INTERNET-DRAFT D. Eastlake
Intended status: Proposed Standard Futurewei Technologies
Expires: January 11, 2022 July 12, 2021
Transient Hiding of Hop-by-Hop Options
<draft-eastlake-6man-hide-options-00.txt>
Abstract
There are increasing requests for a variety IPv6 hop-by-hop options
but such IPv6 options and all IPv4 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...........................................5
2.2 IPv4 Options...........................................6
3. Overview of a Solution..................................8
3.1 Transiently Hiding IPv6 Options........................9
3.2 Transiently Hiding IPv4 Options........................9
3.3 Evolution to Greater Option Support...................10
4. IANA Considerations....................................11
5. Security Considerations................................11
Normative References......................................12
Informative References....................................12
Authors' Address..........................................14
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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 and all IPv4
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:
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, IP routers, especially in the core of the Internet,
typically became 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 and following fields to be at a fixed offset from the
beginning of the packet. Meanwhile, the control plane may be
implemented through a relatively low power general purpose computer
which can only handle a small 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 is relatively slow. 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 amount of
traffic, a strategy is adopted of dropping IP packets with such
header options or ignoring IPv4 header options and IPv6 Hop-by-Hop
header options.
See [Options3] for a further discussion of these option handling
problems.
Further details concerning IPv6 and IPv4 options are given in the
subsections below.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|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 including 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
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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
"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
2.2 IPv4 Options
Figure 3 shows the IPv4 header [RFC791]. The value of the initial
4-bit Version field indicates the IP version number and has value 4.
The IPv4 header has many similarities to the iPv6 header. For
example, the IPv4 header 8-bit field called "Protocol" is the like
the "Next Header" field in the IPv6 header and the IPv4 header 8-bit
"Type of Service" field, as amended by RFCs issued after [RFC791], is
the same as the IPv6 header "Traffic Class" field. But some things
that are handled by header extensions for IPv6 are integrated into
the more complex IPv4 header. For example, fragmentation, where an
Internet Protocol packet is split into pieces that can be later
combined because the packet might be too big to traverse part of its
path, is indicated through an extension header for IPv6 but through
fields in the main IPv4 header for IPv4. Similarly, IPv4 options are
considered part of the IPv4 header and the size of the options can be
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determined from the value of the IHL (Internet Header Length) field
which gives the size of the IPv4 header in units of 4-octet words.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| IHL |Type of Service| Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |Flags| Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live | Protocol | Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: IPv4 Header
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3. Overview of a Solution
Figure 4 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, is usually connected through one or
more levels of lower tier service provider before connecting to a
Tier 1 provider that connects to the default free Internet core.)
- - - - - - - - - - - - - - - - . . - - - - - - - - - -
. Network 1 . . Core Internet .
. . . .
. +------+ +---+ +---+ . . +---+ .
. |Host A|---|R10|-...-|R19|------------------|R90| .
. +------+ +---+ +---+ . . +---+ .
. . . | | .
. - - - - - - - - - - - - - - - - . ...
. .....
. .......
. .......
- - - - - - - - - - - - - - - - . . .....
. Network 2 . . ...
. . . | | .
. +------+ +---+ +---+ . . +---+ .
. |Host B|---|R20|-...-|R29|------------------|R99| .
. +------+ +---+ +---+ . . +---+ .
. . . .
. - - - - - - - - - - - - - - - - - - - - - - - - - - .
Figure 4: High Level View of an Internet Path
There are efforts to improve and streamline handling of IPv6 Hop-by-
Hop options such as in [Options1] and [Options2]. However, even if
popular and even if fully deployed in some network areas, there is
likely to be substantial delay before they are deployed in 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.
The solution in this document is to hide options before IP packets
arrive at the core. This hiding is done in as easily detectable
fashion so that options can be unhidden after leaving the core. IPv6
Hop-by-Hop options or IPv4 options used with this solution may 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 knowable in many cases such as
traffic between branches of the same company or between a customer
and a data center.
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To obtain more uniform handling of packets in a flow, it may be
desireable to treat all packet in the flow, or all packets including
and after the first with problematic options, as if they had such
options in that the packet would be transformed to hide and unhide
options even if there were none.
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 the opaque IP protocol number in the IPv6 header back to
zero.
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 [RFC6438] [RFC7098]. This
is a good idea anyway since IPv6 extension headers may move some
fields, such as port numbers, on which flow identity might be based,
so deep into a packet that they are hard to use by routers.
3.2 Transiently Hiding IPv4 Options
A similar technique can be used for hiding IPv4 options but
significantly more complex manipulations of the packet are required.
As shown in Figure 5, the IPv4 header is made to appear to have no
options by setting the IHL (Internet Header Length) field to its
minimum value of 5, the Protocol field is changed to the opaque IP
protocol number TBD, and the Header Checksum is adjusted to be
correct for the optionless header. To be able to restore the IPv4
header, the old IHL, Protocol, and Header Checksum fields are saved
in a 4-octet word inserted after the Destination Address and before
any Options. The placement of the saved fields is such that their
alignment within 4-octet word is the same as in the unmodified IPv4
header. The field labeled MBZ MUST be sent as zero and ignored on
receipt.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| IHL=5 |Type of Service| Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |Flags| Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live |Protocol=Opaque| Adjusted Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ |SavdIHL| Saved Protocol| Saved Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Options | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Modified IPv4 Header
These modifications increase the size of the IPv4 packet, increasing
the chance that fragmentation or MTU problems could occur. For any
node ignorant of the opaque IP protocol number, they will also
interfere with flow determination based on the traditional 5-tuple
(source and destination address, source and destination port, and IP
protocol) or deep packet inspection.
3.3 Evolution to Greater Option Support
This solution supports the evolution of the Internet toward more
widespread support of options including the following:
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 or 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
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 analysis of the following packet content. This would make
firewalls, deep packet analysis, and the like less effective.
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Normative References
[RFC791] - Postel, J., "Internet Protocol", STD 5, RFC 791, DOI
10.17487/RFC0791, September 1981, https://www.rfc-
editor.org/info/rfc791
[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, "Processing of
the Hop-by-Hop Options Header", Internet draft-peng-v6ops-
hbh-04, June 2021,
https://datatracker.ietf.org/doc/draft-peng-v6ops-hbh/
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[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
2386 Panoramic Circle
Apopka, FL 32703 USA
Tel: +1-508-333-2270
Email: d3e3e3@gmail.com
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