Security of Messages Exchanged Between Servers and Relay Agents
draft-volz-dhc-relay-server-security-00

Network Working Group                                            B. Volz
Internet-Draft                                             Cisco Systems
Updates: 1542, 3315 (if approved)                                 Y. Pal
Intended status: Standards Track                     Cisco Systems, Inc.
Expires: October 22, 2016                                 April 20, 2016

    Security of Messages Exchanged Between Servers and Relay Agents
              draft-volz-dhc-relay-server-security-00.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 recommend
   encryption.  And, with recent concerns about pervasive monitoring it
   is appropriate to provide recommendations for DHCPv4 and also improve
   the recommendations for DHCPv6.  This document updates RFC1542 and
   RFC3315.

Status of This Memo

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   carefully, as they describe your rights and restrictions with respect
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Security of Messages Exchanged Between Servers and Relay
       Agents  . . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   4
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   5
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

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 provide
   recommendations for DHCPv4 and also improve the recommendations for
   DHCPv6.

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2.  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 in
   [RFC2119].

   This document uses terminology from [RFC1542], [RFC2131], and
   [RFC3315].

3.  Security of Messages Exchanged Between Servers and Relay Agents

   The following text replaces the text in RFC3315 section 21.1 and also
   applies to DHCPv4 (RFC1542).  This revised text essentially adds
   encryption.  While IPsec is not mandated for relay to relay, relay to
   server, and server to relay communication, is it highly recommended
   unless some other security mechanisms are already in place (such as
   VPN tunnels) that protect this potentially sensitive traffic from
   pervasive monitoring.

   Relay agents and servers that exchange messages securely use the
   IPsec mechanisms for IPv6 [RFC4301].  If a client message is relayed
   through multiple relay agents, 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.

   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 Encapsulating Security
                           Payload (ESP).

   Encryption and authentication algorithms

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                           This document recommends combined mode
                           algorithms for ESP authenticated encryption,
                           ESP encryption algorithms, ESP authentication
                           algorithms as per section 2.1, 2.2, 2.3 of
                           [RFC7321] respectively for data encryption
                           and authentication.

   Key management          Because the relay agents and servers are used
                           within an organization, public key schemes
                           are not necessary.  Because the relay agents
                           and servers must be manually configured,
                           manually configured key management may
                           suffice, but does not provide defense against
                           replayed messages.  Accordingly, IKE with
                           preshared secrets SHOULD be supported.  IKE
                           with public keys MAY be supported.

   Security policy         DHCP messages between relay agents and
                           servers should 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.

   Availability            Appropriate IPsec implementations are likely
                           to be available for servers and for relay
                           agents in more full featured devices used in
                           enterprise and core ISP networks.  IPsec is
                           less likely to be available for relay agents
                           in low end devices primarily used in the home
                           or small office markets.

4.  Security Considerations

   This entire document is about security considerations and thus there
   is little else to add in this particular section.

   As this document addresses 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 [I-D.ietf-dhc-anonymity-profile] 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:

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   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 recommendations 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).

5.  IANA Considerations

   This document has no requests of the fantastic IANA team.

6.  Acknowledgments

   The motivation for this document was several IESG discusses on recent
   DHCP relay agent options.

   Thanks to Kim Kinnear for reviewing early 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, <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>.

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   [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>.

7.2.  Informative References

   [I-D.ietf-dhc-anonymity-profile]
              Huitema, C., Mrugalski, T., and S. Krishnan, "Anonymity
              profile for DHCP clients", draft-ietf-dhc-anonymity-
              profile-08 (work in progress), February 2016.

   [I-D.ietf-dhc-sedhcpv6]
              Jiang, S., Li, L., Cui, Y., Jinmei, T., Lemon, T., and D.
              Zhang, "Secure DHCPv6", draft-ietf-dhc-sedhcpv6-11 (work
              in progress), March 2016.

   [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>.

   [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>.

Authors' Addresses

   Bernie Volz
   Cisco Systems, Inc.
   1414 Massachusetts Ave
   Boxborough, MA  01719
   USA

   Email: volz@cisco.com

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   Yogendra Pal
   Cisco Systems, Inc.
   Cessna Business Park,
   Varthur Hobli, Outer Ring Road,
   Bangalore, Karnataka  560103
   India

   Email: yogpal@cisco.com

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