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Internet Engineering Task Force (IETF)                           B. VolzRequest for Comments: 8213                                        Y. PalCategory: Standards Track                                  Cisco SystemsISSN: 2070-1721                                              August 2017Security of Messages Exchanged between Servers and Relay AgentsAbstract   The Dynamic Host Configuration Protocol for IPv4 (DHCPv4) has no   guidance for how to secure messages exchanged between servers and   relay agents.  The Dynamic Host Configuration Protocol for IPv6   (DHCPv6) states that IPsec should be used to secure messages   exchanged between servers and relay agents but does not require   encryption.  With recent concerns about pervasive monitoring and   other attacks, it is appropriate to require securing relay-to-relay   and relay-to-server communication for DHCPv6 and relay-to-server   communication for DHCPv4.Status of This Memo   This is an Internet Standards Track document.   This document is a product of the Internet Engineering Task Force   (IETF).  It represents the consensus of the IETF community.  It has   received public review and has been approved for publication by the   Internet Engineering Steering Group (IESG).  Further information on   Internet Standards is available inSection 2 of RFC 7841.   Information about the current status of this document, any errata,   and how to provide feedback on it may be obtained athttp://www.rfc-editor.org/info/rfc8213.Copyright Notice   Copyright (c) 2017 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents   (http://trustee.ietf.org/license-info) in effect on the date of   publication of this document.  Please review these documents   carefully, as they describe your rights and restrictions with respect   to this document.  Code Components extracted from this document must   include Simplified BSD License text as described in Section 4.e of   the Trust Legal Provisions and are provided without warranty as   described in the Simplified BSD License.Volz & Pal                   Standards Track                    [Page 1]

RFC 8213               DHCP Relay/Server Security            August 2017   This document may contain material from IETF Documents or IETF   Contributions published or made publicly available before November   10, 2008.  The person(s) controlling the copyright in some of this   material may not have granted the IETF Trust the right to allow   modifications of such material outside the IETF Standards Process.   Without obtaining an adequate license from the person(s) controlling   the copyright in such materials, this document may not be modified   outside the IETF Standards Process, and derivative works of it may   not be created outside the IETF Standards Process, except to format   it for publication as an RFC or to translate it into languages other   than English.Table of Contents1. Introduction ....................................................22. Requirements Language and Terminology ...........................3   3. Security of Messages Exchanged between Servers and Relay      Agents ..........................................................34. Security Considerations .........................................55. IANA Considerations .............................................56. References ......................................................66.1. Normative References .......................................66.2. Informative References .....................................6   Acknowledgments ....................................................8   Authors' Addresses .................................................81.  Introduction   The Dynamic Host Configuration Protocol for IPv4 (DHCPv4) [RFC2131]   and the Bootstrap Protocol [RFC1542] have no guidance for how to   secure messages exchanged between servers and relay agents.  The   Dynamic Host Configuration Protocol for IPv6 (DHCPv6) [RFC3315]   states that IPsec should be used to secure messages exchanged between   servers and relay agents but does not recommend encryption.  With   recent concerns about pervasive monitoring [RFC7258], it is   appropriate to require use of IPsec with encryption for relay-to-   server communication for DHCPv4 and require use of IPsec with   encryption for relay-to-relay and relay-to-server communication for   DHCPv6.   This document specifies the optional requirements for relay agent and   server implementations to support IPsec authentication and encryption   and recommends that operators enable this IPsec support.Volz & Pal                   Standards Track                    [Page 2]

RFC 8213               DHCP Relay/Server Security            August 20172.  Requirements Language and Terminology   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 inBCP14 [RFC2119] [RFC8174] when, and only when, they appear in all   capitals, as shown here.   This document uses terminology from [RFC1542], [RFC2131], and   [RFC3315].3.  Security of Messages Exchanged between Servers and Relay Agents   For DHCPv6 [RFC3315], this specification REQUIRES relay and server   implementations to support IPsec encryption of relay-to-relay and   relay-to-server communication as documented below.  The remainder of   this section replaces the text inSection 21.1 of [RFC3315] when this   specification is followed.   For DHCPv4 [RFC2131], this specification REQUIRES relay and server   implementations to support IPsec encryption of relay-to-server   communication as documented below.   This specification RECOMMENDS that operators enable IPsec for this   communication.   By using IPsec with encryption for this communication, potentially   sensitive client message and relay included information, such as the   DHCPv4 Relay Agent Information option (82) [RFC3046], vendor-specific   information (for example, the options defined in [CableLabs-DHCP]),   and Access-Network-Identifier option(s) [RFC7839], are protected from   pervasive monitoring and other attacks.   Relay agents and servers MUST be able to exchange messages using the   IPsec mechanisms described in [RFC4301] with the conditions below.   If a client message is relayed through multiple relay agents (relay   chain), each of the relay agents MUST have established independent,   pairwise trust relationships.  That is, if messages from client C   will be relayed by relay agent A to relay agent B and then to the   server, relay agents A and B MUST be configured to use IPsec for the   messages they exchange, and relay agent B and the server MUST be   configured to use IPsec for the messages they exchange.Volz & Pal                   Standards Track                    [Page 3]

