Network Working Group S. Deering
Internet-Draft Retired
Obsoletes: 2460 (if approved) R. Hinden
Intended status: Standards Track Check Point Software
Expires: October 23, 2017 April 21, 2017

Internet Protocol, Version 6 (IPv6) Specification
draft-ietf-6man-rfc2460bis-10

Abstract

This document specifies version 6 of the Internet Protocol (IPv6). It obsoletes RFC2460

Status of This Memo

This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.

Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at http://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on October 23, 2017.

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Table of Contents

1. Introduction

IP version 6 (IPv6) is a new version of the Internet Protocol (IP), designed as the successor to IP version 4 (IPv4) [RFC0791]. The changes from IPv4 to IPv6 fall primarily into the following categories:

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 [RFC4291]. The IPv6 version of ICMP, which all IPv6 implementations are required to include, is specified in [RFC4443]

The data transmission order for IPv6 is the same as for IPv4 as defined in Appendix B of [RFC0791].

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 for a device with multiple interfaces to be configured to forward non-self-destined packets 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                      +
|                                                               |
+                                                               +
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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 is a small number of such extension headers, each one identified by a distinct Next Header value.

Extension Headers are numbered from IANA IP Protocol Numbers [IANA-PN], the same values used for IPv4 and IPv6. When processing a sequence of Next Header values in a packet, the first one that is not an Extension Header [IANA-EH] indicates that the next item in the packet is the corresponding upper-layer header. A special "No Next Header" value is used if there is no upper-layer header.

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:

+---------------+------------------------
|  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, processed, inserted, or deleted 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 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 may 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.

NOTE: While [RFC2460] required that all nodes must examine and process the Hop-by-Hop Options header, it is now expected that nodes along a packet's delivery path only examine and process the Hop-by-Hop Options header if explicitly configured to do so.

If, as a result of processing a header, the destination 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:

The first four are specified in this document; the last two are specified in [RFC4302] and [RFC4303], respectively. The current list of IPv6 extension headers can be found at [IANA-EH].

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:

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.

4.2. Options

Two of the currently-defined extension headers defined in this document -- 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
   

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:

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.

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:

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       |
   +-+-+-+-+-+-+-+-+

PadN option (alignment requirement: none)

   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -
   |       1       |  Opt Data Len |  Option Data
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+- - - - - - - - -

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 may be examined and processed 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                            .
 .                                                               .
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 

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                      .
 .                                                               .
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 

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, 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                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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.

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:

+------------------+-------------------------+---//----------------+
|  Per-Fragment    | Extension & Upper-Layer |   Fragmentable      |
|    Headers       |       Headers           |      Part           |
+------------------+-------------------------+---//----------------+

The Fragmentable Part of the original packet is divided into fragments. 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). Each complete fragment, 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:

+-----------------+-----------------+--------+--------+-//-+--------+
|  Per-Fragment   |Ext & Upper-Layer|  first | second |    |  last  |
|    Headers      |    Headers      |fragment|fragment|....|fragment|
+-----------------+-----------------+--------+--------+-//-+--------+

fragment packets:

+------------------+---------+-------------------+----------+
|  Per-Fragment    |Fragment | Ext & Upper-Layer |  first   |
|    Headers       | Header  |   Headers         | fragment |
+------------------+---------+-------------------+----------+

+------------------+--------+-------------------------------+
|  Per-Fragment    |Fragment|    second                     |
|    Headers       | Header |   fragment                    |
+------------------+--------+-------------------------------+
                      o
                      o
                      o
+------------------+--------+----------+
|  Per-Fragment    |Fragment|   last   |
|    Headers       | Header | fragment |
+------------------+--------+----------+

The first fragment packet is composed of:

The subsequent fragment packets are composed of:

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:

+---------------+-----------------+---------+--------+-//--+--------+
| Per-Fragment  |Ext & Upper-Layer|  first  | second |     | last   |
|    Headers    |   Headers       |frag data|fragment|.....|fragment|
+---------------+-----------------+---------+--------+-//--+--------+

The following rules govern reassembly:

The following error conditions may arise when reassembling fragmented packets:

The following conditions are not expected to occur frequently, but are not considered errors if they do:

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                            .
 .                                                               .
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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 approach. Which approach can be used depends on what action is desired of a destination node that does not understand the optional information:

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 Extension Headers and Options

New extension headers that require hop-by-hop behavior must not be defined because, as specified in Section 4 of this document, the only Extension Header that has hop-by-hop behavior is the Hop-by-Hop Options header.

New hop-by-hop options are not recommended because nodes may be configured to 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 be a very clear justification why any new hop-by-hop option is needed before it is standardized.

