Internet Draft R. Atkinson draft-rja-ilnp-nonce-01.txt Extreme Networks Expires: 10 June 2009 10 December 2008 Category: Experimental Nonce Destination Option draft-rja-ilnp-nonce-01.txt Status of this Memo Distribution of this memo is unlimited. By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This document is a contribution to the IRTF Routing Research Group. It is neither a contribution to the IETF, nor to any IETF Working Group, nor to any IETF Area. Abstract This document describes an experimental Nonce Destination Option that could be used as part of an Identifier Locator Network Protocol (ILNP) that is based upon IPv6. Atkinson Expires in 6 Months [Page 1] Internet Draft ILNP Nonce 10 DEC 2009 Table of Contents 1. Introduction ...............................................2 2. Syntax......................................................3 3. Transport Protocol Effects..................................4 4. Location Changes............................................4 5. Implementation Considerations...............................5 6. Backwards Compatibility.....................................6 7. Security Considerations ....................................8 8. IANA Considerations ........................................9 9. References .................................................9 1. Introduction At present, the IRTF Routing Research Group is studying several different approaches to evolving the Internet Architecture. Several different classes of evolution are being considered. One class is often called "Map and Encapsulate", where traffic would be mapped and then tunnelled through the inter-domain core of the Internet. Another class being considered is sometimes known as "Identifier/Locator Split".[GSE][8+8] This document relates to a proposal that is in the latter class of evoluationary approaches. This particular approach, the Identifier Locator Network Protocol (ILNP), described in this document and in related Internet-Drafts, is a possible evolutionary direction for IPv6.[ILNP-Intro] [ILNP-DNS][ILNP-ICMP][RFC-2460] The Nonce Destination Option described in this document provides two functions. First, it provides protection against off-path attacks for packets when an Identifier/ Locator split is in use. Second, it provides a signal during initial IP session creation that the Identifier/ Locator Split operating mode is proposed for use with this session. This last function is particularly important for ensuring that the new Identifier/Locator Split operating mode is both incrementally deployable and backwards compatible with classical IPv6. Further, each Nonce value is unidirectional. Since packets often travel asymmetric paths between two correspondents, having separate Nonces for each direction limits the number of on-path nodes that can easily learn a session's nonce. So a typical TCP session will have 2 different nonce values in use: one nonce is used from Local Node to the Correspondent Node and a different nonce is used from the Correspondent Node to the Local Node. Before reading this draft, readers should read the related Atkinson Expires in 6 Months [Page 2] Internet Draft ILNP Nonce 10 DEC 2009 Internet-Draft titled "ILNP Concept of Operations", as that document will help the reader understand the overall context for this option. 2. Syntax The Nonce Option is an IPv6 Destination Option. In the diagram below, we show not only the Nonce Option, but also the 2-byte header for the IPv6 Destination Option. More than one option might be inside the IPv6 Destination Option, however at most 1 Nonce Option exists in a given IPv6 packet. A system that receives a packet containing more than one Nonce Option should discard the packet as "Authentication Failed" (instead of passing the packet up to the appropriate transport-layer protocol or to ICMP). As of this writing, IPv6 Destination Options are extremely uncommon in the deployed Internet. So, it is expected that most commonly Nonce Option would be the only IPv6 Destination Option present in a given IPv6 packet. ------------------------------------------------------------ | Next Header | Hdr Ext Len | Option Type | Option Length| +-------------+---------------+-------------+--------------+ / Nonce Value / +-------------+---------------+-------------+--------------+ Next Header: 8-bit selector. Identifies the type of header immediately following the Destination Options header. Uses the same values as the IPv4 Protocol field [RFC-1700 et seq.]. Hdr Ext Len: 8-bit unsigned integer. Length of the Destination Options header in 8-octet units, not including the first 8 octets. Option Type: This contains the value 0x1e, which is used (for now) to indicate the start of the Nonce Option. Option Length: This indicates the length in 8-bit octets of the Nonce Value field of the Nonce Option. This value must be selected so that the enveloping IPv6 Destination Option complies with the IPv6 header alignment rules. Common values are 4 (when the Nonce Value is 32-bits), Atkinson Expires in 6 Months [Page 3] Internet Draft ILNP Nonce 10 DEC 2009 and 12 (when the Nonce value is 96-bits). Nonce Value: This is an unpredictable cryptographically random value used to prevent off-path off-path attacks on an ILNP session. [RFC-4086] This field has variable length, with the length indicated by the Option Length field preceding it. Note that the overall IPv6 IPv6 Destination Option must comply with IPv6 header alignment rules. Implementations must support sending and receiving 32-bit and 96-bit Nonce values. 