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draft-clw-rfc6434-bis-00.xml
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<?xml version="1.0" encoding="US-ASCII"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?xml-stylesheet type='text/xsl' href='rfc2629.xslt' ?>
<!-- used by XSLT processors -->
<!-- For a complete list and description of processing instructions (PIs),
please see http://xml.resource.org/authoring/README.html -->
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(Here they are set differently than their defaults in xml2rfc v1.35) -->
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<?rfc strict="yes"?>
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<!-- generate a ToC -->
<?rfc toc="yes"?>
<!-- the number of levels of subsections in ToC. default: 3 -->
<?rfc tocdepth="3"?>
<!-- control references -->
<!-- use anchors instead of numbers for refs, i.e, [RFC2119] instead of [1] -->
<?rfc symrefs="yes"?>
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<?rfc sortrefs="no" ?>
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(using these PIs as follows is recommended by the RFC Editor) -->
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<?rfc compact="yes" ?>
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<?rfc subcompact="no" ?>
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<rfc category="info" ipr="trust200902" obsoletes="6434" docName="draft-clw-rfc6434-bis-00">
<front>
<title>IPv6 Node Requirements</title>
<author fullname="Tim Chown" initials="T." surname="Chown">
<organization> Jisc </organization>
<address>
<postal>
<street> Lumen House, Library Avenue </street>
<city> Harwell Oxford, Didcot</city>
<code> OX11 0SG </code>
<country> United Kingdom </country>
</postal>
<email> tim.chown@jisc.ac.uk </email>
</address>
</author>
<author fullname="John Loughney" initials="J" surname="Loughney">
<organization>Nokia</organization>
<address>
<postal>
<street>200 South Mathilda Ave.</street>
<city> Sunnyvale, CA</city>
<code>94086</code>
<country>USA</country>
</postal>
<phone>+1 650 283 8068</phone>
<email>john.loughney@nokia.com</email>
</address>
</author>
<author fullname="Tim Winters" initials="T." surname="Winters">
<organization> University of New Hampshire </organization>
<address>
<postal>
<street> InterOperability Laboratory</street>
<city> Durham</city>
<code> NH </code>
<country> United States </country>
</postal>
<email>twinters@iol.unh.edu</email>
</address>
</author>
<date month="October" year="2016" />
<area> Internet </area>
<workgroup>Internet Engineering Task Force</workgroup>
<keyword>IPv6</keyword>
<keyword>Internet Protocol Version 6</keyword>
<keyword>Internet Protocol</keyword>
<keyword>IP</keyword>
<abstract>
<t>This document defines requirements for IPv6 nodes. It is
expected that IPv6 will be deployed in a wide range of devices and
situations. Specifying the requirements for IPv6 nodes allows
IPv6 to function well and interoperate in a large number of
situations and deployments.</t>
<t>This document obsoletes RFC 6434, and in turn RFC 4294.</t>
<t>
NB. This is a first -00 version of the update to RFC 6434. We have
not yet edited original text from RFC 6434 apart from the author
and acknowledgement texts, which carry forward from the older versions.
</t>
<t>
We have indicated intended changes (additions, updates or deletion of
text at a high level in the sections below with text delimited by
**BIS ... ** comments, e.g.
</t>
<t>
**BIS Add discussion of the impact of RFC xxxx **
</t>
<t>
**BIS Update reference of RFC 3484 and note new address selection
implications**
</t>
<t>
etc. These will become edits in future versions once the substance of
the changes is agreed.
