IPv6 maintenance Working Group (6man) F. Gont Internet-Draft SI6 Networks / UTN-FRH Updates: 2460 (if approved) V. Manral Intended status: Standards Track Hewlett-Packard Corp. Expires: January 16, 2014 R. Bonica Juniper Networks July 15, 2013 Implications of Oversized IPv6 Header Chains draft-ietf-6man-oversized-header-chain-03 Abstract The IPv6 specification allows IPv6 header chains of an arbitrary size. The specification also allows options which can in turn extend each of the headers. In those scenarios in which the IPv6 header chain or options are unusually long and packets are fragmented, or scenarios in which the fragment size is very small, the first fragment of a packet may fail to include the entire IPv6 header chain. This document discusses the interoperability and security problems of such traffic, and updates RFC 2460 such that the first fragment of a packet is required to contain the entire IPv6 header chain. 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 January 16, 2014. Copyright Notice Copyright (c) 2013 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 Gont, et al. Expires January 16, 2014 [Page 1]
Internet-Draft Implications of Oversized Header Chains July 2013 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 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 4 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5 4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 6 5. Updates to RFC 2460 . . . . . . . . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 9.1. Normative References . . . . . . . . . . . . . . . . . . . 11 9.2. Informative References . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 Gont, et al. Expires January 16, 2014 [Page 2]
Internet-Draft Implications of Oversized Header Chains July 2013 1. Introduction With IPv6, optional internet-layer information is carried in one or more IPv6 Extension Headers [RFC2460]. Extension headers are placed between the IPv6 header and the upper-layer header in a packet. The term "header chain" refers collectively to the IPv6 header, extension headers and upper-layer header occurring in a packet. In those scenarios in which the IPv6 header chain is unusually long and packets are fragmented, or scenarios in which the fragment size is very small, the header chain may span multiple fragments. While IPv4 had a fixed maximum length for the set of all IPv4 options present in a single IPv4 packet, IPv6 does not have any equivalent maximum limit at present. This document updates the set of IPv6 specifications to create an overall limit on the size of the combination of IPv6 options and IPv6 Extension Headers that is allowed in a single IPv6 packet. Namely, it updates RFC 2460 such that the first fragment of a fragmented datagram is required to contain the entire IPv6 header chain. It should be noted that this requirement does not preclude the use of e.g. IPv6 jumbo payloads but instead merely requires that all *headers*, starting from IPv6 base header and continuing up to the upper layer header (e.g. TCP or the like) be present in the first fragment. Gont, et al. Expires January 16, 2014 [Page 3]
Internet-Draft Implications of Oversized Header Chains July 2013 2. Requirements Language 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 RFC 2119 [RFC2119]. Gont, et al. Expires January 16, 2014 [Page 4]
Internet-Draft Implications of Oversized Header Chains July 2013 3. Terminology Extension Header: Extension Headers are defined in Section 4 of [RFC2460]. Currently, six extension header types are defined. [RFC2460] defines the hop-by-hop, routing, fragment and destination options extension header types. [RFC4302] defines the authentication header type and [RFC4303] defines the encapsulating security payload (ESP) header type. First Fragment: An IPv6 fragment with fragment offset equal to 0. IPv6 Header Chain: The initial portion of an IPv6 datagram containing headers, starting from the fixed IPv6 header up to (and including) the upper layer protocol header (TCP, UDP, etc. -- assuming there is one of those), including any intermediate IPv6 extension headers. For a header to qualify as a member of the header chain, it must be referenced by the "Next Header" field of the previous member of the header chain. Upper-layer Header: The first member of the header chain that is neither an IPv6 header nor an IPv6 extension header. For the purposes of this document, ICMPv6 is considered to be an upper-layer protocol, even though ICMPv6 operates at the same layer as IPv6. Also for the purposes of this document, the first 32 bits of the ICMPv6 message (i.e., the type, code fields and checksum fields) are considered to be the ICMPv6 header. NOTES: The upper-layer payload is not part of the upper-layer header and therefore, is not part of the IPv6 header chain. For example, if the upper-layer protocol is TCP, the TCP payload is not part of the TCP header or the IPv6 header chain. When a packet contains an ESP header [RFC4303], such header is considered to be the last header in the IPv6 header chain. For the sake of clarity, we note that only the Security Parameters Index (SPI) and the Sequence Number fields (i.e., the first 64 bits of the ESP packet) are part of the ESP header (i.e., the Payload Data and trailer are NOT part of the ESP header). Gont, et al. Expires January 16, 2014 [Page 5]
