dhc                                                             S. Jiang
Internet-Draft                              Huawei Technologies Co., Ltd
Intended status: Informational                               S. Krishnan
Expires: July 21, 2016                                          Ericsson
                                                            T. Mrugalski
                                                        January 18, 2016

                   Privacy considerations for DHCPv4


   DHCP is a protocol that is used to provide addressing and
   configuration information to IPv4 hosts.  This document discusses the
   various identifiers used by DHCP and the potential privacy issues.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on July 21, 2016.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Requirements Language and Terminology . . . . . . . . . . . .   3
   3.  DHCP Options Carrying Identifiers . . . . . . . . . . . . . .   3
     3.1.  Client Identifier Option  . . . . . . . . . . . . . . . .   4
     3.2.  Address Fields & Options  . . . . . . . . . . . . . . . .   4
     3.3.  Client FQDN Option  . . . . . . . . . . . . . . . . . . .   5
     3.4.  Parameter Request List Option . . . . . . . . . . . . . .   5
     3.5.  Vendor Class and Vendor-Identifying Vendor Class Options    5
     3.6.  Civic Location Option . . . . . . . . . . . . . . . . . .   5
     3.7.  Coordinate-Based Location Option  . . . . . . . . . . . .   6
     3.8.  Client System Architecture Type Option  . . . . . . . . .   6
     3.9.  Relay Agent Information Option and Sub-options  . . . . .   6
   4.  Existing Mechanisms That Affect Privacy . . . . . . . . . . .   7
     4.1.  DNS Updates . . . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  Allocation strategies . . . . . . . . . . . . . . . . . .   7
   5.  Attacks . . . . . . . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  Device type discovery . . . . . . . . . . . . . . . . . .   8
     5.2.  Operating system discovery  . . . . . . . . . . . . . . .   9
     5.3.  Finding location information  . . . . . . . . . . . . . .   9
     5.4.  Finding previously visited networks . . . . . . . . . . .   9
     5.5.  Finding a stable identity . . . . . . . . . . . . . . . .   9
     5.6.  Pervasive monitoring  . . . . . . . . . . . . . . . . . .   9
     5.7.  Finding client's IP address or hostname . . . . . . . . .  10
     5.8.  Correlation of activities over time . . . . . . . . . . .  10
     5.9.  Location tracking . . . . . . . . . . . . . . . . . . . .  10
     5.10. Leasequery & bulk leasequery  . . . . . . . . . . . . . .  10
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   7.  Privacy Considerations  . . . . . . . . . . . . . . . . . . .  11
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     10.2.  Informative References . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   Dynamic Host Configuration Protocol (DHCP) [RFC2131] is a protocol
   that is used to provide addressing and configuration information to
   IPv4 hosts.  The DHCP protocol uses several identifiers that could
   become a source for gleaning information about the IPv4 host.  This
   information may include device type, operating system information,
   location(s) that the device may have previously visited, etc.  This

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   document discusses the various identifiers used by DHCP and the
   potential privacy issues [RFC6973].  In particular, it also takes
   into consideration the problem of pervasive monitoring [RFC7258].

   Future works may propose protocol changes to fix the privacy issues
   that have been analyzed in this document.  It is out of scope for
   this document.

   The primary focus of this document is around privacy considerations
   for clients to support client mobility and connection to random
   networks.  The privacy of DHCP servers and relay agents are
   considered less important as they are typically open for public
   services.  And, it is generally assumed that relay agent to server
   communication is protected from casual snooping, as that
   communication occurs in the provider's backbone.  Nevertheless, the
   topics involving relay agents and servers are explored to some
   degree.  However, future work may want to further explore privacy of
   DHCP servers and relay agents.

2.  Requirements Language and Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [RFC2119].  When these
   words are not in ALL CAPS (such as "should" or "Should"), they have
   their usual English meanings, and are not to be interpreted as
   [RFC2119] key words.

   In addition the following terminology is used:

   Stable identifier  - Any property disclosed by a DHCP client that
           does not change over time or changes very infrequently and is
           unique for said client in a given context.  Examples may
           include MAC address, client-id or a hostname.  Some
           identifiers may be considered stable only under certain
           conditions, for example one client implementation may keep
           its client-id stored in stable storage while other may
           generate it on the fly and use a different one after each
           boot.  Stable identifier may or may not be globally unique.