</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>This document defines common functionality required from both
IPv6 hosts and routers. Many IPv6 nodes will implement optional
or additional features, but this document collects and summarizes
requirements from other published Standards Track documents in one
place.</t>
<t>This document tries to avoid discussion of protocol details
and references RFCs for this purpose. This document is intended
to be an applicability statement and to provide guidance as to which
IPv6 specifications should be implemented in the general case and
which specifications may be of interest to specific deployment
scenarios. This document does not update any individual protocol
document RFCs.</t>
<t>Although this document points to different specifications, it
should be noted that in many cases, the granularity of a
particular requirement will be smaller than a single specification,
as many specifications define multiple, independent pieces, some
of which may not be mandatory. In addition, most specifications
define both client and server behavior in the same specification,
while many implementations will be focused on only one of those
roles. </t>
<t> This document defines a minimal level of requirement needed
for a device to provide useful internet service and considers a
broad range of device types and deployment scenarios. Because of
the wide range of deployment scenarios, the minimal requirements
specified in this document may not be sufficient for all
deployment scenarios. It is perfectly reasonable (and indeed
expected) for other profiles to define additional or stricter
requirements appropriate for specific usage and deployment
environments. For example, this document does not mandate that all
clients support DHCP, but some deployment scenarios may deem
it appropriate to make such a requirement. For example,
government agencies in the USA have defined profiles for
specialized requirements for IPv6 in target environments (see
<xref target='DODv6' /> and <xref target='USGv6' />).</t>
<t>
**BIS Is the DODv6 references still appopriate? **
</t>
<t>As it is not always possible for an implementer to know the
exact usage of IPv6 in a node, an overriding requirement for IPv6
nodes is that they should adhere to Jon Postel's Robustness
Principle: "Be conservative in what you do, be liberal in what you accept
from others" <xref target='RFC0793' />.</t>
<section title="Scope of This Document">
<t> IPv6 covers many specifications. It is intended that IPv6
will be deployed in many different situations and environments.
Therefore, it is important to develop requirements for IPv6
nodes to ensure interoperability. </t>
<t>This document assumes that all IPv6 nodes meet the minimum
requirements specified here.</t>
</section>
<section title="Description of IPv6 Nodes">
<t>From the Internet Protocol, Version 6 (IPv6) Specification <xref target='RFC2460' />, we have
the following definitions:</t>
<figure><artwork><![CDATA[
IPv6 node - a device that implements IPv6.
IPv6 router - a node that forwards IPv6 packets not explicitly
addressed to itself.
IPv6 host - any node that is not a router.
]]></artwork></figure>
<t>
**BIS We will need to refer to 2460-bis, as well as 1981-bis and
4291-bis, throughout this document. These are still in flux, but we
will know the final versions of these documents before this -bis
is published, so can adapt text here once those updates are complete.**
</t>
</section>
</section>
<section title="Requirements Language">
<t>The key words "MUST", "MUST NOT",
"REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED",
"MAY", and "OPTIONAL" in this document are to be
interpreted as described in <xref target="RFC2119">RFC 2119</xref>.</t>
</section>
<section title="Abbreviations Used in This Document">
<figure><artwork><![CDATA[
ATM Asynchronous Transfer Mode
AH Authentication Header
DAD Duplicate Address Detection
ESP Encapsulating Security Payload
ICMP Internet Control Message Protocol
IKE Internet Key Exchange
MIB Management Information Base
MLD Multicast Listener Discovery
MTU Maximum Transmission Unit
NA Neighbor Advertisement
NBMA Non-Broadcast Multiple Access
ND Neighbor Discovery
NS Neighbor Solicitation
NUD Neighbor Unreachability Detection
PPP Point-to-Point Protocol
]]></artwork></figure>
</section>
<section title="Sub-IP Layer">
<t>An IPv6 node must include support for one or more IPv6
link-layer specifications. Which link-layer specifications an
implementation should include will depend upon what link-layers
are supported by the hardware available on the system. It is
possible for a conformant IPv6 node to support IPv6 on some of its
interfaces and not on others. </t>
<t>As IPv6 is run over new layer 2 technologies, it is expected
that new specifications will be issued. In the following, we list some of
the layer 2 technologies for which an IPv6 specification has been developed.
