Internet Engineering Task Force D. O'Reilly
Internet-Draft January 3, 2018
Intended status: Informational
Expires: July 7, 2018
Approaches to Address the Availability of Information in Criminal
Investigations Involving Large-Scale IP Address Sharing Technologies
draft-daveor-cgn-logging-02
Abstract
The use of large-scale IP address sharing technologies (commonly
known as "Carrier-Grade NAT" and "A+P") presents a challenge for law
enforcement agencies due to the fact that incoming source port
information is not routinely logged by Internet-facing servers. The
absence of this information means that it is becoming increasingly
difficult for law enforcement agencies to identify suspects in
criminal activity online. This document considers the reasons why
source port information is not routinely logged by Internet-facing
servers and proposes some immediate-term actions that can be taken to
help improve the situation. A deployment maturity model has been
developed and a study of the support for logging incoming source port
information in common server software is also presented.
Status of This Memo
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Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Centralised Connection Logging . . . . . . . . . . . . . . . 5
4. Challenges to Capturing Source Port . . . . . . . . . . . . . 7
4.1. Lack of Awareness . . . . . . . . . . . . . . . . . . . . 7
4.2. Lack of Support for Logging Source Port . . . . . . . . . 8
4.3. Additional Storage Requirements . . . . . . . . . . . . . 8
4.4. Default Log Formats . . . . . . . . . . . . . . . . . . . 8
4.5. Breaking Existing Tooling . . . . . . . . . . . . . . . . 9
4.6. Accuracy of Recorded Time . . . . . . . . . . . . . . . . 9
4.7. Translation of Source Port by Intermediate Infrastructure 9
5. Comparison Model . . . . . . . . . . . . . . . . . . . . . . 10
6. Support for Logging Source Port . . . . . . . . . . . . . . . 10
7. Conclusions and Next Steps . . . . . . . . . . . . . . . . . 11
7.1. Raise Awareness of the Importance of Logging Source Port 12
7.2. Increase Support for Logging Source Port . . . . . . . . 12
7.3. Update Default Log Formats . . . . . . . . . . . . . . . 12
7.4. Parallel Logging to a Connection Log . . . . . . . . . . 12
7.5. Adequate Timestamp Accuracy in Logs . . . . . . . . . . . 13
7.6. Address Source Port Translation in Intermediate
Infrastructure . . . . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9. Security Considerations . . . . . . . . . . . . . . . . . . . 14
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Informative References . . . . . . . . . . . . . . . . . 14
10.2. Normative References . . . . . . . . . . . . . . . . . . 15
Appendix A. Support for Source Port Logging in Various Server
Software . . . . . . . . . . . . . . . . . . . . . . 17
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 17
1. Introduction
Large-scale IP address sharing technologies (often collectively
referred to as "Carrier-Grade NAT", [RFC6888]) are a helpful tool for
extending the life of IPv4 addresses by allowing multiple endpoints
to share a small number of IPv4 addresses. A number of such
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technologies have been discussed and deployed, such as Dual-Stack
Lite [RFC6333], NAT64 [RFC6146] and NAT444 [I-D.shirasaki-nat444]. A
related category of technologies, known as "Address plus Port", or
"A+P" [RFC6346], are also used for large-scale IP address sharing,
achieved in these cases by using some of the port number bits for
addressing purposes. Multiple examples of this category of
technologies are also available, including Lightweight 4over6
[RFC7596], MAP-E [RFC7597] and MAP-T [RFC7599].
All of these technologies involve extending the space of available
IPv4 addresses by mapping communication from multiple endpoints to a
single, or small number of shared addresses, through the use of port
numbers. The detail of how this is achieved in each technology
varies, but the principle remains the same in all cases.
From the perspective of a server on the Internet, endpoint traffic
that has passed through IP address sharing infrastructure appears to
be originating from the IP address of the address sharing appliance.
Common practice at the present time is for servers to log the
connection time and source IP address of incoming connections.
However, the IP address of the address sharing appliance is not
sufficient to identify the true source of the traffic because
potentially hundreds or thousands of individual endpoints were using
that IP address at the same time. If the need arises during a
criminal investigation to identify the source of a specific
connection, the source port and exact connection time will also be
required. Without this additional information it is highly unlikely
that it will be possible for law enforcement authorities to progress
their investigations.