RFC 8213               DHCP Relay/Server Security            August 2017   Relay agents and servers use IPsec with the following conditions:   Selectors        Relay agents are manually configured with the                    addresses of the relay agent or server to which DHCP                    messages are to be forwarded.  Each relay agent and                    server that will be using IPsec for securing DHCP                    messages MUST also be configured with a list of the                    relay agents to which messages will be returned.                    The selectors for the relay agents and servers will                    be the pairs of addresses defining relay agents and                    servers and the direction of DHCP message exchange                    on DHCPv4 UDP port 67 or DHCPv6 UDP port 547.   Mode             Relay agents and servers MUST use IPsec in transport                    mode and use Encapsulating Security Payload (ESP).   Encryption and authentication algorithms                    This document REQUIRES combined mode algorithms for                    ESP authenticated encryption, ESP encryption                    algorithms, and ESP authentication algorithms as per                    Sections2.1,2.2, and2.3 of [RFC7321],                    respectively.  Encryption is required as relay                    agents may forward unencrypted client messages as                    well as include additional sensitive information,                    such as vendor-specific information (for example,                    the options defined in [CableLabs-DHCP]) and the                    Access-Network-Identifier Option defined in                    [RFC7839].   Key management   Because both relay agents and servers tend to be                    managed by a single organizational entity, public                    key schemes MAY be optional.  Manually configured                    key management MAY suffice but does not provide                    defense against replayed messages.  Accordingly,                    Internet Key Exchange Protocol Version 2 (IKEv2)                    [RFC7296] with pre-shared secrets SHOULD be                    supported.  IKEv2 with public keys MAY be supported.                    Additional information on manual vs. automated key                    management and when one should be used over the                    other can be found in [RFC4107].   Security policy  DHCP messages between relay agents and servers MUST                    only be accepted from DHCP peers as identified in                    the local configuration.   Authentication   Shared keys, indexed to the source IP address of the                    received DHCP message, are adequate in this                    application.Volz & Pal                   Standards Track                    [Page 4]

RFC 8213               DHCP Relay/Server Security            August 2017   Note: As using IPsec with multicast has additional complexities (see   [RFC5374]), relay agents SHOULD be configured to forward DHCP   messages to unicast addresses.4.  Security Considerations   The security model specified in this document is hop by hop.  For   DHCPv6, there could be multiple relay agents between a client and   server, and each of these hops needs to be secured.  For DHCPv4,   there is no support for multiple relays.   As this document only mandates securing messages exchanged between   relay agents and servers, the message exchanges between clients and   the first-hop relay agent or server are not secured.  Clients may   follow the recommendations in [RFC7844] to minimize what information   they expose or make use of secure DHCPv6 [SEC-DHCPv6] to secure   communication between the client and server.   As mentioned inSection 14 of [RFC4552], the following are known   limitations of the usage of manual keys:   o  As the sequence numbers cannot be negotiated, replay protection      cannot be provided.  This leaves DHCP insecure against all the      attacks that can be performed by replaying DHCP packets.   o  Manual keys are usually long lived (changing them often is a      tedious task).  This gives an attacker enough time to discover the      keys.   It should be noted that if the requirements in this document are   followed, while the DHCP traffic on the wire between relays and   servers is encrypted, the unencrypted data may still be available   through other attacks on the DHCP servers, relays, and related   systems.  Securing these systems and the data in databases and logs   also needs to be considered on both the systems themselves and when   transferred over a network (i.e., to network attached storage for   backups or to operational support systems).   Use of IPsec as described herein is also applicable to Lightweight   DHCPv6 Relay Agents [RFC6221], as they have a link-local address that   can be used to secure communication with their next-hop relay(s).5.  IANA Considerations   This document makes no request of IANA.Volz & Pal                   Standards Track                    [Page 5]

