draft-irtf-pearg-numeric-ids-history-10.xml

<?xml version="1.0" encoding="US-ASCII"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd" [
]>
<?xml-stylesheet type="text/xsl" href="rfc2629.xslt" ?> <!-- used by XSLT processors -->
<!-- OPTIONS, known as processing instructions (PIs) go here. -->
<?rfc toc="yes" ?>
<?rfc symrefs="yes" ?>
<?rfc strict="no" ?>

<rfc category="info" docName="draft-irtf-pearg-numeric-ids-history-10" ipr="trust200902" submissionType="IRTF">

<front>
<title abbrev="Predictable Transient Numeric IDs">Unfortunate History of Transient Numeric Identifiers</title>

    <author fullname="Fernando Gont" initials="F." surname="Gont">
      <organization abbrev="SI6 Networks">SI6 Networks</organization>

      <address>
        <postal>
	  <street>Segurola y Habana 4310 7mo piso</street>	
          <city>Ciudad Autonoma de Buenos Aires</city>
          <region>Buenos Aires</region>
          <country>Argentina</country>
        </postal>

<!--       <phone>+54 11 4650 8472</phone> -->
        <email>fgont@si6networks.com</email>
        <uri>https://www.si6networks.com</uri>

       </address>
    </author>
    
    <author fullname="Ivan Arce" initials="I." surname="Arce">
      <organization abbrev="Quarkslab">Quarkslab</organization>

      <address>
        <postal>
	  <street>Segurola y Habana 4310 7mo piso</street>	
          <city>Ciudad Autonoma de Buenos Aires</city>
          <region>Buenos Aires</region>
          <country>Argentina</country>
        </postal>

        <email>iarce@quarkslab.com</email>

        <uri>https://www.quarkslab.com</uri>

       </address>
    </author>

<date/>

<workgroup>Internet Research Task Force (IRTF)</workgroup>
<!--
<area>Internet</area>
<workgroup>Dynamic Host Configuration (dhc)</workgroup>
-->
<!-- <area/> -->
<!-- <workgroup/> -->

    <abstract>
    <t>
This document analyzes the timeline of the specification and implementation of different types of "transient numeric identifiers" used in IETF protocols, and how the security and privacy properties of such protocols have been affected as a result of it. It provides empirical evidence that advice in this area is warranted. This document is a product of the Privacy Enhancement and Assessment Research Group (PEARG) in the IRTF.
    </t>
    </abstract>
</front>

  <middle>
  
<section title="Introduction" anchor="intro">
<t>
Networking protocols employ a variety of transient numeric identifiers for different protocol objects, such as IPv4 and IPv6 Fragment Identifiers <xref target="RFC0791"/> <xref target="RFC8200"/>, IPv6 Interface Identifiers (IIDs) <xref target="RFC4291"/>, transport protocol ephemeral port numbers <xref target="RFC6056"/>, TCP Initial Sequence Numbers (ISNs) <xref target="RFC0793"/>, NTP Reference IDs (REFIDs) <xref target="RFC5905"/>, and DNS Query IDs <xref target="RFC1035"/>. These identifiers typically have specific interoperability requirements (e.g. uniqueness during a specified period of time), and associated failure severities when such requirements are not met <xref target="I-D.irtf-pearg-numeric-ids-generation"/>.
</t>

<t>For more than 30 years, a large number of implementations of the IETF protocols have been subject to a variety of attacks, with effects ranging from Denial of Service (DoS) or data injection, to information leakages that could be exploited for pervasive monitoring <xref target="RFC7258"/>. The root cause of these issues has been, in many cases, poor selection of transient numeric identifiers, usually as a result of insufficient or misleading specifications.</t>

<t>For example, implementations have been subject to security or privacy issues resulting from:


<list style="symbols">
<t>Predictable IPv4 or IPv6 Fragment Identifiers (see e.g. <xref target="Sanfilippo1998a"/>, <xref target="RFC6274"/>, and <xref target="RFC7739"/>)</t>
<t>Predictable IPv6 IIDs (see e.g. <xref target="RFC7721"/>, <xref target="RFC7707"/>, and <xref target="RFC7217"/>)</t> 
<t>Predictable transport protocol ephemeral port numbers (see e.g. <xref target="RFC6056"/> and <xref target="Silbersack2005"/>)</t>
<t>Predictable TCP Initial Sequence Numbers (ISNs) (see e.g. <xref target="Morris1985"/>, <xref target="Bellovin1989"/>, and <xref target="RFC6528"/>)</t>
<t>Predictable DNS Query IDs (see e.g. <xref target="Arce1997"/> and <xref target="Klein2007"/>)</t>
</list>



These examples indicate that when new protocols are standardized or implemented, the security and privacy properties of the associated transient numeric identifiers tend to be overlooked, and inappropriate algorithms to generate such identifiers (i.e. that negatively affect the security or privacy properties of the protocol) are either suggested in the specification or selected by implementers. 
</t>
<t>This document contains a non-exhaustive timeline of the specification and vulnerability disclosures related to some sample transient numeric identifiers, including other work that has led to advances in this area. This analysis indicates that:
<list style="symbols">
<t>Vulnerabilities associated with the inappropriate generation of transient numeric identifiers have affected protocol implementations for an extremely long period of time.</t>

<t>Such vulnerabilities, even when addressed for a given protocol version, were later reintroduced in new versions or new implementations of the same protocol.</t>

<t>Standardization efforts that discuss and provide advice in this area can have a positive effect on IETF specifications and their corresponding implementations.</t>
</list>
</t>


<t>While it is generally possible to identify an algorithm that can satisfy the interoperability requirements for a given transient numeric identifier, this document provides empirical evidence that doing so without negatively affecting the security or privacy properties of the aforementioned protocols is non-trivial. Other related documents (<xref target="I-D.irtf-pearg-numeric-ids-generation"/> and <xref target="I-D.gont-numeric-ids-sec-considerations"/>) provide guidance in this area, as motivated by the present document.</t>

<t>This document represents the consensus of the Privacy Enhancement and Assessment Research Group (PEARG).</t>
</section>


<section title="Terminology" anchor="terminology">

<t>
<list style="hanging">

<t hangText="Transient Numeric Identifier:">
<vspace blankLines="0" />A data object in a protocol specification that can be used to definitely distinguish a protocol object (a datagram, network interface, transport protocol endpoint, session, etc) from all other objects of the same type, in a given context. Transient numeric identifiers are usually defined as a series of bits, and represented using integer values. These identifiers are typically dynamically selected, as opposed to statically-assigned numeric identifiers (see e.g. <xref target="IANA-PROT"/>). We note that different identifiers may have additional requirements or properties depending on their specific use in a protocol. We use the term "transient numeric identifier" (or simply "numeric identifier" or "identifier" as short forms) as a generic term to refer to any data object in a protocol specification that satisfies the identification property stated above.
</t>


</list>
</t>

<t>
   The terms "constant IID", "stable IID", and "temporary IID" are to be
   interpreted as defined in <xref target="RFC7721"/>.

</t>

<!--
<t>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 <xref target='RFC2119' /> <xref target='RFC8174' /> when, and only when, they
      appear in all capitals, as shown here.
</t>
-->
</section>


<!--
<section title="Threat Model" anchor="threat-model">
<t>Throughout this document, we assume an attacker does not have physical or logical access to the system(s) being attacked, and cannot necessarily observe all the packets being transferred between the sender and the receiver(s) of the
target protocol, but may be able to observe some of them. However, we assume the attacker can send any traffic to the target device(s), to e.g. sample transient numeric identifiers employed by such device(s).
</t>
</section>
-->

<section title="Threat Model" anchor="threat-model">
<!--
<t>Throughout this document, we assume an attacker does not have physical or logical access to the system(s) being attacked, and cannot necessarily observe all the packets being transferred between the sender and the receiver(s) of the
target protocol, but may be able to observe some of them. However, we assume the attacker can send any traffic to the target device(s), to e.g. sample transient numeric identifiers employed by such device(s).
</t>
-->

<t>Throughout this document, we assume an attacker does not have physical or logical access to the system(s) being attacked, and that the attacker can only observe traffic explicitly directed to the attacker. For example, an attacker cannot observe traffic transferred between a sender and the receiver(s) of a target protocol, but may be able to interact with any of these entities, including by e.g. sending any traffic to them to sample transient numeric identifiers employed by the target systems when communicating with the attacker.
</t>

<t>For example, when analyzing vulnerabilities associated with TCP Initial Sequence Numbers (ISNs), we consider the attacker is unable to capture network traffic corresponding to a TCP connection between two other hosts. However, we consider the attacker is able to communicate with any of these hosts (e.g., establish a TCP connection with any of them), to e.g. sample the TCP ISNs employed by these systems when communicating with the attacker.</t>

<t>Similarly, when considering host-tracking attacks based on IPv6 interface identifiers, we consider an attacker may learn the IPv6 address employed by a victim node if e.g. the address becomes exposed as a result of the victim node communicating with an attacker-operated server. Subsequently, an attacker may perform host-tracking by probing a set of target addresses composed by a set of target prefixes and the IPv6 interface identifier originally learned by the attacker. Alternatively, an attacker may perform host tracking if e.g. the victim node communicates with an attacker-operated server as it moves from one location to another, those exposing its configured addresses. We note that none of these scenarios requires the attacker observe traffic not explicitly directed to the attacker.
</t>


</section>


<section title="Issues with the Specification of Transient Numeric Identifiers" anchor="issues">
<t>While assessing IETF protocol specifications regarding the use of transient numeric identifiers, we have found that most of the issues discussed in this document arise as a result of one of the following conditions:

<list style="symbols">
<t>Protocol specifications that under-specify the requirements for their transient numeric identifiers</t>
<t>Protocol specifications that over-specify their transient numeric identifiers</t>
<t>Protocol implementations that simply fail to comply with the specified requirements</t>
</list>
</t>

<t>A number of IETF protocol specifications have simply overlooked the security and privacy implications of transient numeric identifiers. Examples of them are the specification of TCP ephemeral ports in <xref target="RFC0793"/>, the specification of TCP sequence numbers in <xref target="RFC0793"/>, or the specification of the DNS TxID in <xref target="RFC1035"/>.</t>

<t>On the other hand, there are a number of IETF protocol specifications that over-specify some of their associated transient numeric identifiers. For example, <xref target="RFC4291"/> essentially overloads the semantics of IPv6 Interface Identifiers (IIDs) by embedding link-layer addresses in the IPv6 IIDs, when the interoperability requirement of uniqueness could be achieved in other ways that do not result in negative security and privacy implications <xref target="RFC7721"/>. Similarly, <xref target="RFC2460"/> suggested the use of a global counter for the generation of Fragment Identification values, when the interoperability properties of uniqueness per {Src IP, Dst IP} could be achieved with other algorithms that do not result in negative security and privacy implications <xref target="RFC7739"/>.</t>