Information is required from at least two sources to establish the
link from the logs of an Internet-facing server to a specific
subscriber endpoint:
1. The administrator of the Internet-facing server must have logged
enough information to enable the operator of the IP address
sharing infrastructure to isolate a specific subscriber endpoint.
2. The operator of the IP address sharing infrastructure must have
logged sufficient information (for a sufficient length of time)
to be able, when provided with adequate data by a law enforcement
agency, to isolate the relevant subscriber endpoint.
The operators of large-scale IP address sharing infrastructure,
typically Internet Service Providers, are usually required by law to
maintain records of which endpoint was using a particular IP address
and port at a particular time. The period of time for which these
records must be retained is defined by national legislation.
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Irrespective of whether (and for how long) these records are
available, a starting point is needed to indicate to an investigating
law enforcement agency that a particular endpoint was involved in a
suspected criminal activity under investigation. Without such a
starting point, it would be very difficult to progress the
investigation even as far as engagement with the operator of the
address sharing infrastructure. The records of Internet-facing
servers are often a crucial source of this type of evidence.
It has been recognised for some time that IP address sharing presents
a challenge to the ability to trace network use and abuse [RFC7620].
Further, it has also been recognised that this challenge is likely to
become more severe and widespread with the increased use of large-
scale address sharing [RFC6269]. More recently, Europol has
highlighted the issue of large-scale IP address sharing as a threat
to Internet governance [EUROPOL_IOCTA]. It is reported that the
problem of crime attribution related to the use of carrier-grade NAT
technologies is regularly encountered by 90% of respondents to a
survey on the topic.
Address sharing, including large-scale address sharing, is required
as long as the use of IPv4 continues. Full deployment of IPv6 has
the potential to ultimately eliminate the current attribution issues
arising from the use of large-scale address sharing technologies,
although presumably new attribution challenges will arise in that
scenario. Since it is impossible to anticipate if or when full
migration to IPv6 will take place, it is prudent to consider the
implications of the transitionary technologies until the need for
them has been eliminated.
2. Scope
Previous work has already suggested as best practice the logging by
Internet-facing servers of source IP address, source port and exact
connection time [RFC6302]. However, this continues to be
exceptional, rather than routine, logging practice. The purpose of
this document is to consider in more detail how it might be possible
to bring about routine logging by Internet-facing servers of the
information needed to re-establish the ability to trace network abuse
for criminal investigative purposes. This document specifically does
not address or consider the logging requirements of operators of
large-scale address sharing infrastructre. Instead, the focus is on
the logging considerations of operators of Internet-facing servers.
The main contributions of this document are:
1. To consider the reasons why source port logging is not routinely
carried out.
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2. To identify some possible solutions and workarounds for the
reasons that source port logging is not routinely carried out.
3. To examine the feasibility of source port logging from the
perspective of software support for this feature.
Clearly no single solution will address the problem of crime
attribution on the Internet. Load balancers, proxies and other
network infrastructure may also, intentionally or as a side-effect,
obfuscate the true source of Internet traffic and these problems will
continue to exist with or without the presence of large-scale address
sharing technologies (like Carrier-Grade NAT and A+P). Nevertheless,
at the time of writing large-scale address sharing technologies
present a significant challenge to crime attribution, as highlighted
by Europol in the above referenced link, and this document attempts
to consider the challenges specifically presented by that category of
technologies.
The discussion begins by considering whether centralised connection
logging is a viable solution to the problem of subscriber
identification in criminal investigations. This is followed by an
examination of the reasons why source port logging is not currently
routinely carried out. A model has been developed for the comparison
of the maturity of various server deployments to log source port and
a study of common server software has been performed to assess the
status of support for this functionality. Many, but not all,
enterprise server solutions that were examined made the logging of
source port either "Possible" or "Feasible", as defined in the
maturity model. Only one type of server software examined made the
logging of source port "Default".
3. Centralised Connection Logging
When large-scale IP address sharing technologies are used, source IP
address is no longer a sufficient identifier of an individual
subscriber. At a minimum, source port and accurate timestamp
information are also required to distinguish between the potentially
large number of individual users of a specific IP address at a
particular time. [RFC6269] points out that there are two solutions
to the question of how adequate information can be recorded to
identify the parties to a particular connection. They are:
1. Operators of IP address sharing infrastructure log mappings
between (source IP address, source port) combinations and their
subscribers. Server operators log the IP address and source port
of incoming connections. This is referred to as source port
logging.