RFC 8213               DHCP Relay/Server Security            August 20176.  References6.1.  Normative References   [RFC1542]  Wimer, W., "Clarifications and Extensions for the              Bootstrap Protocol",RFC 1542, DOI 10.17487/RFC1542,              October 1993, <http://www.rfc-editor.org/info/rfc1542>.   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119,              DOI 10.17487/RFC2119, March 1997,              <http://www.rfc-editor.org/info/rfc2119>.   [RFC2131]  Droms, R., "Dynamic Host Configuration Protocol",RFC 2131, DOI 10.17487/RFC2131, March 1997,              <http://www.rfc-editor.org/info/rfc2131>.   [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>.   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the              Internet Protocol",RFC 4301, DOI 10.17487/RFC4301,              December 2005, <http://www.rfc-editor.org/info/rfc4301>.   [RFC7321]  McGrew, D. and P. Hoffman, "Cryptographic Algorithm              Implementation Requirements and Usage Guidance for              Encapsulating Security Payload (ESP) and Authentication              Header (AH)",RFC 7321, DOI 10.17487/RFC7321, August 2014,              <http://www.rfc-editor.org/info/rfc7321>.   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase inRFC2119 Key Words",BCP 14,RFC 8174, DOI 10.17487/RFC8174,              May 2017, <http://www.rfc-editor.org/info/rfc8174>.6.2.  Informative References   [CableLabs-DHCP]              CableLabs, "CableLabs' DHCP Options Registry",              <https://apps.cablelabs.com/specification/CL-SP-CANN-DHCP-Reg>.   [RFC3046]  Patrick, M., "DHCP Relay Agent Information Option",RFC 3046, DOI 10.17487/RFC3046, January 2001,              <http://www.rfc-editor.org/info/rfc3046>.Volz & Pal                   Standards Track                    [Page 6]

RFC 8213               DHCP Relay/Server Security            August 2017   [RFC4107]  Bellovin, S. and R. Housley, "Guidelines for Cryptographic              Key Management",BCP 107,RFC 4107, DOI 10.17487/RFC4107,              June 2005, <http://www.rfc-editor.org/info/rfc4107>.   [RFC4552]  Gupta, M. and N. Melam, "Authentication/Confidentiality              for OSPFv3",RFC 4552, DOI 10.17487/RFC4552, June 2006,              <http://www.rfc-editor.org/info/rfc4552>.   [RFC5374]  Weis, B., Gross, G., and D. Ignjatic, "Multicast              Extensions to the Security Architecture for the Internet              Protocol",RFC 5374, DOI 10.17487/RFC5374, November 2008,              <http://www.rfc-editor.org/info/rfc5374>.   [RFC6221]  Miles, D., Ed., Ooghe, S., Dec, W., Krishnan, S., and A.              Kavanagh, "Lightweight DHCPv6 Relay Agent",RFC 6221,              DOI 10.17487/RFC6221, May 2011,              <http://www.rfc-editor.org/info/rfc6221>.   [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>.   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.              Kivinen, "Internet Key Exchange Protocol Version 2              (IKEv2)", STD 79,RFC 7296, DOI 10.17487/RFC7296, October              2014, <http://www.rfc-editor.org/info/rfc7296>.   [RFC7839]  Bhandari, S., Gundavelli, S., Grayson, M., Volz, B., and              J. Korhonen, "Access-Network-Identifier Option in DHCP",RFC 7839, DOI 10.17487/RFC7839, June 2016,              <http://www.rfc-editor.org/info/rfc7839>.   [RFC7844]  Huitema, C., Mrugalski, T., and S. Krishnan, "Anonymity              Profiles for DHCP Clients",RFC 7844,              DOI 10.17487/RFC7844, May 2016,              <http://www.rfc-editor.org/info/rfc7844>.   [SEC-DHCPv6]              Li, L., Jiang, S., Cui, Y., Jinmei, T., Lemon, T., and D.              Zhang, "Secure DHCPv6", Work in Progress,draft-ietf-dhc-sedhcpv6-21, February 2017.Volz & Pal                   Standards Track                    [Page 7]

RFC 8213               DHCP Relay/Server Security            August 2017Acknowledgments   The motivation for this document was several IESG DISCUSSes on recent   DHCP relay agent options.   Thanks to Kim Kinnear, Jinmei Tatuya, Francis Dupont, and Tomek   Mrugalski for reviewing and helping to improve the document.  Thanks   to the authors of [RFC3315] for the originalSection 21.1 text.Authors' Addresses   Bernie Volz   Cisco Systems, Inc.   1414 Massachusetts Ave   Boxborough, MA  01719   United States of America   Email: volz@cisco.com   Yogendra Pal   Cisco Systems   Cessna Business Park   Varthur Hobli, Outer Ring Road   Bangalore, Karnataka  560103   India   Email: yogpal@cisco.comVolz & Pal                   Standards Track                    [Page 8]