Network Working Group S. Deering
Internet-Draft Retired
Obsoletes: 2460 (if approved) R. Hinden
Intended status: Standards Track Check Point Software
Expires: March 31, 2016 September 28, 2015
Internet Protocol, Version 6 (IPv6) Specification
draft-hinden-6man-rfc2460bis-07
Abstract
This document specifies version 6 of the Internet Protocol (IPv6),
also sometimes referred to as IP Next Generation or IPng. It
obsoletes RFC2460
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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This Internet-Draft will expire on March 31, 2016.
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This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
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material may not have granted the IETF Trust the right to allow
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. IPv6 Header Format . . . . . . . . . . . . . . . . . . . . . 5
4. IPv6 Extension Headers . . . . . . . . . . . . . . . . . . . 6
4.1. Extension Header Order . . . . . . . . . . . . . . . . . 9
4.2. Options . . . . . . . . . . . . . . . . . . . . . . . . . 10
4.3. Hop-by-Hop Options Header . . . . . . . . . . . . . . . . 12
4.4. Routing Header . . . . . . . . . . . . . . . . . . . . . 13
4.5. Fragment Header . . . . . . . . . . . . . . . . . . . . . 14
4.6. Destination Options Header . . . . . . . . . . . . . . . 21
4.7. No Next Header . . . . . . . . . . . . . . . . . . . . . 22
4.8. Defining New Extention Headers and Options . . . . . . . 22
5. Packet Size Issues . . . . . . . . . . . . . . . . . . . . . 23
6. Flow Labels . . . . . . . . . . . . . . . . . . . . . . . . . 24
7. Traffic Classes . . . . . . . . . . . . . . . . . . . . . . . 25
8. Upper-Layer Protocol Issues . . . . . . . . . . . . . . . . . 25
8.1. Upper-Layer Checksums . . . . . . . . . . . . . . . . . . 25
8.2. Maximum Packet Lifetime . . . . . . . . . . . . . . . . . 27
8.3. Maximum Upper-Layer Payload Size . . . . . . . . . . . . 27
8.4. Responding to Packets Carrying Routing Headers . . . . . 27
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 28
10. Security Considerations . . . . . . . . . . . . . . . . . . . 28
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 28
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 28
12.1. Normative References . . . . . . . . . . . . . . . . . . 28
12.2. Informative References . . . . . . . . . . . . . . . . . 29
Appendix A. Formatting Guidelines for Options . . . . . . . . . 30
Appendix B. CHANGES SINCE RFC2460 . . . . . . . . . . . . . . . 33
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 36
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1. Introduction
IP version 6 (IPv6) is a new version of the Internet Protocol,
designed as the successor to IP version 4 (IPv4) [RFC0791]. The
changes from IPv4 to IPv6 fall primarily into the following
categories:
o Expanded Addressing Capabilities
IPv6 increases the IP address size from 32 bits to 128 bits, to
support more levels of addressing hierarchy, a much greater
number of addressable nodes, and simpler auto-configuration of
addresses. The scalability of multicast routing is improved by
adding a "scope" field to multicast addresses. And a new type
of address called an "anycast address" is defined, used to send
a packet to any one of a group of nodes.
o Header Format Simplification
Some IPv4 header fields have been dropped or made optional, to
reduce the common-case processing cost of packet handling and
to limit the bandwidth cost of the IPv6 header.
o Improved Support for Extensions and Options
Changes in the way IP header options are encoded allows for
more efficient forwarding, less stringent limits on the length
of options, and greater flexibility for introducing new options
in the future.
o Flow Labeling Capability
A new capability is added to enable the labeling of sequences
of packets for which the sender requests to be treated in the
network as a single flow.
o Authentication and Privacy Capabilities
Extensions to support authentication, data integrity, and
(optional) data confidentiality are specified for IPv6.
This document specifies the basic IPv6 header and the initially-
defined IPv6 extension headers and options. It also discusses packet
size issues, the semantics of flow labels and traffic classes, and
the effects of IPv6 on upper-layer protocols. The format and
semantics of IPv6 addresses are specified separately in
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[I-D.hinden-6man-rfc4291bis]. The IPv6 version of ICMP, which all
IPv6 implementations are required to include, is specified in
[RFC4443]
Note: As this document obsoletes [RFC2460], any document referenced
in this document that includes pointers to RFC2460, should be
interpreted as referencing this document.
2. Terminology
node a device that implements IPv6.
router a node that forwards IPv6 packets not explicitly
addressed to itself. [See Note below].
host any node that is not a router. [See Note below].
upper layer a protocol layer immediately above IPv6. Examples are
transport protocols such as TCP and UDP, control
protocols such as ICMP, routing protocols such as OSPF,
and internet or lower-layer protocols being "tunneled"
over (i.e., encapsulated in) IPv6 such as IPX,
AppleTalk, or IPv6 itself.
link a communication facility or medium over which nodes can
communicate at the link layer, i.e., the layer
immediately below IPv6. Examples are Ethernets (simple
or bridged); PPP links; X.25, Frame Relay, or ATM
networks; and internet (or higher) layer "tunnels", such
as tunnels over IPv4 or IPv6 itself.
neighbors nodes attached to the same link.
interface a node's attachment to a link.
address an IPv6-layer identifier for an interface or a set of
interfaces.
packet an IPv6 header plus payload.
link MTU the maximum transmission unit, i.e., maximum packet size
in octets, that can be conveyed over a link.
path MTU the minimum link MTU of all the links in a path between
a source node and a destination node.
Note: it is possible, though unusual, for a device with multiple
interfaces to be configured to forward non-self-destined packets
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arriving from some set (fewer than all) of its interfaces, and to
discard non-self-destined packets arriving from its other interfaces.
Such a device must obey the protocol requirements for routers when
receiving packets from, and interacting with neighbors over, the
former (forwarding) interfaces. It must obey the protocol
requirements for hosts when receiving packets from, and interacting
with neighbors over, the latter (non-forwarding) interfaces.