<t>Finally, there are implementations that simply fail to comply with the corresponding IETF protocol specifications or recommendations. For example, some popular operating systems (notably Microsoft Windows) still fail to implement transport protocol ephemeral port randomization, as recommended in <xref target="RFC6056"/>.</t>


<t>The following subsections document the timelines for a number of sample transient numeric identifiers, that illustrate how the problem discussed in this document has affected protocols from different layers over time. These sample transient numeric identifiers have different interoperability requirements and failure severities (see Section 6 of <xref target="I-D.irtf-pearg-numeric-ids-generation"/>), and thus are considered to be representative of the problem being analyzed in this document.</t>

<section title="IPv4/IPv6 Identification" anchor="ipid">
<t>This section presents the timeline of the Identification field employed by IPv4 (in the base header) and IPv6 (in Fragment Headers). The reason for presenting both cases in the same section is to make it evident that while the Identification value serves the same purpose in both IPv4 and IPv6, the work and research done for the IPv4 case did not affect IPv6 specifications or implementations.</t>

<t>The IPv4 Identification is specified in <xref target="RFC0791"/>, which specifies the interoperability requirements for the Identification field: the sender must choose the Identification field to be unique for a  given source address, destination address, and protocol, for the time the datagram (or any fragment of it) could be alive in the internet. It suggests that a node may keep "a table of Identifiers, one entry for each destination it has communicated with in the last maximum packet lifetime for the internet", and suggests that "since the Identifier field allows 65,536 different values, hosts may be able to simply use unique identifiers independent of destination". The above has been interpreted numerous times as a suggestion to employ per-destination or global counters for the generation of Identification values. While <xref target="RFC0791"/> does not suggest any flawed algorithm for the generation of Identification values, the specification omits a discussion of the security and privacy implications of predictable Identification values. This has resulted in many IPv4 implementations generating predictable fragment Identification values by means of a global counter, at least at some point in time.
</t>

<t>
The IPv6 Identification was originally specified in <xref target="RFC1883"/>. It serves the same purpose as its IPv4 counterpart, with the only difference residing in the length of the corresponding field, and that while the IPv4 Identification field is part of the base IPv4 header, in the IPv6 case it is part of the Fragment header (which may or may not be present in an IPv6 packet). <xref target="RFC1883"/> states, in Section 4.5, that the Identification must be different than that of any other fragmented packet sent recently (within the maximum likely lifetime of a packet) with the same Source Address and Destination Address. Subsequently, it notes that this requirement can be met by means of a wrap-around 32-bit counter that is incremented each time a packet must be fragmented, and that it is an implementation choice whether to use a global or a per-destination counter. Thus, the implementation of the IPv6 Identification is similar to that of the IPv4 case, with the only difference that in the IPv6 case the suggestions to use simple counters is more explicit. <xref target="RFC2460"/> was the first revision of the core IPv6 specification, and maintained the same text for the specification of the IPv6 Identification field. <xref target="RFC8200"/>, the second revision of the core IPv6 specification, removes the suggestion from <xref target="RFC2460"/> to use a counter for the generation of IPv6 Identification values, and points to <xref target="RFC7739"/> for sample algorithms for their generation.
</t>


<t>
<list style="hanging">
<t hangText="September 1981:">
<vspace blankLines="0" /><xref target="RFC0791"/> specifies the interoperability requirements for IPv4 Identification value, but does not perform a vulnerability assessment of this transient numeric identifier.
</t>

<t hangText="December 1995:">
<vspace blankLines="0" /><xref target="RFC1883"/>, the first specification of the IPv6 protocol, is published. It suggests that a counter be used to generate the IPv6 Identification value, and notes that it is an implementation choice whether to maintain a single counter for the node or multiple counters, e.g., one for each of the node's possible source addresses, or one for each active (source address, destination address) combination.
</t>

<t hangText="December 1998:">
<vspace blankLines="0" /><xref target="Sanfilippo1998a"/> finds that predictable IPv4 Identification values (generated by most popular implementations) can be leveraged to count the number of packets sent by a target node. <xref target="Sanfilippo1998b"/> explains how to leverage the same vulnerability to implement a port-scanning technique known as &quot;dumb/idle scan&quot;. A tool that implements this attack is publicly released.
</t>

<t hangText="December 1998:">
<vspace blankLines="0" /><xref target="RFC2460"/>, a revision of the IPv6 specification, is published, obsoleting <xref target="RFC1883"/>. It maintains the same specification of the IPv6 Identification field as its predecessor (<xref target="RFC1883"/>).
</t>

<t hangText="December 1998:">
<vspace blankLines="0" />OpenBSD implements randomization of the IPv4 Identification field <xref target="OpenBSD-IPv4-ID"/>. <!--This feature eventually shipped with OpenBSD 2.5.-->
</t>


<t hangText="November 1999:">
<vspace blankLines="0" /><xref target="Sanfilippo1999"/> discusses how to leverage predictable IPv4 Identification to uncover the rules of a number of firewalls.
</t>



<t hangText="September 2002:">
<vspace blankLines="0" /><xref target="Fyodor2002"/> documents the implementation of the "idle/dumb scan" technique in the popular nmap tool.
</t>


<t hangText="November 2002:">
<vspace blankLines="0" /><xref target="Bellovin2002"/> explains how the IPv4 Identification field can be exploited to count the number of systems behind a NAT.
</t>

<t hangText="October 2003:">
<vspace blankLines="0" />OpenBSD implements randomization of the IPv6 Identification field <xref target="OpenBSD-IPv6-ID"/>.<!-- This feature eventually shipped with OpenBSD 3.4.-->
</t>

<t hangText="December 2003:">
<vspace blankLines="0" /><xref target="Zalewski2003"/> explains a technique to perform TCP data injection attacks based on predictable IPv4 identification values, which requires less effort than TCP injection attacks performed with bare TCP packets.
</t>


<t hangText="November 2005:">
<vspace blankLines="0" /><xref target="Silbersack2005"/> discusses shortcomings in a number of techniques to mitigate predictable IPv4 Identification values.
</t>


<t hangText="October 2007:">
<vspace blankLines="0" /><xref target="Klein2007"/> describes a weakness in the pseudo random number generator (PRNG) in use for the generation of the IP Identification by a number of operating systems.
</t> 

<t hangText="June 2011:">
<vspace blankLines="0" /><xref target="Gont2011"/> describes how to perform dumb/idle scan attacks in IPv6.
</t> 

<t hangText="November 2011:">
<vspace blankLines="0" />Linux mitigates predictable IPv6 Identification values <xref target="RedHat2011"/> <xref target="SUSE2011"/> <xref target="Ubuntu2011"/>.
</t>


<t hangText="December 2011:">
<vspace blankLines="0" /><xref target="draft-gont-6man-predictable-fragment-id-00"/> describes the security implications of predictable IPv6 Identification values, and possible mitigations. This document has the Intended Status of &quot;Standards Track&quot;, with the intention to formally update <xref target="RFC2460"/>, to introduce security and privacy requirements on the generation of IPv6 Identification values.
</t>

<t hangText="May 2012:">
<vspace blankLines="0" /><xref target="Gont2012"/> notes that some major IPv6 implementations still employ predictable IPv6 Identification values.
</t>

<!-- [fgont] Historia de RFC7739 -->
<t hangText="March 2013:">
<vspace blankLines="0" />The 6man WG adopts <xref target="I-D.gont-6man-predictable-fragment-id"/>, but changes the track to "BCP" (while still formally updating <xref target="RFC2460"/>), publishing the resulting document as <xref target="draft-ietf-6man-predictable-fragment-id-00"/>.
</t>

 
<t hangText="June 2013:">
<vspace blankLines="0" />A patch to incorporate support for IPv6-based idle/dumb scans in nmap is submitted <xref target="Morbitzer2013"/>.
</t>

<t hangText="December 2014:">
<vspace blankLines="0" />The 6man WG changes the Intended Status of <xref target="draft-ietf-6man-predictable-fragment-id-01"/> to "Informational" and publishes it as <xref target="draft-ietf-6man-predictable-fragment-id-02"/>. As a result, it no longer formally updates <xref target="RFC2460"/>, and security and privacy requirements on the generation of IPv6 Identification values are eliminated.
</t>


<t hangText="June 2015:">
<vspace blankLines="0" /><xref target="draft-ietf-6man-predictable-fragment-id-08"/> notes that some popular host and router implementations still employ predictable IPv6 Identification values.
</t>

<t hangText="February 2016:">
<vspace blankLines="0" /><xref target="RFC7739"/> (based on <xref target="I-D.ietf-6man-predictable-fragment-id"/>) analyzes the security and privacy implications of predictable IPv6 Identification values, and provides guidance for selecting an algorithm to generate such values. However, being published with the Intended Status of &quot;Informational&quot;, it does not formally update <xref target="RFC2460"/>, and does not introduce security and privacy requirements on the generation of IPv6 Identification values. <!--Note: The oiginal individual submission IP, revision of <xref target="RFC2460"/> removes the suggestion from RFC2460 to employ a global counter for the generation of IPv6 Identification values, but does specify any security and privacy requirements for the IPv6 Identification value.-->
</t>

<t hangText="June 2016:">
<vspace blankLines="0" /><xref target="I-D.ietf-6man-rfc2460bis"/>, revision of <xref target="RFC2460"/>, removes the suggestion from RFC2460 to use a counter for the generation of IPv6 Identification values, but does not perform a vulnerability assessment of the generation of IPv6 Identification values, and does not introduce security and privacy requirements on the generation of IPv6 Identification values.
</t>

<t hangText="July 2017:">
<vspace blankLines="0" /><xref target="I-D.ietf-6man-rfc2460bis"/> is finally published as <xref target="RFC8200"/>, obsoleting <xref target="RFC2460"/>, and pointing to <xref target="RFC7739"/> for sample algorithms for the generation of IPv6 Fragment Identification values. However, it does not introduce security and privacy requirements on the generation of IPv6 Identification values.
</t>

<t hangText="June 2019:">
<vspace blankLines="0" /><xref target="IPID-DEV"/> notes that the IPv6 ID generators of two popular operating systems are flawed.
</t>


