    Internet Engineering Task Force (IETF)                          T. Chown
    Request for Comments: 8504                                          Jisc
    BCP: 220                                                     J. Loughney
    Obsoletes: 6434                                                    Intel
    Category: Best Current Practice                               T. Winters
    ISSN: 2070-1721                                                  UNH-IOL
                                                                January 2019

                             IPv6 Node Requirements

    Abstract

       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.

       This document obsoletes RFC 6434, and in turn RFC 4294.

    Status of This Memo

       This memo documents an Internet Best Current Practice.

       This document is a product of the Internet Engineering Task Force
       (IETF).  It represents the consensus of the IETF community.  It has
       received public review and has been approved for publication by the
       Internet Engineering Steering Group (IESG).  Further information on
       BCPs is available in Section 2 of RFC 7841.

       Information about the current status of this document, any errata,
       and how to provide feedback on it may be obtained at
       https://www.rfc-editor.org/info/rfc8504.

    Chown, et al.             Best Current Practice                 [Page 1]

    RFC 8504                 IPv6 Node Requirements             January 2019

    Copyright Notice

       Copyright (c) 2019 IETF Trust and the persons identified as the
       document authors.  All rights reserved.

       This document is subject to BCP 78 and the IETF Trust's Legal
       Provisions Relating to IETF Documents
       (https://trustee.ietf.org/license-info) in effect on the date of
       publication of this document.  Please review these documents
       carefully, as they describe your rights and restrictions with respect
       to this document.  Code Components extracted from this document must
       include Simplified BSD License text as described in Section 4.e of
       the Trust Legal Provisions and are provided without warranty as
       described in the Simplified BSD License.

    Table of Contents

       1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
         1.1.  Scope of This Document  . . . . . . . . . . . . . . . . .   4
         1.2.  Description of IPv6 Nodes . . . . . . . . . . . . . . . .   5
       2.  Requirements Language . . . . . . . . . . . . . . . . . . . .   5
       3.  Abbreviations Used in This Document . . . . . . . . . . . . .   5
       4.  Sub-IP Layer  . . . . . . . . . . . . . . . . . . . . . . . .   5
       5.  IP Layer  . . . . . . . . . . . . . . . . . . . . . . . . . .   6
         5.1.  Internet Protocol Version 6 - RFC 8200  . . . . . . . . .   6
         5.2.  Support for IPv6 Extension Headers  . . . . . . . . . . .   7
         5.3.  Protecting a Node from Excessive Extension Header Options   8
         5.4.  Neighbor Discovery for IPv6 - RFC 4861  . . . . . . . . .   9
         5.5.  SEcure Neighbor Discovery (SEND) - RFC 3971 . . . . . . .  11
         5.6.  IPv6 Router Advertisement Flags Option - RFC 5175 . . . .  11
         5.7.  Path MTU Discovery and Packet Size  . . . . . . . . . . .  11
           5.7.1.  Path MTU Discovery - RFC 8201 . . . . . . . . . . . .  11
           5.7.2.  Minimum MTU Considerations  . . . . . . . . . . . . .  12
         5.8.  ICMP for the Internet Protocol Version 6 (IPv6) -
               RFC 4443  . . . . . . . . . . . . . . . . . . . . . . . .  12
         5.9.  Default Router Preferences and More-Specific Routes -
               RFC 4191  . . . . . . . . . . . . . . . . . . . . . . . .  12
         5.10. First-Hop Router Selection - RFC 8028 . . . . . . . . . .  12
         5.11. Multicast Listener Discovery (MLD) for IPv6 - RFC 3810  .  13
         5.12. Explicit Congestion Notification (ECN) - RFC 3168 . . . .  13
       6.  Addressing and Address Configuration  . . . . . . . . . . . .  13
         6.1.  IP Version 6 Addressing Architecture - RFC 4291 . . . . .  13
         6.2.  Host Address Availability Recommendations . . . . . . . .  13
         6.3.  IPv6 Stateless Address Autoconfiguration - RFC 4862 . . .  14
         6.4.  Privacy Extensions for Address Configuration in IPv6 -
               RFC 4941  . . . . . . . . . . . . . . . . . . . . . . . .  15

    Chown, et al.             Best Current Practice                 [Page 2]

