................4
8. Table Composition...............................................5
9. Offered Packet Load.............................................5
10. Packet Format/Size.............................................6
11. Determining The Maximum Fib Size...............................6
12. Methodology....................................................7
12.1 Baseline Measurements.........................................7
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12.2 Maximum Fib Size Test.........................................7
12.3 Fib Size Impact On Packet Forwarding Performance..............8
13. Security Considerations........................................9
14. References.....................................................9
15. Acknowledgments................................................9
16. Author's Addresses.............................................9
1. Introduction
This document covers the measurement of the IP packet forwarding
performance of IP routers on the basis of the forwarding information
base (FIB) installed within a router. [2] describes the terminology
associated with this document.
The purpose of this document is to describe a methodology for
measuring the impact of a FIB of a particular size and composition
on the forwarding performance of a router. The objective is to
determine whether a router can maintain performance levels as FIBs
continue to grow in size.
This document utilizes the methodology described in [3] for
measuring the FIB-dependent throughput, FIB-dependent latency and
FIB-dependent frame loss rate of IP packets as they traverse the
router under test. The forwarding performance of a router should be
observed under different FIB sizes and compositions.
In this document, the FIB is modified only when traffic is not
traversing the router. The effect of dynamic changes on the
forwarding performance of a router is outside the scope of this
document.
2. Terms Of Reference
This document utilizes the methodologies for packet throughput,
latency and loss measurements described in [3].
Definitions unique to this test methodology are covered in [2].
This document covers only IPv4 packets traversing an IP router.
Applicability of this document to other packet types (such as MPLS-
prefixed packets or non-IP packets) is not appropriate.
3. Overview
This methodology takes into account two key features of a FIB - the
FIB size and the FIB prefix distribution.
This methodology does not specify a particular means of populating a
FIB - a routing protocol should be used, although a FIB could be
manually entered into a router. One implication of this is that
there needs to be protocol-independent means for determining when a
router's FIB has been fully populated (described in 12.2).
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Once a FIB of a particular size and prefix distribution is entered
into the router, [3] style measurements are performed in order to
gauge the effect of the FIB on packet FIB-dependent throughput, FIB-
dependent latency and FIB-dependent frame loss rate.
4. Router Setup
This is an out-of-service methodology. The router should be
configured realistically. That is, it should be configured with
physical interface cards, switching fabrics, and route processors
providing the basis for realistic product comparisons.
5. Test Setup
The router is connected to test equipment capable of advertising
network prefixes into the router under test and generating IP
packets to these advertised networks. In the absence of test gear
capable of advertising network prefixes into the router under test,
the network prefixes could be manually entered into the router.
This methodology does not specify or require a particular physical
interface type: all measurements are performed exclusively on IP
packets.
6. Methodology Of Route Advertisements
It is recommended that routes be advertised into the router under
test by using a routing protocol to speed the advertisement of
routes. Routes may be entered into the FIB manually, but this is
both tedious, and makes the correlation between entered routes and
offered traffic awkward (see section 9).
Routes may be advertised into the router on a single interface, or
over multiple interfaces. This methodology does not distinguish
between either method.
6.1 Order of Route Advertisements
Routes can be advertised into the router in any order - a router may
organize its FIB to maximize its performance - the impact of order
of advertisement cannot be presupposed to have an impact on the
structure of the FIB.
6.2 Prevention of Route Aggregation
Routes should be advertised into the router in such a manner as to
prevent route aggregation. Routes may be aggregated as follows. If
100 routes are advertised on a single interface within a common
prefix of 192.47.0.0, and no other advertisements on any other
interface have a prefix of 192.47.0.0, then the router may enter a
single /16 entry into the FIB, directing all traffic with a
192.47.0.0 prefix to a particular interface. Care must be taken to
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prevent this from occurring, as it will result in smaller than
intended FIBs being entered within the router under test.
As an example of a means of router advertisement designed to prevent
route aggregation, consider the advertisement of 16 /16 prefixes
into a 4-port router in the diagram below:
+---------------+
1.1,2.1,3.1,4.1 -----| |----- 1.3,2.3,3.3,4.3
| |
| |
| |
1.2,2.2,3.2,4.2 -----| |----- 1.4,2.4,3.4,4.4
+---------------+
In this example, the router will not be able to aggregate the
entries from 1.0, since an entry exists on every port - the same
applies for the entries from 2.0, 3.0 and 4.0. This method of route
advertisement into the router must be used.
6.3 Learning time
A router takes time to "learn" routes. The overhead associated with
learning a route may include processing the routing protocol message
containing a new FIB entry, placing the entry into the FIB, and
then, in some modern routers, distributing the updated FIB to each
interface in the router.