3. IPv6 Header Format
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Traffic Class | Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Length | Next Header | Hop Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Source Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Destination Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Version 4-bit Internet Protocol version number = 6.
Traffic Class 8-bit traffic class field. See section 7.
Flow Label 20-bit flow label. See section 6.
Payload Length 16-bit unsigned integer. Length of the IPv6
payload, i.e., the rest of the packet
following this IPv6 header, in octets. (Note
that any extension headers [section 4] present
are considered part of the payload, i.e.,
included in the length count.)
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Next Header 8-bit selector. Identifies the type of header
immediately following the IPv6 header. Uses
the same values as the IPv4 Protocol field
[IANA-PN].
Hop Limit 8-bit unsigned integer. Decremented by 1 by
each node that forwards the packet. The
packet is discarded if Hop Limit is
decremented to zero, or is received with a
zero Hop Limit.
Source Address 128-bit address of the originator of the
packet. See [I-D.hinden-6man-rfc4291bis].
Destination Address 128-bit address of the intended recipient of
the packet (possibly not the ultimate
recipient, if a Routing header is present).
See [I-D.hinden-6man-rfc4291bis] and section
4.4.
4. IPv6 Extension Headers
In IPv6, optional internet-layer information is encoded in separate
headers that may be placed between the IPv6 header and the upper-
layer header in a packet. There are a small number of such extension
headers, each identified by a distinct Next Header value. As
illustrated in these examples, an IPv6 packet may carry zero, one, or
more extension headers, each identified by the Next Header field of
the preceding header:
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+---------------+------------------------
| IPv6 header | TCP header + data
| |
| Next Header = |
| TCP |
+---------------+------------------------
+---------------+----------------+------------------------
| IPv6 header | Routing header | TCP header + data
| | |
| Next Header = | Next Header = |
| Routing | TCP |
+---------------+----------------+------------------------
+---------------+----------------+-----------------+-----------------
| IPv6 header | Routing header | Fragment header | fragment of TCP
| | | | header + data
| Next Header = | Next Header = | Next Header = |
| Routing | Fragment | TCP |
+---------------+----------------+-----------------+-----------------
With one exception, extension headers are not examined or processed
by any node along a packet's delivery path, until the packet reaches
the node (or each of the set of nodes, in the case of multicast)
identified in the Destination Address field of the IPv6 header.
There, normal demultiplexing on the Next Header field of the IPv6
header invokes the module to process the first extension header, or
the upper-layer header if no extension header is present. The
contents and semantics of each extension header determine whether or
not to proceed to the next header. Therefore, extension headers must
be processed strictly in the order they appear in the packet; a
receiver must not, for example, scan through a packet looking for a
particular kind of extension header and process that header prior to
processing all preceding ones.
With one exception, extension headers are not processed by any node
along a packet's delivery path, until the packet reaches the node (or
each of the set of nodes, in the case of multicast) identified in the
Destination Address field of the IPv6 header. Note: If an
intermediate forwarding node examines an extension header for any
reason, it must do so in accordance with the provisions of [RFC7045].
At the Destination node, normal demultiplexing on the Next Header
field of the IPv6 header invokes the module to process the first
extension header, or the upper-layer header if no extension header is
present. The contents and semantics of each extension header
determine whether or not to proceed to the next header. Therefore,
extension headers must be processed strictly in the order they appear
in the packet; a receiver must not, for example, scan through a
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packet looking for a particular kind of extension header and process
that header prior to processing all preceding ones.
The exception referred to in the preceding paragraph is the Hop-by-
Hop Options header, which carries information that should be examined
and processed by every node along a packet's delivery path, including
the source and destination nodes. The Hop-by-Hop Options header,
when present, must immediately follow the IPv6 header. Its presence
is indicated by the value zero in the Next Header field of the IPv6
header.
It should be noted that due to performance restrictions nodes may
ignore the Hop-by-Hop Option header, drop packets containing a hop-
by-hop option header, or assign packets containing a hop-by-hop
option header to a slow processing path. Designers planning to use a
hop-by-hop option need to be aware of this likely behaviour.
If, as a result of processing a header, a node is required to proceed
to the next header but the Next Header value in the current header is
unrecognized by the node, it should discard the packet and send an
ICMP Parameter Problem message to the source of the packet, with an
ICMP Code value of 1 ("unrecognized Next Header type encountered")
and the ICMP Pointer field containing the offset of the unrecognized
value within the original packet. The same action should be taken if
a node encounters a Next Header value of zero in any header other
than an IPv6 header.
Each extension header is an integer multiple of 8 octets long, in
order to retain 8-octet alignment for subsequent headers. Multi-
octet fields within each extension header are aligned on their
natural boundaries, i.e., fields of width n octets are placed at an
integer multiple of n octets from the start of the header, for n = 1,
2, 4, or 8.
A full implementation of IPv6 includes implementation of the
following extension headers:
Hop-by-Hop Options
Fragment
Destination Options
Authentication
Encapsulating Security Payload
The first three are specified in this document; the last two are
specified in [RFC4302] and [RFC4303], respectively.
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4.1. Extension Header Order
When more than one extension header is used in the same packet, it is
recommended that those headers appear in the following order:
IPv6 header
Hop-by-Hop Options header
Destination Options header (note 1)
Routing header
Fragment header
Authentication header (note 2)
Encapsulating Security Payload header (note 2)
Destination Options header (note 3)
upper-layer header
note 1: for options to be processed by the first destination that
appears in the IPv6 Destination Address field plus
subsequent destinations listed in the Routing header.
note 2: additional recommendations regarding the relative order of
the Authentication and Encapsulating Security Payload
headers are given in [RFC4303].
note 3: for options to be processed only by the final destination
of the packet.
Each extension header should occur at most once, except for the
Destination Options header which should occur at most twice (once
before a Routing header and once before the upper-layer header).
If the upper-layer header is another IPv6 header (in the case of IPv6
being tunneled over or encapsulated in IPv6), it may be followed by
its own extension headers, which are separately subject to the same
ordering recommendations.