</list>
</t>
</section>

<section title="TCP Initial Sequence Numbers (ISNs)" anchor="tcp-isns">
<t>
<xref target="RFC0793"/> suggests that the choice of the ISN of a connection is not arbitrary, but aims to reduce the chances of a stale segment from being accepted by a new incarnation of a previous connection. <xref target="RFC0793"/> suggests the use of a global 32-bit ISN generator that is incremented by 1 roughly every 4 microseconds. However, as a matter of fact, protection against stale segments from a previous incarnation of the connection is enforced by preventing the creation of a new incarnation of a previous connection before 2*MSL have passed since a segment corresponding to the old incarnation was last seen (where "MSL" is the "Maximum Segment Lifetime" <xref target="RFC0793"/>). This is accomplished by the TIME-WAIT state and TCP's "quiet time" concept (see Appendix B of <xref target="RFC1323"/>). Based on the assumption that ISNs are monotonically increasing across connections, many stacks (e.g., 4.2BSD-derived) use the ISN of an incoming SYN segment to perform "heuristics" that enable the creation of a new incarnation of a connection while the previous incarnation is still in the TIME-WAIT state (see p. 945 of <xref target="Wright1994"/>). This avoids an interoperability problem that may arise when a node establishes connections to a specific TCP end-point at a high rate <xref target="Silbersack2005"/>.</t>

<t>The interoperability requirements for TCP ISNs are probably not as clearly spelled out as one would expect. Furthermore, the suggestion of employing a global counter in <xref target="RFC0793"/> negatively affects the security and privacy properties of the protocol.</t>

<t>
<list style="hanging">
<t hangText="September 1981:">
<vspace blankLines="0" /><xref target="RFC0793"/>, suggests the use of a global 32-bit ISN
generator, whose lower bit is incremented roughly every 4 microseconds. However, such an ISN generator makes it trivial to predict the ISN that a TCP instance will use for new connections, thus allowing a variety of attacks against TCP.
</t>

<!--
<t hangText="September 1981:">
<vspace blankLines="0" /><xref target="RFC0793"/>, suggests the use of a global 32-bit ISN
generator, whose lower bit is incremented roughly every 4 microseconds. However, such an ISN generator makes it trivial to predict the ISN that a TCP will use for new connections, thus allowing a variety of attacks against TCP.

</t>
-->

<t hangText="February 1985:">
<vspace blankLines="0" /><xref target="Morris1985"/> was the first to describe how to exploit predictable TCP ISNs for forging TCP connections that could then be leveraged for trust relationship exploitation.
</t>

<t hangText="April 1989:">
<vspace blankLines="0" /><xref target="Bellovin1989"/> discussed the security considerations for predictable ISNs (along with a range of other protocol-based vulnerabilities).
</t>


<t hangText="February 1995:">
<vspace blankLines="0" /><xref target="Shimomura1995"/> reported a real-world exploitation of the attack described in <xref target="Morris1985"/> ten years before (in 1985).
</t>


<t hangText="May 1996:">
<vspace blankLines="0" /><xref target="RFC1948"/> was the first IETF effort, authored by Steven Bellovin, to address predictable TCP ISNs. However, <xref target="RFC1948"/> does not formally update <xref target="RFC0793"/>. The same concept specified in this document for TCP ISNs was later proposed for TCP ephemeral ports <xref target="RFC6056"/>, TCP Timestamps, and eventually even IPv6 Interface Identifiers <xref target="RFC7217"/>.
</t>


<t hangText="July 1996:">
<vspace blankLines="0" />OpenBSD implements TCP ISN randomization based on random increments (please see Appendix A.2 of <xref target="I-D.irtf-pearg-numeric-ids-generation"/>) <xref target="OpenBSD-TCP-ISN-I"/>. <!-- This feature eventually shipped with OpenBSD 2.0. -->
</t>

<t hangText="December 2000:">
<vspace blankLines="0" />OpenBSD implements TCP ISN randomization using simple randomization (please see Section 7.1 of <xref target="I-D.irtf-pearg-numeric-ids-generation"/>)  <xref target="OpenBSD-TCP-ISN-R"/>. <!-- This feature eventually shipped with OpenBSD 2.9. -->
</t>

<t hangText="March 2001:">
<vspace blankLines="0" /><xref target="Zalewski2001"/> provides a detailed analysis of statistical weaknesses in some ISN generators, and includes a survey of the algorithms in use by popular TCP implementations.
</t>

<t hangText="May 2001:">
<vspace blankLines="0" />Vulnerability advisories <xref target="CERT2001"/> <xref target="USCERT2001"/> were released regarding statistical weaknesses in some ISN generators, affecting popular TCP implementations.
</t>

<t hangText="March 2002:">
<vspace blankLines="0" /><xref target="Zalewski2002"/> updates and complements <xref target="Zalewski2001"/>. It concludes that "while some vendors [...] reacted promptly and tested their solutions properly, many still either ignored the issue and never evaluated their implementations, or implemented a flawed solution that apparently was not tested using a known approach" <xref target="Zalewski2002"/>. 
</t>

<t hangText="June 2007:">
<vspace blankLines="0" />OpenBSD implements TCP ISN randomization based on the algorithm specified in <xref target="RFC1948"/> (currently obsoleted and replaced by <xref target="RFC6528"/>) for the TCP endpoint that performs the active open, while keeping the simple randomization scheme for the endpoint performing the passive open <xref target="OpenBSD-TCP-ISN-H"/>. This provides monotonically-increasing ISNs for the client side (allowing the BSD heuristics to work as expected), while avoiding any patterns in the ISN generation for the server side.<!-- This feature eventually shipped with OpenBSD 4.2.  -->
</t>

<t hangText="February 2012:">
<vspace blankLines="0" /><xref target="RFC6528"/>, published 27 years after Morris' original work <xref target="Morris1985"/>, formally updates <xref target="RFC0793"/> to mitigate predictable TCP ISNs. 
</t>

<t hangText="August 2014:">
<vspace blankLines="0" /><xref target="I-D.eddy-rfc793bis-04"/>, the upcoming revision of the core TCP protocol specification, incorporates the algorithm specified in <xref target="RFC6528"/> as the recommended ("SHOULD") algorithm for TCP ISN generation. 
</t>

</list>
</t>
</section>


<section title="IPv6 Interface Identifiers (IIDs)" anchor="ipv6-iids">
<t>IPv6 Interface Identifiers can be generated as a result of different mechanisms, including SLAAC <xref target="RFC4862"/>, DHCPv6 <xref target="RFC8415"/>, and manual configuration. This section focuses on Interface Identifiers resulting from SLAAC.</t>

<t>The Interface Identifier of stable (traditional) IPv6 addresses resulting from SLAAC have traditionally resulted in the underlying link-layer address being embedded in the IID.<!-- IPv6 addresses resulting from SLAAC are currently required to employ Modified EUI-64 format identifiers, which essentially embed the underlying link-layer address of the corresponding network interface. -->  At the time, employing the underlying link-layer address for the IID was seen as a convenient way to obtain a unique address. However, recent awareness about the security and privacy properties of this approach <xref target="RFC7707"/> <xref target="RFC7721"/> has led to the replacement of this flawed scheme with an alternative one <xref target="RFC7217"/> <xref target="RFC8064"/> that does not negatively affect the security and privacy properties of the protocol.
</t>

<t>
<list style="hanging">
<t hangText="January 1997:">
<vspace blankLines="0" /><xref target="RFC2073"/> specifies the syntax of IPv6 global addresses (referred to as "An IPv6 Provider-Based Unicast Address Format" at the time), consistent with the IPv6 addressing architecture specified in <xref target="RFC1884"/>. Hosts are recommended to "generate addresses using link-specific addresses as Interface ID such as 48 bit IEEE-802 MAC addresses".
</t>

<t hangText="July 1998:">
<vspace blankLines="0" /><xref target="RFC2374"/> specifies "An IPv6 Aggregatable Global Unicast Address Format" (obsoleting <xref target="RFC2373"/>) changing the size of the IID to 64 bits, and specifies that IIDs must be constructed in IEEE EUI-64 format. How such identifiers are constructed becomes specified in the corresponding "IPv6 over &lt;link&gt;" specifications, such as "IPv6 over Ethernet".
</t>



<t hangText="January 2001:">
<vspace blankLines="0" /><xref target="RFC3041"/> recognizes the problem of network activity correlation, and specifies temporary addresses. Temporary addresses are to be used along with stable addresses.
</t>


<t hangText="August 2003:">
<vspace blankLines="0" /><xref target="RFC3587"/> obsoletes <xref target="RFC2374"/>, making the TLA/NLA structure historic. The syntax and recommendations for the traditional stable IIDs remain unchanged, though.
</t>

<t hangText="February 2006:">
<vspace blankLines="0" /><xref target="RFC4291"/> is published as the latest "IP Version 6 Addressing Architecture", requiring the IIDs of the traditional (stable) IPv6 addresses resulting from SLAAC to employ the Modified EUI-64 format. The details of constructing such interface identifiers are defined in the corresponding "IPv6 over &lt;link&gt;" specifications.
</t>


<t hangText="March 2008:">
<vspace blankLines="0" /><xref target="RFC5157"/> provides hints regarding how patterns in IPv6 addresses could be leveraged for the purpose of address scanning.
</t>

<t hangText="December 2011:">
<vspace blankLines="0" /><xref target="draft-gont-6man-stable-privacy-addresses-00"/> notes that the traditional scheme for generating stable addresses allows for address scanning, and also does not prevent active node tracking. It also specifies an alternative algorithm meant to replace IIDs based on Modified EUI-64 format identifiers.
</t>

<t hangText="November 2012:">
<vspace blankLines="0" />The 6man WG adopts <xref target="I-D.gont-6man-stable-privacy-addresses"/> as a working group item (as <xref target="draft-ietf-6man-stable-privacy-addresses-00"/>). However, the document no longer formally updates <xref target="RFC4291"/>, and therefore the specified algorithm no longer formally replaces the Modified EUI-64 format identifiers.
</t>


<t hangText="February 2013:">
<vspace blankLines="0" />An address-scanning tool (scan6 of <xref target="IPv6-Toolkit"/>) that leverages IPv6 address patterns is released <xref target="Gont2013"/>.
</t>


<t hangText="July 2013:">
<vspace blankLines="0" /><xref target="I-D.cooper-6man-ipv6-address-generation-privacy"/> elaborates on the security and privacy properties of all known algorithms for generating IPv6 IIDs.
</t>


<t hangText="January 2014:">
<vspace blankLines="0" />The 6man WG publishes <xref target="draft-ietf-6man-default-iids-00"/> ("Recommendation on Stable IPv6 Interface Identifiers"), recommending <xref target="I-D.ietf-6man-stable-privacy-addresses"/> for the generation of stable addresses.
</t>

<t hangText="April 2014:">
<vspace blankLines="0" /><xref target="RFC7217"/> (formerly <xref target="I-D.ietf-6man-stable-privacy-addresses"/>) is published, specifying "A Method for Generating Semantically Opaque Interface Identifiers with IPv6 Stateless Address Autoconfiguration (SLAAC)" as an alternative to (but *not* replacement of) Modified EUI-64 format IIDs.
</t>