It is provided for informational purposes only and may
not be complete.</t>
<t>
<list style="hanging">
<t hangText="-"> Transmission of IPv6 Packets over Ethernet
Networks <xref target='RFC2464' /></t>
<t hangText="-"> IPv6 over ATM Networks
<xref target='RFC2492' /></t>
<t hangText="-"> Transmission of IPv6 Packets over Frame
Relay Networks Specification <xref target='RFC2590' /></t>
<t hangText="-"> Transmission of IPv6 Packets over IEEE 1394
Networks <xref target='RFC3146' /></t>
<t hangText="-"> Transmission of IPv6, IPv4, and Address
Resolution Protocol (ARP) Packets over Fibre Channel
<xref target='RFC4338' /></t>
<t hangText="-"> Transmission of IPv6 Packets over IEEE
802.15.4 Networks <xref target='RFC4944' /></t>
<t hangText="-"> Transmission of IPv6 via the IPv6
Convergence Sublayer over IEEE 802.16 Networks
<xref target='RFC5121' /></t>
<t hangText="-"> IP version 6 over PPP
<xref target='RFC5072' /></t>
</list>
</t>
<t>
**BIS Add 6LoWPAN RFC 4919 here. Refresh the list. **
</t>
<t> In addition to traditional physical link-layers, it is also
possible to tunnel IPv6 over other protocols. Examples
include:</t>
<t>
<list style="hanging">
<t hangText="-"> Teredo: Tunneling IPv6 over UDP through
Network Address Translations (NATs) <xref target='RFC4380'
/></t>
<t hangText="-"> Section 3 of "Basic Transition Mechanisms for IPv6
Hosts and Routers" <xref target='RFC4213' /></t>
</list>
</t>
<t>
**BIS Do we want a small "over IP" section on UDP IPv6 tunneling, and issues like RFC 6935, or 6936?**
</t>
</section>
<section title="IP Layer">
<section title="Internet Protocol Version 6 - RFC 2460">
<t>The Internet Protocol Version 6 is specified in <xref target='RFC2460' />. This specification MUST be supported.</t>
<t>
**BIS Again, update for RFC 2460 -bis **
</t>
<t>Any unrecognized extension headers or options MUST be
processed as described in RFC 2460.</t>
<t>The node MUST follow the packet transmission rules in RFC 2460.</t>
<t>Nodes MUST always be able to send, receive, and process
fragment headers. All conformant IPv6 implementations MUST be
capable of sending and receiving IPv6 packets; the forwarding
functionality MAY be supported. Overlapping fragments MUST be
handled as described in <xref target='RFC5722' />. </t>
<t>
**BIS Add note on atomic fragments, RFC 6946, which updates RFC 5722,
and on draft-ietf-6man-deprecate-atomfrag-generation **
</t>
<t>
**BIS Add note on predictable fragment IDs, RFC 7739 **
</t>
<t>RFC 2460 specifies extension headers and the processing for
these headers.</t>
<t> An IPv6 node MUST be able to process these headers. An
exception is Routing Header type 0 (RH0), which was deprecated
by <xref target='RFC5095' /> due to security concerns and
which MUST be treated as an unrecognized routing type.</t>
<t>
**BIS Add note on new uniform IPv6 extension header format, RFC 6564 **
</t>
<t>
**BIS Add note on forwarding of EHs, as per RFC 7045 **
</t>
<t>
**BIS Add note on oversized header chains, RFC 7112 **
</t>
<t>
**BIS Wait to see outcome of insertion of EHs from 2460-bis - or leave any mention out from here? **
</t>
<t>All nodes SHOULD support the setting and use of the IPv6 Flow
Label field as defined in the IPv6 Flow Label specification
<xref target='RFC6437' />. Forwarding nodes such as routers and load distributors
MUST NOT depend only on Flow Label values being uniformly
distributed. It is RECOMMENDED that source hosts support the flow
label by setting the Flow Label field for all packets of a given
flow to the same value chosen from an approximation to a discrete
uniform distribution.
</t>
</section>
<section title="Neighbor Discovery for IPv6 - RFC 4861" anchor="ND">
<t>Neighbor Discovery is defined in <xref target='RFC4861' />; the
definition was updated by <xref target='RFC5942' />. Neighbor Discovery
SHOULD be supported. RFC 4861 states:</t>
<t><list style='hanging'> <t>
Unless specified otherwise (in a document that covers operating IP
over a particular link type) this document applies to all link types.
However, because ND uses link-layer multicast for some of its
services, it is possible that on some link types (e.g., Non-Broadcast
Multi-Access (NBMA) links), alternative protocols or mechanisms to
implement those services will be specified (in the appropriate
document covering the operation of IP over a particular link type).
