INTERNET-DRAFT D. Eastlake
Intended status: Proposed Standard Futurewei Technologies
Expires: October 10, 2022 April 11, 2022
Transient Hiding of Hop-by-Hop Options
<draft-eastlake-6man-hide-options-02.txt>
Abstract
There are increasing requests for a variety IPv6 hop-by-hop options
but such IPv6 options are poorly handled, particularly by high-speed
routers in the core Internet where packets having options are
commonly discarded. This document proposes a simple method of
transiently hiding such options for part of a packet's path to
protect the packet from discard.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction............................................3
1.1 Conventions Used in This Document......................3
2. IP Options and Option Handling Problems.................4
2.1 IPv6 Options...........................................4
3. Overview of a Solution..................................7
3.1 Transiently Hiding IPv6 Options........................8
3.2 Evolution to Greater Option Support....................8
4. IANA Considerations....................................10
5. Security Considerations................................10
6. Acknowledgements.......................................10
Normative References......................................11
Informative References....................................11
Authors' Address..........................................12
Appendix: Revision History................................13
-00 to -01................................................13
-01 to -02................................................13
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1. Introduction
As discussed in [Options3] there are increasing requests for a
variety IPv6 hop-by-hop options but such IPv6 options, are poorly
handled, particularly by high-speed routers in the core Internet
where packets having options are commonly discarded. This document
proposes a simple method of transiently hiding such options for part
of a packet's path to protect the packet from discard.
1.1 Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Terms:
ASIC - Application Specific Integrated Circuit.
field - an area of one or more contiguous bits within a larger
structure.
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2. IP Options and Option Handling Problems
This Section 2 is informational and intended to provide background
information.
In the early days of the Internet, much of the traffic was text,
transmission speeds were slow, and IP routers were commonly small
general-purpose computers. Under these conditions, parsing IP headers
with various options or combinations of options, handling variable
length options, etc., was relatively easy.
However, as the Internet increased in size bandwidth grew including
more voluminous media such as video, transmission speeds increased
enormously, and latency/responsiveness requirements became much more
stringent. This leads to IP routers, especially in the core of the
Internet, becoming less flexible and more specialized. To be able to
handle data faster and more efficiently, such core IP routers are
divided into a forwarding plane and a control plane where the
forwarding plan handles the usual data forwarding while the control
plan handles routing control messages and other packets that the data
plane cannot handle. In some IP routers, the forwarding plane is
implemented with Application Specific Integrated Circuits (ASICs)
that are inflexible and may need fields they examine in an IP packet
header to be at a fixed offset from the beginning of the packet.
Meanwhile, the control plane may be implemented through a general
purpose computer which can only handle a limited number of packets
per unit time.
For these reasons, many IP routers do not implement many or any types
of IPv6 Hop-by-Hop options (or IPv4 header options) except through
the control plane which has limited capacity. Sending packets with
such options to the control plane can overwhelm the control plane and
interfere with routing control messages or other critical functions.
Very often, particularly for IP routers handling a large volume of
traffic, a strategy is adopted of dropping IP packets with such
header options or ignoring the header options.
See [Options3] for a further discussion of these option handling
problems.
2.1 IPv6 Options
Figure 1 shows the IPv6 header [RFC8200]. The value of the initial
4-bit Version field indicates the IP version number and has the value
6.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Traffic Class | Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Length | Next Header | Hop Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Source Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Destination Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: IPv6 Header
The value of the 8-bit Next Header field specifies the type and
format of information immediately following the header. For example,
a value of 17 in the Next Header field indicates that the header is
immediately followed by a User Datagram Protocol (UDP) message and a
value of 6 would indicate the header is followed by a Transmission
Control Protocol (TCP) message. In some cases, the data immediately
after the IPv6 header can be a header that itself includes a Next
Header field for the type of data following it and so on as shown in
Figure 2. Such headers, after the initial IPv6 header and before the
main payload, are called Extension Headers and can be viewed as
extensions to the IPv6 header. At this time, specified extension
headers include the six listed below, additional extension headers
have been proposed, and likely more extension headers will be
proposed and specified in the future.