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2. Instead of relying on server operators to log the source port of
incoming connections, operators of IP address sharing
infrastructure log all combinations of (external IP address,
external port, destination IP address) for outgoing connections.
This is referred to as connection logging. Server operators log
the IP address and timestamp of incoming connections, which is
the common current practice.
Two challenges to the use of connection logging by operators of IP
address sharing infrastructure are also presented in RFC6269.
Briefly:
o The volumes of data involved make centralised recording of
destination IP addresses infeasible.
o Many individuals using the same IP address to access a popular
destination (e.g. a popular website) might mean that it is not
possible to distinguish between the activity of one subscriber and
another, even if connection records are kept by the operator of
the address sharing infrastructure.
The first issue raised is that the volumes of data involved make
centralised recording of destination IP addresses infeasible.
Whether destination IP addresses are recorded or not, the volume of
logs generated by a large-scale IP address sharing infrastructure
will be substantial, and some approaches have been proposed to
address this hurdle and make central connection logging more
feasible, such as deterministic allocation of ports
[RFC6269],[RFC7422] or allocation of port ranges [RFC7768],
[RFC6346]. While arguments of infeasibility are not arguments in
principle why such logging cannot be done, the volumes of data
involved in recording every single outgoing connection in a large
Internet service provider represent legitimate technical, commercial
and operational arguments for why it can not work in practice. Some
representative figures for the scales of data involved can be found
in [RFC7422], wherein it is estimated that the logging overhead would
be of the order of 150MB per subscriber, per month. For a service
provider with one million subscribers, this would produce a volume of
logs (uncompressed) of the order of 150 terabytes per month. Aside
from the technical overhead of storing such a volume of data,
searching and locating relevant records over an extended, legally
mandated retention period would also present a significant technical
challenge.
The second point raised in [RFC6269] against connection logging by
operators of IP address sharing infrastructure suggests that even if
connection logs store all combinations of (timestamp, source IP,
source port, destination IP), if this information is queried in the
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absence of source port because source port has not been recorded by
the destination IP, this would not be sufficient to distinguish the
activity of one individual from another in cases where the
destination IP is a popular one. This problem is further exacerbated
in the case of protocols that make multiple connections per session
(e.g. HTTP/HTTPS). The implication of this point is that connection
logging, despite potential significant technical and operational
overhead, cannot guarantee that the information retained is
sufficient to identify an individual suspect, even when all required
records are available.
Finally, the privacy concerns arising from connection logging in this
scenario have been repeatedly raised [RFC6888] and
[I-D.ietf-behave-ipfix-nat-logging].
In summary, it is certainly clear that operators of address sharing
infrastructure need to retain records to enable the identification of
suspects, and such records must consist of, at least, sufficient
information to identify an individual subscriber when provided with a
timestamp, source IP, source port and destination IP. However, there
is no centralised solution available that removes the need for server
operators to retain source port information.
4. Challenges to Capturing Source Port
It is relatively easy to articulate the reason why the operator of an
Internet-facing server would wish to retain source port information
for incoming connections. If the server operator (or the users that
they serve) finds themselves the victim of a crime, it is preferable
that all information that could be needed by the server operator to
facilitate a criminal investigation is available. On the other hand,
there are reasons why a server operator might not have the required
source port information. This section enumerates the factors that
could negatively influence both the ability and the inclination of
server operators to capture and record source port information.
4.1. Lack of Awareness
Server operators are principally focussed on delivering the services
for which they are operating their infrastructure. One of the main
problems with the increasing use of IP address sharing technologies
is the lack of awareness on the part of server operators that there
are direct implications for them in case they should become the
victim of a crime.
At the time of writing, a minimal amount of material is available
online concerning this issue, even for those actively seeking to find
out about source port logging. Where specific guidance or
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information has been provided by vendors in relation to the
configuration of source port logging, no explanation is provided for
why this might be something that server operators might consider
desirable. For example [MSDN_IIS_LOG].
There is, therefore, a considerable awareness gap between the
importance of this issue for the purpose of investigating criminal
activity online and the awareness of those who need to act in advance
of any criminality taking place to ensure that the information needed
to facilitate a future investigation is available.
4.2. Lack of Support for Logging Source Port
Before a server operator can decide to log source port information,
the server software must support logging of the source port of
incoming connections. Many, but not all major software distributions
support the logging of the source port of incoming connections.