If and when other extension headers are defined, their ordering
constraints relative to the above listed headers must be specified.
IPv6 nodes must accept and attempt to process extension headers in
any order and occurring any number of times in the same packet,
except for the Hop-by-Hop Options header which is restricted to
appear immediately after an IPv6 header only. Nonetheless, it is
strongly advised that sources of IPv6 packets adhere to the above
recommended order until and unless subsequent specifications revise
that recommendation.
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4.2. Options
Two of the currently-defined extension headers -- the Hop-by-Hop
Options header and the Destination Options header -- carry a variable
number of type-length-value (TLV) encoded "options", of the following
format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
| Option Type | Opt Data Len | Option Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
Option Type 8-bit identifier of the type of option.
Opt Data Len 8-bit unsigned integer. Length of the Option
Data field of this option, in octets.
Option Data Variable-length field. Option-Type-specific
data.
The sequence of options within a header must be processed strictly in
the order they appear in the header; a receiver must not, for
example, scan through the header looking for a particular kind of
option and process that option prior to processing all preceding
ones.
The Option Type identifiers are internally encoded such that their
highest-order two bits specify the action that must be taken if the
processing IPv6 node does not recognize the Option Type:
00 - skip over this option and continue processing the header.
01 - discard the packet.
10 - discard the packet and, regardless of whether or not the
packet's Destination Address was a multicast address, send an
ICMP Parameter Problem, Code 2, message to the packet's
Source Address, pointing to the unrecognized Option Type.
11 - discard the packet and, only if the packet's Destination
Address was not a multicast address, send an ICMP Parameter
Problem, Code 2, message to the packet's Source Address,
pointing to the unrecognized Option Type.
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The third-highest-order bit of the Option Type specifies whether or
not the Option Data of that option can change en-route to the
packet's final destination. When an Authentication header is present
in the packet, for any option whose data may change en-route, its
entire Option Data field must be treated as zero-valued octets when
computing or verifying the packet's authenticating value.
0 - Option Data does not change en-route
1 - Option Data may change en-route
The three high-order bits described above are to be treated as part
of the Option Type, not independent of the Option Type. That is, a
particular option is identified by a full 8-bit Option Type, not just
the low-order 5 bits of an Option Type.
The same Option Type numbering space is used for both the Hop-by-Hop
Options header and the Destination Options header. However, the
specification of a particular option may restrict its use to only one
of those two headers.
Individual options may have specific alignment requirements, to
ensure that multi-octet values within Option Data fields fall on
natural boundaries. The alignment requirement of an option is
specified using the notation xn+y, meaning the Option Type must
appear at an integer multiple of x octets from the start of the
header, plus y octets. For example:
2n means any 2-octet offset from the start of the header.
8n+2 means any 8-octet offset from the start of the header, plus 2
octets.
There are two padding options which are used when necessary to align
subsequent options and to pad out the containing header to a multiple
of 8 octets in length. These padding options must be recognized by
all IPv6 implementations:
Pad1 option (alignment requirement: none)
+-+-+-+-+-+-+-+-+
| 0 |
+-+-+-+-+-+-+-+-+
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NOTE! the format of the Pad1 option is a special case -- it does
not have length and value fields.
The Pad1 option is used to insert one octet of padding into the
Options area of a header. If more than one octet of padding is
required, the PadN option, described next, should be used, rather
than multiple Pad1 options.
PadN option (alignment requirement: none)
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
| 1 | Opt Data Len | Option Data
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
The PadN option is used to insert two or more octets of padding
into the Options area of a header. For N octets of padding, the
Opt Data Len field contains the value N-2, and the Option Data
consists of N-2 zero-valued octets.
Appendix A contains formatting guidelines for designing new options.
4.3. Hop-by-Hop Options Header
The Hop-by-Hop Options header is used to carry optional information
that must be examined by every node along a packet's delivery path.
The Hop-by-Hop Options header is identified by a Next Header value of
0 in the IPv6 header, and has the following format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
. .
. Options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header 8-bit selector. Identifies the type of header
immediately following the Hop-by-Hop Options
header. Uses the same values as the IPv4
Protocol field [IANA-PN].
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Hdr Ext Len 8-bit unsigned integer. Length of the Hop-by-
Hop Options header in 8-octet units, not
including the first 8 octets.
Options Variable-length field, of length such that the
complete Hop-by-Hop Options header is an
integer multiple of 8 octets long. Contains
one or more TLV-encoded options, as described
in section 4.2.
The only hop-by-hop options defined in this document are the Pad1 and
PadN options specified in section 4.2.
4.4. Routing Header
The Routing header is used by an IPv6 source to list one or more
intermediate nodes to be "visited" on the way to a packet's
destination. This function is very similar to IPv4's Loose Source
and Record Route option. The Routing header is identified by a Next
Header value of 43 in the immediately preceding header, and has the
following format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | Routing Type | Segments Left |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. type-specific data .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header 8-bit selector. Identifies the type of header
immediately following the Routing header.
Uses the same values as the IPv4 Protocol
field [IANA-PN].
Hdr Ext Len 8-bit unsigned integer. Length of the Routing
header in 8-octet units, not including the
first 8 octets.
Routing Type 8-bit identifier of a particular Routing
header variant.
Segments Left 8-bit unsigned integer. Number of route
segments remaining, i.e., number of explicitly
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listed intermediate nodes still to be visited
before reaching the final destination.
type-specific data Variable-length field, of format determined by
the Routing Type, and of length such that the
complete Routing header is an integer multiple
of 8 octets long.
If, while processing a received packet, a node encounters a Routing
header with an unrecognized Routing Type value, the required behavior
of the node depends on the value of the Segments Left field, as
follows:
If Segments Left is zero, the node must ignore the Routing header
and proceed to process the next header in the packet, whose type
is identified by the Next Header field in the Routing header.
If Segments Left is non-zero, the node must discard the packet and
send an ICMP Parameter Problem, Code 0, message to the packet's
Source Address, pointing to the unrecognized Routing Type.
