Internet Engineering Task Force (IETF) G. Lencse
Request for Comments: 9693 Széchenyi István University
Category: Informational K. Shima
ISSN: 2070-1721 SoftBank Corp.
December 2024
Benchmarking Methodology for Stateful NATxy Gateways Using RFC 4814
Pseudorandom Port Numbers
Abstract
RFC 2544 defines a benchmarking methodology for network interconnect
devices. RFC 5180 addresses IPv6 specificities, and it also provides
a technology update but excludes IPv6 transition technologies. RFC
8219 addresses IPv6 transition technologies, including stateful
NAT64. However, none of them discuss how to apply pseudorandom port
numbers from RFC 4814 to any stateful NATxy (such as NAT44, NAT64,
and NAT66) technologies. This document discusses why using
pseudorandom port numbers with stateful NATxy gateways is a difficult
problem. It recommends a solution that limits the port number ranges
and uses two test phases (phase 1 and phase 2). This document shows
how the classic performance measurement procedures (e.g., throughput,
frame loss rate, latency, etc.) can be carried out. New performance
metrics and measurement procedures are also defined for measuring the
maximum connection establishment rate, connection tear-down rate, and
connection tracking table capacity.
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 candidates for any level of Internet
Standard; see Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9693.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction
1.1. Requirements Language
2. Pseudorandom Port Numbers and Stateful Translation
3. Test Setup and Terminology
3.1. When Testing with a Single IP Address Pair
3.2. When Testing with Multiple IP Addresses
4. Recommended Benchmarking Method
4.1. Restricted Number of Network Flows
4.2. Test Phase 1
4.3. Consideration of the Cases of Stateful Operation
4.4. Control of the Connection Tracking Table Entries
4.5. Measurement of the Maximum Connection Establishment Rate
4.6. Validation of Connection Establishment
4.7. Test Phase 2
4.8. Measurement of the Connection Tear-Down Rate
4.9. Measurement of the Connection Tracking Table Capacity
4.10. Writing and Reading Order of the State Table
5. Scalability Measurements
5.1. Scalability Against the Number of Network Flows
5.2. Scalability Against the Number of CPU Cores
6. Reporting Format
7. Implementation and Experience
8. Limitations of Using UDP as a Transport Layer Protocol
9. IANA Considerations
10. Security Considerations
11. References
11.1. Normative References
11.2. Informative References
Acknowledgements
Authors' Addresses
1. Introduction
[RFC2544] defines a comprehensive benchmarking methodology for
network interconnect devices that is still in use. It is mainly
indpendent of IP version, but it uses IPv4 in its examples.
[RFC5180] addresses IPv6 specificities and also adds technology
updates but declares IPv6 transition technologies are out of its
scope. [RFC8219] addresses the IPv6 transition technologies,
including stateful NAT64. It reuses several benchmarking procedures
from [RFC2544] (e.g., throughput, frame loss rate), and it redefines
the latency measurement and adds further ones (e.g., the Packet Delay
Variation (PDV) measurement).
However, none of them discuss how to apply pseudorandom port numbers
from [RFC4814] when benchmarking stateful NATxy gateways (such as
NAT44 [RFC3022], NAT64 [RFC6146], and NAT66). (It should be noted
that stateful NAT66 is not an IETF specification but refers to an
IPv6 version of the stateful NAT44 specification.) The authors are
not aware of any other RFCs that address this question.
First, this document discusses why using pseudorandom port numbers
with stateful NATxy gateways is a difficult problem. Then, a
solution is recommended.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Pseudorandom Port Numbers and Stateful Translation
In its appendix, [RFC2544] defines a frame format for test frames,
including specific source and destination port numbers. [RFC4814]
recommends using pseudorandom and uniformly distributed values for
both source and destination port numbers. However, stateful NATxy
(such as NAT44, NAT64, and NAT66) solutions use the port numbers to
identify connections. The usage of pseudorandom port numbers causes
different problems depending on the direction:
* For the client-to-server direction, pseudorandom source and
destination port numbers could be used; however, this approach
would be a denial-of-service attack against the stateful NATxy
gateway, because it would exhaust its connection tracking table
capacity. To that end, let us see some calculations using the
recommendations of [RFC4814]:
- The recommended source port range is 1024-65535; thus, its size
is 64512.
- The recommended destination port range is 1-49151; thus, its
size is 49151.
- The number of source and destination port number combinations
is 3,170,829,312.
It should be noted that the usage of different source and
destination IP addresses further increases the number of
connection tracking table entries.
* For the server-to-client direction, the stateful Device Under Test
(DUT) would drop any packets that do not belong to an existing
connection; therefore, the direct usage of pseudorandom port
numbers from the ranges mentioned above is not feasible.
3. Test Setup and Terminology
Section 12 of [RFC2544] requires testing using a single protocol
source and destination address pair first and then also using
multiple protocol addresses. The same approach is followed: first, a
single source and destination IP address pair is used, and then it is
explained how to use multiple IP addresses.
3.1. When Testing with a Single IP Address Pair
The methodology works with any IP version to benchmark stateful NATxy
gateways, where x and y are in {4, 6}. To facilitate an easy
understanding, two typical examples are used: stateful NAT44 and
stateful NAT64.
The test setup for the well-known stateful NAT44 (also called Network
Address and Port Translation (NAPT)) solution is shown in Figure 1.
Note that the private IP addresses from [RFC1918] are used to
facilitate an easy understanding of the example, and the usage of the
IP addresses reserved for benchmarking is absolutely legitimate.
+--------------------------------------+
10.0.0.2 |Initiator Responder| 198.19.0.2
+-------------| Tester |<------------+
| private IPv4| [state table]| public IPv4 |
| +--------------------------------------+ |
| |
| +--------------------------------------+ |
| 10.0.0.1 | DUT: | 198.19.0.1 |
+------------>| Stateful NAT44 gateway |-------------+
private IPv4| [connection tracking table] | public IPv4
+--------------------------------------+
Figure 1: Test Setup for Benchmarking Stateful NAT44 Gateways
The test setup for the stateful NAT64 solution [RFC6146], which is
also widely used, is shown in Figure 2.