3. Transport Protocol Effects When the initial packet(s) of an IPv6 session contain this Nonce Destination Option, the Identifier/Locator Split operating mode is in use for that IP session. When an IPv6 session is in the Identifier/Locator Split operating mode, the transport-layer pseudo-header calculations zero the high-order 64-bits ("Locator" or "Routing Prefix") of each IPv6 address. This has the effect that the transport-layer is no longer cognizant of the topological network location of either node in the session. The preceding rule applies not only to unicast sessions, but also to multicast or anycast sessions when the Identifier/Locator Split operating mode is in use. 4. Location Changes When a node has an unexpected change in its Locator set that causes all previously valid Locators to become invalid, the node must send an ICMP Locator Update message (containing the Nonce Option with the appropriate nonce value) to each of its correspondents. In the deployed Internet, packets sometimes arrive at a destination out of order. A receiving node will drop a packet arriving from a correspondent if the Source Locator of the received packet is not in the receiving node's ILNP Correspondents Cache's Correspondent Locator Set UNLESS that packet contains a Nonce Option with the appropriate nonce value for that Source Identifier and Destination Identifier pair. This is done to reduce the risk of session hijacking or session interference attacks. Hence, the node that unexpectedly had all previously valid Locators become invalid must include the Nonce Option with the appropriate Atkinson Expires in 6 Months [Page 4] Internet Draft ILNP Nonce 10 DEC 2009 nonce value in all packets (data or otherwise) to all correspondents for at least 3 round-trip times for each correspondent. (NB: An implementation need not actually calculate RTT values; it could just use a fixed timer with a time long enough to cover the longest RTT path, such as 1 minute.) This 'gratuitous authentication' ensures that the correspondent can authenticate any received packet, even if the ICMP Locator Update control message arrives and is processed AFTER some other packet using the new Source Locator(s). If a session is using IP Security, then of course IP Security should continue to be used in this case. Because IP Security for ILNP binds only to the Identifiers, and not to the Locators in the packet, changes in Locator value have no impact on IP Security sessions. As mobility and multi-homing are functionally equivalent, this section applies equally to either situation. 5. Implementation Considerations Implementers may use any internal implementation they wish, provided that the external appearance is the same as this implementation approach. 5.1 Mode Indicator To support the Identifier/Locator Split operating mode, and retain the incremental deployability and backwards compatibility needed, the network layer needs a mode bit in the Transport Control Block (or equivalent for one's implementation) to track which IP sessions are using the classic IPv6 mode, and which IP sessions are using the Identifier/Locator Split mode. If a given transport-layer session is in the I/L Split Mode, then an entry corresponding to that session will exist in the Correspondent Cache. Note that multiple transport-layer sessions between a given pair of nodes normally share a single entry in the Correspondent Cache. 5.2 Correspondent Cache Further, when in the Identifier/Locator Split mode, nodes will need to retain a Correspondent cache containing several variables for each correspondent. This cache is per-correspondent, rather than per-flow or per-session so that if there are multiple sessions with a single correspondent, Locator changes for all sessions with that correspondent are handled with a single Locator Update message. Conceptually, and architecturally, this Correspondents Cache is at the top of the network-layer since it contains network-layer information (e.g. Locators) that ought not be made visible to the transport-layer. Atkinson Expires in 6 Months [Page 5] Internet Draft ILNP Nonce 10 DEC 2009 The Correspondent Cache contains, for each correspondent, at least: - Local Identifier(s) in use - Local Locator(s) in use - Correspondent's Identifier(s) in use - Correspondent's Locator(s) in use - Session Nonce value used Local Node to Correspondent - Session Nonce value used Correspondent to Local Node - Information about whether IPsec is being used with this correspondent. 5.3 IP Security Note that (whether or not the I/L-Split Mode is in use) the IPsec subsystem is required to maintain an IPsec Security Association Database (SAD) and also information about which IPsec Selectors apply to traffic received by or sent from the local node. [RFC-4301] By combining the information in the IPsec SAD, of what IPsec Selectors apply, and the Correspondent Cache, an implementation has sufficient knowledge to apply IPsec properly to both received and transmitted packets. 6. Backwards Compatibility If a node has been enhanced to support the Identifier/Locator Split operating mode, that node's fully-qualified domain name will normally have one or more I records and one or more L records associated with it in the DNS. When a host ("initiator") initiates a new IP session with a correspondent ("responder"), it normally will perform a DNS lookup to determine the address(es) of the responder. A host that has been enhanced to support the Identifier/ Locator Split operating mode normally will look for Identifier ("I") and Locator ("L") records in any received DNS replies. DNS servers that support I and L records should include them (when they exist) as additional data in all DNS replies to queries for DNS AAAA records. If the initiator supports the I/L Split mode and from DNS data learns that the responder also supports the I/L Split mode, then the initiator will generate an unpredictable nonce value, store that value in a local session cache, and will include the Nonce Destination