Clearly lack of support in server software is a technical obstacle
for a server operator to logging source port at the endpoint. It may
still be possible to log source port at some location before the
server endpoint (e.g. at a reverse proxy) but absence of support in
server software will mean that endpoint logging will not be possible.
4.3. Additional Storage Requirements
In cases where it is possible to simply add source port to the list
of fields recorded in log entries, the additional storage required to
preserve source port data is minimal; in the region of six bytes per
log entry (maximum of five ASCII digits for the source port plus an
additional delimiter).
However, in some cases where software supports logging source port of
incoming connections, it has been noted that this can only be
achieved by enabling verbose or debug logging in the software. This
would substantially (and unnecessarily) increase the size of logs
produced by the server and would also, in all probability, reduce the
production performance of the server. These factors would
undoubtedly negatively influence the decision by a server operator to
log incoming source port.
4.4. Default Log Formats
Many major software distributions provide default log formats in
their configuration files. A review of the default log format of
some common server software has been carried out and in only one case
was it found that the source port of incoming connections is logged
by any of the default log formats.
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4.5. Breaking Existing Tooling
Much commercial and free log analysis software, by default, expects
logs to be in a particular format. Consider, for example, the
ubiquity of the Apache Common and Extended Log Formats. The software
can usually be configured to parse arbitrary log formats, but this is
additional configuration work for a server operator. For example:
[ANALOG_LOG_CONFIG],[AWSTATS_LOG_CONFIG]. Without migration
planning, a change to default log formats would most likely cause
substantial disruption to a considerable amount of downstream
processing of server log files. In addition to commercially
available software, many administrators have developed or downloaded
scripts that expect logs to be in a standard log format.
Therefore, log processing software, and in particular custom scripts,
may break if default log formats change unexpectedly. At least, the
tooling may need to be updated to correctly process the additional
fields newly present in log file.
4.6. Accuracy of Recorded Time
As well as recording the IP address and source port of the
connection, it is important to record the exact time of the
connection. It has been suggested that there is a need for keeping
the exact time against some sort of global standard (e.g. NTP)
[RFC6302], however this may not be possible for practical, security
or legacy reasons. In practice, it is usually not necessary to keep
time against a global standard, as long as time is recorded
consistently. The reason for this is that any time offset between
the server and the time recorded in another organisation's records
(running address sharing infrastructure) can be calculated and
compensated for manually. Time offsets of this nature are commonly
encountered and well understood in the digital forensics world.
4.7. Translation of Source Port by Intermediate Infrastructure
It is common for an incoming connection to terminate somewhere other
than the actual server that is intended to ultimately handle the
connection. For example, it is possible that a server operator has
deployed intermediate infrastructure to improve the efficiency or
availability of their platform. Load balancers, proxies or denial of
service countermeasures may be present, any one of which could
potentially terminate the incoming connection. The operation of
these types of intermediate infrastructure can cause translation of
the incoming connection parameters (including source port) before the
connection is established to the actual server endpoint.
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In such cases the source port presented at the server endpoint is a
source port that only has meaning in the intermediate infrastructure
and in most cases will not carry any information about the source
port in use at the connection origin. In the worst case scenario
(from the point of view of crime attribution), the intermediate
infrastructure may obfuscate the true source connection information
in a way that is unrecoverable.
5. Comparison Model
A model has been developed to assist with comparison of the maturity
of server software deployments to store and retrieve source port
information for incoming connections. The model is depicted in
Figure 1.
+-------------------------------------------------------------+
| Possible -> Feasible -> Default -> Manageable -> Accessible |
+-------------------------------------------------------------+
Figure 1
o "Possible": Means that the server software supports, in any way,
the ability to record source ports for incoming connections.
o "Feasible": Means that it there are no significant performance or
storage implications for enabling the storage of source ports.
o "Default": Means that, at a minimum, at least one of the default
log formats provided with the software distribution enables the
storage of source ports.
o "Manageable": Means that tooling is, or has been, build or adapted
to support the storage of source ports.
o "Accessible": Means that it is possible to identify and retrieve
relevant records in the stored log data.
6. Support for Logging Source Port
Open-source research has been conducted to assess the status of
support for logging of source port information in common server
software.
The assessment criteria were as follows:
o Server software is categorised as "Possible" if there was any way
identified to cause the logging of source port.
