RFC 8213

Security of Messages Exchanged between Servers and Relay Agents

📅 published August 2017, from ietf

RFC 8213: Security of Messages Exchanged between Servers and Relay Agents 🎀

okay bestie, this is RFC 8213 💖 It's an IETF doc by B. Volz and Y. Pal, both at Cisco Systems. It's on the Standards Track, dated August 2017, and its ISSN is 2070-1721 ✨ The title block doesn't list any obsoletes or updates, so it's not replacing or changing any other RFC 💅

Abstract 🦋

DHCPv4 has zero guidance on securing messages between servers and relay agents 💀 DHCPv6 says IPsec should be used for those messages, but it doesn't actually require encryption. With all the pervasive monitoring and other attacks going around, it's appropriate to require securing relay-to-relay and relay-to-server traffic for DHCPv6, and relay-to-server traffic 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 got public review and was approved for publication by the Internet Engineering Steering Group (IESG). For more on Internet Standards, check Section 2 of RFC 7841 🌸

Info about the current status of this doc, any errata, and how to give feedback lives at http://www.rfc-editor.org/info/rfc8213 🧚

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 it was published. Please actually read those, because they spell out your rights and restrictions for this doc 🫶 Code Components pulled out of this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions, and they come 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 that material may not have given the IETF Trust the right to allow modifications outside the IETF Standards Process. Unless you get an adequate license from those copyright holders, 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 either. The exceptions are formatting it for publication as an RFC or translating 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. References ......................................................6
      6.1. Normative References .......................................6
      6.2. Informative References .....................................6
   Acknowledgments ....................................................8
   Authors' Addresses .................................................8

1. Introduction ✨

DHCPv4 [RFC2131] and the Bootstrap Protocol [RFC1542] have no guidance for securing messages between servers and relay agents 🙈 DHCPv6 [RFC3315] says IPsec should be used for those messages, but it doesn't recommend encryption. With the recent worries about pervasive monitoring [RFC7258], it's appropriate to require IPsec with encryption for relay-to-server traffic in DHCPv4, and for relay-to-relay and relay-to-server traffic in DHCPv6 💅

This document lays out the optional requirements for relay agent and server implementations to support IPsec authentication and encryption, and it recommends that operators turn this IPsec support on 🎀

2. Requirements Language and Terminology 🧠

Here's the deal with the key words: "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document get interpreted as described in BCP 14 [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 rest of this section replaces the text in Section 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 gets protected from pervasive monitoring and other attacks 🛡️ That covers things like 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].

Relay agents and servers MUST be able to exchange messages using the IPsec mechanisms described in [RFC4301], under the conditions below. If a client message is relayed through multiple relay agents (a relay chain), each of the relay agents MUST have established independent, pairwise trust relationships. For example, if messages from client C get relayed by relay agent A to relay agent B and then to the server, then 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.  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
                    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,
                    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.
Note: As using IPsec with multicast has additional complexities (see [RFC5374]), relay agents SHOULD be configured to forward DHCP messages to unicast addresses.

6.1. Normative References 📚✨

okay bestie, here are the normative refs, the big-deal docs this spec is built on 🫶

6.2. Informative References 🌸

these ones are the extra reading, the "ooh, go deeper" pile 💜

Acknowledgments 🙌

the whole reason this doc exists? a bunch of IESG DISCUSSes on recent DHCP relay agent options 😭 those reviews made it way better

huge thanks to Kim Kinnear, Jinmei Tatuya, Francis Dupont, and Tomek Mrugalski for reviewing and helping to improve the document 🎀 and a shoutout to the authors of [RFC3315] for the original Section 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.com
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