Network Working Group B. Volz Internet-Draft Cisco Systems Intended status: Standards Track Y. Pal Expires: October 21, 2017 Cisco Systems, Inc. April 19, 2017 Security of Messages Exchanged Between Servers and Relay Agents draft-ietf-dhc-relay-server-security-05.txt Abstract 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. And, 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 Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on October 21, 2017. Copyright Notice Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 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 Volz & Pal Expires October 21, 2017 [Page 1] Internet-Draft DHCP Relay/Server Security April 2017 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. 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 Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Requirements Language and Terminology . . . . . . . . . . . . 3 3. Security of Messages Exchanged Between Servers and Relay Agents . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Security Considerations . . . . . . . . . . . . . . . . . . . 5 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5 6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 6 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 7.1. Normative References . . . . . . . . . . . . . . . . . . 6 7.2. Informative References . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction The Dynamic Host Configuration Protocol for IPv4 (DHCPv4) [RFC2131] and [RFC1542] has 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. And, 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 operators enable this IPsec support. Volz & Pal Expires October 21, 2017 [Page 2] Internet-Draft DHCP Relay/Server Security April 2017 2. Requirements Language and Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] when they appear in ALL CAPS. 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. 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 (this replaces the text in RFC3315 Section 21.1). 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, the potentially sensitive client message and relay included information, such as the DHCPv4 relay-agent information option (82) [RFC3046], vendor-specific information (for example, [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] and with the conditions below. If a client message is relayed through multiple relay agents (relay chain), each of the relay agents MUST have an 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. 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. Volz & Pal Expires October 21, 2017 [Page 3] Internet-Draft DHCP Relay/Server Security April 2017 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 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 Sections 2.1, 2.2, and 2.3 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, [CableLabs-DHCP]) and [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, 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 Expires October 21, 2017 [Page 4] Internet-Draft DHCP Relay/Server Security April 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 [I-D.ietf-dhc-sedhcpv6] to secure communication between the client and server. As mentioned in [RFC4552] Section 14, 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 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 the systems themselves and if 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 which can be used to secure communication with their next hop relay(s). 5. IANA Considerations This document has no requests of the fantastic IANA team. Volz & Pal Expires October 21, 2017 [Page 5] Internet-Draft DHCP Relay/Server Security April 2017 6. Acknowledgments 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 drafts and helping to improve the document. And, thanks to the authors of [RFC3315] for the original Section 21.1 text. 7. References 7.1. Normative References [RFC1542] Wimer, W., "Clarifications and Extensions for the Bootstrap Protocol", RFC 1542, DOI 10.17487/RFC1542, October 1993, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, DOI 10.17487/RFC2131, March 1997, . [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, . [RFC4301] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, December 2005, . [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, . 7.2. Informative References [CableLabs-DHCP] "CableLabs' DHCP Options Registry", . Volz & Pal Expires October 21, 2017 [Page 6] Internet-Draft DHCP Relay/Server Security April 2017 [I-D.ietf-dhc-sedhcpv6] Li, L., Jiang, S., Cui, Y., Jinmei, T., Lemon, T., and D. Zhang, "Secure DHCPv6", draft-ietf-dhc-sedhcpv6-21 (work in progress), February 2017. [RFC3046] Patrick, M., "DHCP Relay Agent Information Option", RFC 3046, DOI 10.17487/RFC3046, January 2001, . [RFC4107] Bellovin, S. and R. Housley, "Guidelines for Cryptographic Key Management", BCP 107, RFC 4107, DOI 10.17487/RFC4107, June 2005, . [RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006, . [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, . [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, . [RFC7258] Farrell, S. and H. Tschofenig, "Pervasive Monitoring Is an Attack", BCP 188, RFC 7258, DOI 10.17487/RFC7258, May 2014, . [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, . [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, . [RFC7844] Huitema, C., Mrugalski, T., and S. Krishnan, "Anonymity Profiles for DHCP Clients", RFC 7844, DOI 10.17487/RFC7844, May 2016, . Volz & Pal Expires October 21, 2017 [Page 7] Internet-Draft DHCP Relay/Server Security April 2017 Authors' Addresses Bernie Volz Cisco Systems, Inc. 1414 Massachusetts Ave Boxborough, MA 01719 USA Email: volz@cisco.com Yogendra Pal Cisco Systems, Inc. Cessna Business Park, Varthur Hobli, Outer Ring Road, Bangalore, Karnataka 560103 India Email: yogpal@cisco.com Volz & Pal Expires October 21, 2017 [Page 8]