3.  DHCP Options Carrying Identifiers

   In DHCP, there are a few options which contain identification
   information or can be used to extract the identification information
   about the client.  This section enumerates various options and
   identifiers conveyed in them, which can be used to disclose client
   identification.  They are targets of various attacks that would be
   analyzed in Section 5.

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3.1.  Client Identifier Option

   The Client Identifier Option [RFC2131] is used to pass an explicit
   client identifier to a DHCP server.

   The client identifier is an opaque key, which must be unique to that
   client within the subnet to which the client is attached.  It
   typically remains stable after it has been initially generated.  It
   may contain a hardware address, identical to the contents of the
   'chaddr' field, or another type of identifier, such as a DNS name.
   [RFC3315] in Section 9.2 specifies DUID-LLT (Link-layer + time) as
   the recommended DUID (DHCP Unique Identifier) type.  [RFC4361],
   Section 6.1 introduces this concept to DHCPv4.  Those two document
   recommend that client identifiers be generated by using the permanent
   link-layer address of the network interface that the client is trying
   to configure.  [RFC4361] updates the recommendation of Client
   Identifiers to be "consists of a type field whose value is normally
   255, followed by a four-byte IA_ID field, followed by the DUID for
   the client as defined in RFC 3315, section 9".  This does not change
   the lifecycle of the Client Identifiers.  Clients are expected to
   generate their Client Identifiers once (during first operation) and
   store it in a non-volatile storage or use the same deterministic
   algorithm to generate the same Client Identifier values again.

   This means that most implementations will use the available link-
   layer address during its first boot.  Even if the administrator
   enables link-layer address randomization, it is likely that it was
   disabled during the first device boot.  Hence the original,
   unobfuscated link-layer address will likely end up being announced as
   client identifier, even if the link- layer address has changed (or
   even if being changed on a periodic basis).  The exposure of the
   original link-layer address in the client identifier will also
   undermine other privacy extensions such as [RFC4941].

3.2.  Address Fields & Options

   The 'yiaddr' field [RFC2131] in DHCP message is used to convey
   allocated address from the server to the client.

   The DHCPv4 specification [RFC2131] provides a way to specify the
   client link-layer address in the DHCPv4 message header.  A DHCPv4
   message header has 'htype' and 'chaddr' fields to specify the client
   link-layer address type and the link-layer address, respectively.
   The 'chaddr' field is used both as a hardware address for
   transmission of reply messages and as a client identifier.

   The 'requested IP address' option [RFC2131] is used by client to
   suggest that a particular IP address be assigned.

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3.3.  Client FQDN Option

   The Client Fully Qualified Domain Name (FQDN) option [RFC4702] is
   used by DHCP clients and servers to exchange information about the
   client's fully qualified domain name and about who has the
   responsibility for updating the DNS with the associated A and PTR

   A client can use this option to convey all or part of its domain name
   to a DHCP server for the IP-address-to-FQDN mapping.  In most case a
   client sends its hostname as a hint for the server.  The DHCP server
   MAY be configured to modify the supplied name or to substitute a
   different name.  The server should send its notion of the complete
   FQDN for the client in the Domain Name field.

3.4.  Parameter Request List Option

   The Parameter Request List option [RFC2131] is used to inform the
   server about options the client wants the server to send to the
   client.  The content of a Parameter Request List option are the
   option codes for an option requested by the client.

3.5.  Vendor Class and Vendor-Identifying Vendor Class Options

   The Vendor Class option [RFC2131], the Vendor-Identifying Vendor
   Class option and Vendor-Identifying Vendor Information option
   [RFC3925] are used by the DHCP client to identify the vendor that
   manufactured the hardware on which the client is running.

   The information contained in the data area of this option is
   contained in one or more opaque fields that identify the details of
   the hardware configuration of the host on which the client is
   running, or of industry consortium compliance, for example, the
   version of the operating system the client is running or the amount
   of memory installed on the client.