+--------------------------------------+
2001:2::2 |Initiator Responder| 198.19.0.2
+-------------| Tester |<------------+
| IPv6 address| [state table]| IPv4 address|
| +--------------------------------------+ |
| |
| +--------------------------------------+ |
| 2001:2::1 | DUT: | 198.19.0.1 |
+------------>| Stateful NAT64 gateway |-------------+
IPv6 address| [connection tracking table] | IPv4 address
+--------------------------------------+
Figure 2: Test Setup for Benchmarking Stateful NAT64 Gateways
As for the transport layer protocol, [RFC2544] recommended testing
with UDP, and it was also kept in [RFC8219]. UDP is also kept for a
general recommendation; thus, the port numbers in the following text
are to be understood as UDP port numbers. The rationale and
limitations of this approach are discussed in Section 8.
The most important elements of the proposed benchmarking system are
defined as follows:
Connection: Although UDP itself is a connectionless protocol,
stateful NATxy gateways keep track of their translation mappings
in the form of a "connection" also as well as in the case of UDP using
the same kind of entries as in the case of TCP.
Connection tracking table: The stateful NATxy gateway uses a
connection tracking table to be able to perform the stateful
translation in the server-to-client direction. Its size, policy,
and content are unknown to the Tester.
Four tuple: The four numbers that identify a connection are source
IP address, source port number, destination IP address, and
destination port number.
State table: The Responder of the Tester extracts the four tuple
from each received test frame and stores it in its state table. A
recommendation is given for the writing and reading order of the
state table in Section 4.10.
Initiator: The port of the Tester that may initiate a connection
through the stateful DUT in the client-to-server direction.
Theoretically, it can use any source and destination port numbers
from the ranges recommended by [RFC4814]: if the used four tuple
does not belong to an existing connection, the DUT will register a
new connection into its connection tracking table.
Responder: The port of the Tester that may not initiate a connection
through the stateful DUT in the server-to-client direction. It
may only send frames that belong to an existing connection. To
that end, it uses four tuples that have been previously extracted
from the received test frames and stores in its state table.
Test phase 1: The test frames are sent only by the Initiator to the
Responder through the DUT to fill both the connection tracking
table of the DUT and the state table of the Responder. This is a
newly introduced operation phase for stateful NATxy benchmarking.
The necessity of this test phase is explained in Section 4.2.
Test phase 2: The measurement procedures defined by [RFC8219] (e.g.,
throughput, latency, etc.) are performed in this test phase after
the completion of test phase 1. Test frames are sent as required
(e.g., a bidirectional test or a unidirectional test in any of the
two directions).
One further definition is used in the text of this document:
Black box testing: A testing approach when the Tester is not aware
of the details of the internal structure and operation of the DUT.
It can send input to the DUT and observe the output of the DUT.
3.2. When Testing with Multiple IP Addresses
This section considers the number of the necessary and available IP
addresses.
In Figure 1, the single 198.19.0.1 IPv4 address is used on the WAN
side port of the stateful NAT44 gateway. However, in practice, it is
not a single IP address, but rather an IP address range that is
assigned to the WAN side port of the stateful NAT44 gateways. Its
required size depends on the number of client nodes and on the type
of the stateful NAT44 algorithm. (The traditional algorithm always
replaces the source port number when a new connection is established.
Thus, it requires a larger range than the extended algorithm, which
replaces the source port number only when it is necessary. Please
refer to Tables 1 and 2 of [LEN2015].)
When router testing is done, Section 12 of [RFC2544] requires testing
using a single source and destination IP address pair first and then
using destination IP addresses from 256 different networks. The
16-23 bits of the 198.18.0.0/24 and 198.19.0.0/24 addresses can be
used to express the 256 networks. As this document does not deal
with router testing, no multiple destination networks are needed;
therefore, these bits are available for expressing multiple IP
addresses that belong to the same "/16" network. Moreover, both the
198.18.0.0/16 and the 198.19.0.0/16 networks can be used on the right
side of the test setup, as private IP addresses from the 10.0.0.0/16
network are used on its left side.
10.0.0.2/16 - 10.0.255.254/16 198.19.0.0/15 - 198.19.255.254/15
\ +--------------------------------------+ /
\ |Initiator Responder| /
+-------------| Tester |<------------+
| private IPv4| [state table]| public IPv4 |
| +--------------------------------------+ |
| |
| +--------------------------------------+ |
| 10.0.0.1/16 | DUT: | public IPv4 |
+------------>| Stateful NAT44 gateway |-------------+
private IPv4| [connection tracking table] | \
+--------------------------------------+ \
198.18.0.1/15 - 198.18.255.255/15
Figure 3: Test Setup for Benchmarking Stateful NAT44 Gateways
Using Multiple IPv4 Addresses
A possible solution for assigning multiple IPv4 addresses is shown in
Figure 3. On the left side, the private IP address range is
abundantly large. (The 16-31 bits were used for generating nearly
64k potential different source addresses, but the 8-15 bits are also
available if needed.) On the right side, the 198.18.0.0./15 network
is used, and it was cut into two equal parts. (Asymmetric division
is also possible, if needed.)
It should be noted that these are the potential address ranges. The
actual address ranges to be used are discussed in Section 4.1.
In the case of stateful NAT64, a single "/64" IPv6 prefix contains a
high number of bits to express different IPv6 addresses. Figure 4
shows an example where bits 96-111 are used for that purpose.