Defining new IPv6 extension headers is not recommended. There has to be a very clear justification why any new extension header 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 must be examined only by a packet's destination node(s), because they provide better handling and backward compatibility.

If new Extension Headers are defined, they need to use the following format:

 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |  Next Header  |  Hdr Ext Len  |                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
 |                                                               |
 .                                                               .
 .                  Header Specific Data                         .
 .                                                               .
 |                                                               |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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.

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.

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].

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 or fragment 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  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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.

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:

9. IANA Considerations

RFC2460 is referenced in a number of IANA registries. These include:

The IANA should update these references to point to this document.

10. Security Considerations

IPv6, from the viewpoint of the basic format and transmission of packets, has security properties that are similar to IPv4. These security issues include:

IPv6 packets can be protected from eavesdropping, replay, packet insertion, packet modification, and man in the middle attacks by use of the "Security Architecture for the Internet Protocol" [RFC4301]. In addition, upper-layer protocols such as TLS or SSH can be used to protect the application layer traffic running on top of IPv6.

There is not any mechanism to protect against "denial of service attacks". Defending against these type of attacks is outside the scope of this specification.

IPv6 addresses are significantly larger than IPv4 address making it much harder to scan the address space across the Internet and even on a single network link (e.g., Local Area Network). See [RFC7707] for more information.

IPv6 addresses of nodes are expected to be more visible on the Internet as compared with IPv4 since the use of address translation technology is reduced. This creates some additional privacy issues such as making it easier to distinguish endpoints. See [RFC7721] for more information.

The design of IPv6 extension headers architecture, while adding a lot of flexibility, also creates new security challenges. As noted below, issues relating the fragment extension header have been resolved, but it's clear that for any new extension header designed in the future, the security implications need to be examined throughly, and this needs to include how the new extension header works with existing extension headers. See [RFC7045] for more information.

This version of the IPv6 specification resolves a number of security issues that were found with the previous version [RFC2460] of the IPv6 specification. These include:

Security issues relating to other parts of IPv6 including addressing, ICMPv6, Path MTU Discovery, etc., are discussed in the appropriate specifications.

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.

The authors would also like to acknowledge the authors of the updating RFCs that were incorporated in this version of the document to move the IPv6 specification to Internet Standard. They are Joe Abley, Shane Amante, Jari Arkko, Manav Bhatia, Ronald P. Bonica, Scott Bradner, Brian Carpenter, P.F. Chimento, Marshall Eubanks, Fernando Gont, James Hoagland, Sheng Jiang, Erik Kline, Suresh Krishnan, Vishwas Manral, George Neville-Neil, Jarno Rajahalme, Pekka Savola, Magnus Westerlund, and James Woodyatt.

12. References

12.1. Normative References

[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791, DOI 10.17487/RFC0791, September 1981.
[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.
[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.
[RFC4291] Hinden, R. and S. Deering, "IP Version 6 Addressing Architecture", RFC 4291, DOI 10.17487/RFC4291, February 2006.
[RFC4443] Conta, A., Deering, S. and M. Gupta, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", RFC 4443, DOI 10.17487/RFC4443, March 2006.
[RFC6437] Amante, S., Carpenter, B., Jiang, S. and J. Rajahalme, "IPv6 Flow Label Specification", RFC 6437, DOI 10.17487/RFC6437, November 2011.

12.2. Informative References

, ", ", ", ", ", ", ", ", "
[IANA-6P]Internet Protocol Version 6 (IPv6) Parameters"
[IANA-EH]IPv6 Extension Header Types"
[IANA-MI]Structure of Management Information (SMI) Numbers (MIB Module Registrations)"
[IANA-NI]ONC RPC Network Identifiers (netids)"
[IANA-NL]Network Layer Protocol Identifiers (NLPIDs) of Interest"
[IANA-NS]Technical requirements for authoritative name servers"
[IANA-PN]Assigned Internet Protocol Numbers"
[IANA-PR]Protocol Registries"
[IANA-RH]IANA Routing Types Parameter Registry"
[RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51, RFC 1661, DOI 10.17487/RFC1661, July 1994.
[RFC1981] McCann, J., Deering, S. and J. Mogul, "Path MTU Discovery for IP version 6", RFC 1981, DOI 10.17487/RFC1981, August 1996.
[RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460, December 1998.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, DOI 10.17487/RFC4301, December 2005.
[RFC4302] Kent, S., "IP Authentication Header", RFC 4302, DOI 10.17487/RFC4302, December 2005.
[RFC4303] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, DOI 10.17487/RFC4303, December 2005.
[RFC5095] Abley, J., Savola, P. and G. Neville-Neil, "Deprecation of Type 0 Routing Headers in IPv6", RFC 5095, DOI 10.17487/RFC5095, December 2007.
[RFC5722] Krishnan, S., "Handling of Overlapping IPv6 Fragments", RFC 5722, DOI 10.17487/RFC5722, December 2009.
[RFC5871] Arkko, J. and S. Bradner, "IANA Allocation Guidelines for the IPv6 Routing Header", RFC 5871, DOI 10.17487/RFC5871, May 2010.
[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.
[RFC6946] Gont, F., "Processing of IPv6 "Atomic" Fragments", RFC 6946, DOI 10.17487/RFC6946, May 2013.
[RFC7045] Carpenter, B. and S. Jiang, "Transmission and Processing of IPv6 Extension Headers", RFC 7045, DOI 10.17487/RFC7045, December 2013.
[RFC7112] Gont, F., Manral, V. and R. Bonica, "Implications of Oversized IPv6 Header Chains", RFC 7112, DOI 10.17487/RFC7112, January 2014.
[RFC7707] Gont, F. and T. Chown, "Network Reconnaissance in IPv6 Networks", RFC 7707, DOI 10.17487/RFC7707, March 2016.
[RFC7721] Cooper, A., Gont, F. and D. Thaler, "Security and Privacy Considerations for IPv6 Address Generation Mechanisms", RFC 7721, DOI 10.17487/RFC7721, March 2016.
[RFC7739] Gont, F., Security Implications of Predictable Fragment Identification Values", RFC 7739, DOI 10.17487/RFC7739, February 2016.