3.6.  Civic Location Option

   DHCP servers use the Civic Location Option [RFC4776] to deliver of
   the location information (the civic and postal addresses) to the DHCP
   clients.  It may refer to three locations: the location of the DHCP
   server, the location of the network element believed to be closest to
   the client, or the location of the client, identified by the "what"
   element within the option.

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3.7.  Coordinate-Based Location Option

   The GeoConf and GeoLoc options [RFC6225] is used by DHCP server to
   provide the coordinate-based geographic location information to the
   DHCP clients.  It enables a DHCP client to obtain its geographic

3.8.  Client System Architecture Type Option

   The Client System Architecture Type Option [RFC4578] is used by DHCP
   client to send a list of supported architecture types to the DHCP
   server.  It is used by clients that must be booted using the network
   rather than from local storage, so the server can decide which boot
   file should be provided to the client.

3.9.  Relay Agent Information Option and Sub-options

   A DHCP relay agent includes a Relay Agent Information [RFC3046] to
   identify the remote host end of the circuit.  It contains a "circuit
   ID" sub-option for the incoming circuit, which is an agent-local
   identifier of the circuit from which a DHCP client-to-server packet
   was received, and a "remote ID" sub-option which provides a trusted
   identifier for the remote high-speed modem.

   Possible encoding of "circuit ID" sub-option includes: router
   interface number, switching hub port number, remote access server
   port number, frame relay DLCI, ATM virtual circuit number, cable data
   virtual circuit number, etc.

   Possible encoding of the "remote ID" sub-option includes: a "caller
   ID" telephone number for dial-up connection, a "user name" prompted
   for by a remote access server, a remote caller ATM address, a "modem
   ID" of a cable data modem, the remote IP address of a point-to-point
   link, a remote X.25 address for X.25 connections, etc.

   The link-selection sub-option [RFC3527] is used by any DHCP relay
   agent that desires to specify a subnet/link for a DHCP client request
   that it is relaying but needs the subnet/link specification to be
   different from the IP address the DHCP server should use when
   communicating with the relay agent.  It contains an IP address, which
   can identify the client's subnet/link.  Also, assuming network
   topology knowledge, it also reveals client location.

   A DHCP relay includes a Subscriber-ID option [RFC3993] to associate
   some provider-specific information with clients' DHCP messages that
   is independent of the physical network configuration through which
   the subscriber is connected.  The "subscriber-id" assigned by the
   provider is intended to be stable as customers connect through

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   different paths, and as network changes occur.  The Subscriber-ID is
   an ASCII string, which is assigned and configured by the network

4.  Existing Mechanisms That Affect Privacy

   This section describes deployed DHCP mechanisms that affect privacy.

4.1.  DNS Updates

   The Client FQDN (Fully Qualified Domain Name) Option [RFC4702] used
   along with DNS Updates [RFC2136] defines a mechanism that allows both
   clients and server to insert into the DNS domain information about
   clients.  Both forward (A) and reverse (PTR) resource records can be
   updated.  This allows other nodes to conveniently refer to a host,
   despite the fact that its IP address may be changing.

   This mechanism exposes two important pieces of information: current
   address (which can be mapped to current location) and client's
   hostname.  The stable hostname can then be used to correlate the
   client across different network attachments even when its IP
   addresses keep changing.

4.2.  Allocation strategies

   A DHCP server running in typical, stateful mode is given a task of
   managing one or more pools of IP address.  When a client requests an
   address, the server must pick an address out of configured pool.
   Depending on the server's implementation, various allocation
   strategies are possible.  Choices in this regard may have privacy
   implications.  Note that the constraints in DHCPv4 and DHCPv6 are
   radically different, but servers that allow allocation strategy
   configuration may allow configuring them in both DHCPv4 and DHCPv6.
   Not every allocation strategy is equally suitable for DHCPv4 and for

   Iterative allocation - a server may choose to allocate addresses one
   by one.  That strategy has the benefit of being very fast, thus can
   be favored in deployments that prefer performance.  However, it makes
   the allocated addresses very predictable.  Also, since the addresses
   allocated tend to be clustered at the beginning of available pool, it
   makes scanning attacks much easier.