The services described in this document that are not directly
dependent on multicast, such as Redirects, next-hop determination,
Neighbor Unreachability Detection, etc., are expected to be provided
as specified in this document.
The details of how one uses ND on
NBMA links are addressed in <xref target='RFC2491' />.
</t> </list></t>
<t>Some detailed analysis of Neighbor Discovery follows:</t>
<t>Router Discovery is how hosts locate routers that reside on
an attached link. Hosts MUST support Router Discovery
functionality.</t>
<t>Prefix Discovery is how hosts discover the set of address
prefixes that define which destinations are on-link for an
attached link. Hosts MUST support Prefix Discovery.</t>
<t>Hosts MUST also implement Neighbor Unreachability Detection
(NUD) for all paths between hosts and neighboring nodes. NUD is
not required for paths between routers. However, all nodes MUST
respond to unicast Neighbor Solicitation (NS) messages.</t>
<t>
**BIS Add note on NUD impatience, RFC 7048 **
</t>
<t>Hosts MUST support the sending of Router Solicitations and
the receiving of Router Advertisements. The ability to
understand individual Router Advertisement options is dependent
on supporting the functionality making use of the particular
option.</t>
<t>
**BIS Add note on RFC 7559 on packet-loss resliency for Router Solicitations **
</t>
<t>All nodes MUST support the sending and receiving of Neighbor
Solicitation (NS) and Neighbor Advertisement (NA) messages. NS
and NA messages are required for Duplicate Address Detection
(DAD).</t>
<t>Hosts SHOULD support the processing of Redirect
functionality. Routers MUST support the sending of Redirects,
though not necessarily for every individual packet (e.g., due to
rate limiting). Redirects are only useful on networks supporting
hosts. In core networks dominated by routers, Redirects are
typically disabled. The sending of Redirects SHOULD be disabled
by default on backbone routers. They MAY be enabled by default
on routers intended to support hosts on edge networks. </t>
<t> "IPv6 Host-to-Router Load Sharing" <xref target='RFC4311'/> includes additional recommendations on how to select from a
set of available routers. <xref target='RFC4311'/> SHOULD be supported. </t>
</section>
<section title="Default Router Preferences and More-Specific
Routes - RFC 4191">
<t>"Default Router Preferences and More-Specific Routes" <xref target='RFC4191' /> provides support for nodes attached to
multiple (different) networks, each providing routers that
advertise themselves as default routers via Router
Advertisements. In some scenarios, one router may provide
connectivity to destinations the other router does not, and
choosing the "wrong" default router can result in reachability
failures. In such cases, RFC 4191 can help.</t>
<t> Small Office/Home Office (SOHO) deployments supported by
routers adhering to <xref target='RFC6204' /> use
RFC 4191 to advertise routes to certain local
destinations. Consequently, nodes that will be deployed in SOHO
environments SHOULD implement RFC 4191.</t>
<t>
** BIS Need to update 6204 to 7084. **
</t>
</section>
<section title="SEcure Neighbor Discovery (SEND) - RFC 3971">
<t>
SEND <xref target='RFC3971' /> and Cryptographically Generated
Address (CGA) <xref target='RFC3972' /> provide a way to
secure the message exchanges of Neighbor Discovery. SEND is a
new technology in that it has no IPv4 counterpart, but it has
significant potential to address certain classes of spoofing
attacks. While there have been some implementations of SEND,
there has been only limited deployment experience to date in
using the technology. In addition, the IETF working group Cga &
Send maIntenance (csi) is currently working on additional
extensions intended to make SEND more attractive for
deployment.</t>
<t>At this time, SEND is considered optional, and IPv6 nodes MAY
provide SEND functionality.</t>
<t>
**BIS SEND seems to have minimal traction - should we reflect this? **
</t>
</section>
<section title="IPv6 Router Advertisement Flags Option - RFC
5175">
<t> Router Advertisements include an 8-bit field of single-bit
Router Advertisement flags. The Router Advertisement Flags
Option extends the number of available flag bits by 48 bits. At
the time of this writing, 6 of the original 8 single-bit flags have
been assigned, while 2 remain available for future
assignment. No flags have been defined that make use of the new
option, and thus, strictly speaking, there is no requirement to
implement the option today. However, implementations that are
able to pass unrecognized options to a higher-level entity that
may be able to understand them (e.g., a user-level process using
a "raw socket" facility) MAY take steps to handle the option in
anticipation of a future usage.</t>
</section>
<section title="Path MTU Discovery and Packet Size">
<section title="Path MTU Discovery - RFC 1981">
<t> "Path MTU Discovery for IP version 6" <xref target='RFC1981' /> SHOULD be
supported. From <xref target='RFC2460' />:</t>
<t><list style='hanging'>
<t> It is strongly recommended that IPv6 nodes implement
Path MTU Discovery <xref target='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.</t>
</list></t>
<t> The rules in <xref target='RFC2460' /> and
<xref target='RFC5722' /> MUST be followed for packet
fragmentation and reassembly. </t>
<t> One operational issue with Path MTU Discovery occurs when
firewalls block ICMP Packet Too Big messages. Path MTU
Discovery relies on such messages to determine what size
messages can be successfully sent. "Packetization Layer Path
MTU Discovery" <xref target='RFC4821' /> avoids having a
dependency on Packet Too Big messages.