This methodology does not measure or dictate the time that a router
takes to build a complete FIB. However, it is vital to the
execution of this methodology to ensure that a router has completed
learning routes and building the forwarding information base before
tests proceed.
There are two methods that can be taken to ensure that a router has
learned all routes. For the first method, the router can be queried
via an attached console to reveal the current FIB size. If access
to the console is not available, then test packets can be sent
through the router at such rate that packet loss does not ordinarily
occur. Test packets should test each entry in the FIB. No packet
loss can indicate that the router has learned all routes, and is
forwarding packets to all advertised destinations. However, this
method is not foolproof - a router may instead have filled its FIB,
and lost packets may indicate that the FIB is full, and not that the
router is still learning routes.
7. Table Size
This methodology does not specify FIB sizes to be installed within
the router under test. However, it is expected that this
methodology will be used through to the maximum possible FIB size
purported to be supported by the router under test.
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This methodology recommends starting with a small FIB size - a
single network per physical interface - in order to perform a basic
performance benchmark on the router under test. Subsequent tests
will increase the FIB by size 'N'. The FIB will be increased
through to the maximum size possible (see section 11 for a
discussion of determining the maximum possible FIB size).
8. Table Composition
The composition of a FIB consists of a number FIB entries, with each
FIB entry containing a network prefix. The network prefix length of
each FIB entry may vary. These network prefixes typically range, in
a typical Internet router's FIB, from 8 to 30 bits in length (/8 to
/30) (this document does not attempt to pre-suppose the composition
of a typical FIB within a router in the Internet, however).
Destination address matches within FIBs consisting entirely of 8-bit
network prefixes may be very rapid (few bits in each destination
address/network prefix need to be matched), whereas it can be
expected that destination address matches within a FIB populated
entirely with 30-bit network prefixes (highly unlikely) will be
slower.
9. Offered Packets
To gauge the impact of a FIB on the performance of a router, IP
packets must be delivered to the router such that the FIB is fully
exercised. That is, packets must be delivered into the router on
every interface directed to stations whose network prefix is
advertised on every other interface.
This method of traffic generation fairly exercises the FIB on the
router. Modern routers may maintain a cache of the most frequently
used routes on a per-interface (or, per-line card) basis, or they
may maintain a complete copy of the FIB on a per-interface (or per-
line card) basis. Generating packets from every interface to every
advertised network ensures that each copy of the FIB is stressed, as
well as ensuring that a router's FIB cannot be optimized (i.e. by
installing summary routes).
Consider the diagram below:
+---------------+
1.1,2.1,3.1,4.1 -----|A C|----- 1.3,2.3,3.3,4.3
| |
| |
| |
1.2,2.2,3.2,4.2 -----|B D|----- 1.4,2.4,3.4,4.4
+---------------+
In this diagram, packets sent into interface A must be directed to a
destination address present in each network advertised on ports B, C
and D. That is, the "transmit packet list" for packets sent into
port A must be:
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1.2.0.1
1.3.0.1
1.4.0.1
2.2.0.1
2.3.0.1
2.4.0.1
3.2.0.1
3.3.0.1
3.4.0.1
4.2.0.1
4.3.0.1
4.4.0.1
and then repeated.
Note that packets are transmitted to destinations on each port in a
round-robin manner. That is, A transmits a packet to B, then a
packet to C and then a packet to D, and then repeats, using the next
destination advertised on port A, and so on. This method ensures
that all aspects of the router (switching fabric, interface cards,
route processor, etc.) are stressed equally.
Also note that packets are sent from all interfaces simultaneously,
again ensuring that all router components are stressed equally. See
section 16 in [3].
10. Packet Format/Size
See [3] for a discussion of packet formats and sizes.
11. Determining The Maximum Fib Size
In order to determine the maximum FIB size, a method similar to that
used to determine whether all routes have been learned (see section
6.3) will be used.
Without observing the exchange of the routing protocol, it is
necessary to ascertain the size of the FIB from observation of
packets sent from the router.
The most methodical way of discovering the maximum FIB size is to
advertise network prefixes to the FIB, test the addition of the
entry by sending packets to the new network, ensure receipt of this
packet and repeat until packets are no longer forwarded to the newly
added network. Care must be taken to ensure that packets continue
to be forwarded to all advertised networks, even while new networks
are added - a router may "age-out" old entries in order to ensure
that its FIB is filled with current entries.
The absence of packets received at a particular network is
indicative of entries not being present within the FIB, and thus
indicates that the FIB has filled.