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o Server software is categorised as "Feasible" if the logging of
source port does not require increasing the log level to cause the
logging of source port to be possible. In other words, if a
server requires enabling verbose, debug or audit logging in order
to be able to record source port then logging is "Possible" but
not "Feasible".
o Server software is categorised as "Default" if at least one of the
available default log formats enables logging of the incoming
source port, or if source port is logged by default.
o The "Manageable" and "Accessible" aspects of the comparison model
relate to specific deployments and are therefore not considered in
the assessment of server software support.
The latest versions of 16 common server software packages have been
examined and documentation has been research to identify if and how
source port logging can be enabled. The findings are described in
Appendix A. Online documentation has been examined to identify if
and how source port logging can be enabled. The results are
presented in the following table:
+----------+----------+---------+------------+------------+
| Possible | Feasible | Default | Manageable | Accessible |
+----------+----------+---------+------------+------------+
| 13 | 11 | 1 | N/A | N/A |
+----------+----------+---------+------------+------------+
Table 1: Support Table
It was noted that only one of the server software packages examined
(OpenSSH version 7.5) enables the logging of incoming source port by
default. This conclusion has been reached despite using the most
generous possible interpretation of "Default", whereby meeting the
criteria for "Default" is achieved when logging of source port is
offered as a possible default, rather than requiring that logging of
source port is enabled by default. In due course, as awareness of
this issue increases, it is envisioned that a stricter interpretation
of "Default" would be more appropriate, requiring that the logging of
source port be enabled by default.
7. Conclusions and Next Steps
There is clearly substantial work to be done to bring about the
regular recording of source port information at Internet-facing
servers and there are undoubtedly criminals free right now because
the information required to identify them from their online activity
is not available.
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The next steps presented below are some possible courses of action
that have been identified based on the current state of source port
logging and the challenges described above.
7.1. Raise Awareness of the Importance of Logging Source Port
Publishers of both free and commercial software should consider
releasing deployment guidance or best practice that describes why
server administrators need to be recording source port information,
with instructions for how this can be done. This will help to
address the lack of awareness of the importance of this issue.
Considering also the awareness of those who are building software
applications, or otherwise involved with coding of Internet-facing
applications, secure coding guidance should be updated to include
reference to source port information, particularly where such
guidance already touches on the issue of logging. For example the
OWASP Secure Coding Practices specifies a list of important log event
data [OWASP_SCP]. However the "important log event data" list does
not, at the time of writing, include source port.
7.2. Increase Support for Logging Source Port
Many software packages support logging of source port information,
but only ten out of the sixteen examined support logging in a way
that would not significantly negatively impact the operation of the
server software. Software publishers therefore need to consider
their level of support of logging source port. In particular,
software should support the logging of source port without needing to
enable a verbose logging level.
7.3. Update Default Log Formats
In cases where a particular software package has support for logging
of incoming source port, one possibility would be to incorporate one
or more log formats that include incoming source port as a field
logged by default. Obviously this will not have any impact on
deployments of the software that are already in place but for future
deployments, the incorporation of source port into the log format
will mean that those administrators that use the unaltered default
log format will automatically store the required information.
7.4. Parallel Logging to a Connection Log
Where possible, configuring parallel logging of connection
information to a separate log stream would be one possible solution
to address the fact that changes to log format might break downstream
tooling. This would also be a possible solution that could be used
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by those server software types that log via syslog. In this case,
software publishers could produce guidance on how to configure syslog
to log connection information parallel to main log files.
Such a solution would help to ease the transition to an alternate log
format since current log formats would not need to be changed because
the required source port information is stored separately, but can
still be correlated with the main log files if needed.
7.5. Adequate Timestamp Accuracy in Logs
Operators of large-scale address sharing infrastructure will, most
likely need connection times specified with at least the granularity
of a second. Most, but not all, server software will log times with
this granularity by default but there is no guarantee that this is
the case.
Consideration should be given by server operators to making sure that
the times that are being recorded in their log files have sufficient
accuracy to allow identification of the required records. As
mentioned earlier, the times do not necessarily need to be recorded
with reference to a centralised time source (e.g. NTP) as long as
times are recorded consistently.
This factor also needs to be considered by software developers when
they are producing software and although the recording of time is
mentioned in the OWASP Secure Coding Practices, the required
accuracy/granularity of the recorded time is not discussed
[OWASP_SCP].
