Internet DRAFT - draft-ietf-6man-oversized-header-chain
draft-ietf-6man-oversized-header-chain
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: May 30, 2014 R. Bonica
Juniper Networks
November 26, 2013
Implications of Oversized IPv6 Header Chains
draft-ietf-6man-oversized-header-chain-09
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
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 30, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Updates to RFC 2460 . . . . . . . . . . . . . . . . . . . . . 4
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 5
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
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.
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It should be noted that this requirement does not preclude the use of
large payloads but instead merely requires that all headers, starting
from the IPv6 base header and continuing up to the upper layer header
(e.g., TCP or the like) be present in the first fragment.
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].
3. Terminology
For the purposes of this document, the terms Extension Header, Header
Chain, First Fragment, and Upper-layer Header are used as follows:
Extension Header:
Extension Headers are defined in Section 4 of [RFC2460]. As a
result of [I-D.ietf-6man-ext-transmit], [IANA-PROTO] provides a
list of assigned Internet Protocol Numbers and designates which of
those protocol numbers also represent extension headers.
First Fragment:
An IPv6 fragment with fragment offset equal to 0.
IPv6 Header Chain:
The header chain contains an initial IPv6 header, zero or more
IPv6 extension headers, and optionally, a single upper-layer
header. If an upper-layer header is present, it terminates the
header chain; otherwise the "No Next Header" value (Next Header =
59) terminates it.
The first member of the header chain is always an IPv6 header.
For a subsequent 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. However, if a second IPv6
header appears in the header chain, as is the case when IPv6 is
tunneled over IPv6, the second IPv6 header is considered to be an
upper-layer header and terminates the header chain. Likewise, if
an Encapsulating Security Payload (ESP) header appears in the
header chain it is considered to be an upper-layer header and it
terminates the header chain.
Upper-layer Header:
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In the general case, the upper-layer header is the first member of
the header chain that is neither an IPv6 header nor an IPv6
extension header. However, if either an ESP header, or a second
IPv6 header occur in the header chain, they are considered to be
upper layer headers and they terminate the header chain.
Neither the upper-layer payload, nor any protocol data following
the upper-layer payload, is considered to be part of the header
chain. In a simple example, if the upper-layer header is a TCP
header, the TCP payload is not part of the header chain. In a
more complex example, if the upper-layer header is an ESP header,
neither the payload data, nor any of the fields that follow the
payload data in the ESP header are part of the header chain.
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 that is destined for a different TCP port,
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.
5. Updates to RFC 2460
When a host fragments an 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 requirement SHOULD discard the packet and SHOULD send
an ICMPv6 error message to the source address of the offending packet
(subject to the rules for ICMPv6 errors specified in [RFC4443]).
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However, for backwards compatibility, implementations MAY include a
configuration option that allows such fragments to be accepted.
Likewise, an intermediate system (e.g., router or firewall) that
receives an IPv6 first-fragment that does not satisfy the above-
stated requirement 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 a first-fragment because it
does not satisfy the above-stated requirement, 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"). The Pointer field
contained by the ICMPv6 Parameter Problem message MUST be set to
zero. The format for the ICMPv6 error message is the same regardless
of whether a host or intermediate system originates it.
As a result of the above mentioned requirement, a packet's header
chain length cannot exceed the Path MTU associated with its
destination. Hosts discover the Path MTU using procedures such as
those defined in [RFC1981] and [RFC4821]. Hosts that do not discover
the Path MTU MUST limit the header chain length to 1280 bytes.
Limiting the header chain length to 1280 bytes ensures that the
header chain length does not exceed the IPv6 minimum MTU [RFC2460].
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
7. Security Considerations
No new security exposures or issues are raised by this document.
This document describes how undesirably-fragmented packets can be
leveraged to evade stateless packet filtering. Having made that
observation, this document updates RFC 2460 [RFC2460] so that so
undesirably-fragmented packets are forbidden. Therefore, a security
vulnerability is removed.
This specification allows nodes that drop the aforementioned packets
to signal such packet drops with ICMPv6 "Parameter Problem, IPv6
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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].
A firewall that performs stateless deep packet inspection (i.e.,
examines application payload content) might still be unable to
correctly process fragmented packets, even if the IPv6 header chain
is not fragmented.
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, Stewart Bryant, Brian Carpenter, Benoit Claise, Dominik
Elsbroek, Wes George, Mike Heard, Bill Jouris, Suresh Krishnan, Dave
Thaler, Ole Troan, Eric Vyncke, and Peter Yee, for providing valuable
comments on earlier versions of this document.
9. References
9.1. Normative References
[RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
for IP version 6", RFC 1981, August 1996.
[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.
[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.
[RFC4821] Mathis, M. and J. Heffner, "Packetization Layer Path MTU
Discovery", RFC 4821, March 2007.
[I-D.ietf-6man-ext-transmit]
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Carpenter, B. and S. Jiang, "Transmission and Processing
of IPv6 Extension Headers", draft-ietf-6man-ext-
transmit-05 (work in progress), October 2013.
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.
[IANA-PROTO]
Internet Assigned Numbers Authority, "Protocol Numbers",
February 2013, <http://www.iana.org/assignments/protocol-
numbers/protocol-numbers.txt>.
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
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Ronald P. Bonica
Juniper Networks
2251 Corporate Park Drive
Herndon, VA 20171
US
Phone: 571 250 5819
Email: rbonica@juniper.net
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