</t>
<t>
**BIS Add note about 1280 MTU and UDP, as per Mark Andrews' comments in Berlin? **
</t>
<t>
**BIS Add note about RFC 4821, PLMTUD - is it appropriate here? **
</t>
</section>
</section>
<section title="IPv6 Jumbograms - RFC 2675">
<t> IPv6 Jumbograms <xref target='RFC2675' /> are an optional
extension that allow the sending of IP datagrams larger than
65.535 bytes. IPv6 Jumbograms make use of IPv6 hop-by-hop
options and are only suitable on paths in which every hop and
link are capable of supporting Jumbograms (e.g., within a campus
or datacenter). To date, few implementations exist, and there is
essentially no reported experience from usage. Consequently,
IPv6 Jumbograms <xref target='RFC2675' /> remain optional at
this time.</t>
<t>
**BIS Are these used? Do we need to modify the text for that? **
</t>
</section>
<section title="ICMP for the Internet Protocol Version 6 (IPv6) -
RFC 4443">
<t>ICMPv6 <xref target='RFC4443' /> MUST be supported. "Extended
ICMP to Support Multi-Part Messages" <xref target='RFC4884' />
MAY be supported.</t>
</section>
<section title="Addressing">
<section title="IP Version 6 Addressing Architecture - RFC 4291">
<t>The IPv6 Addressing Architecture <xref target='RFC4291' />
MUST be supported.</t>
<t>
**BIS Update to 4291-bis **
</t>
<t>
**BIS Add note on Why /64? RFC 7421.
But no need for /127 p2p text RFC 6164.
And no need for note on IID significance, as per RFC 7136. **
</t>
<t>
**BIS Add note discussing the impact of having multiple Addeses**
</t>
</section>
<section title="IPv6 Stateless Address Autoconfiguration - RFC 4862">
<t>Hosts MUST support IPv6 Stateless Address Autoconfiguration
as defined in <xref target='RFC4862' />. Configuration of
static address(es) may be supported as well.</t>
<t>
**BIS Is this a must any more? Add note on RFC 7721 on privacy issues for
address generation mechanisms. Add note on stable privacy addresses,
as per RFC 7217. **
</t>
<t>Nodes that are routers MUST be able to generate link-local
addresses as described in <xref target='RFC4862'/>.</t>
<t>From RFC 4862:</t>
<t><list style='hanging'> <t>
The autoconfiguration process specified in this document
applies only to hosts and not routers. Since host
autoconfiguration uses information advertised by routers,
routers will need to be configured by some other means.
However, it is expected that routers will generate link-local
addresses using the mechanism described in this document. In
addition, routers are expected to successfully pass the
Duplicate Address Detection procedure described in this
document on all addresses prior to assigning them to an
interface.</t> </list></t>
<t>All nodes MUST implement Duplicate Address Detection. Quoting
from Section 5.4 of RFC 4862:</t>
<t><list style='hanging'> <t> Duplicate Address Detection MUST
be performed on all unicast addresses prior to assigning them
to an interface, regardless of whether they are obtained
through stateless autoconfiguration, DHCPv6, or manual
configuration, with the following [exceptions noted therein].