2001:2::[0000-ffff]:0002/64 198.19.0.0/15 - 198.19.255.254/15
\ +--------------------------------------+ /
IPv6 \ |Initiator Responder| /
+-------------| Tester |<------------+
| addresses | [state table]| public IPv4 |
| +--------------------------------------+ |
| |
| +--------------------------------------+ |
| 2001:2::1/64| DUT: | public IPv4 |
+------------>| Stateful NAT64 gateway |-------------+
IPv6 address | [connection tracking table] | \
+--------------------------------------+ \
198.18.0.1/15 - 198.18.255.255/15
Figure 4: Test Setup for Benchmarking Stateful NAT64 Gateways
Using Multiple IPv6 and IPv4 Addresses
4. Recommended Benchmarking Method
4.1. Restricted Number of Network Flows
When a single IP address pair is used for testing, then the number of
network flows is determined by the number of source and destination
port number combinations.
The Initiator SHOULD use restricted ranges for source and destination
port numbers to avoid the exhaustion of the connection tracking table
capacity of the DUT as described in Section 2. If it is possible,
the size of the source port number range SHOULD be larger (e.g., in
the order of a few times ten thousand), tens of thousands), whereas the size of the
destination port number range SHOULD be smaller (e.g., it may vary
from a few to several hundreds or thousands as needed). The
rationale is that source and destination port numbers that can be
observed in Internet traffic are not symmetrical. Whereas source
port numbers may be random, there are a few very popular destination
port numbers (e.g., 443 or 80; see [IIR2020]), and others hardly
occur. Additionally, it was found that their role is also asymmetric
in the Linux kernel routing hash function [LEN2020].
However, in some special cases, the size of the source port range is
limited. For example, when benchmarking the Customer Edge (CE) and
Border Relay (BR) of a Mapping of Address and Port using Translation
(MAP-T) system [RFC7599] together (as a compound system performing
stateful NAT44), the source port range is limited to the number of
source port numbers assigned to each subscriber. (It could be as low
as 2048 ports.)
When multiple IP addresses are used, then the port number ranges
should be even more restricted, as the number of potential network
flows is the product of the size of:
* the source IP address range,
* the source port number range,
* the destination IP address range, and
* the destination port number range.
In addition, the recommended method requires the enumeration of all
their possible combinations in test phase 1 as described in
Section 4.4.
The number of network flows can be used as a parameter. The
performance of the stateful NATxy gateway MAY be examined as a
function of this parameter as described in Section 5.1.
4.2. Test Phase 1
Test phase 1 serves two purposes:
1. The connection tracking table of the DUT is filled. This is
important because its maximum connection establishment rate may
be lower than its maximum frame forwarding rate (that is is, its
throughput).
2. The state table of the Responder is filled with valid four
tuples. It is a precondition for the Responder to be able to
transmit frames that belong to connections that exist in the
connection tracking table of the DUT.
Whereas the above two things are always necessary before test phase
2, test phase 1 can be used without test phase 2. This is done when
the maximum connection establishment rate is measured (as described
in Section 4.5).
Test phase 1 MUST be performed before all tests are performed in test
phase 2. The following things happen in test phase 1:
1. The Initiator sends test frames to the Responder through the DUT
at a specific frame rate.
2. The DUT performs the stateful translation of the test frames, and
it also stores the new connections in its connection tracking
table.
3. The Responder receives the translated test frames and updates its
state table with the received four tuples. The Responder
transmits no test frames during test phase 1.
When test phase 1 is performed in preparation for test phase 2, the
applied frame rate SHOULD be safely lower than the maximum connection
establishment rate. (It implies that maximum connection
establishment rate measurement MUST be performed first.) Please
refer to Section 4.4 for further conditions regarding timeout and the
enumeration of all possible four tuples.
4.3. Consideration of the Cases of Stateful Operation
The authors consider the most important events that may happen during
the operation of a stateful NATxy gateway and the Actions of the
gateway as follows.
1. EVENT: A packet not belonging to an existing connection arrives
in the client-to-server direction.
ACTION: A new connection is registered into the connection
tracking table, and the packet is translated and forwarded.
2. EVENT: A packet not belonging to an existing connection arrives
in the server-to-client direction.
ACTION: The packet is discarded.
3. EVENT: A packet belonging to an existing connection arrives (in
any direction).
ACTION: The packet is translated and forwarded, and the timeout
counter of the corresponding connection tracking table entry is
reset.
4. EVENT: A connection tracking table entry times out.
ACTION: The entry is deleted from the connection tracking table.
Due to "black box" testing, the Tester is not able to directly
examine (or delete) the entries of the connection tracking table.
However, the entries can and MUST be controlled by setting an
appropriate timeout value and carefully selecting the port numbers of
the packets (as described in Section 4.4) to be able to produce
meaningful and repeatable measurement results.
This document aims to support the measurement of the following
performance characteristics of a stateful NATxy gateway:
* maximum connection establishment rate
* all "classic" performance metrics like throughput, frame loss
rate, latency, etc.
* connection tear-down rate
* connection tracking table capacity
4.4. Control of the Connection Tracking Table Entries
It is necessary to control the connection tracking table entries of
the DUT to achieve clear conditions for the measurements. One can
simply achieve the following two extreme situations:
1. All frames create a new entry in the connection tracking table of
the DUT, and no old entries are deleted during the test. This is
required for measuring the maximum connection establishment rate.
2. No new entries are created in the connection tracking table of
the DUT, and no old ones are deleted during the test. This is
ideal for the measurements to be executed in phase 2, like
throughput, latency, etc.
From this point, the following two assumptions are used:
1. The connection tracking table of the stateful NATxy is large
enough to store all connections defined by the different four
tuples.
2. Each experiment is started with an empty connection tracking
table. (This can be ensured by deleting its content before the
experiment.)
The first extreme situation can be achieved by:
* using different four tuples for every single test frame in test
phase 1 and
* setting the UDP timeout of the NATxy gateway to a value higher
than the length of test phase 1.
The second extreme situation can be achieved by:
* enumerating all possible four tuples in test phase 1 and
* setting the UDP timeout of the NATxy gateway to a value higher
than the length of test phase 1 plus the gap between the two
phases plus the length of test phase 2.