    RFC 8504                 IPv6 Node Requirements             January 2019

         6.5.  Stateful Address Autoconfiguration (DHCPv6) - RFC 3315  .  16
         6.6.  Default Address Selection for IPv6 - RFC 6724 . . . . . .  16
       7.  DNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  16
       8.  Configuring Non-address Information . . . . . . . . . . . . .  17
         8.1.  DHCP for Other Configuration Information  . . . . . . . .  17
         8.2.  Router Advertisements and Default Gateway . . . . . . . .  17
         8.3.  IPv6 Router Advertisement Options for DNS
               Configuration - RFC 8106  . . . . . . . . . . . . . . . .  17
         8.4.  DHCP Options versus Router Advertisement Options for Host
               Configuration . . . . . . . . . . . . . . . . . . . . . .  18
       9.  Service Discovery Protocols . . . . . . . . . . . . . . . . .  18
       10. IPv4 Support and Transition . . . . . . . . . . . . . . . . .  18
         10.1.  Transition Mechanisms  . . . . . . . . . . . . . . . . .  19
           10.1.1.  Basic Transition Mechanisms for IPv6 Hosts and
                    Routers - RFC 4213  . . . . . . . . . . . . . . . . . 19
       11. Application Support . . . . . . . . . . . . . . . . . . . . .  19
         11.1.  Textual Representation of IPv6 Addresses - RFC 5952  . .  19
         11.2.  Application Programming Interfaces (APIs)  . . . . . . .  19
       12. Mobility  . . . . . . . . . . . . . . . . . . . . . . . . . .  20
       13. Security  . . . . . . . . . . . . . . . . . . . . . . . . . .  20
         13.1.  Requirements . . . . . . . . . . . . . . . . . . . . . .  22
         13.2.  Transforms and Algorithms  . . . . . . . . . . . . . . .  22
       14. Router-Specific Functionality . . . . . . . . . . . . . . . .  22
         14.1.  IPv6 Router Alert Option - RFC 2711  . . . . . . . . . .  22
         14.2.  Neighbor Discovery for IPv6 - RFC 4861 . . . . . . . . .  22
         14.3.  Stateful Address Autoconfiguration (DHCPv6) - RFC 3315 .  23
         14.4.  IPv6 Prefix Length Recommendation for Forwarding -
                BCP 198  . . . . . . . . . . . . . . . . . . . . . . . .  23
       15. Constrained Devices . . . . . . . . . . . . . . . . . . . . .  23
       16. IPv6 Node Management  . . . . . . . . . . . . . . . . . . . .  24
         16.1.  Management Information Base (MIB) Modules  . . . . . . .  24
           16.1.1.  IP Forwarding Table MIB  . . . . . . . . . . . . . .  24
           16.1.2.  Management Information Base for the Internet
                    Protocol (IP)  . . . . . . . . . . . . . . . . . . .  24
           16.1.3.  Interface MIB  . . . . . . . . . . . . . . . . . . .  24
         16.2.  YANG Data Models . . . . . . . . . . . . . . . . . . . .  25
           16.2.1.  IP Management YANG Model . . . . . . . . . . . . . .  25
           16.2.2.  Interface Management YANG Model  . . . . . . . . . .  25
       17. Security Considerations . . . . . . . . . . . . . . . . . . .  25
       18. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  25
       19. References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
         19.1.  Normative References . . . . . . . . . . . . . . . . . .  25
         19.2.  Informative References . . . . . . . . . . . . . . . . .  32
       Appendix A.  Changes from RFC 6434  . . . . . . . . . . . . . . .  38
       Appendix B.  Changes from RFC 4294 to RFC 6434  . . . . . . . . .  39
       Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . .  41
       Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  42

    Chown, et al.             Best Current Practice                 [Page 3]

    RFC 8504                 IPv6 Node Requirements             January 2019

    1.  Introduction

       This document defines common functionality required by 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.

       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.

       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.

       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.  As an example, this document does
       not mandate that all clients support DHCP, but some deployment
       scenarios may deem it appropriate to make such a requirement.  As
       another example, NIST has defined profiles for specialized
       requirements for IPv6 in target environments (see [USGv6]).

       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" [RFC793].

    1.1.  Scope of This Document

       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.

    Chown, et al.             Best Current Practice                 [Page 4]

    RFC 8504                 IPv6 Node Requirements             January 2019

    1.2.  Description of IPv6 Nodes

       From "Internet Protocol, Version 6 (IPv6) Specification" [RFC8200],
       we have the following definitions:

       IPv6 node   - a device that implements IPv6.
       IPv6 router - a node that forwards IPv6 packets not explicitly
                     addressed to itself.
       IPv6 host   - any IPv6 node that is not a router.

    2.  Requirements Language

       The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
       "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
       "OPTIONAL" in this document are to be interpreted as described in
       BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
       capitals, as shown here.