<t hangText="March 2016:">
<vspace blankLines="0" /><xref target="RFC7707"/> (formerly <xref target="I-D.gont-opsec-ipv6-host-scanning"/>, and later <xref target="I-D.ietf-opsec-ipv6-host-scanning"/>), about "Network Reconnaissance in IPv6 Networks", is published.
</t>


<t hangText="March 2016:">
<vspace blankLines="0" /><xref target="RFC7721"/> (formerly <xref target="I-D.cooper-6man-ipv6-address-generation-privacy"/> and later <xref target="I-D.ietf-6man-ipv6-address-generation-privacy"/>), about "Security and Privacy Considerations for IPv6 Address Generation Mechanisms", is published.
</t>

<t hangText="May 2016:">
<vspace blankLines="0" /><xref target="draft-gont-6man-non-stable-iids-00"/> is published, with the goal of specifying requirements for non-stable addresses, and updating <xref target="RFC4941"/> such that use of only temporary addresses is allowed.
</t>

<t hangText="May 2016:">
<vspace blankLines="0" /><xref target="draft-gont-6man-address-usage-recommendations-00"/> is published, providing an analysis of how different aspects on an address (from stability to usage mode) affect their corresponding security and privacy properties, and meaning to eventually provide advice in this area.
</t>

<t hangText="February 2017:">
<vspace blankLines="0" />The 6man WG publishes <xref target="RFC8064"/> ("Recommendation on Stable IPv6 Interface Identifiers") (formerly <xref target="I-D.ietf-6man-default-iids"/>), with requirements for stable addresses and a recommendation to employ <xref target="RFC7217"/> for the generation of stable addresses. It formally updates a large number of RFCs.
</t>

<t hangText="March 2018:">
<vspace blankLines="0" /><xref target="draft-fgont-6man-rfc4941bis-00"/> is published (as suggested by the 6man WG), to address flaws in <xref target="RFC4941"/> by revising it (as an alternative to the <xref target="draft-gont-6man-non-stable-iids-00"/> effort, published in March 2016).
</t>

<t hangText="July 2018:">
<vspace blankLines="0" /><xref target="draft-fgont-6man-rfc4941bis-00"/> is adopted (as <xref target="draft-ietf-6man-rfc4941bis-00"/>) as a WG item of the 6man WG.
</t>

<t hangText="December 2020:">
<vspace blankLines="0" /><xref target="I-D.ietf-6man-rfc4941bis"/> is approved by the IESG for publication as an RFC.
</t>
<t hangText="February 2021:">
<vspace blankLines="0" /><xref target="I-D.ietf-6man-rfc4941bis"/> is finally published as <xref target="RFC8981"/>.
</t>
</list>
</t>
</section>



<section title="NTP Reference IDs (REFIDs)" anchor="ntp-refid">


<t>The NTP <xref target="RFC5905"/> Reference ID is a 32-bit code identifying the particular server or reference clock. Above stratum 1 (secondary servers and clients), this value can be employed to avoid degree-one timing loops; that is, scenarios where two NTP peers are (mutually) the time source of each other. If using the IPv4 address family, the identifier is the four-octet IPv4 address.  If using the IPv6 address family, it is the first four octets of the MD5 hash of the IPv6 address.</t>

<t>
<list style="hanging">
<t hangText="June 2010:">
<vspace blankLines="0" /><xref target="RFC5905"/>, "Network Time Protocol Version 4: Protocol and Algorithms Specification" is published. It specifies that for NTP peers with stratum higher than 1 the REFID embeds the IPv4 Address of the time source or an MD5 hash of the IPv6 address of the time source.
</t>

<t hangText="July 2016:">
<vspace blankLines="0" /><xref target="draft-stenn-ntp-not-you-refid-00"/> is published, describing the information leakage produced via the NTP REFID. It proposes that NTP returns a special REFID when a packet employs an IP Source Address that is not believed to be a current NTP peer, but otherwise generates and returns the traditional REFID. It is subsequently adopted by the NTP WG as <xref target="I-D.ietf-ntp-refid-updates"/>.
</t>

<t hangText="April 2019:">
<vspace blankLines="0" /><xref target="Gont-NTP"/> notes that the proposed fix specified in <xref target="draft-ietf-ntp-refid-updates-00"/> is, at the very least, sub-optimal.
</t>


</list>
</t>

</section>


<section title="Transport Protocol Ephemeral Port Numbers" anchor="port-numbers">
<t>Most (if not all) transport protocols employ "port numbers" to demultiplex packets to the corresponding transport protocol instances.</t>
<!-- [fgont] esto hay que expandirlo, como en los otros casos -->


<t>
<list style="hanging">

<t hangText="August 1980:">
<vspace blankLines="0" /><xref target="RFC0768"/> notes that the UDP source port is optional and identifies the port of the sending process. It does not specify interoperability requirements for source port selection, nor does it suggest possible ways to select port numbers. Most popular implementations end up selecting source ports from a system-wide global counter.</t>

<t hangText="September 1981:">
<vspace blankLines="0" /><xref target="RFC0793"/> (the TCP specification) essentially describes the use of port numbers, and specifies that port numbers should result in a unique socket pair (local address, local port, remote address, remote port). How ephemeral ports (i.e. port numbers for "active opens") are selected, and the port range from which they are selected, are left unspecified.
</t>

<t hangText="July 1996:">
<vspace blankLines="0" />OpenBSD implements ephemeral port randomization <xref target="OpenBSD-PR"/>.<!-- This feature eventually shipped with OpenBSD 2.0.-->
</t>

<t hangText="July 2008:">
<vspace blankLines="0" />The CERT Coordination Centre published details of what became known as the &quot;Kaminsky Attack&quot; <xref target="VU-800113"/> <xref target="Kaminsky2008"/> on the DNS. The attack exploited the lack of source port randomization in many major DNS implementations to perform cache poisoning in an effective and practical manner.
</t>

<t hangText="January 2009:">
<vspace blankLines="0" /><xref target="RFC5452"/> mandates the use of port randomization for DNS resolvers, and mandates that implementations must randomize ports from the range (53 or 1024, and above) or the largest possible port range. It does not recommend possible algorithms for port randomization, although the document specifically targets DNS resolvers, for which a simple port randomization suffices (e.g. Algorithm 1 of <xref target="RFC6056"/>). This document led to the implementation of port randomization in the DNS resolver themselves, rather than in the underlying transport-protocols.
</t>

<t hangText="January 2011:">
<vspace blankLines="0" /><xref target="RFC6056"/> notes that many TCP and UDP implementations result in predictable port numbers, and also notes that many implementations select port numbers from a small portion of the whole port number space. It recommends the implementation and use of ephemeral port randomization, proposes a number of possible algorithms for port randomization, and also recommends to randomize port numbers over the range 1024-65535.
</t>


<t hangText="March 2016:">
<vspace blankLines="0" /><xref target="NIST-NTP"/> reports a non-normal distribution of the ephemeral port numbers employed by the NTP clients of an Internet Time Service.
</t>

<t hangText="April 2019:">
<vspace blankLines="0" /><xref target="I-D.gont-ntp-port-randomization"/> notes that some NTP implementations employ the NTP service port (123) as the local port for non-symmetric modes, and aims to update the NTP specification to recommend port randomization in such cases, in line with <xref target="RFC6056"/>. The proposal experiences some push-back in the relevant working group (NTP WG) <xref target="NTP-PORTR"/>, but is finally adopted as a working group item as <xref target="I-D.ietf-ntp-port-randomization"/>.
</t>

<t hangText="August 2021:">
<vspace blankLines="0" /><xref target="I-D.ietf-ntp-port-randomization"/> is finally published as <xref target="RFC9109"/>.
</t>
</list>
</t>

</section>


<section title="DNS Query ID" anchor="dns-query-id">

<t>The DNS Query ID <xref target="RFC1035"/> can be employed to match DNS replies to outstanding DNS queries.


<list style="hanging">
<t hangText="November 1987:">
<vspace blankLines="0" /><xref target="RFC1035"/> specifies that the ID is a 16 bit identifier assigned by the program that
generates any kind of query, and that this identifier is copied in the corresponding reply and can be used by the requester to match up replies to outstanding queries. It does not specify the interoperability requirements for these numeric identifiers, nor does it suggest an algorithm for generating them.</t>

<t hangText="1993:">
<vspace blankLines="0" /><xref target="Schuba1993"/> describes DNS cache poisoning attacks that require the attacker to guess the Query ID.</t>

<t hangText="June 1995:">
<vspace blankLines="0" /><xref target="Vixie1995"/> suggests that both the UDP source port and the ID of query packets should be randomized, although that might not provide enough entropy to prevent an attacker from guessing these values.</t>


<t hangText="April 1997:">
<vspace blankLines="0" /><xref target="Arce1997"/> finds that implementations employ predictable UDP source ports and predictable Query IDs, and argues that both should be randomized.</t>

<t hangText="November 2002:">
<vspace blankLines="0" /><xref target="Sacramento2002"/> finds that by spoofing multiple requests for the same domain name from different IP addresses, an attacker may guess the Query ID employed for a victim with a high probability of success, thus performing DNS cache poisoning attacks.</t>

<t hangText="July 2007:">
<vspace blankLines="0" /><xref target="Klein2007b"/> finds that a popular DNS server software (BIND 9) that randomizes the Query ID is still subject to DNS cache poisoning attacks by forging a large number of queries and leveraging the birthday paradox.
</t>

<t hangText="March 2007:">
<vspace blankLines="0" /><xref target="Klein2007c"/> finds that Microsoft Windows DNS Server generates predictable Query ID values.
</t>

<t hangText="October 2007:">
<vspace blankLines="0" /><xref target="Klein2007"/> finds that OpenBSD's DNS software (based on ISC's BIND DNS Sercer) generates predictable Query ID values.
</t>

<t hangText="January 2009:">
<vspace blankLines="0" /><xref target="RFC5452"/> is published, requiring resolvers to randomize the Query ID of DNS queries, and to verify that the Query ID of a DNS reply matches that of the DNS query as part of the DNS reply validation process.
</t>

<t hangText="May 2010:">
<vspace blankLines="0" /><xref target="Economou2010"/> finds that Windows SMTP Service implements its own DNS resolver that results in predictable Query ID values. Additionally, it fails to validate that the Query ID of DNS reply matches the one from the DNS query that supposedly elicited the reply.
</t>

</list>
</t>
</section>


</section>




<section title="Conclusions" anchor="conclusions">
<t>
   For more than 30 years, a large number of implementations of the IETF protocols have been subject to a variety of attacks, with
   effects ranging from Denial of Service (DoS) or data injection, to
   information leakages that could be exploited for pervasive monitoring
   <xref target="RFC7258"/>.  The root cause of these issues has been, in many cases,
   poor selection of transient numeric identifiers, usually as a result
   of insufficient or misleading specifications.
</t>