Internet-Draft Implications of Oversized Header Chains July 2013 4. Motivation Many forwarding devices implement stateless firewalls. A stateless firewall enforces a forwarding policy on packet-by-packet basis. In order to enforce its forwarding policy, the stateless firewall may need to glean information from both the IPv6 and upper-layer headers. For example, assume that a stateless firewall discards all traffic received from an interface unless it destined for a particular TCP port on a particular IPv6 address. When this firewall is presented with a fragmented packet, and the entire header chain is contained within the first fragment, the firewall discards the first fragment and allows subsequent fragments to pass. Because the first fragment was discarded, the packet cannot be reassembled at the destination. Insomuch as the packet cannot be reassembled, the forwarding policy is enforced. However, when the firewall is presented with a fragmented packet and the header chain spans multiple fragments, the first fragment does not contain enough information for the firewall to enforce its forwarding policy. Lacking sufficient information, the stateless firewall either forwards or discards that fragment. Regardless of the action that it takes, it may fail to enforce its forwarding policy. Gont, et al. Expires January 16, 2014 [Page 6]
Internet-Draft Implications of Oversized Header Chains July 2013 5. Updates to RFC 2460 When a host fragments a IPv6 datagram, it MUST include the entire header chain in the first fragment. A host that receives a first-fragment that does not satisfy the above-stated requirements SHOULD discard that packet, and also MAY send an ICMPv6 error message to the source address of the offending packet (subject to the rules for ICMPv6 errors specified in [RFC4443]). Likewise, an intermediate system (e.g. router, firewall) that receives an IPv6 first-fragment that does not satisfy the above- stated requirements MAY discard that packet, and MAY send an ICMPv6 error message to the source address of the offending packet (subject to the rules for ICMPv6 error messages specified in [RFC4443]). Intermediate systems having this capability SHOULD support configuration (e.g. enable/disable) of whether such packets are dropped or not by the intermediate system. If a host or intermediate system discards an first-fragment because it does not satisfy the above-stated requirements, and sends an ICMPv6 error message due to the discard, then the ICMPv6 error message MUST be Type 4 ("Parameter Problem") and MUST use Code TBD ("First-fragment has incomplete IPv6 Header Chain"). Gont, et al. Expires January 16, 2014 [Page 7]
Internet-Draft Implications of Oversized Header Chains July 2013 6. IANA Considerations IANA is requested to add a the following entry to the "Reason Code" registry for ICMPv6 "Type 4 - Parameter Problem" messages: CODE NAME/DESCRIPTION TBD IPv6 first-fragment has incomplete IPv6 header chain Gont, et al. Expires January 16, 2014 [Page 8]
Internet-Draft Implications of Oversized Header Chains July 2013 7. Security Considerations This document describes how improperly-fragmented packets can prevent traditional stateless packet filtering. This document updates RFC 2460 such that those packets are forbidden, thus enabling stateless packet filtering for IPv6. This specification allows nodes that drop the aforementioned packets to signal such packet drops with ICMPv6 "Parameter Problem, IPv6 first-fragment has incomplete IPv6 header chain" (Type 4, Code TBD) error messages. As with all ICMPv6 error/diagnostic messages, deploying Source Address Forgery Prevention filters helps reduce the chances of an attacker successfully performing a reflection attack by sending forged illegal packets with the victim/target's IPv6 address as the IPv6 Source Address of the illegal packet [RFC2827] [RFC3704]. Gont, et al. Expires January 16, 2014 [Page 9]
Internet-Draft Implications of Oversized Header Chains July 2013 8. Acknowledgements The authors of this document would like to thank Ran Atkinson for contributing text and ideas that were incorporated into this document. The authors would like to thank (in alphabetical order) Ran Atkinson, Fred Baker, Brian Carpenter, Dominik Elsbroek, Bill Jouris, Suresh Krishnan, Dave Thaler, and Eric Vyncke, for providing valuable comments on earlier versions of this document. Gont, et al. Expires January 16, 2014 [Page 10]
Internet-Draft Implications of Oversized Header Chains July 2013 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, December 1998. [RFC4302] Kent, S., "IP Authentication Header", RFC 4302, December 2005. [RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, December 2005. [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", RFC 4443, March 2006. 9.2. Informative References [RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering: Defeating Denial of Service Attacks which employ IP Source Address Spoofing", BCP 38, RFC 2827, May 2000. [RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed Networks", BCP 84, RFC 3704, March 2004. Gont, et al. Expires January 16, 2014 [Page 11]
Internet-Draft Implications of Oversized Header Chains July 2013 Authors' Addresses Fernando Gont SI6 Networks / UTN-FRH Evaristo Carriego 2644 Haedo, Provincia de Buenos Aires 1706 Argentina Phone: +54 11 4650 8472 Email: fgont@si6networks.com URI: http://www.si6networks.com Vishwas Manral Hewlett-Packard Corp. 191111 Pruneridge Ave. Cupertino, CA 95014 US Phone: 408-447-1497 Email: vishwas.manral@hp.com URI: Ronald P. Bonica Juniper Networks 2251 Corporate Park Drive Herndon, VA 20171 US Phone: 571 250 5819 Email: rbonica@juniper.net Gont, et al. Expires January 16, 2014 [Page 12]