Network Working Group B. Volz
Internet-Draft Cisco Systems
Intended status: Standards Track Y. Pal
Expires: September 30, 2017 Cisco Systems, Inc.
March 29, 2017
Security of Messages Exchanged Between Servers and Relay Agents
draft-ietf-dhc-relay-server-security-04.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 September 30, 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 September 30, 2017 [Page 1]
Internet-Draft DHCP Relay/Server Security March 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 . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
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.
Volz & Pal Expires September 30, 2017 [Page 2]
Internet-Draft DHCP Relay/Server Security March 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 IPsec encryption of
relay to relay and relay to server communication and replaces the
text in RFC3315 Section 21.1.
For DHCPv4 [RFC2131], this specification REQUIRES IPsec encryption of
relay to server 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 exchange messages securely using the
IPsec mechanisms described in [RFC4301]. 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.
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
Volz & Pal Expires September 30, 2017 [Page 3]
Internet-Draft DHCP Relay/Server Security March 2017
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.
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
Volz & Pal Expires September 30, 2017 [Page 4]
Internet-Draft DHCP Relay/Server Security March 2017
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.
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.
Volz & Pal Expires September 30, 2017 [Page 5]
Internet-Draft DHCP Relay/Server Security March 2017
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>.
[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
[CableLabs-DHCP]
"CableLabs' DHCP Options Registry",
<http://www.cablelabs.com/specification/
cablelabs-dhcp-options-registry-2/>.
[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,
<http://www.rfc-editor.org/info/rfc3046>.
Volz & Pal Expires September 30, 2017 [Page 6]
Internet-Draft DHCP Relay/Server Security March 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>.
Authors' Addresses
Bernie Volz
Cisco Systems, Inc.
1414 Massachusetts Ave
Boxborough, MA 01719
USA
Email: volz@cisco.com
Volz & Pal Expires September 30, 2017 [Page 7]
Internet-Draft DHCP Relay/Server Security March 2017
Yogendra Pal
Cisco Systems, Inc.
Cessna Business Park,
Varthur Hobli, Outer Ring Road,
Bangalore, Karnataka 560103
India
Email: yogpal@cisco.com
Volz & Pal Expires September 30, 2017 [Page 8]