<t>
   While it is generally possible to identify an algorithm that can
   satisfy the  interoperability requirements for a given transient
   numeric identifier, this document provides empirical evidence that
   doing so without negatively affecting the security or privacy
   properties of the aforementioned protocols is non-trivial. It is thus
   evident that advice in this area is warranted.
</t>

<t>
   <xref target="I-D.gont-numeric-ids-sec-considerations"/> aims at requiring future
   IETF protocol specifications to contain analysis of the security and
   privacy properties of any transient numeric identifiers specified by
   the protocol, and to recommend an algorithm for the generation
   of such transient numeric identifiers. <xref target="I-D.irtf-pearg-numeric-ids-generation"/> specifies a number of sample algorithms for generating
   transient numeric identifiers with specific interorability
   requirements and failure severities. 
</t>
</section>



	<section title="IANA Considerations" anchor="iana-considerations">
<t>There are no IANA registries within this document. The RFC-Editor can remove this section before publication of this document as an RFC.</t>
</section>



    <section title="Security Considerations">

<t>This document analyzes the timeline of the specification and implementation of the transient numeric identifiers of some sample IETF protocols, and how the security and privacy properties of such protocols have been affected as a result of it. It provides concrete evidence that advice in this area is warranted.</t>

<t><xref target="I-D.gont-numeric-ids-sec-considerations"/> formally requires IETF protocol specifications to specify the interoperability requirements for their transient numeric identifiers, to do a warranted vulnerability assessment of such transient numeric identifiers, and to recommend possible algorithms for their generation, such that the interoperability requirements are complied with, while any negative security and privacy properties of these transient numeric identifiers are mitigated.</t>
<t><xref target="I-D.irtf-pearg-numeric-ids-generation"/> analyzes and categorizes transient numeric identifiers based on their interoperability requirements and their associated failure severities, and recommends possible algorithms that can comply with those requirements without negatively affecting the security and privacy properties of the corresponding protocols.</t>

    </section>

    <section title="Acknowledgements">

<t>The authors would like to thank (in alphabetical order) Bernard Aboba, Dave Crocker, Spencer Dawkins, Theo de Raadt, Sara Dickinson, Guillermo Gont, Christian Huitema, Colin Perkins, Vincent Roca, Kris Shrishak, Joe Touch, Brian Trammell, and Christopher Wood, for providing valuable comments on earlier versions of this document.</t>

<t>The authors would like to thank (in alphabetical order) Steven Bellovin, Joseph Lorenzo Hall, Gre Norcie, and Martin Thomson, for providing valuable comments on <xref target="I-D.gont-predictable-numeric-ids"/>, on which this document is based.</t>

<t><xref target="tcp-isns"/> of this document borrows text from <xref target="RFC6528"/>, authored by Fernando Gont and Steven Bellovin.</t>

<t>The authors would like to thank Sara Dickinson and Christopher Wood, for their guidance during the publication process of this document.</t>

 <t>The authors would like to thank Diego Armando Maradona for his magic and inspiration.</t> 

    </section>

  </middle>

  <back>
  <references title='Normative References'>
  <!--
	<?rfc include="reference.RFC.2119" ?>
	<?rfc include="reference.RFC.2119" ?>
-->

<!-- UDP -->
	<?rfc include="reference.RFC.0768" ?>
<!-- TCP sequence numbers -->
	<?rfc include="reference.RFC.0793" ?>
	<?rfc include="reference.RFC.6528" ?> <!-- TCP SEQ randomization -->



<!-- IPv4-->
	<?rfc include="reference.RFC.0791" ?>
	



<!-- IPv6 -->
	<?rfc include="reference.RFC.1883" ?>
	<?rfc include="reference.RFC.2460" ?>
	<?rfc include="reference.RFC.8200" ?>




<!-- Randomness requirements-->
<!--
<?rfc include="reference.RFC.4086" ?>

-->



<!--
	<?rfc include="reference.RFC.6151" ?>

-->

<!-- IPv6 Addresses -->
	<?rfc include="reference.RFC.7217" ?>
	<?rfc include="reference.RFC.3041" ?>
	<?rfc include="reference.RFC.2073" ?>
	<?rfc include="reference.RFC.2374" ?>
	<?rfc include="reference.RFC.3587" ?>
	<?rfc include="reference.RFC.1884" ?>
	<?rfc include="reference.RFC.4291" ?>
	<?rfc include="reference.RFC.4941" ?>
	<?rfc include="reference.RFC.2373" ?>
	<?rfc include="reference.RFC.4862" ?>
	<?rfc include="reference.RFC.8415" ?>

<!-- TCP ISNs -->

	<?rfc include="reference.RFC.1323" ?> 


<!-- Port randomization -->
	<?rfc include="reference.RFC.6056" ?> 
	<?rfc include="reference.RFC.5452" ?> 


	

  </references>

  <references title='Informative References'>

	<reference anchor="OpenBSD-PR" target="https://cvsweb.openbsd.org/src/sys/netinet/in_pcb.c?rev=1.6">
		<front>
			<title>Implementation of port randomization</title>
			<author>
				<organization>OpenBSD</organization>
			</author>
			<date day="29" month="July" year="1996"/>
		</front>
	</reference>
	
		<reference anchor="VU-800113" target="https://www.kb.cert.org/vuls/id/800113">
		<front>
			<title>Multiple DNS implementations vulnerable to cache poisoning (Vulnerability Note VU#800113)</title>
			<author>
				<organization>CERT/CC</organization>
			</author>
			<date day="8" month="July" year="2008"/>
		</front>
	</reference>


	<reference anchor="IANA-PROT" target="https://www.iana.org/protocols">
		<front>
			<title>Protocol Registries</title>
			<author initials="" surname="IANA" fullname="IANA">
				<organization></organization>
			</author>

			<date/>

		</front>
<!--
		<seriesInfo name="" value="Federal Information Processing Standards Publication 180-4"/>
-->
	</reference>


<!-- IPv6 Addresses -->
	<?rfc include="reference.RFC.5157" ?>
	<?rfc include="reference.RFC.8981" ?>
	<?rfc include="reference.I-D.ietf-6man-rfc4941bis" ?>
	<?rfc include="reference.I-D.gont-opsec-ipv6-host-scanning" ?>
	<?rfc include="reference.I-D.ietf-opsec-ipv6-host-scanning" ?>
	<?rfc include="reference.I-D.gont-6man-stable-privacy-addresses" ?>
	<?rfc include="reference.I-D.ietf-6man-stable-privacy-addresses" ?>
	<?rfc include="reference.I-D.cooper-6man-ipv6-address-generation-privacy" ?>
	<?rfc include="reference.I-D.ietf-6man-ipv6-address-generation-privacy" ?>

	<reference anchor="Gont2013" target="https://lists.si6networks.com/pipermail/ipv6hackers/2013-February/000947.html">
		<front>
			<title>Beta release of the SI6 Network's IPv6 Toolkit (help wanted!)</title>
   <author fullname="Fernando Gont" initials="F." surname="Gont">
    </author>

			<date year="2013"/>

		</front>
		<seriesInfo name="Message posted to the IPv6 Hackers mailing-list" value=" Message-ID: &lt;51184548.3030105@si6networks.com&gt;"/>

	</reference>


	<reference anchor="IPv6-Toolkit" target="https://www.si6networks.com/tools/ipv6toolkit">
		<front>
			<title>SI6 Networks' IPv6 Toolkit</title>
			<author>
				<organization>SI6 Networks</organization>
			</author>
			<date/>
		</front>
	</reference>





	<reference anchor='draft-gont-6man-stable-privacy-addresses-00'>
	<front>
	<title>A method for Generating Stable Privacy-Enhanced Addresses with IPv6 Stateless Address Autoconfiguration (SLAAC)</title>

	    <author fullname="Fernando Gont" initials="F." surname="Gont">
	    </author>


	<date month='December' day='15' year='2011' />

	</front>

	<seriesInfo name='Internet-Draft' value='draft-gont-6man-stable-privacy-addresses-00' />
	<format type='TXT'
		target='https://tools.ietf.org/id/draft-gont-6man-stable-privacy-addresses-00.txt' />
	</reference>



	<reference anchor='draft-ietf-6man-stable-privacy-addresses-00'>
	<front>
	<title>A method for Generating Stable Privacy-Enhanced Addresses with IPv6 Stateless Address Autoconfiguration (SLAAC)</title>

	    <author fullname="Fernando Gont" initials="F." surname="Gont">
	    </author>


	<date month='May' day='18' year='2012' />

	</front>

	<seriesInfo name='Internet-Draft' value='draft-ietf-6man-stable-privacy-addresses-00' />
	<format type='TXT'
		target='https://tools.ietf.org/id/draft-ietf-6man-stable-privacy-addresses-00.txt' />
	</reference>




	<reference anchor='draft-gont-6man-address-usage-recommendations-00'>
	<front>
	<title>IPv6 Address Usage Recommendations</title>

	    <author fullname="Fernando Gont" initials="F." surname="Gont">
	    </author>

	    <author initials="W." surname="Liu" fullname="Will Liu">
	    </author>


	<date month='May' day='27' year='2016' />

	</front>

	<seriesInfo name='Internet-Draft' value='draft-gont-6man-address-usage-recommendations-00' />
	<format type='TXT'
		target='https://tools.ietf.org/id/draft-gont-6man-address-usage-recommendations-00.txt' />
	</reference>



	<reference anchor='draft-gont-6man-non-stable-iids-00'>
	<front>
	<title>Recommendation on Non-Stable IPv6 Interface Identifiers</title>

	    <author fullname="Fernando Gont" initials="F." surname="Gont">
	    </author>

	    <author initials="W." surname="Liu" fullname="Will Liu">
	    </author>


	<date month='May' day='23' year='2016' />

	</front>

	<seriesInfo name='Internet-Draft' value='draft-gont-6man-non-stable-iids-00' />
	<format type='TXT'

		target='https://tools.ietf.org/id/draft-gont-6man-non-stable-iids-00.txt' />
	</reference>





	<reference anchor='draft-ietf-6man-default-iids-00'>
	<front>
	<title>Recommendation on Stable IPv6 Interface Identifiers</title>

	    <author fullname="Fernando Gont" initials="F." surname="Gont">
	    </author>

	<author initials="A." surname="Cooper" fullname="Alissa Cooper">
	  </author>

		<author
			fullname="Dave Thaler"
			initials="D."
			surname="Thaler">

		    </author>

	    <author initials="W." surname="Liu" fullname="Will Liu">
	    </author>


	<date month='July' day='28' year='2014' />

	</front>

	<seriesInfo name='Internet-Draft' value='draft-ietf-6man-default-iids-00' />
	<format type='TXT'
		target='https://tools.ietf.org/id/draft-ietf-6man-default-iids-00.txt' />
	</reference>