   Identifier-based allocation - some server implementations may choose
   to allocate an address that is based on one of available identifiers,
   e.g. client identifier or MAC address.  It is also convenient, as
   returning client is very likely to get the same address.  Those
   properties are convenient for system administrators, so DHCP server

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   implementors are often requested to implement it.  The downside of
   such allocation is that the client has a very stable IP address.
   That means that correlation of activities over time, location
   tracking, address scanning and OS/vendor discovery apply.  This is
   certainly an issue in DHCPv6, but due to much smaller address space
   is almost never a problem in DHCPv4.

   Hash allocation - it's an extension of identifier based allocation.
   Instead of using the identifier directly, it is being hashed first.
   If the hash is implemented correctly, it removes the flaw of
   disclosing the identifier, a property that eliminates susceptibility
   to address scanning and OS/vendor discovery.  If the hash is poorly
   implemented (e.g. can be reverted), it introduces no improvement over
   identifier-based allocation.

   Random allocation - a server can pick a resource randomly out of
   available pool.  That strategy works well in scenarios where pool
   utilization is small, as the likelihood of collision (resulting in
   the server needing to repeat randomization) is small.  With the pool
   allocation increasing, the collision is disproportionally large, due
   to birthday paradox.  With high pool utilization (e.g. when 90% of
   available resources being allocated already), the server will use
   most computational resources to repeatedly pick a random resource,
   which will degrade its performance.  This allocation scheme
   essentially prevents returning clients from getting the same address
   again.  On the other hand, it is beneficial from privacy perspective
   as addresses generated that way are not susceptible to correlation
   attacks, OS/vendor discovery attacks or identity discovery attacks.
   Note that even though the address itself may be resilient to a given
   attack, the client may still be susceptible if additional information
   is disclosed other way, e.g. client's address can be randomized, but
   it still can leak its MAC address in client-id option.

   Other allocation strategies may be implemented.

   Given the limited size of most IPv4 public address pools, allocation
   mechanisms in IPv4 may not provide much privacy protection or leak
   much useful information, if misused.

5.  Attacks

5.1.  Device type discovery

   The type of device used by the client can be guessed by the attacker
   using the Vendor Class Option, the 'chaddr' field, and by parsing the
   Client ID Option.  All of those options may contain an
   Organizationally Unique Identifier (OUI) that represents the device's

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   vendor.  That knowledge can be used for device-specific vulnerability
   exploitation attacks.

5.2.  Operating system discovery

   The operating system running on a client can be guessed using the
   Vendor Class option, the Client System Architecture Type option, or
   by using fingerprinting techniques on the combination of options
   requested using the Parameter Request List option.

5.3.  Finding location information

   The location information can be obtained by the attacker by many
   means.  The most direct way to obtain this information is by looking
   into a message originating from the server that contains the Civic
   Location, GeoConf, or GeoLoc options.  It can also be indirectly
   inferred using the Relay Agent Information option, with the remote ID
   sub-option, the circuit ID option (e.g. if an access circuit on an
   Access Node corresponds to a civic location), or the Subscriber ID
   Option (if the attacker has access to subscriber info).

5.4.  Finding previously visited networks

   When DHCP clients connect to a network, they attempt to obtain the
   same address they had used before they attached to the network.  They
   do this by putting the previously assigned address in the requested
   IP address option.  By observing these addresses, an attacker can
   identify the network the client had previously visited.

5.5.  Finding a stable identity

   An attacker might use a stable identity gleaned from DHCP messages to
   correlate activities of a given client on unrelated networks.  The
   Client FQDN option, the Subscriber ID Option and the Client ID
   options can serve as long lived identifiers of DHCP clients.  The
   Client FQDN option can also provide an identity that can easily be
   correlated with web server activity logs.

5.6.  Pervasive monitoring

   This is an enhancement, or a combination of most aforementioned
   mechanisms.  Operator who controls non-trivial number of access
   points or network segments, may use obtained information about a
   single client and observer client's habits.