Specified extension headers:
Hop-by-Hop Options
Fragment
Destination Options
Routing
Authentication
Encapsulating Security Payload
In the two "options" types of extension header, the "Hop-by-Hop
Options" and "Destination Options", the extension header content is
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further structured into options each of which, except for a one byte
"pad1" option, is an 8-bit type followed by an 8-bit option length,
followed by the option value. Hop-by-Hop options were initially
specified to require that every router pay attention to them. While
this has been relaxed in the most recent IPv6 specification, they are
still frequently viewed as imposing a burden on every IP router
through which they pass.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
. .
. Options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: IPv6 Option Extension Header
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3. Overview of a Solution
Figure 3 shows a very high-level view of a network path between two
hosts within local networks through the Internet core. (In reality
there will be more levels with a local network, whether a home,
office, data center, or whatever, usually connected through one or
more levels of lower tier service provider before connecting to a
Tier 1 provider that connects to the Internet core also known as the
defalt free zone.)
- - - - - - - - - - - - - - - - . . - - - - - - - - - -
. Network 1 . . Core Internet .
. . . .
. +------+ +---+ +---+ . . +---+ .
. |Host A|---|R10|-...-|R19|------------------|R90| .
. +------+ +---+ +---+ . . +---+ .
. . . | | .
. - - - - - - - - - - - - - - - - . ...
. .....
. .......
. .......
- - - - - - - - - - - - - - - - . . .....
. Network 2 . . ...
. . . | | .
. +------+ +---+ +---+ . . +---+ .
. |Host B|---|R20|-...-|R29|------------------|R99| .
. +------+ +---+ +---+ . . +---+ .
. . . .
. - - - - - - - - - - - - - - - - - - - - - - - - - - .
Figure 3: High Level View of an Internet Path
There are efforts to improve and streamline handling of IPv6 Hop-by-
Hop options such as the methods in [Options1] and [Options2].
However, even if such a method were popular and fully deployed in
some network areas, there is likely to be substantial delay before it
would be deployed in most of the Internet core. While some Internet
core routers may ignore options, others discard all packets with
options and, as long as there is a significant chance of such
discard, options are rendered essentially useless on paths through
the core.
A solution is to hide options before IP packets arrive at the core.
This hiding is done in an easily detectable and reversible fashion so
that options can be unhidden after leaving the core. IPv6 Hop-by-Hop
options so hidden might not be effective in the core but the
situation is an improvement over the traffic using such options being
discarded.
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This solution requires destination support but that should be
knowable in many cases such as traffic between branches of the same
company or between a customer and a data center.
To obtain more uniform handling of packets in a flow, it may be
desireable to treat all packet in the flow as if they had such
options in that the packet would be transformed to hide and unhide
options even if there were none. This transformation could also be
applied to all packets starting with the first having a problematic
option.
3.1 Transiently Hiding IPv6 Options
IPv6 Hop-by-Hop options are hidden by replacing the zero Next Header
field in the IPv6 Header by the opaque IP protocol number TBD. This
is a very simple modification of one 8-bit field in a fixed location
that has no effect of the size of the packet. They are unhidden by
changing this opaque IP protocol number in the IPv6 header back to
zero. The points of hiding and unhiding in the packet's path (or
paths if multicast) should be chosen to maximize the routers at the
beginning and end of the path (Figure 3) that implement the options
seeing the options while minimizing he chance of unwanted packet
discard.
The use of the opaque IP protocol number can defeat deeper IPv6
packet analysis that is intended to identify flows. It is therefore
RECOMMENDED that, when this hiding technique is used, the IPv6 header
Flow Label field be set [RFC6437] and used to identify flows
[RFC6438] [RFC7098]. Using the Flow Label is a good idea anyway since
IPv6 extension headers can move some fields on which flow identity
might be based, such as port numbers, deeper into a packet so that
they are harder to use by routers.