If, after processing a Routing header of a received packet, an
intermediate node determines that the packet is to be forwarded onto
a link whose link MTU is less than the size of the packet, the node
must discard the packet and send an ICMP Packet Too Big message to
the packet's Source Address.
The currently defined IPv6 Routing Headers and their status can be
found at [IANA-RH]. Allocation guidelines for IPv6 Routing Headers
can be found in [RFC5871].
4.5. Fragment Header
The Fragment header is used by an IPv6 source to send a packet larger
than would fit in the path MTU to its destination. (Note: unlike
IPv4, fragmentation in IPv6 is performed only by source nodes, not by
routers along a packet's delivery path -- see section 5.) The
Fragment header is identified by a Next Header value of 44 in the
immediately preceding header, and has the following format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Reserved | Fragment Offset |Res|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Next Header 8-bit selector. Identifies the initial header
type of the Fragmentable Part of the original
packet (defined below). Uses the same values
as the IPv4 Protocol field [IANA-PN].
Reserved 8-bit reserved field. Initialized to zero for
transmission; ignored on reception.
Fragment Offset 13-bit unsigned integer. The offset, in
8-octet units, of the data following this
header, relative to the start of the
Fragmentable Part of the original packet.
Res 2-bit reserved field. Initialized to zero for
transmission; ignored on reception.
M flag 1 = more fragments; 0 = last fragment.
Identification 32 bits. See description below.
In order to send a packet that is too large to fit in the MTU of the
path to its destination, a source node may divide the packet into
fragments and send each fragment as a separate packet, to be
reassembled at the receiver.
For every packet that is to be fragmented, the source node generates
an Identification value. The Identification must be different than
that of any other fragmented packet sent recently* with the same
Source Address and Destination Address. If a Routing header is
present, the Destination Address of concern is that of the final
destination.
* "recently" means within the maximum likely lifetime of a
packet, including transit time from source to destination and
time spent awaiting reassembly with other fragments of the same
packet. However, it is not required that a source node know
the maximum packet lifetime. Rather, it is assumed that the
requirement can be met by maintaining the Identification value
as a simple, 32-bit, "wrap-around" counter, incremented each
time a packet must be fragmented. It is an implementation
choice whether to maintain a single counter for the node or
multiple counters, e.g., one for each of the node's possible
source addresses, or one for each active (source address,
destination address) combination.
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The initial, large, unfragmented packet is referred to as the
"original packet", and it is considered to consist of three parts, as
illustrated:
original packet:
+------------------+-------------------------+---//----------------+
| Unfragmentable | Extention & Upper-Layer | Fragmentable |
| Headers | Headers | Part |
+------------------+-------------------------+---//----------------+
The Unfragmentable Headers consists of the IPv6 header plus any
extension headers that must be processed by nodes en route to the
destination, that is, all headers up to and including the Routing
header if present, else the Hop-by-Hop Options header if present,
else no extension headers.
The Ext Hdrs are all other extension headers that are not included
in the Unfragmentable headers part of the packet. For this
purpose, the IP Authentication Header (AH) and the Encapsulating
Security Payload (ESP) are not considered extension headers. The
Upper-Layer Header is the first upper-layer header that is not an
IPv6 extension header. Examples of upper-layer headers include
TCP, UDP, IPv4, IPv6, ICMPv6, and as noted AH and ESP.
The Fragmentable Part consists of the rest of the packet after the
upper-layer header.
The Fragmentable Part of the original packet is divided into
fragments, each, except possibly the last ("rightmost") one, being an
integer multiple of 8 octets long. The fragments are transmitted in
separate "fragment packets" as illustrated:
original packet:
+-----------------+-----------------+--------+--------+-//-+--------+
| Unfragmentable |Ext & Upper-Layer| first | second | | last |
| Headers | Headers |fragment|fragment|....|fragment|
+-----------------+-----------------+--------+--------+-//-+--------+
fragment packets:
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+------------------+---------+-------------------+----------+
| Unfragmentable |Fragment | Ext & Upper-Layer | first |
| Headers | Header | Headers | fragment |
+------------------+---------+-------------------+----------+
+------------------+--------+-------------------------------+
| Unfragmentable |Fragment| second |
| Headers | Header | fragment |
+------------------+--------+-------------------------------+
o
o
o
+------------------+--------+----------+
| Unfragmentable |Fragment| last |
| Headers | Header | fragment |
+------------------+--------+----------+
The first fragment packet is composed of:
(1) The Unfragmentable Headers of the original packet, with the
Payload Length of the original IPv6 header changed to contain the
length of this fragment packet only (excluding the length of the
IPv6 header itself), and the Next Header field of the last header
of the Unfragmentable Headers changed to 44.
(2) A Fragment header containing:
The Next Header value that identifies the first header after
the Unfragmentable Headers of the original packet.
A Fragment Offset containing the offset of the fragment, in
8-octet units, relative to the start of the Fragmentable Part
of the original packet. The Fragment Offset of the first
("leftmost") fragment is 0.
An M flag value of 1 as this is the first fragment.
The Identification value generated for the original packet.
(3) Extension Headers, if any, and the Upper-Layer header. These
headers must be in the first fragment.
(4) The first fragment.
The subsequent fragment packets are composed of:
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(1) The Unfragmentable Headers of the original packet, with the
Payload Length of the original IPv6 header changed to contain the
length of this fragment packet only (excluding the length of the
IPv6 header itself), and the Next Header field of the last header
of the Unfragmentable Headers changed to 44.
(2) A Fragment header containing:
The Next Header value that identifies the first header after
the Unfragmentable Headers of the original packet.
A Fragment Offset containing the offset of the fragment, in
8-octet units, relative to the start of the Fragmentable part
of the original packet.
An M flag value of 0 if the fragment is the last ("rightmost")
one, else an M flag value of 1.
The Identification value generated for the original packet.
(3) The fragment itself.
The lengths of the fragments must be chosen such that the resulting
fragment packets fit within the MTU of the path to the packets'
destination(s).
Fragments must not be created that overlap with any other fragments
created from the original packet.