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5.7.  Finding client's IP address or hostname

   Many DHCP deployments use DNS Updates [RFC4702] that put client's
   information (current IP address, client's hostname) into DNS, where
   it is easily accessible by anyone interested.  Client ID is also
   disclosed, albeit in not easily accessible form (SHA-256 digest of
   the client-id).  As SHA-256 is considered irreversible, DHCID can't
   be converted back to client-id.  However, SHA-256 digest can be used
   as an unique identifier that is accessible by any host.

5.8.  Correlation of activities over time

   As with other identifiers, an IP address can be used to correlate the
   activities of a host for at least as long as the lifetime of the
   address.  If that address was generated from some other, stable
   identifier and that generation scheme can be deducted by an attacker,
   the duration of correlation attack extends to that identifier.  In
   many cases, its lifetime is equal to the lifetime of the device

5.9.  Location tracking

   If a stable identifier is used for assigning an address and such
   mapping is discovered by an attacker, e.g. a hostname being put into
   DNS, it can be used for tracking user.  In particular both passive (a
   service that the client connects to can log client's address and draw
   conclusions regarding its location and movement patterns based on
   address it is connecting from) and active (attacker can send ICMP
   echo requests or other probe packets to networks of suspected client
   locations) methods can be used.  To give specific example, by
   accessing a social portal from tomek-
   laptop.coffee.somecity.com.example, tomek-
   laptop.mycompany.com.example and tomek-laptop.myisp.example.com, the
   portal administrator can draw conclusions about tomek-laptop's owner
   current location and his habits.

5.10.  Leasequery & bulk leasequery

   Attackers may pretend as an access concentrator, either DHCP relay
   agent or DHCP client, to obtain location information directly from
   the DHCP server(s) using the DHCP leasequery [RFC4388] mechanism.

   Location information is information needed by the access concentrator
   to forward traffic to a broadband-accessible host.  This information
   includes knowledge of the host hardware address, the port or virtual
   circuit that leads to the host, and/or the hardware address of the
   intervening subscriber modem.

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   Furthermore, the attackers may use DHCP bulk leasequery [RFC6926]
   mechanism to obtain bulk information about DHCP bindings, even
   without knowing the target bindings.

   Additionally, active leasequery [RFC7724] is a mechanism for
   subscribing to DHCPv4 lease update changes in near real-time.  The
   intent of this mechanism is to update operator's database, but if
   misused, an attacker could defeat server's authentication mechanisms
   and subscribe to all updates.  He then could continue receiving
   updates, without any need for local presence.

6.  Security Considerations

   In current practice, the client privacy and the client authentication
   are mutually exclusive.  The client authentication procedure reveals
   additional client information in their certificates/identifiers.
   Full privacy for the clients may mean the clients are also anonymous
   for the server and the network.

7.  Privacy Considerations

   This document at its entirety discusses privacy considerations in
   DHCP.  As such, no dedicated discussion is needed.

8.  IANA Considerations

   This draft does not request any IANA action.

9.  Acknowledgements

   The authors would like to thank the valuable comments made by Stephen
   Farrell, Ted Lemon, Ines Robles, Russ White, Christian Huitema,
   Bernie Volz, Jinmei Tatuya, Marcin Siodelski, Christian Schaefer and
   other members of DHC WG.

   This document was produced using the xml2rfc tool [RFC2629].

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

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   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",
              RFC 2131, DOI 10.17487/RFC2131, March 1997,

   [RFC2136]  Vixie, P., Ed., Thomson, S., Rekhter, Y., and J. Bound,
              "Dynamic Updates in the Domain Name System (DNS UPDATE)",
              RFC 2136, DOI 10.17487/RFC2136, April 1997,

   [RFC6973]  Cooper, A., Tschofenig, H., Aboba, B., Peterson, J.,
              Morris, J., Hansen, M., and R. Smith, "Privacy
              Considerations for Internet Protocols", RFC 6973,
              DOI 10.17487/RFC6973, July 2013,

   [RFC7258]  Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an
              Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May
              2014, <http://www.rfc-editor.org/info/rfc7258>.