7.6. Address Source Port Translation in Intermediate Infrastructure
In cases described above where intermediate infrastructure terminates
incoming connections (proxies, load balancers, etc.), and the
infrastructure is translating incoming source port information, there
is a risk that the important crime attribution information may be
lost. One possibility is to log source port information at the
intermediate infrastructure and this may be an appropriate solution
in some cases. The problem is that this may lead to an excessive
volume of logging, depending on the particular scenario. For example
if the intermediate infrastructure is being used to mitigate DDoS
attacks, logging all incoming traffic would potentially lead to
logging of all incoming DDoS connections. This would clearly be an
undesirable outcome.
An alternative solution is to pass information about the original
connection (before mapping/translation of connection information
takes place) to the actual endopint. Solutions to achieve this
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already exist for certain application layer protocols. The Forwarded
HTTP Extention [RFC7239], for example, supports (as an optional
feature) the tranfer of source port information in the "Forwarded
For" header, and this technique can also support multiple layers of
proxying without loss of attribution.
8. IANA Considerations
This memo includes no request to IANA.
9. Security Considerations
Clearly a balance needs to be struck between individual right to
privacy and law enforcement access to data during criminal
investigations. On the one hand, the routine logging of any
additional information has the potential to introduce risks related
to privacy and human rights. On the other hand, it is fair to say
that there are criminals free today because the data required to
identify them is not available due to the use of large-scale address
sharing technologies. Across the world there are also a broad
spectrum of legislative regimes and human rights challenges,
interpretation of which relate directly to this question.
IP addresses are routinely logged today and this information can be
used for identification of people online in some cases. The cases in
which an IP addresses does not identify an individual directly are
not necessarily apparent to the person performing the logging (who
cannot tell, for example, if the true source of the traffic is behind
a NAT or other form of proxy) and the same is true even if source
port is logged. It is not apparent that there is any additional risk
to individual privacy between the case when a single piece of
endpoint identifying information (source IP address) is logged versus
the case when two pieces of endpoint identifying information (source
IP address and source port) are logged. Balancing this against the
significant advantages from the crime attribution point of view
suggests that this may be a worthwhile approach.
10. References
10.1. Informative References
[I-D.ietf-behave-ipfix-nat-logging]
Sivakumar, S. and R. Penno, "IPFIX Information Elements
for logging NAT Events", draft-ietf-behave-ipfix-nat-
logging-13 (work in progress), January 2017.
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[I-D.shirasaki-nat444]
Yamagata, I., Shirasaki, Y., Nakagawa, A., Yamaguchi, J.,
and H. Ashida, "NAT444", draft-shirasaki-nat444-06 (work
in progress), July 2012.
10.2. Normative References
[ANALOG_LOG_CONFIG]
Analog, "Analog 6.0: Log formats", 2017,
<http://mirror.reverse.net/pub/analog/docs/logfmt.html>.
[AWSTATS_LOG_CONFIG]
AWStats, "AWStats Installation, Configuration and
Reporting (for version 7.6)", 2017,
<https://awstats.sourceforge.io/docs/awstats_setup.html>.
[EUROPOL_IOCTA]
Europol, "The Internet Organised Crime Threat Assessment",
2016, <https://www.europol.europa.eu/activities-services/
main-reports/
internet-organised-crime-threat-assessment-iocta-2016>.
[MSDN_IIS_LOG]
Microsoft, "IIS 8.5 - How to log client port number",
2015, <https://blogs.msdn.microsoft.com/amb/2015/11/12/
iis-8-5-how-to-log-client-port-number/>.
[OWASP_SCP]
OWASP, "OWASP Secure Coding Practices Quick Reference
Guide", 2010, <https://www.owasp.org/images/0/08/
OWASP_SCP_Quick_Reference_Guide_v2.pdf>.
[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>.
[RFC6269] Ford, M., Ed., Boucadair, M., Durand, A., Levis, P., and
P. Roberts, "Issues with IP Address Sharing", RFC 6269,
DOI 10.17487/RFC6269, June 2011,
<https://www.rfc-editor.org/info/rfc6269>.
[RFC6302] Durand, A., Gashinsky, I., Lee, D., and S. Sheppard,
"Logging Recommendations for Internet-Facing Servers",
BCP 162, RFC 6302, DOI 10.17487/RFC6302, June 2011,
<https://www.rfc-editor.org/info/rfc6302>.
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[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011,
<https://www.rfc-editor.org/info/rfc6333>.