At the destination, fragment packets are reassembled into their
original, unfragmented form, as illustrated:
reassembled original packet:
+---------------+-----------------+---------+--------+-//--+--------+
| Unfragmentable|Ext & Upper-Layer| first | second | | last |
| Headers | Headers |frag data|fragment|.....|fragment|
+---------------+-----------------+---------+--------+-//--+--------+
The following rules govern reassembly:
An original packet is reassembled only from fragment packets that
have the same Source Address, Destination Address, and Fragment
Identification.
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The Unfragmentable Headers of the reassembled packet consists of
all headers up to, but not including, the Fragment header of the
first fragment packet (that is, the packet whose Fragment Offset
is zero), with the following two changes:
The Next Header field of the last header of the Unfragmentable
Headers is obtained from the Next Header field of the first
fragment's Fragment header.
The Payload Length of the reassembled packet is computed from
the length of the Unfragmentable Headers and the length and
offset of the last fragment. For example, a formula for
computing the Payload Length of the reassembled original packet
is:
PL.orig = PL.first - FL.first - 8 + (8 * FO.last) + FL.last
where
PL.orig = Payload Length field of reassembled packet.
PL.first = Payload Length field of first fragment packet.
FL.first = length of fragment following Fragment header of
first fragment packet.
FO.last = Fragment Offset field of Fragment header of last
fragment packet.
FL.last = length of fragment following Fragment header of
last fragment packet.
The Fragmentable Part of the reassembled packet is constructed
from the fragments following the Fragment headers in each of
the fragment packets. The length of each fragment is computed
by subtracting from the packet's Payload Length the length of
the headers between the IPv6 header and fragment itself; its
relative position in Fragmentable Part is computed from its
Fragment Offset value.
The Fragment header is not present in the final, reassembled
packet.
If any of the fragments being reassembled overlaps with any
other fragments being reassembled for the same packet,
reassembly of that packet must be abandoned and all the
fragments that have been received for that packet must be
discarded.
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If the fragment is a whole datagram (that is, both the Fragment
Offset field and the M flag are zero), then it does not need
any further reassembly and should be processed as a fully
reassembled packet (i.e., updating Next Header, adjust Payload
Length, removing the Fragmentation Header, etc.). Any other
fragments that match this packet (i.e., the same IPv6 Source
Address, IPv6 Destination Address, and Fragment Identification)
should be processed independently.
The following error conditions may arise when reassembling fragmented
packets:
If insufficient fragments are received to complete reassembly of a
packet within 60 seconds of the reception of the first-arriving
fragment of that packet, reassembly of that packet must be
abandoned and all the fragments that have been received for that
packet must be discarded. If the first fragment (i.e., the one
with a Fragment Offset of zero) has been received, an ICMP Time
Exceeded -- Fragment Reassembly Time Exceeded message should be
sent to the source of that fragment.
If the length of a fragment, as derived from the fragment packet's
Payload Length field, is not a multiple of 8 octets and the M flag
of that fragment is 1, then that fragment must be discarded and an
ICMP Parameter Problem, Code 0, message should be sent to the
source of the fragment, pointing to the Payload Length field of
the fragment packet.
If the length and offset of a fragment are such that the Payload
Length of the packet reassembled from that fragment would exceed
65,535 octets, then that fragment must be discarded and an ICMP
Parameter Problem, Code 0, message should be sent to the source of
the fragment, pointing to the Fragment Offset field of the
fragment packet.
If the first fragment does not include all headers through an
Upper-Layer header, then that fragment should be discarded and an
ICMP Parameter Problem, Code 3, message should be sent to the
source of the fragment, with the Pointer field set to zero.
The following conditions are not expected to occur, but are not
considered errors if they do:
The number and content of the headers preceding the Fragment
header of different fragments of the same original packet may
differ. Whatever headers are present, preceding the Fragment
header in each fragment packet, are processed when the packets
arrive, prior to queueing the fragments for reassembly. Only
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those headers in the Offset zero fragment packet are retained in
the reassembled packet.
The Next Header values in the Fragment headers of different
fragments of the same original packet may differ. Only the value
from the Offset zero fragment packet is used for reassembly.
4.6. Destination Options Header
The Destination Options header is used to carry optional information
that need be examined only by a packet's destination node(s). The
Destination Options header is identified by a Next Header value of 60
in the immediately preceding header, and has the following format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
. .
. Options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header 8-bit selector. Identifies the type of header
immediately following the Destination Options
header. Uses the same values as the IPv4
Protocol field [IANA-PN].
Hdr Ext Len 8-bit unsigned integer. Length of the
Destination Options header in 8-octet units,
not including the first 8 octets.
Options Variable-length field, of length such that the
complete Destination Options header is an
integer multiple of 8 octets long. Contains
one or more TLV-encoded options, as described
in section 4.2.
The only destination options defined in this document are the Pad1
and PadN options specified in section 4.2.
Note that there are two possible ways to encode optional destination
information in an IPv6 packet: either as an option in the Destination
Options header, or as a separate extension header. The Fragment
header and the Authentication header are examples of the latter
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approach. Which approach can be used depends on what action is
desired of a destination node that does not understand the optional
information:
o If the desired action is for the destination node to discard
the packet and, only if the packet's Destination Address is not
a multicast address, send an ICMP Unrecognized Type message to
the packet's Source Address, then the information may be
encoded either as a separate header or as an option in the
Destination Options header whose Option Type has the value 11
in its highest-order two bits. The choice may depend on such
factors as which takes fewer octets, or which yields better
alignment or more efficient parsing.
o If any other action is desired, the information must be encoded
as an option in the Destination Options header whose Option
Type has the value 00, 01, or 10 in its highest-order two bits,
specifying the desired action (see section 4.2).
4.7. No Next Header
The value 59 in the Next Header field of an IPv6 header or any
extension header indicates that there is nothing following that
header. If the Payload Length field of the IPv6 header indicates the
presence of octets past the end of a header whose Next Header field
contains 59, those octets must be ignored, and passed on unchanged if
the packet is forwarded.