</t> </list></t>
<t>"Optimistic Duplicate Address Detection (DAD) for
IPv6" <xref target='RFC4429' /> specifies a mechanism to reduce
delays associated with generating addresses via Stateless
Address Autoconfiguration <xref target='RFC4862' />. RFC 4429
was developed in conjunction with Mobile IPv6 in order to reduce
the time needed to acquire and configure addresses as devices
quickly move from one network to another, and it is desirable to
minimize transition delays. For general purpose devices, RFC 4429 remains optional at this time.
</t>
<t>
**BIS Add note on enhanced DAD, RFC 7527 **
</t>
</section>
<section title="Privacy Extensions for Address Configuration in IPv6 - RFC 4941">
<t>
Privacy Extensions for Stateless Address
Autoconfiguration <xref target='RFC4941' /> addresses a
specific problem involving a client device whose user is
concerned about its activity or location being
tracked. The problem arises both for a static client and
for one that regularly changes its point of attachment to
the Internet. When using Stateless Address
Autoconfiguration <xref target='RFC4862' />, the Interface Identifier
portion of formed addresses stays constant and is
globally unique. Thus, although a node's global IPv6
address will change if it changes its point of
attachment, the Interface Identifier portion of those
addresses remains the same, making it possible for servers
to track the location of an individual device as it moves
around or its pattern of activity if it remains in one
place. This may raise privacy concerns as described in
<xref target='RFC4862' />.
</t>
<t>
In such situations, RFC 4941 SHOULD be implemented. In
other cases, such as with dedicated servers in a data
center, RFC 4941 provides limited or no benefit.
</t>
<t>Implementers of RFC 4941 should be aware that certain
addresses are reserved and should not be chosen for use as
temporary addresses. Consult "Reserved IPv6 Interface
Identifiers" <xref target='RFC5453' /> for more details.
</t>
<t>
**BIS Add note about ensuring there's a configurable way to turn Privacy Addresses on / off? **
</t>
</section>
<section title="Default Address Selection for IPv6 - RFC 3484">
<t>The rules specified in the Default Address Selection for
IPv6 <xref target='RFC3484' /> document MUST be implemented.
IPv6 nodes will need to deal with multiple addresses
configured simultaneously.</t>
<t>
**BIS Update to RFC 6724. Briefly mention key changes? **
</t>
</section>
<section title="Stateful Address Autoconfiguration (DHCPv6) - RFC 3315" anchor="stateful1">
<t> DHCPv6 <xref target='RFC3315' /> can be used to obtain and
configure addresses. In general, a network may provide for the
configuration of addresses through Router Advertisements,
DHCPv6, or both. There will be a wide range of IPv6 deployment
models and differences in address assignment requirements,
some of which may require DHCPv6 for address assignment.
