Internet DRAFT - draft-baker-6man-hbh-header-handling
draft-baker-6man-hbh-header-handling
IPv6 Maintenance F. Baker
Internet-Draft Cisco Systems
Updates: 2460,7045 (if approved) October 6, 2015
Intended status: Standards Track
Expires: April 8, 2016
IPv6 Hop-by-Hop Header Handling
draft-baker-6man-hbh-header-handling-03
Abstract
This note updates the IPv6 Specification (RFC 2460), specifically
commenting on the Hop-by-Hop Options Header (section 4.3) and option
format and handling (section 4.2).
It also updates RFC 7045, which noted that RFC 2460 is widely
violated in this respect, but merely legitimized this situation with
a SHOULD. The present document tries to address the issue more
fundamentally.
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 April 8, 2016.
Copyright Notice
Copyright (c) 2015 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 of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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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 . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Handling of options in extension headers . . . . . . . . . . 3
2.1. Hop-by_hop Options . . . . . . . . . . . . . . . . . . . 3
2.2. Changing options in transit . . . . . . . . . . . . . . . 4
2.3. Adding headers or options in transit . . . . . . . . . . 5
2.4. Interactions with the Security Extension Header . . . . . 5
3. Interoperation with RFC 2460 . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 6
6. Privacy Considerations . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 7
Appendix A. Change Log . . . . . . . . . . . . . . . . . . . . . 8
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The IPv6 Specification [RFC2460] specifies a number of extension
headers. These, and the ordering considerations given, were defined
based on experience with IPv4 options. They were, however, prescient
with respect to their actual use - the IETF community did not know
how they would be used. In at least one case, the Hop-by-Hop option,
most if not all implementations implement it by punting to a software
path. In the words of [RFC7045],
The IPv6 Hop-by-Hop Options header SHOULD be processed by
intermediate forwarding nodes as described in [RFC2460]. However,
it is to be expected that high-performance routers will either
ignore it or assign packets containing it to a slow processing
path. Designers planning to use a Hop-by-Hop option need to be
aware of this likely behaviour.
Fernando Gont, in his Observations on IPv6 EH Filtering in the Real
World [I-D.ietf-v6ops-ipv6-ehs-in-real-world], and the operational
community in IPv6 Operations, consider any punt to a software path to
be an attack vector. Hence, IPv6 packets containing the Hop-by-Hop
Extension Header (and in some cases, any extension header) get
dropped in transit.
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The subject of this document is implementation approaches to obviate
or mitigate the attack vector, and updating the Hop-by-Hop option
with respect to current issues.
1.1. 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 [RFC2119].
2. Handling of options in extension headers
Packets containing the Hop-by-Hop Extension Header SHOULD be
processed at substantially the same rate as packets that do not.
If a hop-by-hop header option is not implemented, or is not in use,
in a given system (such as, for example, an interface that is not
configured for RSVP receiving an RSVP Alert Option), the option MUST
be skipped.
If a hop-by-hop header is present in a packet's extension header
chain and it is not the first extension header, the packet MUST be
discarded by the first system that observes the fact (Section 2.2 of
[RFC7045]). This will normally be in the system using the IPv6
address in the Destination Address, as [RFC2460] precludes other
routers from parsing the header chain. The only obvious exception to
that is a router or firewall configured to parse the IPv6 header
chain.
2.1. Hop-by_hop Options
At this writing, there are several defined Hop-by-Hop options:
PAD Options: The PAD1 and PADn options [RFC2460] define empty space.
Router Alert Option: The IPv6 Router Alert Option [RFC2711]
[RFC6398] is intended to force the punting of a datagram to
software, in cases in which RSVP or other protocols need that to
happen.
Jumbo Payload: Carries a length field for a packet whose length
exceeds 0xFFFF octets. [RFC2675]
RPL Option: The RPL option carries routing information used in a RPL
network[RFC6553]
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Quickstart Option Identifies TCP quick-start configuration, and
allows an intermediate router to reduce the configuration
parameters as appropriate. [RFC4782]
Common Architecture Label IPv6 Security Option: Encodes security
labels on packets [RFC5570]
SMF Option: Simplified Multicast Forwarding Option[RFC6621]
MPL Option: Supports multicast in an RPL network
[I-D.ietf-roll-trickle-mcast]
DFF Option: Depth-First Forwarding [RFC6971]
There are also options that have been defined for the Destination
Options header. These are not listed here.