4.8. Defining New Extention Headers and Options
No new extension headers that require hop-by-hop behavior should be
defined.
New hop-by-hop options are not recommended because, due to
performance restrictions, nodes may ignore the Hop-by-Hop Option
header, drop packets containing a hop-by-hop header, or assign
packets containing a hop-by-hop header to a slow processing path.
Designers considering defining new hop-by-hop options need to be
aware of this likely behaviour. There has to a very clear
justification why any new hop-by-hop option is needed before it is
standardized.
Instead of defining new Extension Headers, it is recommended that the
Destination Options header is used to carry optional information that
need be examined only by a packet's destination node(s), because they
provide better handling and backward compatibility. Defining new
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IPv6 extension headers is not recommended. There has to a very clear
justification why any new extension header is needed before it is
standardized.
If new Extension Headers are defined, they need to use the following
format:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| |
. .
. Header Specific Data .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Next Header 8-bit selector. Identifies the type of
header immediately following the extension
header. Uses the same values as the IPv4
Protocol field [IANA-PN].
Hdr Ext Len 8-bit unsigned integer. Length of the
Destination Options header in 8-octet units,
not including the first 8 octets.
Header Specific Data Variable-length field, Fields specific to
the extension header.
5. Packet Size Issues
IPv6 requires that every link in the internet have an MTU of 1280
octets or greater. On any link that cannot convey a 1280-octet
packet in one piece, link-specific fragmentation and reassembly must
be provided at a layer below IPv6.
Links that have a configurable MTU (for example, PPP links [RFC1661])
must be configured to have an MTU of at least 1280 octets; it is
recommended that they be configured with an MTU of 1500 octets or
greater, to accommodate possible encapsulations (i.e., tunneling)
without incurring IPv6-layer fragmentation.
From each link to which a node is directly attached, the node must be
able to accept packets as large as that link's MTU.
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It is strongly recommended that IPv6 nodes implement Path MTU
Discovery [RFC1981], in order to discover and take advantage of path
MTUs greater than 1280 octets. However, a minimal IPv6
implementation (e.g., in a boot ROM) may simply restrict itself to
sending packets no larger than 1280 octets, and omit implementation
of Path MTU Discovery.
In order to send a packet larger than a path's MTU, a node may use
the IPv6 Fragment header to fragment the packet at the source and
have it reassembled at the destination(s). However, the use of such
fragmentation is discouraged in any application that is able to
adjust its packets to fit the measured path MTU (i.e., down to 1280
octets).
A node must be able to accept a fragmented packet that, after
reassembly, is as large as 1500 octets. A node is permitted to
accept fragmented packets that reassemble to more than 1500 octets.
An upper-layer protocol or application that depends on IPv6
fragmentation to send packets larger than the MTU of a path should
not send packets larger than 1500 octets unless it has assurance that
the destination is capable of reassembling packets of that larger
size.
In response to an IPv6 packet that is sent to an IPv4 destination
(i.e., a packet that undergoes translation from IPv6 to IPv4), the
originating IPv6 node may receive an ICMP Packet Too Big message
reporting a Next-Hop MTU less than 1280. In that case, the IPv6 node
is not required to reduce the size of subsequent packets to less than
1280, but must include a Fragment header in those packets so that the
IPv6-to-IPv4 translating router can obtain a suitable Identification
value to use in resulting IPv4 fragments. Note that this means the
payload may have to be reduced to 1232 octets (1280 minus 40 for the
IPv6 header and 8 for the Fragment header), and smaller still if
additional extension headers are used.
6. Flow Labels
The 20-bit Flow Label field in the IPv6 header is used by a source to
label sequences of packets to be treated in the network as a single
flow.
The current definition of the IPv6 Flow Label can be found in
[RFC6437].
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7. Traffic Classes
The 8-bit Traffic Class field in the IPv6 header is used by the
network for traffic management. The value of the Traffic Class bits
in a received packet might be different from the value sent by the
packet's source.
The current use of the Traffic Class field for Differentiated
Services and Explicit Congestion Notification is specified in
[RFC2474] and [RFC3168].
8. Upper-Layer Protocol Issues
8.1. Upper-Layer Checksums
Any transport or other upper-layer protocol that includes the
addresses from the IP header in its checksum computation must be
modified for use over IPv6, to include the 128-bit IPv6 addresses
instead of 32-bit IPv4 addresses. In particular, the following
illustration shows the TCP and UDP "pseudo-header" for IPv6:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Source Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Destination Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Upper-Layer Packet Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| zero | Next Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
o If the IPv6 packet contains a Routing header, the Destination
Address used in the pseudo-header is that of the final
destination. At the originating node, that address will be in
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the last element of the Routing header; at the recipient(s),
that address will be in the Destination Address field of the
IPv6 header.
o The Next Header value in the pseudo-header identifies the
upper-layer protocol (e.g., 6 for TCP, or 17 for UDP). It will
differ from the Next Header value in the IPv6 header if there
are extension headers between the IPv6 header and the upper-
layer header.
o The Upper-Layer Packet Length in the pseudo-header is the
length of the upper-layer header and data (e.g., TCP header
plus TCP data). Some upper-layer protocols carry their own
length information (e.g., the Length field in the UDP header);
for such protocols, that is the length used in the pseudo-
header. Other protocols (such as TCP) do not carry their own
length information, in which case the length used in the
pseudo-header is the Payload Length from the IPv6 header, minus
the length of any extension headers present between the IPv6
header and the upper-layer header.
o Unlike IPv4, the default behavior when UDP packets are
originated by an IPv6 node, is that the UDP checksum is not
optional. That is, whenever originating a UDP packet, an IPv6
node must compute a UDP checksum over the packet and the
pseudo-header, and, if that computation yields a result of
zero, it must be changed to hex FFFF for placement in the UDP
header. IPv6 receivers must discard UDP packets containing a
zero checksum, and should log the error.
o As an exception to the default behaviour, protocols that use
UDP as a tunnel encapsulation may enable zero-checksum mode for
a specific port (or set of ports) for sending and/or receiving.