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:

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:

                                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                | 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:

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  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:

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  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.

o
Clarification that extension headers are not examined, processed, inserted, or deleted by any node along a packet's delivery path.
o
Added paragraph to Section 4 to clarify how Extension Headers are numbered and which are upper-layer headers.
o
Revision Section 4.5 on IPv6 Fragmentation based on updates from RFC5722, RFC6946 RFC7112, and RFC8021. This include:
-
Revised the text to handle the case of fragments that are whole datagrams (i.e., both the Fragment Offset field and the M flag are zero). If received they should be processed as a reassembled packet. Any other fragments that match should be processed independently. The revised Fragment creation process was modified to not create whole datagram fragments (Fragment Offset field and the M flag are zero).
-
Changed the text to require that IPv6 nodes must not create overlapping fragments. Also, when reassembling an IPv6 datagram, if one or more its constituent fragments is determined to be an overlapping fragment, the entire datagram (and any constituent fragments) must be silently discarded. Includes a clarification that no ICMP error message should be sent if overlapping fragments are received.
-
Revised the text 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.
-
Added text to Fragment Header process on handling exact duplicate fragments.
-
Updated the Fragmentation header text to correct the inclusion of AH and note no next header case.
-
Change terminology in Fragment header section from "Unfragmentable Headers" to "Per-Fragment Headers".
-
Removed the paragraph in Section 5 that required including a fragment header to outgoing packets if a ICMP Packet Too Big message reporting a Next-Hop MTU less than 1280.
-
Changed the text to clarify MTU restriction and 8-byte restrictions, and noting the restriction on headers in first fragment.
o
Changed requirement for HBH header to a may, and added a note to indicate what is expected regarding HBH headers.
o
Clarified the text in Section 3 about decrementing the hop limit.
o
Removed IP Next Generation from the Abstract.
o
Add reference to the end of Section 4 to IPv6 Extension Header IANA registry.
o
Added text in Section 1 that the Data Transmission Order is the same as IPv4 as defined in RFC791.
o
Add instruction to the IANA Considerations section to change references to RFC2460 to this document
o
Add a paragraph to the acknowledgement section acknowledging the authors of the updating documents
o
Update references to current versions and assign references to normative and informative.
o
Incorporated the update from RFC6564 to add a new Section 4.8 that describes recommendations for defining new Extension headers and options
o
Incorporate the update in made by RFC6935 "UDP Checksums for Tunneled Packets" in Section 8. Added an exception to the default behaviour for the handling of handling UDP packets with zero checksums for tunnels.
o
Incorporate the updates from RFC5095 and RFC5871 to remove the description of the RH0 Routing Header, that the allocations guidelines for routing headers are specified in RFC5871, and removed RH0 Routing Header from the list of required extension headers.
o
Changes to resolve the open Errata on RFC2460. These are:
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 of this draft.
Errata ID: 2843: This errata is marked rejected. No change was made.
o
Simplify the text in Section 6 about Flow Labels and remove Appendix A, and instead 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].
o
Revised and expanded the Security Consideration section.

B.1. Change History Since RFC2460

NOTE TO RFC EDITOR: Please remove this subsection prior to RFC Publication

This section describes change history made in each Internet Draft that went into producing this version. The numbers identify the Internet-Draft version in which the change was made.

Working Group Internet Drafts

Individual Internet Drafts

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