3.2 Evolution to Greater Option Support
This solution supports the evolution of the Internet toward more
widespread support of options as follows:
o As acceptable option support is more widely implemented, probably
starting at lower bandwidth routers nearer the edge, the
boundaries at which options are hidden and unhidden can migrate
closer to the core.
o If scattered core routers improve to provide acceptable option
support, they can recognize the opaque protocol number and perform
options, perhaps in a limited way, on packets where those options
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are hidden to unimproved routers.
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4. IANA Considerations
IANA is request to assign a number from the "Assigned Internet
Protocol Numbers" registry as follows:
Decimal Keyword Protocol IPv6 Ex Hdr Reference
------- -------- -------- ----------- --------------
TBD Opaque Opaque [this document]
5. Security Considerations
The use of the opaque IP Protocol to mask options is intended to
defeat normal analysis of the following packet content, specifically
options in the IP header. This would make firewalls, deep packet
analysis, and the like less effective. On the other hand, firewalls
tend to only admit packets with known permissable values in protocol
header fields such as the IP protocol field. The rejection by a
firewall of a packet with the opaque IP protocol value will protect
the nodes behind that firewall from possible damage due to the
receipt of a packet modified as specified in this document. If the
firewall does know the opaque IP Protocol value, it should be
configured to treat packets with that value safely, possibly by
reversing the option hiding transformation.
Should an IPv6 packet modified to hide options get through to a host
that does not understand this modification, it would almost certainly
be discarded due to having an unknown IP Protocol.
[More to be added]
6. Acknowledgements
The helpful comments of the following are gratefully acknowledged:
Peng Shuping
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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>.
[RFC6437] - Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
"IPv6 Flow Label Specification", RFC 6437, DOI
10.17487/RFC6437, November 2011,
<https://www.rfc-editor.org/info/rfc6437>.
[RFC6438] - Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
for Equal Cost Multipath Routing and Link Aggregation in
Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
<https://www.rfc-editor.org/info/rfc6438>.
[RFC8174] - Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May
2017, <http://www.rfc-editor.org/info/rfc8174>
[RFC8200] - Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200,
July 2017, https://www.rfc-editor.org/info/rfc8200
Informative References
[Options1] - Li, Z., Peng, S., and G. Mishra, "Hop-by-Hop Forwarding
Options Header", Internet draft-li-6man-hbh-fwd-hdr-01,
February 2021,
https://datatracker.ietf.org/doc/draft-li-6man-hbh-fwd-hdr/
[Options2] - Hinden, R., and G. Fairhurst, "IPv6 Hop-by-Hop options
Processing Procedures", Internet draft-hinden-6man-hbh-
processing-01, June 2021,
https://datatracker.ietf.org/doc/draft-hinden-6man-hbh-
processing/
[Options3] - Peng, S., Li, Z., Xie, C., and Z. Qin, "Operational
Issues with Processig of the Hop-by-Hop Options Header",
Internet draft-ietf-v6ops-hbh-00, June 2021,
https://datatracker.ietf.org/doc/draft-ietf-v6ops-hbh/
[RFC7098] - Carpenter, B., Jiang, S., and W. Tarreau, "Using the IPv6
Flow Label for Load Balancing in Server Farms", RFC 7098, DOI
10.17487/RFC7098, January 2014,
<https://www.rfc-editor.org/info/rfc7098>.
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Authors' Address
Donald E. Eastlake 3rd
Futurewei Technologies, Inc.
2386 Panoramic Circle
Apopka, FL 32703 USA
Tel: +1-508-333-2270
Email: d3e3e3@gmail.com
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Appendix: Revision History
RFC Editor: Please delete this appendix before publication.
-00 to -01
Minor editorial changes. Add more Security Considerations. Add
Acknowledgements section.
-01 to -02
Delete IPv4 material. It was a bit complex and no one really cares
about IPv4 options. Also minor editorial changes.
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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
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include Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.
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