[RFC4814] REQUIRES
As described in [RFC4814], pseudorandom port numbers, numbers are REQUIRED,
which the authors believe is a good approximation of the distribution
of the source port numbers a NATxy gateway on the Internet may be
faced with.
Although the enumeration of all possible four tuples is not a
requirement for the first extreme situation and the usage of
different four tuples in test phase 1 is not a requirement for the
second extreme situation, pseudorandom enumeration of all possible
four tuples in test phase 1 is a good solution in both cases. It
Pseudorandom enumeration of all possible four tuples may be computing
efficiently generated by preparing a random permutation of the
previously enumerated all possible four tuples using Durstenfeld's
random shuffle algorithm [DUST1964].
The enumeration of the four tuples in increasing or decreasing order
(or in any other specific order) MAY be used as an additional
measurement.
4.5. Measurement of the Maximum Connection Establishment Rate
The maximum connection establishment rate is an important
characteristic of the stateful NATxy gateway, and its determination
is necessary for the safe execution of test phase 1 (without frame
loss) before test phase 2.
The measurement procedure of the maximum connection establishment
rate is very similar to the throughput measurement procedure defined
in [RFC2544].
The procedure is as follows:
* The Initiator sends a specific number of test frames using all
different four tuples at a specific rate through the DUT.
* The Responder counts the frames that are successfully translated
by the DUT.
* If the count of offered frames is equal to the count of received
frames, the rate of the offered stream is raised and the test is
rerun.
* If fewer frames are received than were transmitted, the rate of
the offered stream is reduced and the test is rerun.
The maximum connection establishment rate is the fastest rate at
which the count of test frames successfully translated by the DUT is
equal to the number of test frames sent to it by the Initiator.
Note: In practice, the usage of binary search is RECOMMENDED.
4.6. Validation of Connection Establishment
Due to "black box" testing, the entries of the connection tracking
table of the DUT may not be directly examined. However, the presence
of the connections can be checked easily by sending frames from the
Responder to the Initiator in test phase 2 using all four tuples
stored in the state table of the Tester (at a low enough frame rate).
The arrival of all test frames indicates that the connections are
indeed present.
The procedure is as follows:
When all the desired N number of test frames are sent by the
Initiator to the Receiver at frame rate R in test phase 1 for the
maximum connection establishment rate measurement and the Receiver
has successfully received all the N frames, the establishment of the
connections is checked in test phase 2 as follows:
* The Responder sends test frames to the Initiator at frame rate
r=R*alpha for the duration of N/r, using a different four tuple
from its state table for each test frame.
* The Initiator counts the received frames, and if all N frames have
arrived, then the R frame rate of the maximum connection
establishment rate measurement (performed in test phase 1) is
raised for the next iteration; otherwise, it is lowered (as well
as in the case that test frames were missing in the preliminary
test phase, as well).
Notes:
* The alpha is a kind of "safety factor"; it aims to make sure that
the frame rate used for the validation is not too high, and the
test may fail only in the case of if at least one connection is
not present in the connection tracking table of the DUT.
(Therefore, alpha should be typically less than 1, e.g., 0.8 or
0.5.)
* The duration of N/r and the frame rate of r means that N frames
are sent for validation.
* The order of four tuple selection is arbitrary, provided that all
four tuples MUST be used.
* Please refer to Section 4.9 for a short analysis of the operation
of the measurement and what problems may occur.
4.7. Test Phase 2
As for the traffic direction, there are three possible cases during
test phase 2:
1. Bidirectional traffic: The Initiator sends test frames to the
Responder, and the Responder sends test frames to the Initiator.
2. Unidirectional traffic from the Initiator to the Responder: The
Initiator sends test frames to the Responder, but the Responder
does not send test frames to the Initiator.
3. Unidirectional traffic from the Responder to the Initiator: The
Responder sends test frames to the Initiator, but the Initiator
does not send test frames to the Responder.
If the Initiator sends test frames, then it uses pseudorandom source
port numbers and destination port numbers from the restricted port
number ranges. (If it uses multiple source and/or destination IP
addresses, then their ranges are also limited.) The Responder
receives the test frames, updates its state table, and processes the
test frames as required by the given measurement procedure (e.g.,
only counts them for the throughput test, handles timestamps for
latency or PDV tests, etc.).
If the Responder sends test frames, then it uses the four tuples from
its state table. The reading order of the state table may follow
different policies (discussed in Section 4.10). The Initiator
receives the test frames and processes them as required by the given
measurement procedure.
As for the actual measurement procedures, the usage of the updated
ones from Section 7 of [RFC8219] is RECOMMENDED.
4.8. Measurement of the Connection Tear-Down Rate
Connection tear-down can cause significant load for the NATxy
gateway. The connection tear-down performance can be measured as
follows:
1. Load a certain number of connections (N) into the connection
tracking table of the DUT (in the same way as done to measure the
maximum connection establishment rate).
2. Record TimestampA.
3. Delete the content of the connection tracking table of the DUT.
4. Record TimestampB.
The connection tear-down rate can be computed as:
connection tear-down rate = N / ( TimestampB - TimestampA)
The connection tear-down rate SHOULD be measured for various values
of N.
It is assumed that the content of the connection tracking table may
be deleted by an out-of-band control mechanism specific to the given
NATxy gateway implementation (e.g., by removing the appropriate
kernel module under Linux).
It is noted that the performance of removing the entire content of
the connection tracking table at one time may be different from
removing all the entries one by one.