While this is not true of older implementations, modern equipment is
capable of parsing the Extension Header chain, and can be extended to
perform at least a cursory examination of the Hop-by-Hop options.
For example, such implementations SHOULD be able to identify and skip
the PAD1 and PADn options, and perform more complicated processing
only if configured by software to do so. More to the point: it isn't
clear what the purpose of the JumboFrame option is if not to be
understood by anyone that looks at it.
Question asked by a reviewer: "Is this configurable? How will
router know that HbH needs to be skipped on one interface and not
on others."
Answer: the system knows whether RSVP has been configured on an
interface. When such configuration is present, it can configure
the hardware with what it wants done with the Router Alert. In
the absence of such configuration, hardware should be configured
to skip the option if found.
2.2. Changing options in transit
Section 4.2 of [RFC2460] explicitly allows for options that may be
updated in transit. It is likely that the original authors intended
that to be very simple, such as having the originating end system
provide the container, and having intermediate systems update it -
perhaps performing some calculation, and in any event storing the
resulting value. Examples of such a use might be in [XCP] or [RCP].
As a side comment, the Routing Header, which is an extension header
rather than a list of options, is treated similarly; when a system is
the destination of a packet and not the last one in the Routing
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Header's list, it swaps the destination address with the indicated
address in the list, and updates the hop count and the list depth
accordingly.
Such options must be marked appropriately (their option type is of
the form XX1XXXXX), and are excluded from checksum calculations in AH
and ESP.
2.3. Adding headers or options in transit
Use cases under current consideration take this a step further: a
router or middleware process MAY add an extension header, MAY add an
option to the header, which may extend the length of the Hop-by-Hop
Extension Header, or MAY process such an option in a manner that
extends both the length of the option and the Extension Header
containing it. The obvious implication is that other equipment in
the network may not understand or implement the new option type. As
such, the Option Type value of such an option MUST indicate that it
is to be skipped by a system that does not understand it. Since, by
definition, it is being updated in transit and not included in any AH
or ESP integrity check if present, the Option Type MUST also indicate
that it may be updated in transit, and so is excluded from AH and ESP
processing. By implication, such an Option Type MUST be of the form
001XXXXX.
2.4. Interactions with the Security Extension Header
The interactions with the IP Authentication Header [RFC4302] and IP
Encapsulating Security Payload (ESP) [RFC4303], as in the case of
existing option uses, is minimally defined. AH and ESP call for the
exclusion of mutable data in their calculations by zeroing it out
prior to performing the integrity check calculation. However, in the
case that network operation has changed the length of the option or
the extension header, that may still cause the integrity check to
fail. Specifications that define such options SHOULD consider the
implications of this for AH and ESP. An option whose insertion would
affect the integrity check MUST be removed prior to the integrity
check, and as a result the packet restored to its state as originally
sent.
3. Interoperation with RFC 2460
There are four possible modes of interaction with routers that don't
implement the Hop-By-Hop Option in the fast path:
1. Presume that they cannot handle the Hop-By-Hop option at close to
wire speed, and that's OK.
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2. Presume that they will drop traffic containing Hop-By-Hop
options.
3. Presume that they can handle the Hop-By-Hop option at or close to
wire speed, and are configured to do so.
4. Presume that they don't exist, perhaps because older routers are
configured to ignore all Hop-by-Hop options.
If the first model actually works in a given network, it may be
acceptable in that domain. It is not a model that will work in the
general Internet, however.
The second model (which is most probable at this writing) is a
description of the general Internet in 2015.
The third and fourth models, if applicable in a given context, are
what one might hope for. Vendors are in a position to either have an
option to ignore the Hop-By-Hop header in older equipment, or add
such an option in upgraded software (fourth model). New equipment is
expected to follow the third model by implementing the
recommendations in Section 2.
4. IANA Considerations
This memo asks the IANA for no new parameters.
5. Security Considerations
In general, modification of a datagram in transit is considered very
closely from the viewpoint of the End-to-End Principle, which in this
context may be summarized as "the network should do nothing that is
of concern to the communicating applications or introduces
operational issues." The concept of changing the length of an
Extension Header or an option contained within it (Section 2.3) is of
concern in that context. The obvious concern is around the
interaction with AH or ESP, and a less obvious concern relates to
Path MTU, which might change if the size of an underlying header
changes. Section 2.4 is intended to mitigate that issue. However,
some ramifications, such as with Path MTU, may not be completely
solvable in the general Internet, but require use cases to be
confined to a network or set of consenting networks.
