Transient Hiding of Hop-by-Hop Options
draft-eastlake-6man-hide-options-03
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| Document | Type |
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|---|---|---|---|
| Author | Donald E. Eastlake 3rd | ||
| Last updated | 2022-07-08 | ||
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draft-eastlake-6man-hide-options-03
INTERNET-DRAFT D. Eastlake
Intended status: Proposed Standard Futurewei Technologies
Expires: January 6, 2023 July 7, 2022
Transient Hiding of Hop-by-Hop Options
<draft-eastlake-6man-hide-options-03.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.
Distribution of this document is unlimited. Comments should be sent
to the IPv6 Maintenance Working Group mailing list <6man@ietf.org> or
to the authors.
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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.....................................9
5. Security Considerations.................................9
6. Acknowledgements........................................9
Normative References......................................10
Informative References....................................10
Authors' Address..........................................11
Appendix: Revision History................................12
-00 to -01................................................12
-01 to -02................................................12
-02 to -03................................................12
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1. Introduction
As discussed in [Options3] there are increasing requests for a
variety of 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 may be 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 time passed, the Internet increased in size, bandwidth
grew including more voluminous media such as video, transmission
speeds increased enormously, and latency/responsiveness requirements
became more stringent. These requirements have led 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 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
further structured into options each of which, except for a one byte
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"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 sometimes 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 high-level view of a network path between two hosts
within local networks through the Internet core. (In reality there
are likely to 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
default 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 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 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.
This solution requires destination support but that should be
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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
desirable 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
while minimizing the chance of unwanted packet discard or other
damaging behavior.
3.2 Evolution to Greater Option Support
This solution supports the evolution of the Internet toward more
widespread support or beneficent handling of hop-by-hop options as
follows:
o As acceptable option handling 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
handling, they can recognize the opaque protocol number and
perform options, perhaps in a limited way, on packets where those
options are hidden to unimproved routers.
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4. IANA Considerations
IANA is requested 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
disable normal analysis of the following packet content, specifically
hop-by-hop options in the IP header. This would make firewalls, deep
packet analysis, and the like less effective. However, such methods
are less likely to be present in the network core where packets might
be obscured. Furthermore, firewalls tend to only admit packets with
known permissible 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.
Performing the specified option hiding header modification only for
packets with options would reveal which packets have that
characteristic and might cause re-ordering of those packets with
respect to other packets in the same flow. Thus, it may be beneficial
to perform the specified modification on all packets in an order
sensitive flow.
Should an IPv6 packet modified to hide options get through to a host
that does not understand this modification, it would likely 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>.
[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-01, June 2021,
https://datatracker.ietf.org/doc/draft-ietf-v6ops-hbh/
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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 almost no one really
cares about IPv4 options. Also, minor editorial changes.
-02 to -03
Minor 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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