Consequently, all hosts SHOULD implement address configuration
via DHCPv6.</t>
<t>
**BIS SHOULD?
</t>
<t> In the absence of a router, IPv6 nodes using DHCP for
address assignment MAY initiate DHCP to obtain IPv6 addresses
and other configuration information, as described in Section
5.5.2 of <xref target='RFC4862' />.</t>
</section> </section>
<section title="Multicast Listener Discovery (MLD) for IPv6" anchor="mld">
<t> Nodes that need to join multicast groups MUST support MLDv1
<xref target='RFC2710' />. MLDv1 is needed by any node that is
expected to receive and process multicast traffic. Note that
Neighbor Discovery (as used on most link types -- see <xref
target="ND" />) depends on multicast and requires that nodes join Solicited
Node multicast addresses.</t>
<t> MLDv2 <xref target='RFC3810' /> extends the functionality of
MLDv1 by supporting Source-Specific Multicast. The original
MLDv2 protocol <xref target='RFC3810' /> supporting
Source-Specific Multicast <xref target='RFC4607' /> supports two
types of "filter modes". Using an INCLUDE filter, a node
indicates a multicast group along with a list of senders for
the group from which it wishes to receive traffic. Using an EXCLUDE
filter, a node indicates a multicast group along with a list of
senders from which it wishes to exclude receiving traffic. In
practice, operations to block source(s) using EXCLUDE mode are
rarely used but add considerable implementation complexity to
MLDv2. Lightweight MLDv2 <xref target='RFC5790' /> is a
simplified subset of the original MLDv2 specification that omits
EXCLUDE filter mode to specify undesired source(s). </t>
<t> Nodes SHOULD implement either MLDv2 <xref target='RFC3810'
/> or Lightweight MLDv2 <xref target='RFC5790' />. Specifically,
nodes supporting applications using Source-Specific Multicast
that expect to take advantage of MLDv2's EXCLUDE functionality
<xref target='RFC3810' /> MUST support MLDv2 as defined in <xref
target='RFC3810' />, <xref target='RFC4604' />, and <xref
target='RFC4607' />. Nodes supporting applications that expect
to only take advantage of MLDv2's INCLUDE functionality as well
as Any-Source Multicast will find it sufficient to support Lightweight
MLDv2 as defined in <xref target='RFC5790' />. </t>
<t> If a node only supports applications that use Any-Source
Multicast (i.e, they do not use Source-Specific Multicast),
implementing MLDv1 <xref target='RFC2710' /> is sufficient. In
all cases, however, nodes are strongly encouraged to implement
MLDv2 or Lightweight MLDv2 rather than MLDv1, as the presence of
a single MLDv1 participant on a link requires that all other
nodes on the link operate in version 1 compatibility mode.</t>
<t>When MLDv1 is used, the rules in the Source Address Selection
for the Multicast Listener Discovery (MLD) Protocol <xref
target='RFC3590' /> MUST be followed.</t>
</section>
</section>
<section title="DHCP versus Router Advertisement Options for Host Configuration">
<t> In IPv6, there are two main protocol mechanisms for
propagating configuration information to hosts: Router
Advertisements (RAs) and DHCP. Historically, RA options have been
restricted to those deemed essential for basic network
functioning and for which all nodes are configured with exactly
the same information. Examples include the Prefix Information
Options, the MTU option, etc. On the other hand, DHCP has
generally been preferred for configuration of more general
parameters and for parameters that may be client-specific. That
said, identifying the exact line on whether a particular option
should be configured via DHCP versus an RA option has not always
been easy. Generally speaking, however, there has been a desire
to define only one mechanism for configuring a given option,
rather than defining multiple (different) ways of configuring
the same information.</t>
<t>One issue with having multiple ways of configuring the same
information is that interoperability suffers if a host chooses one
mechanism but the
network operator chooses a different mechanism. For "closed"
environments, where the network operator
has significant influence over what devices connect to the
network and thus what configuration mechanisms they support, the
operator may be able to ensure that a particular mechanism is
supported by all connected hosts. In more open environments,
however, where arbitrary devices may connect (e.g., a WIFI
hotspot), problems can arise. To maximize interoperability in
such environments, hosts would need to implement multiple
configuration mechanisms to ensure interoperability.</t>
<t>Originally, in IPv6, configuring information about DNS servers
was performed exclusively via DHCP. In 2007, an RA option was
defined but was published as Experimental <xref
target='RFC5006' />. In 2010, "IPv6 Router Advertisement Options
for DNS Configuration" <xref target='RFC6106' /> was published
as a Standards Track document. Consequently, DNS configuration
information can now be learned either through DHCP or through
RAs. Hosts will need to decide which mechanism (or whether both)