Option in its initial packet(s) to the responder. [RFC-4086] If the responder supports the I/L Split mode and receives initial packet(s) containing the Nonce Destination Option, the responder will thereby know that the initiator supports the I/L Split mode and the responder will also operate in Atkinson Expires in 6 Months [Page 6] Internet Draft ILNP Nonce 10 DEC 2009 I/L Split mode for this new IP session. If the responder supports the I/L Split mode and receives initial packet(s) NOT containing the Nonce Destination Option, the responder will thereby know that the initiator does NOT support the I/L Split mode and the responder will operate in classic IPv6 mode for this new IP session. If the responder does not support the I/L Split mode and receives initial packet(s) containing the Nonce Destination Option, the responder will drop the packet and send an ICMP Parameter Problem error message back to the initiator. If the initiator EITHER does not receive a response from the responder in a timely manner (e.g. within the applicable TCP timeout for a TCP session) and also does not receive an ICMP Unreachable error message for that packet, OR if the initiator receives an ICMP Parameter Problem error message for that packet, then the initiator knows that the responder is not able to support the I/L Split Operating mode. In this case, the initiator should try again to create the new IP session but this time using classic IPv6 mode and hence OMITTING the Nonce Destination Option. Atkinson Expires in 6 Months [Page 7] Internet Draft ILNP Nonce 10 DEC 2009 6. Security Considerations The Nonce Destination Option is used ONLY for IPv6 sessions using Identifier/Locator Split mode, because this option is part of the backwards-compatibility and incremental-deployment approach for the Identifier/Locator Network Protocol (ILNP). The Nonce Destination Option only seeks to provide protection against off-path attacks on an IP session. Ordinary IPv6 is vulnerable to on-path attacks unless the IP Authentication Header or IP Encapsulating Security Payload are in use. This option exists to provide equivalent protection for non-IPsec traffic when the Identifier/Locator Split mode is in use for an IP session. When the Identifier/Locator split mode is in use for an existing IP session, the Nonce Destination Option must be included in any ICMP control messages (e.g. ICMP Unreachable, ICMP Locator Update) sent with regard to that IPv6 session, even if IP Security is also in use for that session. When in the I/L Split operating mode for an existing IPv6 session, any ICMP control messages received without a Nonce Destination Option must be discarded as forgeries. This security event should be logged. When in the I/L Split operating mode for an existing IPv6 session, ICMP control messages received without a correct nonce value inside the Nonce Destination Option must be discarded as forgeries. This security event should be logged. Of course, longer nonce values provide greater resistance to random guessing of the nonce value. However, ID/Locator Split mode sessions operating in higher risk environments should use the cryptographic authentication provided by IP Authentication Header. Note that the Nonce Option must be present -- even if the IP Authentication Header is in use for a given session. As an implementation optimisation, it is suggested that when both the Nonce Option and IP Security are present in a packet, that the Nonce Option value be checked for validity before beginning IP Security processing. For environments with data at differing sensitivity levels operating over common infrastructure, it is recommended that the Nonce Option is encrypted by using ESP Transport-Mode or ESP Tunnel-Mode in order to reduce the covert channel bandwidth potential created by the Nonce Option. In all cases, the Nonce Value must be unpredictable and Atkinson Expires in 6 Months [Page 8] Internet Draft ILNP Nonce 10 DEC 2009 cryptographically random. RFC-4086 provides concrete advice on how to generate a suitable nonce value.[RFC-4086] This option could be designed to optionally carry a 64-bit unsigned Identifier for the sender as well, if that were considered important. 7. IANA Considerations A new option number will need to be assigned by IANA to the Nonce Option described in this note. Temporarily, for early experimentation, the value 0x1e is used to mark the Nonce Option. 8. References 8.1. Normative References [RFC-2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC-2460] S. Deering & R. Hinden, "Internet Protocol Version 6 Specification", RFC-2460, December 1998. 8.2. Informative References [8+8] M. O'Dell, "8+8 - An Alternate Addressing Architecture for IPv6", Internet-Draft, October 1996. [GSE] M. O'Dell, "GSE - An Alternate Addressing Architecture for IPv6", Internet-Draft, February 1997. [ILNP-Intro] Atkinson, R, "Identifier/Locator Concept of Operations", draft-rja-ilnp-intro-01.txt, June 2008. [ILNP-DNS] Atkinson, R, "DNS Resource Records for Identifier/Locator Use", draft-rja-ilnp-dns-00.txt, June 2008. [ILNP-ICMP] Atkinson, R, "ICMP Locator Update message" draft-rja-ilnp-icmp-00.txt, June 2008. [RFC-4086] D. Eastlake 3rd, J. Schiller, & S. Crocker, Atkinson Expires in 6 Months [Page 9] Internet Draft ILNP Nonce 10 DEC 2009 "Randomness Requirements for Security", RFC-4086, June 2005. (Additional references to be added later.) Author's Address R. Atkinson Extreme Networks 3585 Monroe Street Santa Clara, CA 95051 USA +1 (408)579-2800 rja@extremenetworks.com Atkinson Expires in 6 Months [Page 10] Internet Draft ILNP Nonce 10 DEC 2009 Full Copyright Statement Copyright (C) The IETF Trust (2008). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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