Any node implementing zero-checksum mode must follow the
requirements specified in "Applicability Statement for the use
of IPv6 UDP Datagrams with Zero Checksums" [RFC6936].
The IPv6 version of ICMP [RFC4443] includes the above pseudo-header
in its checksum computation; this is a change from the IPv4 version
of ICMP, which does not include a pseudo-header in its checksum. The
reason for the change is to protect ICMP from misdelivery or
corruption of those fields of the IPv6 header on which it depends,
which, unlike IPv4, are not covered by an internet-layer checksum.
The Next Header field in the pseudo-header for ICMP contains the
value 58, which identifies the IPv6 version of ICMP.
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8.2. Maximum Packet Lifetime
Unlike IPv4, IPv6 nodes are not required to enforce maximum packet
lifetime. That is the reason the IPv4 "Time to Live" field was
renamed "Hop Limit" in IPv6. In practice, very few, if any, IPv4
implementations conform to the requirement that they limit packet
lifetime, so this is not a change in practice. Any upper-layer
protocol that relies on the internet layer (whether IPv4 or IPv6) to
limit packet lifetime ought to be upgraded to provide its own
mechanisms for detecting and discarding obsolete packets.
8.3. Maximum Upper-Layer Payload Size
When computing the maximum payload size available for upper-layer
data, an upper-layer protocol must take into account the larger size
of the IPv6 header relative to the IPv4 header. For example, in
IPv4, TCP's MSS option is computed as the maximum packet size (a
default value or a value learned through Path MTU Discovery) minus 40
octets (20 octets for the minimum-length IPv4 header and 20 octets
for the minimum-length TCP header). When using TCP over IPv6, the
MSS must be computed as the maximum packet size minus 60 octets,
because the minimum-length IPv6 header (i.e., an IPv6 header with no
extension headers) is 20 octets longer than a minimum-length IPv4
header.
8.4. Responding to Packets Carrying Routing Headers
When an upper-layer protocol sends one or more packets in response to
a received packet that included a Routing header, the response
packet(s) must not include a Routing header that was automatically
derived by "reversing" the received Routing header UNLESS the
integrity and authenticity of the received Source Address and Routing
header have been verified (e.g., via the use of an Authentication
header in the received packet). In other words, only the following
kinds of packets are permitted in response to a received packet
bearing a Routing header:
o Response packets that do not carry Routing headers.
o Response packets that carry Routing headers that were NOT
derived by reversing the Routing header of the received packet
(for example, a Routing header supplied by local
configuration).
o Response packets that carry Routing headers that were derived
by reversing the Routing header of the received packet IF AND
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ONLY IF the integrity and authenticity of the Source Address
and Routing header from the received packet have been verified
by the responder.
9. IANA Considerations
None.
10. Security Considerations
The security features of IPv6 are described in the Security
Architecture for the Internet Protocol [RFC4301].
11. Acknowledgments
The authors gratefully acknowledge the many helpful suggestions of
the members of the IPng working group, the End-to-End Protocols
research group, and the Internet Community At Large.
12. References
12.1. Normative References
[I-D.hinden-6man-rfc4291bis]
Hinden, B. and S. Deering, "IP Version 6 Addressing
Architecture", draft-hinden-6man-rfc4291bis-00 (work in
progress), September 2015.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474, DOI
10.17487/RFC2474, December 1998,
<http://www.rfc-editor.org/info/rfc2474>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP", RFC
3168, DOI 10.17487/RFC3168, September 2001,
<http://www.rfc-editor.org/info/rfc3168>.
[RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet
Control Message Protocol (ICMPv6) for the Internet
Protocol Version 6 (IPv6) Specification", RFC 4443, DOI
10.17487/RFC4443, March 2006,
<http://www.rfc-editor.org/info/rfc4443>.
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[RFC6437] Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
"IPv6 Flow Label Specification", RFC 6437, DOI 10.17487/
RFC6437, November 2011,
<http://www.rfc-editor.org/info/rfc6437>.
12.2. Informative References
[IANA-PN] "Assigned Internet Protocol Numbers",
<https://www.iana.org/assignments/protocol-numbers/
protocol-numbers.xhtml>.
[IANA-RH] "IANA Routing Types Parameter Registry",
<https://www.iana.org/assignments/ipv6-parameters/
ipv6-parameters.xhtml#ipv6-parameters-3>.
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, DOI
10.17487/RFC0791, September 1981,
<http://www.rfc-editor.org/info/rfc791>.
[RFC1661] Simpson, W., Ed., "The Point-to-Point Protocol (PPP)", STD
51, RFC 1661, DOI 10.17487/RFC1661, July 1994,
<http://www.rfc-editor.org/info/rfc1661>.
[RFC1981] McCann, J., Deering, S., and J. Mogul, "Path MTU Discovery
for IP version 6", RFC 1981, DOI 10.17487/RFC1981, August
1996, <http://www.rfc-editor.org/info/rfc1981>.
[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>.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
December 2005, <http://www.rfc-editor.org/info/rfc4301>.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302, DOI
10.17487/RFC4302, December 2005,
<http://www.rfc-editor.org/info/rfc4302>.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC
4303, DOI 10.17487/RFC4303, December 2005,
<http://www.rfc-editor.org/info/rfc4303>.
[RFC5871] Arkko, J. and S. Bradner, "IANA Allocation Guidelines for
the IPv6 Routing Header", RFC 5871, DOI 10.17487/RFC5871,
May 2010, <http://www.rfc-editor.org/info/rfc5871>.
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[RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement
for the Use of IPv6 UDP Datagrams with Zero Checksums",
RFC 6936, DOI 10.17487/RFC6936, April 2013,
<http://www.rfc-editor.org/info/rfc6936>.
[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>.