4.9. Measurement of the Connection Tracking Table Capacity
The connection tracking table capacity is an important metric of
stateful NATxy gateways. Its measurement is not easy, because an
elementary step of a validated maximum connection establishment rate
measurement (defined in Section 4.6) may have only a few distinct
observable outcomes, but some of them may have different root causes:
* During test phase 1, the number of test frames received by the
Responder is less than the number of test frames sent by the
Initiator. It may have different root causes, including:
- The R frame sending rate was higher than the maximum connection
establishment rate. (Note that now the maximum connection
establishment rate is considered unknown because one cannot
measure the maximum connection establishment without assumption
1 in Section 4.4.) This root cause may be eliminated by
lowering the R rate and re-executing the test. (This step may
be performed multiple times while R>0.)
- The capacity of the connection tracking table of the DUT has
been exhausted (and either the DUT does not want to delete
connections or the deletion of the connections makes it slower;
this case is not investigated further in test phase 1).
* During test phase 1, the number of test frames received by the
Responder equals the number of test frames sent by the Initiator.
In this case, the connections are validated in test phase 1. 2. The
validation may have two kinds of observable results:
1. The number of validation frames received by the Initiator
equals the number of validation frames sent by the Responder.
(It proves that the capacity of the connection tracking table
of the DUT is enough and both R and r were chosen properly.)
2. The number of validation frames received by the Initiator is
less than the number of validation frames sent by the
Responder. This phenomenon may have various root causes:
- The capacity of the connection tracking table of the DUT
has been exhausted. (It does not matter whether some
existing connections are discarded and new ones are stored
or if the new connections are discarded. Some connections
are lost anyway, and it makes validation fail.)
- The R frame sending rate used by the Initiator was too high
in test phase 1; thus, some connections were not
established even though all test frames arrived at the
Responder. This root cause may be eliminated by lowering
the R rate and re-executing the test. (This step may be
performed multiple times while R>0.)
- The r frame sending rate used by the Responder was too high
in test phase 2; thus, some test frames did not arrive at
the Initiator even though all connections were present in
the connection tracking table of the DUT. This root cause
may be eliminated by lowering the r rate and re-executing
the test. (This step may be performed multiple times while
r>0.)
This is the problem: As the above three root causes are
indistinguishable, it is not easy to decide whether R or r
should be decreased.
Experience shows that the DUT may collapse if its memory is
exhausted. Such a situation may make the connection tracking table
capacity measurements rather inconvenient. This possibility is
included in the recommended measurement procedure, but the detection
and elimination of such a situation is not addressed (e.g., how the
algorithm can reset the DUT).
For the connection tracking table size measurement, first, one needs
a safe number: C0. It is a precondition that C0 number of
connections can surely be stored in the connection tracking table of
the DUT. Using C0, one can determine the maximum connection
establishment rate using C0 number of connections. It is done with a
binary search using validation. The result is R0. The values C0 and
R0 will serve as "safe" starting values for the following two
searches.
First, an exponential search is performed to find the order of
magnitude of the connection tracking table capacity. The search
stops if the DUT collapses OR the maximum connection establishment
rate severely drops (e.g., to its one tenth) due to doubling the
number of connections.
Then, the result of the exponential search gives the order of
magnitude of the size of the connection tracking table. Before
disclosing the possible algorithms to determine the exact size of the
connection tracking table, three possible replacement policies for
the NATxy gateway are considered:
1. The gateway does not delete any live connections until their
timeout expires.
2. The gateway replaces the live connections according to the Least
Recently Used (LRU) policy.
3. The gateway does a garbage collection when its connection
tracking table is full and a frame with a new four tuple arrives.
During the garbage collection, it deletes the K LRU connections,
where K is greater than 1.
Now, it is examined what happens and how many validation frames
arrive in the three cases. Let the size of the connection tracking
table be S and the number of preliminary frames be N, where S is less
than N.
1. The connections defined by the first S test frames are registered
into the connection tracking table of the DUT, and the last N-S
connections are lost. (It is another question if the last N-S
test frames are translated and forwarded in test phase 1 or
simply dropped.) During validation, the validation frames with
four tuples corresponding to the first S test frames will arrive
at the Initiator and the other N-S validation frames will be
lost.
2. All connections are registered into the connection tracking table
of the DUT, but the first N-S connections are replaced (and thus
lost). During validation, the validation frames with four tuples
corresponding to the last S test frames will arrive to the
Initiator, and the other N-S validation frames will be lost.
3. Depending on the values of K, S, and N, maybe less than S
connections will survive. In the worst case, only S-K+1
validation frames arrive, even though the size of the connection
tracking table is S.
If one knows that the stateful NATxy gateway uses the first or second
replacement policy and one also knows that both R and r rates are low
enough, then the final step of determining the size of the connection
tracking table is simple. If the Responder sent N validation frames
and the Initiator received N' of them, then the size of the
connection tracking table is N'.
In the general case, a binary search is performed to find the exact
value of the connection tracking table capacity within E error. The
search chooses the lower half of the interval if the DUT collapses OR
the maximum connection establishment rate severely drops (e.g., to
its half); otherwise, it chooses the higher half. The search stops
if the size of the interval is less than the E error.
The algorithms for the general case are defined using C, like the C-like
pseudocode in Figure 5. In practice, this algorithm may be made more
efficient in the way that the binary search for the maximum
connection establishment rate stops if an elementary test fails at a
rate under RS*beta or RS*gamma during the external search or during
the final binary search for the capacity of the connection tracking
table, respectively. (This saves a high amount of execution time by
eliminating the long-lasting tests at low rates.)
// The binarySearchForMaximumConnectionCstablishmentRate(c,r)
// function performs a binary search for the maximum connection
// establishment rate in the [0, r] interval using c number of
// connections.
// This is an exponential search for finding the order of magnitude
// of the connection tracking table capacity
// Variables:
// C0 and R0 are beginning safe values for the connection
// tracking table size and connection establishment rate,
// respectively
// CS and RS are their currently used safe values
// CT and RT are their values for the current examination
// beta is a factor expressing an unacceptable drop in R (e.g.,
// beta=0.1)
// maxrate is the maximum frame rate for the media
R0=binarySearchForMaximumConnectionCstablishmentRate(C0,maxrate);
for ( CS=C0, RS=R0; 1; CS=CT, RS=RT )
{
CT=2*CS;
RT=binarySearchForMaximumConnectionCstablishmentRate(CT,RS);
if ( DUT_collapsed || RT < RS*beta )
break;
}
// At this point, the size of the connection tracking table is
// between CS and CT.