    3.  Abbreviations Used in This Document

       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 Multi-Access
       ND    Neighbor Discovery
       NS    Neighbor Solicitation
       NUD   Neighbor Unreachability Detection
       PPP   Point-to-Point Protocol

    4.  Sub-IP Layer

       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.

       As IPv6 is run over new Layer 2 technologies, it is expected that new
       specifications will be issued.  We list here 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.

    Chown, et al.             Best Current Practice                 [Page 5]

    RFC 8504                 IPv6 Node Requirements             January 2019

       -  Transmission of IPv6 Packets over Ethernet Networks [RFC2464]

       -  Transmission of IPv6 Packets over Frame Relay Networks
          Specification [RFC2590]

       -  Transmission of IPv6 Packets over IEEE 1394 Networks [RFC3146]

       -  Transmission of IPv6, IPv4, and Address Resolution Protocol (ARP)
          Packets over Fibre Channel [RFC4338]

       -  Transmission of IPv6 Packets over IEEE 802.15.4 Networks [RFC4944]

       -  Transmission of IPv6 via the IPv6 Convergence Sublayer over IEEE
          802.16 Networks [RFC5121]

       -  IP version 6 over PPP [RFC5072]

       In addition to traditional physical link layers, it is also possible
       to tunnel IPv6 over other protocols.  Examples include:

       -  Teredo: Tunneling IPv6 over UDP through Network Address
          Translations (NATs) [RFC4380]

       -  Basic Transition Mechanisms for IPv6 Hosts and Routers (see
          Section 3 of [RFC4213])

    5.  IP Layer

    5.1.  Internet Protocol Version 6 - RFC 8200

       The Internet Protocol version 6 is specified in [RFC8200].  This
       specification MUST be supported.

       The node MUST follow the packet transmission rules in RFC 8200.

       All conformant IPv6 implementations MUST be capable of sending and
       receiving IPv6 packets; forwarding functionality MAY be supported.
       Nodes MUST always be able to send, receive, and process Fragment
       headers.

       IPv6 nodes MUST not create overlapping fragments.  Also, when
       reassembling an IPv6 datagram, if one or more of its constituent
       fragments is determined to be an overlapping fragment, the entire
       datagram (and any constituent fragments) MUST be silently discarded.
       See [RFC5722] for more information.

    Chown, et al.             Best Current Practice                 [Page 6]

    RFC 8504                 IPv6 Node Requirements             January 2019

       As recommended in [RFC8021], nodes MUST NOT generate atomic
       fragments, i.e., where the fragment is a whole datagram.  As per
       [RFC6946], if a receiving node reassembling a datagram encounters an
       atomic fragment, it should be processed as a fully reassembled
       packet, and any other fragments that match this packet should be
       processed independently.

       To mitigate a variety of potential attacks, nodes SHOULD avoid using
       predictable Fragment Identification values in Fragment headers, as
       discussed in [RFC7739].

       All nodes SHOULD support the setting and use of the IPv6 Flow Label
       field as defined in the IPv6 Flow Label specification [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.

    5.2.  Support for IPv6 Extension Headers

       RFC 8200 specifies extension headers and the processing for these
       headers.

       Extension headers (except for the Hop-by-Hop Options header) are not
       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.

       Any unrecognized extension headers or options MUST be processed as
       described in RFC 8200.  Note that where Section 4 of RFC 8200 refers
       to the action to be taken when a Next Header value in the current
       header is not recognized by a node, that action applies whether the
       value is an unrecognized extension header or an unrecognized upper-
       layer protocol (ULP).

       An IPv6 node MUST be able to process these extension headers.  An
       exception is Routing Header type 0 (RH0), which was deprecated by
       [RFC5095] due to security concerns and which MUST be treated as an
       unrecognized routing type.

       Further, [RFC7045] adds specific requirements for the processing of
       extension headers, in particular that any forwarding node along an
       IPv6 packet's path, which forwards the packet for any reason, SHOULD
       do so regardless of any extension headers that are present.

    Chown, et al.             Best Current Practice                 [Page 7]

    RFC 8504                 IPv6 Node Requirements             January 2019

       As per RFC 8200, when a node fragments an IPv6 datagram, it MUST
       include the entire IPv6 Header Chain in the first fragment.  The Per-
       Fragment headers MUST consist 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.  On reassembly, 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.  See [RFC7112] for a discussion of why oversized IPv6
       Extension Header Chains are avoided.

