Internet DRAFT - draft-volz-dhc-relay-server-security
draft-volz-dhc-relay-server-security
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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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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