// This is the final binary search for finding the connection
// tracking table capacity within E error
// Variables:
// CS and RS are the safe values for connection tracking table size
// and connection establishment rate, respectively
// C and R are the values for the current examination
// gamma is a factor expressing an unacceptable drop in R
// (e.g., gamma=0.5)
for ( D=CT-CS; D>E; D=CT-CS )
{
C=(CS+CT)/2;
R=binarySearchForMaximumConnectionCstablishmentRate(C,RS);
if ( DUT_collapsed || R < RS*gamma )
CT=C; // take the lower half of the interval
else
CS=C,RS=R; // take the upper half of the interval
}
// At this point, the size of the connection tracking table is
// CS within E error.
Figure 5: Measurement of the Connection Tracking Table Capacity
4.10. Writing and Reading Order of the State Table
As for the writing policy of the state table of the Responder, round
robin is RECOMMENDED, because it ensures that its entries are
automatically kept fresh and consistent with that of the connection
tracking table of the DUT.
The Responder can read its state table in various orders, for
example:
* pseudorandom
* round robin
Pseudorandom is RECOMMENDED to follow the approach of [RFC4814].
Round robin may be used as a computationally cheaper alternative.
5. Scalability Measurements
As for scalability measurements, no new types of performance metrics
are defined, but it is RECOMMENDED to perform measurement series
through which the value of one or more parameter(s) are changed to
discover how the various values of the given parameter(s) influence
the performance of the DUT.
5.1. Scalability Against the Number of Network Flows
The scalability measurements aim to quantify how the performance of
the stateful NATxy gateways degrades with the increase of the number
of network flows.
As for the actual values for the number of network flows to be used
during the measurement series, it is RECOMMENDED to use some
representative values from the range of the potential number of
network flows the DUT may be faced with during its intended usage.
It is important how the given number of network flows are generated.
The sizes of the ranges of the source and destination IP addresses
and port numbers are essential parameters to be reported together
with the results. Please also see Section 6 about the reporting
format.
If a single IP address pair is used, then it is RECOMMENDED to use:
* a fixed, larger source port number range (e.g., a few times
10,000) and
* a variable-size destination port number range (e.g., 10, 100,
1,000, etc.), where its expedient granularity depends on the
purpose.
5.2. Scalability Against the Number of CPU Cores
Stateful NATxy gateways are often implemented in software that is not
bound to a specific hardware but can be executed by commodity
servers. To facilitate the comparison of their performance, it can
be useful to determine:
* the performance of the various implementations using a single core
of a well-known CPU and
* the scale-up of the performance of the various implementations
with the number of CPU cores.
If the number of the available CPU cores is a power of two, then it
is RECOMMENDED to perform the tests with 1, 2, 4, 8, 16, etc. number
of active CPU cores of the DUT.
6. Reporting Format
Measurements MUST be executed multiple times. The necessary number
of repetitions to achieve statistically reliable results may depend
on the consistent or scattered nature of the results. The report of
the results MUST contain the number of repetitions of the
measurements. The median is RECOMMENDED as the summarizing function
of the results complemented with the first percentile and the 99th
percentile as indices of the dispersion of the results. The average
and standard deviation MAY also be reported.
All parameters and settings that may influence the performance of the
DUT MUST be reported. Some of them may be specific to the given
NATxy gateway implementation, like the "hashsize" (hash table size)
and "nf_conntrack_max" (number of connection tracking table entries)
values for iptables or the limit of the number of states for OpenBSD
PF (set by the "set limit states number" command in the pf.conf
file).
+----------------------------+--------+--------+--------+--------+
| number of sessions (req.) | 0.4M | 4M | 40M | 400M |
+----------------------------+--------+--------+--------+--------+
| source port numbers (req.) | 40,000 | 40,000 | 40,000 | 40,000 |
+----------------------------+--------+--------+--------+--------+
| destination port numbers | 10 | 100 | 1,000 | 10,000 |
| (req.) | | | | |
+----------------------------+--------+--------+--------+--------+
| "hashsize" (i.s.) | 2^17 | 2^20 | 2^23 | 2^27 |
+----------------------------+--------+--------+--------+--------+
| "nf_conntrack_max" (i.s.) | 2^20 | 2^23 | 2^26 | 2^30 |
+----------------------------+--------+--------+--------+--------+
| num. sessions / "hashsize" | 3.05 | 3.81 | 4.77 | 2.98 |
| (i.s.) | | | | |
+----------------------------+--------+--------+--------+--------+
| number of experiments | 10 | 10 | 10 | 10 |
| (req.) | | | | |
+----------------------------+--------+--------+--------+--------+
| error of binary search | 1,000 | 1,000 | 1,000 | 1,000 |
| (req.) | | | | |
+----------------------------+--------+--------+--------+--------+
| connections/s median | | | | |
| (req.) | | | | |
+----------------------------+--------+--------+--------+--------+
| connections/s 1st perc. | | | | |
| (req.) | | | | |
+----------------------------+--------+--------+--------+--------+
| connections/s 99th perc. | | | | |
| (req.) | | | | |
+----------------------------+--------+--------+--------+--------+
Table 1: Example Table of the Maximum Connection Establishment
Rate of Iptables Against the Number of Sessions
Table 1 shows an example of table headings for reporting the
measurement results regarding the scalability of the iptables
stateful NAT44 implementation against the number of sessions. The
table indicates the required fields (req.) and the implementation-
specific ones (i.s.). A computed value was also added in row 6; it
is the number of sessions per hashsize ratio, which helps the reader
to interpret the achieved maximum connection establishment rate. (A
lower value results in shorter linked lists hanging on the entries of
the hash table, thus facilitating higher performance. The ratio is
varying, because the number of sessions is always a power of 10,
whereas the hash table size is a power of 2.) To reflect the
accuracy of the results, the table contains the value of the "error"
of the binary search, which expresses the stopping criterion for the
binary search. The binary search stops when the difference between
the "higher limit" and "lower limit" of the binary search is less
than or equal to the "error".