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If the approximate FIB size is known in advance, a larger number of
routes can be advertised into the router, then the maximum table
size can be found incrementally from this point.
When using IP packets to discover the maximum sized FIB supported by
the DUT, IP packets should be sent in at a rate that is
significantly below that of the maximum measured throughput of the
router discovered during baseline measurements (see section 12.1).
12. Methodology
This methodology makes use of the packet forwarding measurements
described in RFC 2544.
12.1 Baseline Measurements
Objective: The objective of the baseline measurement is to
determine the nominal packet forwarding performance of the router,
with a minimal sized FIB.
Procedure: A route to a single network should be advertised on each
port of the router under test - a router with 64 ports would thus
have an installed FIB of 64 entries.
As described in section 9, packets should be offered to the router
in order to create a full mesh between all advertised networks.
Using measurements described in [3] for the throughput, latency,and
frame loss rates (as per sections 26.1, 26.2, 26.3 and 26.4 in [3]),
the FIB-dependent throughput, FIB-dependent latency and FIB-
dependent frame loss rate should be measured and the results duly
noted.
Reporting Format: Results should be reported as per [3].
12.2 Maximum FIB Size Test
Objective: The objective of this test is to determine the maximum
size of the FIB that can be accommodated within the DUT. Discovery
of the maximum limit of the size of the FIB is necessary for the
establishment of limits in subsequent tests.
Procedure: Initially, advertise a single network on every port as
per section 12.1. Establish a traffic mesh between all advertised
networks as per section 9. Transmit IP packets through the DUT to
all advertised networks at a rate well below the maximum throughput
rate of the router, discovered in section 12.1. Ensure that packet
loss is zero (indicating that packets are being forwarded to all
advertised networks).
Repeatedly advertise additional networks into the DUT and add these
networks into the traffic mesh established through the DUT to the
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advertised networks. Stop when packet loss is detected, or when an
ICMP destination unreachable message with a code value of 0 (network
unreachable) or 6 (destination network unknown) is received. This
will indicate that the FIB has filled (or, that the DUT is unable to
add additional entries into the FIB). The test should continue in
order to establish increasing packet loss as a consequence of
increasing networks advertised into the DUT.
Reporting Format: The results should be reported as a single number
(the maximum FIB size). The results should be backed up with a
graph of the packet loss (on the y-axis) versus the networks
advertised into the DUT (on the x-axis).
12.3 FIB Size Impact On Packet Forwarding Performance
Objective: The objective of this test is to evaluate the impact of
FIB size and composition upon the packet forwarding performance of
the DUT.
Procedure: This iterative test changes both the size and
composition of the FIB, and makes performance measurements for each
iteration. That is, the FIB is set to a certain size and
composition, then performance measurements are made for packet
throughput, latency, and packet loss rate. The FIB is incremented,
then the tests are repeated, through to the maximum sized FIB
supported by the DUT.
The following code segment illustrates this methodology:
set forward_table_compositions [List 16 22 24 realistic]
for (forwarding_table_size = num_physical_interfaces;
Forwarding_table_size <= maximum_forwarding_table_size;
Forwarding_table_size += increment)
{
foreach value forward_table_compositions_
{
set_forwarding_table_composition $value
measure_FIB-dependent_throughput;
measure_FIB-dependent_latency;
measure_FIB-dependent_packet loss rate;
measure_FIB-dependent_back-to-back frames;
}
}
Reporting Format: Results will be reported as a series of [3]-style
graphs, with a separate set of graphs for each individual FIB size /
FIB composition test. Results could be overlaid onto a single set
of graphs.
It may be useful to create a set of graphs to aid in direct
interpretation of this test. One recommended graph would be, for a
particular frame size, a graph of the appropriate metric on the y-
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axis (FIB-dependent throughput, FIB-dependent latency, FIB-dependent
packet loss) versus the FIB size, with overlaid lines for each FIB
composition.
13. Security Considerations
As this document is solely for the purpose of providing metric
methodology and describes neither a protocol nor a protocol's
implementation, there are no security considerations associated with
this document.
14. References
1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP
9, RFC 2026, October 1996.
2 Trotter, G., " Terminology for Forwarding Information Base (FIB)
based Router Performance", RFC 3222, December, 2001.
3 Bradner, S., McQuaid, J., "Benchmarking Methodology for Network
Interconnect Devices", RFC 2544, March 1999
15. Acknowledgements
16. Author's Addresses
Guy Trotter
Agilent Technologies (Canada) Inc.
#2500 4710 Kingsway
Burnaby, British Columbia
Canada
V5H 4M2
Phone: +1 604 454 3516
Email: Guy_Trotter@agilent.com
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