Appendix A. Formatting Guidelines for Options
This appendix gives some advice on how to lay out the fields when
designing new options to be used in the Hop-by-Hop Options header or
the Destination Options header, as described in section 4.2. These
guidelines are based on the following assumptions:
o One desirable feature is that any multi-octet fields within the
Option Data area of an option be aligned on their natural
boundaries, i.e., fields of width n octets should be placed at
an integer multiple of n octets from the start of the Hop-by-
Hop or Destination Options header, for n = 1, 2, 4, or 8.
o Another desirable feature is that the Hop-by-Hop or Destination
Options header take up as little space as possible, subject to
the requirement that the header be an integer multiple of 8
octets long.
o It may be assumed that, when either of the option-bearing
headers are present, they carry a very small number of options,
usually only one.
These assumptions suggest the following approach to laying out the
fields of an option: order the fields from smallest to largest, with
no interior padding, then derive the alignment requirement for the
entire option based on the alignment requirement of the largest field
(up to a maximum alignment of 8 octets). This approach is
illustrated in the following examples:
Example 1
If an option X required two data fields, one of length 8 octets and
one of length 4 octets, it would be laid out as follows:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type=X |Opt Data Len=12|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4-octet field |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ 8-octet field +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Its alignment requirement is 8n+2, to ensure that the 8-octet field
starts at a multiple-of-8 offset from the start of the enclosing
header. A complete Hop-by-Hop or Destination Options header
containing this one option would look as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len=1 | Option Type=X |Opt Data Len=12|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4-octet field |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ 8-octet field +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Example 2
If an option Y required three data fields, one of length 4 octets,
one of length 2 octets, and one of length 1 octet, it would be laid
out as follows:
+-+-+-+-+-+-+-+-+
| Option Type=Y |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Opt Data Len=7 | 1-octet field | 2-octet field |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4-octet field |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Its alignment requirement is 4n+3, to ensure that the 4-octet field
starts at a multiple-of-4 offset from the start of the enclosing
header. A complete Hop-by-Hop or Destination Options header
containing this one option would look as follows:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len=1 | Pad1 Option=0 | Option Type=Y |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Opt Data Len=7 | 1-octet field | 2-octet field |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4-octet field |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PadN Option=1 |Opt Data Len=2 | 0 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Example 3
A Hop-by-Hop or Destination Options header containing both options X
and Y from Examples 1 and 2 would have one of the two following
formats, depending on which option appeared first:
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len=3 | Option Type=X |Opt Data Len=12|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4-octet field |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ 8-octet field +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PadN Option=1 |Opt Data Len=1 | 0 | Option Type=Y |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Opt Data Len=7 | 1-octet field | 2-octet field |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4-octet field |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PadN Option=1 |Opt Data Len=2 | 0 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Next Header | Hdr Ext Len=3 | Pad1 Option=0 | Option Type=Y |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Opt Data Len=7 | 1-octet field | 2-octet field |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4-octet field |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PadN Option=1 |Opt Data Len=4 | 0 | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 | 0 | Option Type=X |Opt Data Len=12|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 4-octet field |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ 8-octet field +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Appendix B. CHANGES SINCE RFC2460
This memo has the following changes from RFC2460. Numbers identify
the Internet-Draft version in which the change was made.
07) The purpose of this draft is to update references to current
versions and assign references to normative and informative.
07) Editorial changes.
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06) The purpose of this draft is to incorporate the updates
dealing with Extension headers as defined in RFC6564,
RFC7045, and RFC7112. The changes include:
RFC6564: Added new Section 4.8 that describe
recommendations for defining new Extension headers and
options
RFC7045: The changes were to add a reference to RFC7045,
change the requirement for processing the hop-by-hop
option to a should, and added a note that due to
performance restrictions some nodes won't process the Hop-
by-Hop Option header.
RFC7112: The changes were to revise the Fragmentation
Section to require that all headers through the first
Upper-Layer Header are in the first fragment. This
changed the text describing how packets are fragmented and
reassembled and added a new error case.
06) Editorial changes.
05) The purpose of this draft is to incorporate the updates
dealing with fragmentation as defined in RFC5722 and RFC6946.
Note: The issue relating to the handling of exact duplicate
fragments identified on the mailing list is left open.
05) Fix text in the end of Section 4.0 to correct the number of
extension headers defined in this document.
05) Editorial changes.
04) The purpose of this draft is to update the document to
incorporate the update made by RFC6935 "UDP Checksums for
Tunneled Packets".
04) Remove Routing (Type 0) header from the list of required
extension headers.
04) Editorial changes.
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Internet-Draft IPv6 Specification September 2015
03) The purpose of this draft is to update the document for the
deprecation of the RH0 Routing Header as specified in RFC5095
and the allocations guidelines for routing headers as
specified in RFC5871. Both of these RFCs updated RFC2460.
02) The purpose of this version of the draft is to update the
document to resolve the open Errata on RFC2460.
Errata ID: 2541: This errata notes that RFC2460 didn't
update RFC2205 when the length of the Flow Label was
changed from 24 to 20 bits from RFC1883. This issue was
resolved in RFC6437 where the Flow Label is defined. This
draft now references RFC6437. No change is required.
Errata ID: 4279: This errata noted that the specification
doesn't handle the case of a forwarding node receiving a
packet with a zero Hop Limit. This is fixed in
Section 3.0 of this draft. Note: No change was made
regarding host behaviour.
Errata ID: 2843: This errata is marked rejected. No
change is required.
02) Editorial changes to the Flow Label and Traffic Class text.
01) The purpose of this version of the draft is to update the
document to point to the current specifications of the IPv6
Flow Label field as defined in [RFC6437] and the Traffic
Class as defined in [RFC2474] and [RFC3168].
00) The purpose of this version is to establish a baseline from
RFC2460. The only intended changes are formatting (XML is
slightly different from .nroff), differences between an RFC
and Internet Draft, fixing a few ID Nits, and updates to the
authors information. There should not be any content changes
to the specification.
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Authors' Addresses
Stephen E. Deering
Retired
Vancouver, British Columbia
Canada
Robert M. Hinden
Check Point Software
959 Skyway Road
San Carlos, CA 94070
USA
Email: bob.hinden@gmail.com
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