The table MUST be complemented with reporting the relevant parameters
of the DUT. If the DUT is a general-purpose computer and some
software NATxy gateway implementation is tested, then the hardware
description SHOULD include: include the following:
* computer type, type
* CPU type and
* number of active CPU cores, cores
* memory type, type
* size and speed, speed
* network interface card type (also reflecting the speed), the fact that speed)
* direct cable connections were used, and or the type of the switch used for
interconnecting the Tester and the DUT. DUT
The operating system type and version, kernel version, and version of
the NATxy gateway implementation (including the last commit date and
number if applicable) SHOULD also be given.
7. Implementation and Experience
The stateful extension of siitperf [SIITPERF] is an implementation of
this concept. Its first version that only supports multiple port
numbers is documented in this (open access) paper: [LEN2022]. Its
extended version that also supports multiple IP addresses is
documented in this (open access) paper: [LEN2024b].
The proposed benchmarking methodology has been validated by
performing benchmarking measurements with three radically different
stateful NAT64 implementations (Jool, tayga+iptables, and OpenBSD PF)
in this (open access) paper: [LEN2023].
Further experience with this methodology of using siitperf for
measuring the scalability of the iptables stateful NAT44 and Jool
stateful NAT64 implementations are described in [SCALABILITY].
This methodology was successfully applied for the benchmarking of
various IPv4-as-a-Service (IPv4aas) technologies without the usage of
technology-specific Testers by reducing the aggregate of their
Customer Edge (CE) and Provider Edge (PE) devices to a stateful NAT44
gateway documented in this (open access) paper: [LEN2024a].
8. Limitations of Using UDP as a Transport Layer Protocol
The test frame format defined in [RFC2544] exclusively uses UDP (and
not TCP) as a transport layer protocol. Testing with UDP was kept in
both [RFC5180] and [RFC8219] regarding the standard benchmarking
procedures (throughput, latency, frame loss rate, etc.). The
benchmarking methodology proposed in this document follows this long-
established benchmarking tradition using UDP as a transport layer
protocol, too. The rationale for this is that the standard
benchmarking procedures require sending frames at arbitrary constant
frame rates, which would violate the flow control and congestion
control algorithms of the TCP protocol. TCP connection setup (using
the three-way handshake) would further complicate testing.
Further potential transport layer protocols, e.g., the Datagram
Congestion Control Protocol (DCCP) [RFC4340] and the Stream Control
Transmission Protocol (SCTP) [RFC9260], are outside of the scope of
this document, as the widely used stateful NAT44 and stateful NAT64
implementations do not support them. Although QUIC [RFC9000] is also
considered a transport layer protocol, QUIC packets are carried in
UDP datagrams; thus, QUIC does not need a special handling.
Some stateful NATxy solutions handle TCP and UDP differently, e.g.,
iptables use a 30s timeout for UDP and a 60s timeout for TCP. Thus,
benchmarking results produced using UDP do not necessarily
characterize the performance of a NATxy gateway well enough when they
are used for forwarding Internet traffic. As for the given example,
timeout values of the DUT may be adjusted, but it requires extra
consideration.
Other differences in handling UDP or TCP are also possible. Thus,
the authors recommend that further investigations should be performed
in this field.
As a mitigation of this problem, this document recommends that
testing with protocols using TCP (like HTTP and HTTPS up to version
2) can be performed as described in [RFC9411]. This approach also
solves the potential problem of protocol helpers that may be present
in the stateful DUT.
As for HTTP/3, it uses QUIC, which uses UDP as stated above. It
should be noted that QUIC is treated as any other UDP payload. The
proposed measurement method does not aim to measure the performance
of QUIC, rather, it aims to measure the performance of the stateful
NATxy gateway.
9. IANA Considerations
This document has no IANA actions.
10. Security Considerations
This document has no further security considerations beyond that of
[RFC8219]. They should be cited here so that they can be applied not
only for the benchmarking of IPv6 transition technologies but also
for the benchmarking of any stateful NATxy gateways (allowing for
x=y, too).
11. References
11.1. Normative References
[RFC1918] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G.
J., and E. Lear, "Address Allocation for Private
Internets", BCP 5, RFC 1918, DOI 10.17487/RFC1918,
February 1996, <https://www.rfc-editor.org/info/rfc1918>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2544] Bradner, S. and J. McQuaid, "Benchmarking Methodology for
Network Interconnect Devices", RFC 2544,
DOI 10.17487/RFC2544, March 1999,
<https://www.rfc-editor.org/info/rfc2544>.
[RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network
Address Translator (Traditional NAT)", RFC 3022,
DOI 10.17487/RFC3022, January 2001,
<https://www.rfc-editor.org/info/rfc3022>.
[RFC4340] Kohler, E., Handley, M., and S. Floyd, "Datagram
Congestion Control Protocol (DCCP)", RFC 4340,
DOI 10.17487/RFC4340, March 2006,
<https://www.rfc-editor.org/info/rfc4340>.
[RFC4814] Newman, D. and T. Player, "Hash and Stuffing: Overlooked
Factors in Network Device Benchmarking", RFC 4814,
DOI 10.17487/RFC4814, March 2007,
<https://www.rfc-editor.org/info/rfc4814>.
[RFC5180] Popoviciu, C., Hamza, A., Van de Velde, G., and D.