	<?rfc include="reference.RFC.8064" ?> 




	<reference anchor='draft-ietf-6man-rfc4941bis-00'>
	<front>
	    <title abbrev="Privacy Extensions to Autoconf">Privacy
	    Extensions for Stateless Address Autoconfiguration in
	    IPv6</title>


	    <author fullname="Fernando Gont" initials="F." surname="Gont">

	      <organization abbrev="SI6 Networks / UTN-FRH">SI6 Networks /
	UTN-FRH</organization>

	    </author>


	    <author initials="S.K." surname="Krishnan"
	    fullname="Suresh Krishnan">
	      <organization>Ericsson Research</organization>

	    </author>

	    <author initials="T.N." surname="Narten"
	    fullname="Thomas Narten">
	      <organization>IBM Corporation</organization>

	    </author>
	    <author initials="R.D." surname="Draves"
	    fullname="Richard Draves">
	      <organization>Microsoft Research</organization>

	    </author>

	<date month='July' day='2' year='2018' />

	</front>

	<seriesInfo name='Internet-Draft' value='draft-ietf-6man-rfc4941bis-00' />
	<format type='TXT'
		target='https://tools.ietf.org/id/draft-ietf-6man-rfc4941bis-00.txt' />
	</reference>



	<reference anchor='draft-fgont-6man-rfc4941bis-00'>
	<front>
	    <title abbrev="Privacy Extensions to Autoconf">Privacy
	    Extensions for Stateless Address Autoconfiguration in
	    IPv6</title>


	    <author fullname="Fernando Gont" initials="F." surname="Gont">

	      <organization abbrev="SI6 Networks / UTN-FRH">SI6 Networks /
	UTN-FRH</organization>

	    </author>


	    <author initials="S.K." surname="Krishnan"
	    fullname="Suresh Krishnan">
	      <organization>Ericsson Research</organization>

	    </author>

	    <author initials="T.N." surname="Narten"
	    fullname="Thomas Narten">
	      <organization>IBM Corporation</organization>

	    </author>
	    <author initials="R.D." surname="Draves"
	    fullname="Richard Draves">
	      <organization>Microsoft Research</organization>

	    </author>

	<date month='March' day='25' year='2018' />

	</front>

	<seriesInfo name='Internet-Draft' value='draft-fgont-6man-rfc4941bis-00' />
	<format type='TXT'
		target='https://tools.ietf.org/id/draft-fgont-6man-rfc4941bis-00.txt' />
	</reference>


	<?rfc include="reference.I-D.ietf-6man-default-iids" ?>
	<?rfc include="reference.RFC.7721" ?>
	<?rfc include="reference.RFC.7707" ?>


	<!--
	<reference anchor="FIPS-SHS" target="http://csrc.nist.gov/publications/fips/fips180-4/fips-180-4.pdf">
		<front>
			<title>Secure Hash Standard (SHS)</title>
			<author initials="" surname="FIPS" fullname="FIPS">
				<organization></organization>
			</author>
			<date month="March" year="2012"/>
		</front>
		<seriesInfo name="" value="Federal Information Processing Standards Publication 180-4"/>
	</reference>
	-->



	<?rfc include="reference.I-D.gont-predictable-numeric-ids" ?>
	<?rfc include="reference.I-D.gont-numeric-ids-sec-considerations" ?>
	<?rfc include="reference.I-D.irtf-pearg-numeric-ids-generation" ?>



	<?rfc include="reference.I-D.ietf-6man-rfc2460bis" ?>



<!-- NTP -->


	<reference anchor='draft-stenn-ntp-not-you-refid-00'>
	<front>
	    <title abbrev="Not You REFID">Network Time Protocol Not You REFID</title>


	    <author fullname="Sharon Goldberg" initials="S." surname="Goldberg">

	      <organization>Boston University</organization>

	    </author>


	    <author initials="H." surname="Stenn"
	    fullname="Harlan Stenn">
	      <organization>Network Time Foundation</organization>

	    </author>


	<date month='July' day='8' year='2016' />

	</front>

	<seriesInfo name='Internet-Draft' value='draft-stenn-ntp-not-you-refid-00' />
	<format type='TXT'
		target='https://tools.ietf.org/id/draft-stenn-ntp-not-you-refid-00.txt' />
	</reference>



	<reference anchor='draft-ietf-ntp-refid-updates-00'>
	<front>
	    <title abbrev="Not You REFID">Network Time Protocol Not You REFID</title>


	    <author fullname="Sharon Goldberg" initials="S." surname="Goldberg">

	      <organization>Boston University</organization>

	    </author>


	    <author initials="H." surname="Stenn"
	    fullname="Harlan Stenn">
	      <organization>Network Time Foundation</organization>

	    </author>


	<date month='November' day='13' year='2016' />

	</front>

	<seriesInfo name='Internet-Draft' value='draft-ietf-ntp-refid-updates-00' />
	<format type='TXT'
		target='https://tools.ietf.org/id/draft-ietf-ntp-refid-updates-00.txt' />
	</reference>


	<reference anchor="Gont-NTP" target="https://mailarchive.ietf.org/arch/msg/ntp/NkfTHxUUOdp14Agh3h1IPqfcRRg">
		<front>
			<title>[Ntp] Comments on draft-ietf-ntp-refid-updates-05</title>
			<author initials="F." surname="Gont" fullname="Fernando Gont">
				<organization></organization>
			</author>
			<date month="April" day="16" year="2019"/>	
		</front>
			<seriesInfo name="Post to the NTP WG mailing list" value=" Message-ID: &lt;d871d66d-4043-d8d0-f924-2191ebb2e2ce@si6networks.com&gt;"/>	
	</reference>

	<?rfc include="reference.I-D.ietf-ntp-refid-updates" ?>

	<?rfc include="reference.RFC.5905" ?>



<!-- md5 -->
<!--
	<?rfc include="reference.RFC.1321" ?>
-->


<!-- Pervasive Monitoring -->
	<?rfc include="reference.RFC.7258" ?>


<!-- TCP ISNs -->

	<?rfc include="reference.RFC.1948" ?> 

	<reference anchor="Wright1994">
		<front>
			<title>TCP/IP Illustrated, Volume 2: The Implementation</title>
			<author initials="G.R." surname="Wright" fullname= "Gary R. Wright">
				<organization></organization>
			</author>

			<author initials="W.R." surname="Stevens" fullname= "W. Richard Stevens">
				<organization></organization>
			</author>
			<date year="Addison-Wesley, 1994"/>
		</front>
 		<!-- The usage of the date element (above) avoids an extra space
		before the comma.
		<seriesInfo name="Addison-Wesley" value=""/>-->
	</reference>

<!--
	<reference anchor="CPNI-TCP" target="http://www.gont.com.ar/papers/tn-03-09-security-assessment-TCP.pdf">
		<front>
			<title>Security Assessment of the Transmission Control Protocol (TCP)</title>
			<author initials="F." surname="Gont" fullname= "Fernando Gont">
				<organization></organization>
			</author>
			<date year="2009"/>
		</front>
		<seriesInfo name="" value="United Kingdom's Centre for the Protection of National Infrastructure (CPNI) Technical Report"/>
	</reference>
-->


	<reference anchor="Zalewski2001" target="https://lcamtuf.coredump.cx/oldtcp/tcpseq.html">
		<front>
			<title>Strange Attractors and TCP/IP Sequence Number Analysis</title>
			<author initials="M." surname="Zalewski" fullname="M. Zalewski">
				<organization></organization>
			</author>
			<date year="2001"/>
		</front>
	</reference>

	<reference anchor="Zalewski2002" target="https://lcamtuf.coredump.cx/newtcp/">
		<front>
			<title>Strange Attractors and TCP/IP Sequence Number Analysis - One Year Later</title>
			<author initials="M." surname="Zalewski" fullname="M. Zalewski">
				<organization></organization>
			</author>
			<date year="2001"/>
		</front>
	</reference>


	<reference anchor="Bellovin1989" target="https://www.cs.columbia.edu/~smb/papers/ipext.pdf">
		<front>
			<title>Security Problems in the TCP/IP Protocol Suite</title>
			<author initials="S." surname="Bellovin" fullname="Bellovin">
				<organization></organization>
			</author>
			<date year="Computer Communications Review, vol. 19, no. 2, pp. 32-48, 1989"/>
		</front>
	</reference>


<!--
	<reference anchor="Joncheray1995">
		<front>
			<title>A Simple Active Attack Against TCP</title>
			<author initials="L." surname="Joncheray" fullname="L. Joncheray">
				<organization></organization>
			</author>
			<date year="Proc. Fifth Usenix UNIX Security Symposium, 1995"/>
		</front>
	</reference>
-->

	<reference anchor="Morris1985" target="https://pdos.csail.mit.edu/~rtm/papers/117.pdf">
		<front>
			<title>A Weakness in the 4.2BSD UNIX TCP/IP Software</title>
			<author initials="R." surname="Morris" fullname="Robert Morris">
				<organization></organization>
			</author>
			<date year="1985"/>
		</front>
		<seriesInfo name="CSTR 117," value="AT&amp;T Bell Laboratories, Murray Hill, NJ"/>
	</reference>



	<reference anchor="USCERT2001" target="https://www.kb.cert.org/vuls/id/498440">
		<front>
			<title>US-CERT Vulnerability Note VU#498440: Multiple TCP/IP implementations may use statistically predictable initial sequence numbers
</title>
			<author initials="" surname="US-CERT" fullname= "US-CERT">
				<organization></organization>
			</author>
			<date year="2001"/>
		</front>
	</reference>

	<reference anchor="CERT2001" target="https://resources.sei.cmu.edu/asset_files/WhitePaper/2001_019_001_496192.pdf">
		<front>
			<title>CERT Advisory CA-2001-09: Statistical Weaknesses in TCP/IP Initial Sequence Numbers
</title>
			<author initials="" surname="CERT" fullname= "CERT">
				<organization></organization>
			</author>
			<date year="2001"/>
		</front>
	</reference>


	<reference anchor="Shimomura1995" target="https://www.gont.com.ar/docs/post-shimomura-usenet.txt">
		<front>
			<title>Technical details of the attack described by Markoff in NYT</title>
			<author initials="T." surname="Shimomura" fullname= "Tsutomu Shimomura">
				<organization></organization>
			</author>
			<date year="1995"/>

		</front>
		<seriesInfo name="Message posted in USENET's comp.security.misc newsgroup" value=" Message-ID: &lt;3g5gkl$5j1@ariel.sdsc.edu&gt;"/>
	</reference>


	<reference anchor='I-D.eddy-rfc793bis-04'>
	<front>
	<title>Transmission Control Protocol Specification</title>

	<author initials='W.' surname='Eddy' fullname='Wesley Eddy'>
	    <organization />
	</author>


	<date month='August' day='25' year='2014' />

	<abstract><t>
	   This document specifies the Internet's Transmission Control Protocol
	   (TCP).  TCP is an important transport layer protocol in the Internet
	   stack, and has continuously evolved over decades of use and growth of
	   the Internet.  Over this time, a number of changes have been made to
	   TCP as it was specified in RFC 793, though these have only been
	   documented in a piecemeal fashion.  This document collects and brings
	   those changes together with the protocol specification from RFC 793.
	   This document obsoletes RFC 793 and several other RFCs (TODO: list
	   all actual RFCs when finished).