should be implemented. Specific guidance regarding DNS server
discovery is discussed in <xref target="DNSandDHCP" />.</t>
</section>
<section title="DNS and DHCP" anchor="DNSandDHCP">
<section title="DNS">
<t>DNS is described in <xref target='RFC1034' />, <xref
target='RFC1035' />, <xref target='RFC3363' />, and <xref
target='RFC3596' />. Not all nodes will need to resolve names;
those that will never need to resolve DNS names do not need to
implement resolver functionality. However, the ability to
resolve names is a basic infrastructure capability on which
applications rely, and most nodes will need to provide
support. All nodes SHOULD implement stub-resolver <xref target='RFC1034'
/> functionality, as in <xref target='RFC1034'/>, Section
5.3.1, with support for:</t>
<t><list style='hanging'>
<t hangText="-">AAAA type Resource Records <xref target='RFC3596' />;</t>
<t hangText="-">reverse addressing in ip6.arpa using PTR records <xref target='RFC3596' />;</t>
<t hangText="-">Extension Mechanisms for DNS (EDNS0) <xref target='RFC2671' /> to allow for DNS packet sizes larger than 512 octets.</t>
</list></t>
<t>Those nodes are RECOMMENDED to support DNS security extensions <xref target='RFC4033' /> <xref target='RFC4034' /> <xref target='RFC4035' />.</t>
<t>Those nodes are NOT RECOMMENDED to support the experimental A6 Resource Records
<xref target='RFC3363' />.</t>
<t>
**BIS Scrub A6 completely now? **
</t>
<t>
**BIS Add DNS-SD? **
</t>
</section>
<section title="Dynamic Host Configuration Protocol for IPv6 (DHCPv6) - RFC 3315">
<section title="Other Configuration Information">
<t>IPv6 nodes use DHCP <xref target='RFC3315' /> to obtain
address configuration information (see <xref target="stateful1" />) and to
obtain additional (non-address) configuration. If a host
implementation supports applications or other protocols that
require configuration that is only available via DHCP, hosts
SHOULD implement DHCP. For specialized devices on which no
such configuration need is present, DHCP may not be
necessary.</t>
<t>An IPv6 node can use the subset of DHCP (described in
<xref target='RFC3736' />) to obtain other configuration
information.</t>
</section>
<section title="Use of Router Advertisements in Managed Environments">
<t>Nodes using the Dynamic Host Configuration Protocol for
IPv6 (DHCPv6) are expected to determine their default router
information and on-link prefix information from received
Router Advertisements.</t>
<t>
**BIS Well, they have no choice, bar manual configuration? No default router DHCPv6 option. **
</t>
</section>
</section>
<section title="IPv6 Router Advertisement Options for DNS
Configuration - RFC 6106">
<t>Router Advertisements have historically limited options to
those that are critical to basic IPv6 functioning. Originally,
DNS configuration was not included as an RA option, and DHCP
was the recommended way to obtain DNS configuration
information. Over time, the thinking surrounding such an
option has evolved. It is now generally recognized that few
nodes can function adequately without having access to a
working DNS resolver. <xref target='RFC5006'/> was published as an
Experimental document in 2007, and recently, a revised version
was placed on the Standards Track <xref target='RFC6106' />.</t>
<t>Implementations SHOULD implement the DNS RA option
<xref target='RFC6106' />. </t>
<t>
**BIS repeats text from section 6 - remove the section 6 duplication? **
</t>
</section>
</section>
<section title="IPv4 Support and Transition">
<t>IPv6 nodes MAY support IPv4.</t>
<section title="Transition Mechanisms">
<section title="Basic Transition Mechanisms for IPv6 Hosts and Routers - RFC 4213">
<t>If an IPv6 node implements dual stack and tunneling, then
<xref target='RFC4213' /> MUST be supported.</t>
</section>
</section>
</section>
<section title="Application Support">
<section title="Textual Representation of IPv6 Addresses - RFC
5952">
<t>Software that allows users and operators to input IPv6
addresses in text form SHOULD support "A Recommendation for
IPv6 Address Text Representation" <xref target='RFC5952' />.</t>
</section>
<section title="Application Programming Interfaces (APIs)">
<t>There are a number of IPv6-related APIs. This document does
not mandate the use of any, because the choice of API does not
directly relate to on-the-wire behavior of
protocols. Implementers, however, would be advised to consider
providing a common API or reviewing existing APIs for the type
of functionality they provide to applications. </t>
<t> "Basic Socket Interface Extensions for IPv6"
<xref target='RFC3493' /> provides IPv6 functionality used by
typical applications. Implementers should note that RFC3493 has
been picked up and further standardized by the Portable Operating System
Interface (POSIX) <xref target='POSIX' />.</t>
<t>"Advanced Sockets Application Program Interface (API) for
IPv6" <xref target='RFC3542' /> provides access to
advanced IPv6 features needed by diagnostic and other
more specialized applications.</t>
<t> "IPv6 Socket API for Source Address Selection"