Dugatkin, "IPv6 Benchmarking Methodology for Network
Interconnect Devices", RFC 5180, DOI 10.17487/RFC5180, May
2008, <https://www.rfc-editor.org/info/rfc5180>.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, DOI 10.17487/RFC6146,
April 2011, <https://www.rfc-editor.org/info/rfc6146>.
[RFC7599] Li, X., Bao, C., Dec, W., Ed., Troan, O., Matsushima, S.,
and T. Murakami, "Mapping of Address and Port using
Translation (MAP-T)", RFC 7599, DOI 10.17487/RFC7599, July
2015, <https://www.rfc-editor.org/info/rfc7599>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8219] Georgescu, M., Pislaru, L., and G. Lencse, "Benchmarking
Methodology for IPv6 Transition Technologies", RFC 8219,
DOI 10.17487/RFC8219, August 2017,
<https://www.rfc-editor.org/info/rfc8219>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
[RFC9260] Stewart, R., Tüxen, M., and K. Nielsen, "Stream Control
Transmission Protocol", RFC 9260, DOI 10.17487/RFC9260,
June 2022, <https://www.rfc-editor.org/info/rfc9260>.
[RFC9411] Balarajah, B., Rossenhoevel, C., and B. Monkman,
"Benchmarking Methodology for Network Security Device
Performance", RFC 9411, DOI 10.17487/RFC9411, March 2023,
<https://www.rfc-editor.org/info/rfc9411>.
11.2. Informative References
[DUST1964] Durstenfeld, R., "Algorithm 235: Random permutation",
Communications of the ACM, vol. 7, no. 7, p. 420,
DOI 10.1145/364520.364540, July 1964,
<https://dl.acm.org/doi/pdf/10.1145/364520.364540>.
[IIR2020] Kurahashi, T., Matsuzaki, Y., Sasaki, T., Saito, T., and
F. Tsutsuji, "Periodic Observation Report: Internet Trends
as Seen from IIJ Infrastructure - 2020", Internet
Initiative Japan Inc., Internet Infrastructure Review,
vol. 49, December 2020,
<https://www.iij.ad.jp/en/dev/iir/pdf/
iir_vol49_report_EN.pdf>.
[LEN2015] Lencse, G., "Estimation of the Port Number Consumption of
Web Browsing", IEICE Transactions on Communications, vol.
E98-B, no. 8. pp. 1580-1588,
DOI 10.1587/transcom.E98.B.1580, August 2015,
<https://www.hit.bme.hu/~lencse/publications/
e98-b_8_1580.pdf>.
[LEN2020] Lencse, G., "Adding RFC 4814 Random Port Feature to
Siitperf: Design, Implementation and Performance
Estimation", International Journal of Advances in
Telecommunications, Electrotechnics, Signals and Systems,
vol 9, no 3, pp. 18-26., DOI 10.11601/ijates.v9i3.291,
November 2020,
<http://ijates.org/index.php/ijates/article/view/291>.
[LEN2022] Lencse, G., "Design and Implementation of a Software
Tester for Benchmarking Stateful NAT64xy Gateways: Theory
and Practice of Extending Siitperf for Stateful Tests",
Computer Communications, vol. 192, pp. 75-88,
DOI 10.1016/j.comcom.2022.05.028, August 2022,
<https://www.sciencedirect.com/science/article/pii/
S0140366422001803>.
[LEN2023] Lencse, G., Shima, K., and K. Cho, "Benchmarking
methodology for stateful NAT64 gateways", Computer
Communications, vol. 210, pp. 256-272,
DOI 10.1016/j.comcom.2023.08.009, October 2023,
<https://www.sciencedirect.com/science/article/pii/
S0140366423002931>.
[LEN2024a] Lencse, G. and Á. Bazsó, "Benchmarking methodology for
IPv4aaS technologies: Comparison of the scalability of the
Jool implementation of 464XLAT and MAP-T", Computer
Communications, vol. 219, pp. 243-258,
DOI 10.1016/j.comcom.2024.03.007, April 2024,
<https://www.sciencedirect.com/science/article/pii/
S0140366424000999>.
[LEN2024b] Lencse, G., "Making stateless and stateful network
performance measurements unbiased", Computer
Communications, vol. 225, pp. 141-155,
DOI 10.1016/j.comcom.2024.05.018, September 2024,
<https://www.sciencedirect.com/science/article/abs/pii/
S0140366424001993>.
[SCALABILITY]
Lencse, G., "Scalability of IPv6 Transition Technologies
for IPv4aaS", Work in Progress, Internet-Draft, draft-
lencse-v6ops-transition-scalability-05, 14 October 2023,
<https://datatracker.ietf.org/doc/html/draft-lencse-v6ops-
transition-scalability-05>.
[SIITPERF] "Siitperf: An RFC 8219 compliant SIIT and stateful NAT64/
NAT44 tester", commit 165cb7f, September 2023,
<https://github.com/lencsegabor/siitperf>.
Acknowledgements
The authors would like to thank Al Morton, Sarah Banks, Edwin
Cordeiro, Lukasz Bromirski, Sándor Répás, Tamás Hetényi, Timothy
Winters, Eduard Vasilenko, Minh Ngoc Tran, Paolo Volpato, Zeqi Lai,
and Bertalan Kovács for their comments.
The authors thank Warren Kumari, Michael Scharf, Alexey Melnikov,
Robert Sparks, David Dong, Roman Danyliw, Erik Kline, Murray
Kucherawy, Zaheduzzaman Sarker, and Éric Vyncke for their reviews and
comments.
This work was supported by the Japan Trust International Research
Cooperation Program of the National Institute of Information and
Communications Technology (NICT), Japan.
Authors' Addresses
Gábor Lencse
Széchenyi István University
Győr
Egyetem tér 1.
H-9026
Hungary
Email: lencse@sze.hu
Keiichi Shima
SoftBank Corp.
1-7-1 Kaigan, Minato-ku, Tokyo
105-7529
Japan
Email: shima@wide.ad.jp
URI: https://softbank.co.jp/