	   RFC EDITOR NOTE: If approved for publication as an RFC, this should
	   be marked additionally as "STD: 7" and replace RFC 793 in that role.</t></abstract>

	</front>

	<seriesInfo name='Internet-Draft' value='draft-eddy-rfc793bis-04' />
	<format type='TXT'
		target='https://tools.ietf.org/id/draft-eddy-rfc793bis-04.txt' />
	</reference>


	<reference anchor="OpenBSD-TCP-ISN-I" target="https://cvsweb.openbsd.org/src/sys/netinet/tcp_subr.c?rev=1.6">
		<front>
			<title>Implementation of TCP ISN randomization based on random increments</title>
			<author>
				<organization>OpenBSD</organization>
			</author>
			<date day="29" month="July" year="1996"/>
		</front>
	</reference>
	
	<reference anchor="OpenBSD-TCP-ISN-R" target="https://cvsweb.openbsd.org/src/sys/netinet/tcp_subr.c?rev=1.37">
		<front>
			<title>Implementation of TCP ISN randomization based on simple randomization</title>
			<author>
				<organization>OpenBSD</organization>
			</author>
			<date day="13" month="December" year="2000"/>
		</front>
	</reference>

	<reference anchor="OpenBSD-TCP-ISN-H" target="https://cvsweb.openbsd.org/src/sys/netinet/tcp_subr.c?rev=1.97">
		<front>
			<title>Implementation of RFC1948 for TCP ISN randomization</title>
			<author>
				<organization>OpenBSD</organization>
			</author>
			<date day="13" month="December" year="2000"/>
		</front>
	</reference>


<!-- NTP Port Randomization -->

	<?rfc include="reference.I-D.gont-ntp-port-randomization" ?>
	<?rfc include="reference.I-D.ietf-ntp-port-randomization" ?>
	<?rfc include="reference.RFC.9109" ?> 

	<reference anchor="NTP-PORTR" target="https://mailarchive.ietf.org/arch/browse/ntp/?gbt=1&amp;index=n09Sb61WkH03lSRtamkELXwEQN4">
		<front>
			<title>[Ntp] New rev of the NTP port randomization I-D (Fwd: New Version Notification for draft-gont-ntp-port-randomization-01.txt)</title>
    <author fullname="Fernando Gont" initials="F." surname="Gont">
      <organization abbrev="SI6 Networks / UTN-FRH">SI6 Networks / UTN-FRH</organization>

      <address>
        <postal>
          <street>Evaristo Carriego 2644</street>
          <code>1706</code>
          <city>Haedo</city>
          <region>Provincia de Buenos Aires</region>
          <country>Argentina</country>
        </postal>

        <phone>+54 11 4650 8472</phone>
        <email>fgont@si6networks.com</email>
        <uri>https://www.si6networks.com</uri>

       </address>
    </author>
			<date year="2019"/>
		</front>
	
	</reference>


	<reference anchor="NIST-NTP" target="https://tf.nist.gov/general/pdf/2818.pdf">
		<front>
			<title>Usage Analysis of the NIST Internet Time Service</title>


			<author initials="J.A." surname="Sherman" fullname="Jeff A. Sherman">
				<organization></organization>
			</author>

			<author initials="J." surname="Levine" fullname="Judah Levine">
				<organization></organization>
			</author>
			<date year="2016" month="March" day="8"/>
		</front>
		<seriesInfo name="Journal of Research of the National Institute of Standards and Technology" value="Volume 121" />
	</reference>





	<reference anchor="IPID-DEV" target="https://arxiv.org/pdf/1906.10478.pdf">
		<front>
			<title>From IP ID to Device ID and KASLR Bypass (Extended Version)</title>


			<author initials="A." surname="Klein" fullname="Amit Klein">
				<organization></organization>
			</author>

			<author initials="B." surname="Pinkas" fullname="Benny Pinkas">
				<organization></organization>
			</author>
			<date year="2019" month="June"/>
		</front>
<!--
		<seriesInfo name="Journal of Research of the National Institute of Standards and Technology" value="Volume 121" />
-->
	</reference>


<!-- ICMP attacks
	<?rfc include="reference.RFC.5927" ?>
 -->

<!-- IPv6 Flow Label 
	<?rfc include="reference.I-D.gont-6man-flowlabel-security" ?>
	<?rfc include="reference.RFC.7098" ?>
-->

<!-- DNS -->
	<?rfc include="reference.RFC.1035" ?>  


<!-- Fragment ID -->

	<!-- IPv4 security -->
	<?rfc include="reference.RFC.6274" ?>


	<?rfc include="reference.RFC.7739" ?>

<!--	<?rfc include="reference.RFC.4963" ?> -->  <!-- IPv4 Reassembly Errors at High Data Rates -->

	<reference anchor="Bellovin2002" target="https://www.cs.columbia.edu/~smb/papers/fnat.pdf">
		<front>
			<title>A Technique for Counting NATted Hosts</title>
			<author initials="S. M." surname="Bellovin" fullname= "Bellovin, S. M.">
				<organization></organization>
			</author>
			<date year="2002"/>
		</front>
		<seriesInfo name="IMW'02" value="Nov. 6-8, 2002, Marseille, France"/>
	</reference>

	<reference anchor="Fyodor2002" target="http://www.insecure.org/nmap/idlescan.html">
		<front>
			<title>Idle scanning and related IP ID games</title>
			<author initials="" surname="Fyodor" fullname= "Fyodor">
				<organization></organization>
			</author>
			<date year="2002"/>
		</front>
	</reference>

	<reference anchor="Sanfilippo1998a" target="http://seclists.org/bugtraq/1998/Dec/48">
		<front>
			<title>about the ip header id</title>
			<author initials="S." surname="Sanfilippo" fullname="S. Sanfilippo">
				<organization></organization>
			</author>
			<date/>
		</front>
		<seriesInfo name="Post to Bugtraq mailing-list," value="Mon Dec 14 1998" />
	</reference>

	<reference anchor="Sanfilippo1998b" target="https://github.com/antirez/hping/raw/master/docs/SPOOFED_SCAN.txt">
		<front>
			<title>Idle scan</title>
			<author initials="S." surname="Sanfilippo" fullname="S. Sanfilippo">
				<organization></organization>
			</author>
			<date year="1998"/>
		</front>
		<seriesInfo name="Post to Bugtraq" value="mailing-list" />
	</reference>

	<reference anchor="Sanfilippo1999" target="https://github.com/antirez/hping/raw/master/docs/MORE-FUN-WITH-IPID">
		<front>
			<title>more ip id</title>
			<author initials="S." surname="Sanfilippo" fullname="S. Sanfilippo">
				<organization></organization>
			</author>
			<date year="1999"/>
		</front>
		<seriesInfo name="Post to Bugtraq" value="mailing-list" />
	</reference>


	<reference anchor="Morbitzer2013" target="https://seclists.org/nmap-dev/2013/q2/394">
		<front>
			<title>[PATCH] TCP Idle Scan in IPv6</title>
			<author initials="M." surname="Morbitzer" fullname= "Mathias Morbitzer">
				<organization></organization>
			</author>
			<date year="2013"/>

		</front>
		<seriesInfo name="" value="Message posted to the nmap-dev mailing-list"/>
	</reference>


	<reference anchor="OpenBSD-IPv4-ID" target="https://cvsweb.openbsd.org/src/sys/netinet/ip_id.c?rev=1.1">
		<front>
			<title>Randomization of the IPv4 Identification field</title>
			<author>
				<organization>OpenBSD</organization>
			</author>
			<date day="26" month="December" year="1998"/>
		</front>
	</reference>


	<reference anchor="OpenBSD-IPv6-ID" target="https://cvsweb.openbsd.org/src/sys/netinet6/ip6_id.c?rev=1.1">
		<front>
			<title>Randomization of the IPv6 Identification field</title>
			<author>
				<organization>OpenBSD</organization>
			</author>
			<date day="1" month="October" year="2003"/>
		</front>
	</reference>
	
	

	<reference anchor="Silbersack2005" target="https://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.91.4542&amp;rep=rep1&amp;type=pdf">
		<front>
			<title>Improving TCP/IP security through randomization without sacrificing interoperability</title>
			<author initials="M.J." surname="Silbersack" fullname="Michael James Silbersack">
				<organization>The FreeBSD Project</organization>
			</author>
			<date year="2005"/>
		</front>
		<seriesInfo name="EuroBSDCon 2005" value="Conference"/>
	</reference>

	<reference anchor="Zalewski2003" target="https://lcamtuf.coredump.cx/ipfrag.txt">
		<front>
			<title>A new TCP/IP blind data injection technique?</title>
			<author initials="M." surname="Zalewski" fullname="M. Zalewski">
				<organization></organization>
			</author>
			<date year="2003"/>
		</front>
	</reference>
	
	
	<reference anchor="Arce1997" target="http://www.openbsd.org/advisories/sni_12_resolverid.txt">
		<front>
			<title>BIND Vulnerabilities and Solutions</title>
			<author initials="I." surname="Arce" fullname="Ivan Arce">
				<organization>Core Seguridad del Informacion</organization>
			</author>
			<author initials="E." surname="Kargieman" fullname="Emiliano Kargieman">
				<organization>Core Seguridad del Informacion</organization>
			</author>
			<date year="1997"/>
		</front>
	
	</reference>
	
	
	<reference anchor="Klein2007" target="https://dl.packetstormsecurity.net/papers/attack/OpenBSD_DNS_Cache_Poisoning_and_Multiple_OS_Predictable_IP_ID_Vulnerability.pdf">
		<front>
			<title>OpenBSD DNS Cache Poisoning and Multiple O/S Predictable IP ID Vulnerability</title>
			<author initials="A." surname="Klein" fullname="Amit Klein">
				<organization></organization>
			</author>
			<date year="2007"/>
		</front>
	
	</reference>

	<reference anchor="Gont2011">
		<front>
			<title>Hacking IPv6 Networks (training course)</title>
			<author initials="F." surname="Gont" fullname="Fernando Gont">
				<organization></organization>
			</author>
			<date month="June" year="2011"/>
		</front>
			<seriesInfo name="Hack In Paris 2011 Conference" value="Paris, France"/>	
	</reference>