       Defining new IPv6 extension headers is not recommended, unless there
       are no existing IPv6 extension headers that can be used by specifying
       a new option for that IPv6 extension header.  A proposal to specify a
       new IPv6 extension header MUST include a detailed technical
       explanation of why an existing IPv6 extension header can not be used
       for the desired new function, and in such cases, it needs to follow
       the format described in Section 8 of RFC 8200.  For further
       background reading on this topic, see [RFC6564].

    5.3.  Protecting a Node from Excessive Extension Header Options

       As per RFC 8200, end hosts are expected to process all extension
       headers, destination options, and hop-by-hop options in a packet.
       Given that the only limit on the number and size of extension headers
       is the MTU, the processing of received packets could be considerable.
       It is also conceivable that a long chain of extension headers might
       be used as a form of denial-of-service attack.  Accordingly, a host
       may place limits on the number and sizes of extension headers and
       options it is willing to process.

       A host MAY limit the number of consecutive PAD1 options in
       destination options or hop-by-hop options to 7.  In this case, if
       there are more than 7 consecutive PAD1 options present, the packet
       MAY be silently discarded.  The rationale is that if padding of 8 or
       more bytes is required, then the PADN option SHOULD be used.

       A host MAY limit the number of bytes in a PADN option to be less than
       8.  In such a case, if a PADN option is present that has a length
       greater than 7, the packet SHOULD be silently discarded.  The
       rationale for this guideline is that the purpose of padding is for
       alignment and 8 bytes is the maximum alignment used in IPv6.

       A host MAY disallow unknown options in destination options or hop-by-
       hop options.  This SHOULD be configurable where the default is to
       accept unknown options and process them per [RFC8200].  If a packet

    Chown, et al.             Best Current Practice                 [Page 8]

    RFC 8504                 IPv6 Node Requirements             January 2019

       with unknown options is received and the host is configured to
       disallow them, then the packet SHOULD be silently discarded.

       A host MAY impose a limit on the maximum number of non-padding
       options allowed in the destination options and hop-by-hop extension
       headers.  If this feature is supported, the maximum number SHOULD be
       configurable, and the default value SHOULD be set to 8.  The limits
       for destination options and hop-by-hop options may be separately
       configurable.  If a packet is received and the number of destination
       or hop-by-hop options exceeds the limit, then the packet SHOULD be
       silently discarded.

       A host MAY impose a limit on the maximum length of Destination
       Options or Hop-by-Hop Options extension headers.  This value SHOULD
       be configurable, and the default is to accept options of any length.
       If a packet is received and the length of the Destination or Hop-by-
       Hop Options extension header exceeds the length limit, then the
       packet SHOULD be silently discarded.

    5.4.  Neighbor Discovery for IPv6 - RFC 4861

       Neighbor Discovery is defined in [RFC4861]; the definition was
       updated by [RFC5942].  Neighbor Discovery MUST be supported with the
       noted exceptions below.  RFC 4861 states:

          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
          [RFC2491].

       Some detailed analysis of Neighbor Discovery follows:

       Router Discovery is how hosts locate routers that reside on an
       attached link.  Hosts MUST support Router Discovery functionality.

       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.

    Chown, et al.             Best Current Practice                 [Page 9]

    RFC 8504                 IPv6 Node Requirements             January 2019

       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.

       [RFC7048] discusses NUD, in particular cases where it behaves too
       impatiently.  It states that if a node transmits more than a certain
       number of packets, then it SHOULD use the exponential backoff of the
       retransmit timer, up to a certain threshold point.

       Hosts MUST support the sending of Router Solicitations and the
       receiving of Router Advertisements (RAs).  The ability to understand
       individual RA options is dependent on supporting the functionality
       making use of the particular option.

       [RFC7559] discusses packet loss resiliency for Router Solicitations
       and requires that nodes MUST use a specific exponential backoff
       algorithm for retransmission of Router Solicitations.

       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).

       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 routers intended to be
       deployed on core networks.  They MAY be enabled by default on routers
       intended to support hosts on edge networks.

       As specified in [RFC6980], nodes MUST NOT employ IPv6 fragmentation
       for sending any of the following Neighbor Discovery and SEcure
       Neighbor Discovery messages: Neighbor Solicitation, Neighbor
       Advertisement, Router Solicitation, Router Advertisement, Redirect,
       or Certification Path Solicitation.  Nodes MUST silently ignore any
       of these messages on receipt if fragmented.  See RFC 6980 for details
       and motivation.

       "IPv6 Host-to-Router Load Sharing" [RFC4311] includes additional
       recommendations on how to select from a set of available routers.
       [RFC4311] SHOULD be supported.

