Implications of Oversized IPv6 Header Chains
draft-ietf-6man-oversized-header-chain-03
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| Document | Type | Active Internet-Draft (6man WG) | |
|---|---|---|---|
| Authors | Fernando Gont , Vishwas Manral , Ron Bonica | ||
| Last updated | 2013-07-15 | ||
| Replaces | draft-gont-6man-oversized-header-chain | ||
| Stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-6man-oversized-header-chain-03
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
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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
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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
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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.
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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].
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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).
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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.
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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").
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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
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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].
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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.
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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.
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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
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