6. Privacy Considerations
Data formats in this memo reveal no personally identifying
information.
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7. Acknowledgements
This note grew out of a discussion among the author, Ole Troan, Mark
Townsley, Frank Brockners, and Shwetha Bhandari, and benefited from
comments by Dennis Ferguson, Brian Carpenter, Panos Kampanakis,
JINMEI Tatuya, and Joe Touch.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
December 1998, <http://www.rfc-editor.org/info/rfc2460>.
8.2. Informative References
[I-D.ietf-roll-trickle-mcast]
Hui, J. and R. Kelsey, "Multicast Protocol for Low power
and Lossy Networks (MPL)", draft-ietf-roll-trickle-
mcast-12 (work in progress), June 2015.
[I-D.ietf-v6ops-ipv6-ehs-in-real-world]
Gont, F., Linkova, J., Chown, T., and S. LIU,
"Observations on IPv6 EH Filtering in the Real World",
draft-ietf-v6ops-ipv6-ehs-in-real-world-00 (work in
progress), April 2015.
[RCP] Dukkipati, N., "Rate Control Protocol (RCP): Congestion
control to make flows complete quickly", Stanford
University , 2006.
[RFC2675] Borman, D., Deering, S., and R. Hinden, "IPv6 Jumbograms",
RFC 2675, DOI 10.17487/RFC2675, August 1999,
<http://www.rfc-editor.org/info/rfc2675>.
[RFC2711] Partridge, C. and A. Jackson, "IPv6 Router Alert Option",
RFC 2711, DOI 10.17487/RFC2711, October 1999,
<http://www.rfc-editor.org/info/rfc2711>.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302,
DOI 10.17487/RFC4302, December 2005,
<http://www.rfc-editor.org/info/rfc4302>.
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[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)",
RFC 4303, DOI 10.17487/RFC4303, December 2005,
<http://www.rfc-editor.org/info/rfc4303>.
[RFC4782] Floyd, S., Allman, M., Jain, A., and P. Sarolahti, "Quick-
Start for TCP and IP", RFC 4782, DOI 10.17487/RFC4782,
January 2007, <http://www.rfc-editor.org/info/rfc4782>.
[RFC5570] StJohns, M., Atkinson, R., and G. Thomas, "Common
Architecture Label IPv6 Security Option (CALIPSO)",
RFC 5570, DOI 10.17487/RFC5570, July 2009,
<http://www.rfc-editor.org/info/rfc5570>.
[RFC6398] Le Faucheur, F., Ed., "IP Router Alert Considerations and
Usage", BCP 168, RFC 6398, DOI 10.17487/RFC6398, October
2011, <http://www.rfc-editor.org/info/rfc6398>.
[RFC6553] Hui, J. and JP. Vasseur, "The Routing Protocol for Low-
Power and Lossy Networks (RPL) Option for Carrying RPL
Information in Data-Plane Datagrams", RFC 6553,
DOI 10.17487/RFC6553, March 2012,
<http://www.rfc-editor.org/info/rfc6553>.
[RFC6621] Macker, J., Ed., "Simplified Multicast Forwarding",
RFC 6621, DOI 10.17487/RFC6621, May 2012,
<http://www.rfc-editor.org/info/rfc6621>.
[RFC6971] Herberg, U., Ed., Cardenas, A., Iwao, T., Dow, M., and S.
Cespedes, "Depth-First Forwarding (DFF) in Unreliable
Networks", RFC 6971, DOI 10.17487/RFC6971, June 2013,
<http://www.rfc-editor.org/info/rfc6971>.
[RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing
of IPv6 Extension Headers", RFC 7045,
DOI 10.17487/RFC7045, December 2013,
<http://www.rfc-editor.org/info/rfc7045>.
[XCP] Katabi, D., Handley, M., and C. Rohrs, "Congestion control
for high bandwidth-delay product networks", SIGCOMM
Symposium proceedings on Communications architectures and
protocols , 2002.
Appendix A. Change Log
Initial Version: June 2015
01 Version: June 2015, responding to list discussion
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02 Version: July 2015, discussed at IETF 93
03 Version: October 2015
Author's Address
Fred Baker
Cisco Systems
Santa Barbara, California 93117
USA
Email: fred@cisco.com
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