	<reference anchor="RedHat2011" target="https://rhn.redhat.com/errata/RHSA-2011-1465.html">
		<front>
			<title>RedHat Security Advisory RHSA-2011:1465-1: Important: kernel security and bug fix update</title>
			<author initials="" surname="RedHat" fullname="RedHat">
				<organization></organization>
			</author>
			<date year="2011"/>
		</front>
		<!--			<seriesInfo name="Hack In Paris 2011 Conference" value="Paris, France"/>	-->
	</reference>



	<reference anchor="Ubuntu2011" target="https://ubuntu.com/security/notices/USN-1253-1">
		<front>
			<title>Ubuntu: USN-1253-1: Linux kernel vulnerabilities</title>
			<author initials="" surname="Ubuntu" fullname="Ubuntu">
				<organization></organization>
			</author>
			<date year="2011"/>
		</front>
		<!--			<seriesInfo name="Hack In Paris 2011 Conference" value="Paris, France"/>	-->
	</reference>


	<reference anchor="SUSE2011" target="https://lists.opensuse.org/opensuse-security-announce/2011-12/msg00011.html">
		<front>
			<title>SUSE Security Announcement: Linux kernel security update (SUSE-SA:2011:046)</title>
			<author initials="" surname="SUSE" fullname="SUSE">
				<organization></organization>
			</author>
			<date year="2011"/>
		</front>
		<!--			<seriesInfo name="Hack In Paris 2011 Conference" value="Paris, France"/>	-->
	</reference>


	<reference anchor="Gont2012" target="https://www.si6networks.com/files/presentations/bsdcan2012/fgont-bsdcan2012-recent-advances-in-ipv6-security.pdf">
		<front>
			<title>Recent Advances in IPv6 Security</title>
			<author initials="F." surname="Gont" fullname="Fernando Gont">
				<organization></organization>
			</author>
			<date month="May" year="2012"/>	
		</front>
			<seriesInfo name="BSDCan 2012 Conference" value="Ottawa, Canada. May 11-12, 2012"/>	
	</reference>



	<?rfc include="reference.I-D.gont-6man-predictable-fragment-id" ?>
	<?rfc include="reference.I-D.ietf-6man-predictable-fragment-id" ?>


	<reference anchor='draft-ietf-6man-predictable-fragment-id-01'>
	<front>
	<title>Security Implications of Predictable Fragment Identification Values</title>

	<author initials='F.' surname='Gont' fullname='Fernando Gont'>
	    <organization />
	</author>


	<date month='April' day='30' year='2014' />

	</front>

	<seriesInfo name='Internet-Draft' value='draft-ietf-6man-predictable-fragment-id-01' />

	<format type='TXT'
		target='https://tools.ietf.org/id/draft-ietf-6man-predictable-fragment-id-01.txt' />
	</reference>



	<reference anchor='draft-ietf-6man-predictable-fragment-id-02'>
	<front>
	<title>Security Implications of Predictable Fragment Identification Values</title>

	<author initials='F.' surname='Gont' fullname='Fernando Gont'>
	    <organization />
	</author>


	<date month='December' day='19' year='2014' />

	</front>

	<seriesInfo name='Internet-Draft' value='draft-ietf-6man-predictable-fragment-id-02' />

	<format type='TXT'
		target='https://tools.ietf.org/id/draft-ietf-6man-predictable-fragment-id-02.txt' />
	</reference>



	<reference anchor='draft-gont-6man-predictable-fragment-id-00'>
	<front>
	<title>Security Implications of Predictable Fragment Identification Values</title>

	<author initials='F.' surname='Gont' fullname='Fernando Gont'>
	    <organization />
	</author>


	<date month='December' day='15' year='2011' />

	<abstract><t>IPv6 specifies the Fragment Header, which is employed for the
	   fragmentation and reassembly mechanisms.  The Fragment Header
	   contains an "Identification" field which, together with the IPv6
	   Source Address and the IPv6 Destination Address of the packet,
	   identifies fragments that correspond to the same original datagram,
	   such that they can be reassembled together at the receiving host.
	   The only requirement for setting the "Identification" value is that
	   it must be different than that of any other fragmented packet sent
	   recently with the same Source Address and Destination Address.  Some
	   implementations simply use a global counter for setting the Fragment
	   Identification field, thus leading to predictable values.  This
	   document analyzes the security implications of predictable
	   Identification values, and updates RFC 2460 specifying additional
	   requirements for setting the Fragment Identification, such that the
	   aforementioned security implications are mitigated.</t></abstract>

	</front>

	<seriesInfo name='Internet-Draft' value='draft-gont-6man-predictable-fragment-id-00' />

	<format type='TXT'
		target='https://tools.ietf.org/id/draft-gont-6man-predictable-fragment-id-00.txt' />
	</reference>



	<reference anchor='draft-ietf-6man-predictable-fragment-id-00'>
	<front>
	<title>Security Implications of Predictable Fragment Identification Values</title>

	<author initials='F.' surname='Gont' fullname='Fernando Gont'>
	    <organization />
	</author>


	<date month='March' day='22' year='2013' />


	</front>

	<seriesInfo name='Internet-Draft' value='draft-ietf-6man-predictable-fragment-id-00' />

	<format type='TXT'
		target='https://tools.ietf.org/id/draft-ietf-6man-predictable-fragment-id-00.txt' />
	</reference>






	<reference anchor='draft-ietf-6man-predictable-fragment-id-08'>
	<front>
	<title>Security Implications of Predictable Fragment Identification Values</title>

	<author initials='F.' surname='Gont' fullname='Fernando Gont'>
	    <organization />
	</author>


	<date month='June' day='9' year='2015' />

	<abstract><t>IPv6 specifies the Fragment Header, which is employed for the
	   fragmentation and reassembly mechanisms.  The Fragment Header
	   contains an "Identification" field which, together with the IPv6
	   Source Address and the IPv6 Destination Address of a packet,
	   identifies fragments that correspond to the same original datagram,
	   such that they can be reassembled together by the receiving host.
	   The only requirement for setting the "Identification" field is that
	   the corresponding value must be different than that employed for any
	   other fragmented packet sent recently with the same Source Address
	   and Destination Address.  Some implementations use a simple global
	   counter for setting the Identification field, thus leading to
	   predictable Identification values.  This document analyzes the
	   security implications of predictable Identification values, and
	   provides implementation guidance for selecting the Identification
	   field of the Fragment Header, such that the aforementioned security
	   implications are mitigated.</t></abstract>

	</front>

	<seriesInfo name='Internet-Draft' value='draft-ietf-6man-predictable-fragment-id-08' />
	<format type='TXT'
		target='https://tools.ietf.org/id/draft-ietf-6man-predictable-fragment-id-08.txt' />
	</reference>


<!--
<reference anchor='I-D.hinden-6man-rfc2460bis-07'>
<front>
<title>Internet Protocol, Version 6 (IPv6) Specification</title>

<author initials='S.E.' surname='Deering' fullname='Stephen E. Deering'>
<author initials='R.M.' surname='Hinden' fullname='Robert M. Hinden'>

    <organization />
</author>


<date month='June' day='9' year='2015' />

<abstract><t>   This document specifies version 6 of the Internet Protocol (IPv6),
   also sometimes referred to as IP Next Generation or IPng.  It
   obsoletes RFC2460.</t></abstract>

</front>

<seriesInfo name='Internet-Draft' value='draft-ietf-6man-rfc2460bis-02' />
<format type='TXT'
        target='http://www.ietf.org/internet-drafts/draft-ietf-6man-rfc2460bis-02.txt' />
</reference>

-->


<!-- http://u.cs.biu.ac.il/~herzbea/security/13-03-frag.pdf -->



<!-- DNS --> 

<reference anchor="Schuba1993" target="http://ftp.cerias.purdue.edu/pub/papers/christoph-schuba/schuba-DNS-msthesis.pdf">
		<front>
			<title>ADDRESSING WEAKNESSES IN THE DOMAIN NAME SYSTEM PROTOCOL</title>
			<author initials="C." surname="Schuba" fullname="Christoph Schuba">
				<organization></organization>
			</author>
			<date year="1993"/>
		</front>
</reference>

	<reference anchor="Vixie1995" target="https://www.usenix.org/legacy/publications/library/proceedings/security95/full_papers/vixie.pdf">
		<front>
			<title>DNS and BIND Security Issues</title>
			<author initials="P." surname="Vixie" fullname="Paul Vixie">
				<organization></organization>
			</author>
			<date month="May" day="2" year="1995"/>	
		</front>
			<seriesInfo name="5th Usenix Security Symposium" value="May 2, 1995"/>	
	</reference>

	<reference anchor="Klein2007b" target="https://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.86.4474">
		<front>
			<title>BIND 9 DNS Cache Poisoning</title>
			<author initials="A." surname="Klein" fullname="Amit Klein">
				<organization></organization>
			</author>
			<date month="March" year="2007"/>	
		</front>

	</reference>
	
		<reference anchor="Klein2007c" target="https://dl.packetstormsecurity.net/papers/attack/Windows_DNS_Cache_Poisoning.pdf">
		<front>
			<title>Windows DNS Server Cache Poisoning</title>
			<author initials="A." surname="Klein" fullname="Amit Klein">
				<organization></organization>
			</author>
			<date month="March" year="2007"/>	 
		</front>

	</reference>
	

	<reference anchor="Sacramento2002" target="https://seclists.org/bugtraq/2002/Nov/331">
		<front>
			<title>CAIS-ALERT: Vulnerability in the sending requests control of BIND</title>
			<author initials="V." surname="Sacramento " fullname="Vagner Sacramento ">
				<organization></organization>
			</author>
			
			<date month="November" day="19" year="2002"/>	
		</front>

	</reference>


	<reference anchor="Kaminsky2008" target="https://www.blackhat.com/presentations/bh-jp-08/bh-jp-08-Kaminsky/BlackHat-Japan-08-Kaminsky-DNS08-BlackOps.pdf">
		<front>
			<title>Black Ops 2008: It's The End Of The Cache As We Know It</title>
			<author initials="D." surname="Kaminsky " fullname="Dan Kaminsky ">
				<organization></organization>
			</author>
			
			<date month="August" year="2008"/>	
		</front>

	</reference>
	

	<reference anchor="Economou2010" target="https://www.coresecurity.com/core-labs/advisories/core-2010-0424-windows-smtp-dns-query-id-bugs">
		<front>
			<title>Windows SMTP Service DNS query Id vulnerabilities</title>
			<author initials="N." surname="Economou" fullname="Nicolas Economou">
				<organization></organization>
			</author>
			
			<date month="May" day="4" year="2010"/>	
		</front>
			<seriesInfo name="Advisory ID Internal CORE-2010-0427" value="May 4, 2010"/>	
	</reference>




</references>

  </back>
</rfc>