10.2.  Informative References

   [RFC2629]  Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
              DOI 10.17487/RFC2629, June 1999,

   [RFC3046]  Patrick, M., "DHCP Relay Agent Information Option",
              RFC 3046, DOI 10.17487/RFC3046, January 2001,

   [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
              C., and M. Carney, "Dynamic Host Configuration Protocol
              for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
              2003, <http://www.rfc-editor.org/info/rfc3315>.

   [RFC3527]  Kinnear, K., Stapp, M., Johnson, R., and J. Kumarasamy,
              "Link Selection sub-option for the Relay Agent Information
              Option for DHCPv4", RFC 3527, DOI 10.17487/RFC3527, April
              2003, <http://www.rfc-editor.org/info/rfc3527>.

   [RFC3925]  Littlefield, J., "Vendor-Identifying Vendor Options for
              Dynamic Host Configuration Protocol version 4 (DHCPv4)",
              RFC 3925, DOI 10.17487/RFC3925, October 2004,

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   [RFC3993]  Johnson, R., Palaniappan, T., and M. Stapp, "Subscriber-ID
              Suboption for the Dynamic Host Configuration Protocol
              (DHCP) Relay Agent Option", RFC 3993,
              DOI 10.17487/RFC3993, March 2005,

   [RFC4361]  Lemon, T. and B. Sommerfeld, "Node-specific Client
              Identifiers for Dynamic Host Configuration Protocol
              Version Four (DHCPv4)", RFC 4361, DOI 10.17487/RFC4361,
              February 2006, <http://www.rfc-editor.org/info/rfc4361>.

   [RFC4388]  Woundy, R. and K. Kinnear, "Dynamic Host Configuration
              Protocol (DHCP) Leasequery", RFC 4388,
              DOI 10.17487/RFC4388, February 2006,

   [RFC4578]  Johnston, M. and S. Venaas, Ed., "Dynamic Host
              Configuration Protocol (DHCP) Options for the Intel
              Preboot eXecution Environment (PXE)", RFC 4578,
              DOI 10.17487/RFC4578, November 2006,

   [RFC4702]  Stapp, M., Volz, B., and Y. Rekhter, "The Dynamic Host
              Configuration Protocol (DHCP) Client Fully Qualified
              Domain Name (FQDN) Option", RFC 4702,
              DOI 10.17487/RFC4702, October 2006,

   [RFC4776]  Schulzrinne, H., "Dynamic Host Configuration Protocol
              (DHCPv4 and DHCPv6) Option for Civic Addresses
              Configuration Information", RFC 4776,
              DOI 10.17487/RFC4776, November 2006,

   [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
              Extensions for Stateless Address Autoconfiguration in
              IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,

   [RFC6225]  Polk, J., Linsner, M., Thomson, M., and B. Aboba, Ed.,
              "Dynamic Host Configuration Protocol Options for
              Coordinate-Based Location Configuration Information",
              RFC 6225, DOI 10.17487/RFC6225, July 2011,

Jiang, et al.             Expires July 21, 2016                [Page 13]

Internet-Draft         DHCP Privacy considerations          January 2016

   [RFC6926]  Kinnear, K., Stapp, M., Desetti, R., Joshi, B., Russell,
              N., Kurapati, P., and B. Volz, "DHCPv4 Bulk Leasequery",
              RFC 6926, DOI 10.17487/RFC6926, April 2013,

   [RFC7724]  Kinnear, K., Stapp, M., Volz, B., and N. Russell, "Active
              DHCPv4 Lease Query", RFC 7724, DOI 10.17487/RFC7724,
              December 2015, <http://www.rfc-editor.org/info/rfc7724>.

Authors' Addresses

   Sheng Jiang
   Huawei Technologies Co., Ltd
   Q14, Huawei Campus, No.156 Beiqing Road
   Hai-Dian District, Beijing, 100095
   P.R. China

   Email: jiangsheng@huawei.com

   Suresh Krishnan
   8400 Decarie Blvd.
   Town of Mount Royal, QC

   Phone: +1 514 345 7900 x42871
   Email: suresh.krishnan@ericsson.com

   Tomek Mrugalski
   Internet Systems Consortium, Inc.
   950 Charter Street
   Redwood City, CA  94063

   Email: tomasz.mrugalski@gmail.com

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