[RFC6346] Bush, R., Ed., "The Address plus Port (A+P) Approach to
the IPv4 Address Shortage", RFC 6346,
DOI 10.17487/RFC6346, August 2011,
<https://www.rfc-editor.org/info/rfc6346>.
[RFC6888] Perreault, S., Ed., Yamagata, I., Miyakawa, S., Nakagawa,
A., and H. Ashida, "Common Requirements for Carrier-Grade
NATs (CGNs)", BCP 127, RFC 6888, DOI 10.17487/RFC6888,
April 2013, <https://www.rfc-editor.org/info/rfc6888>.
[RFC7239] Petersson, A. and M. Nilsson, "Forwarded HTTP Extension",
RFC 7239, DOI 10.17487/RFC7239, June 2014,
<https://www.rfc-editor.org/info/rfc7239>.
[RFC7422] Donley, C., Grundemann, C., Sarawat, V., Sundaresan, K.,
and O. Vautrin, "Deterministic Address Mapping to Reduce
Logging in Carrier-Grade NAT Deployments", RFC 7422,
DOI 10.17487/RFC7422, December 2014,
<https://www.rfc-editor.org/info/rfc7422>.
[RFC7596] Cui, Y., Sun, Q., Boucadair, M., Tsou, T., Lee, Y., and I.
Farrer, "Lightweight 4over6: An Extension to the Dual-
Stack Lite Architecture", RFC 7596, DOI 10.17487/RFC7596,
July 2015, <https://www.rfc-editor.org/info/rfc7596>.
[RFC7597] Troan, O., Ed., Dec, W., Li, X., Bao, C., Matsushima, S.,
Murakami, T., and T. Taylor, Ed., "Mapping of Address and
Port with Encapsulation (MAP-E)", RFC 7597,
DOI 10.17487/RFC7597, July 2015,
<https://www.rfc-editor.org/info/rfc7597>.
[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>.
[RFC7620] Boucadair, M., Ed., Chatras, B., Reddy, T., Williams, B.,
and B. Sarikaya, "Scenarios with Host Identification
Complications", RFC 7620, DOI 10.17487/RFC7620, August
2015, <https://www.rfc-editor.org/info/rfc7620>.
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[RFC7768] Tsou, T., Li, W., Taylor, T., and J. Huang, "Port
Management to Reduce Logging in Large-Scale NATs",
RFC 7768, DOI 10.17487/RFC7768, January 2016,
<https://www.rfc-editor.org/info/rfc7768>.
Appendix A. Support for Source Port Logging in Various Server Software
The table below enumerates the findings of best-effort, open-source
review of documentation of the various products. Where it has been
indicated that it is not possible to log source port then either (a)
no reference has been identified in online documentation to indicate
how source port logging can be enabled, or (b) a reference positively
indicating that logging of source port is not possible has been
found.
+---------+------------+------------+----------+----------+---------+
| Categor | Server | Version | Possible | Feasible | Default |
| y | | | | | |
+---------+------------+------------+----------+----------+---------+
| HTTP | Apache | 2.4.25 | Yes | Yes | No |
| | HTTPD | | | | |
| HTTP | IIS | 10 | Yes | Yes | No |
| HTTP | Tomcat | 8.5.15 | Yes | Yes | No |
| HTTP | Squid | 3.5.25 | Yes | Yes | No |
| HTTP | nginx | 1.12.0 | Yes | Yes | No |
| Mail | sendmail | 8.15.2 | Yes | Yes | No |
| Mail | Microsoft | 2016 | Yes | No | No |
| | Exchange | | | | |
| | Server | | | | |
| Mail | Postfix | 2.10.0 | Yes | Yes | No |
| Mail | Exim | 4.89 | Yes | Yes | No |
| Mail | Dovecot | 2.2.30.1 | Yes | Yes | No |
| Mail | UW IMAP | imap-2007f | No | No | No |
| DBase | Oracle | 12.2.0.1 | No | No | No |
| DBase | MySQL | 5.7.18 | No | No | No |
| DBase | Microsoft | 2016 | Yes | No | No |
| | SQL Server | | | | |
| DBase | PostgreSQL | 9.6.3 | Yes | Yes | No |
| SSH | OpenSSHD | 7.5 | Yes | Yes | Yes |
+---------+------------+------------+----------+----------+---------+
Table 2: Support for Logging Incoming Source Port
Author's Address
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David O'Reilly
Ireland
Email: rfc@daveor.com
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