    Chown, et al.             Best Current Practice                [Page 10]

    RFC 8504                 IPv6 Node Requirements             January 2019

    5.5.  SEcure Neighbor Discovery (SEND) - RFC 3971

       SEND [RFC3971] and Cryptographically Generated Addresses (CGAs)
       [RFC3972] provide a way to secure the message exchanges of Neighbor
       Discovery.  SEND has the potential to address certain classes of
       spoofing attacks, but it does not provide specific protection for
       threats from off-link attackers.

       There have been relatively few implementations of SEND in common
       operating systems and platforms since its publication in 2005; thus,
       deployment experience remains very limited to date.

       At this time, support for SEND is considered optional.  Due to the
       complexity in deploying SEND and its heavyweight provisioning, its
       deployment is only likely to be considered where nodes are operating
       in a particularly strict security environment.

    5.6.  IPv6 Router Advertisement Flags Option - RFC 5175

       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; 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.

    5.7.  Path MTU Discovery and Packet Size

    5.7.1.  Path MTU Discovery - RFC 8201

       "Path MTU Discovery for IP version 6" [RFC8201] SHOULD be supported.
       From [RFC8200]:

          It is strongly recommended that IPv6 nodes implement Path MTU
          Discovery [RFC8201], 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.

       The rules in [RFC8200] and [RFC5722] MUST be followed for packet
       fragmentation and reassembly.

    Chown, et al.             Best Current Practice                [Page 11]

    RFC 8504                 IPv6 Node Requirements             January 2019

       As described in RFC 8201, nodes implementing Path MTU Discovery and
       sending packets larger than the IPv6 minimum link MTU are susceptible
       to problematic connectivity if ICMPv6 messages are blocked or not
       transmitted.  For example, this will result in connections that
       complete the TCP three-way handshake correctly but then hang when
       data is transferred.  This state is referred to as a black-hole
       connection [RFC2923].  Path MTU Discovery relies on ICMPv6 Packet Too
       Big (PTB) to determine the MTU of the path (and thus these MUST NOT
       be filtered, as per the recommendation in [RFC4890]).

       An alternative to Path MTU Discovery defined in RFC 8201 can be found
       in [RFC4821], which defines a method for Packetization Layer Path MTU
       Discovery (PLPMTUD) designed for use over paths where delivery of
       ICMPv6 messages to a host is not assured.

    5.7.2.  Minimum MTU Considerations

       While an IPv6 link MTU can be set to 1280 bytes, it is recommended
       that for IPv6 UDP in particular, which includes DNS operation, the
       sender use a large MTU if they can, in order to avoid gratuitous
       fragmentation-caused packet drops.

    5.8.  ICMP for the Internet Protocol Version 6 (IPv6) - RFC 4443

       ICMPv6 [RFC4443] MUST be supported.  "Extended ICMP to Support Multi-
       Part Messages" [RFC4884] MAY be supported.

    5.9.  Default Router Preferences and More-Specific Routes - RFC 4191

       "Default Router Preferences and More-Specific Routes" [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 that the other router does not, and
       choosing the "wrong" default router can result in reachability
       failures.  In order to resolve this scenario, IPv6 nodes MUST
       implement [RFC4191] and SHOULD implement the Type C host role defined
       in RFC 4191.

    5.10.  First-Hop Router Selection - RFC 8028

       In multihomed scenarios, where a host has more than one prefix, each
       allocated by an upstream network that is assumed to implement BCP 38
       ingress filtering, the host may have multiple routers to choose from.

       Hosts that may be deployed in such multihomed environments SHOULD
       follow the guidance given in [RFC8028].

    Chown, et al.             Best Current Practice                [Page 12]

    RFC 8504                 IPv6 Node Requirements             January 2019

    5.11.  Multicast Listener Discovery (MLD) for IPv6 - RFC 3810

       Nodes that need to join multicast groups MUST support MLDv2
       [RFC3810].  MLD is needed by any node that is expected to receive and
       process multicast traffic; in particular, MLDv2 is required for
       support for source-specific multicast (SSM) as per [RFC4607].

       Previous versions of this specification only required MLDv1 [RFC2710]
       to be implemented on all nodes.  Since participation of any
       MLDv1-only nodes on a link require that all other nodes on the link
       then operate in version 1 compatibility mode, the requirement to
       support MLDv2 on all nodes was upgraded to a MUST.  Further, SSM is
       now the preferred multicast distribution method, rather than Any-
       Source Multicast (ASM).

       Note that Neighbor Discovery (as used on most link types -- see
       Section 5.4) depends on multicast and requires that nodes join
       Solicited Node multicast addresses.

    5.12.  Explicit Congestion Notification (ECN) - RFC 3168

       An ECN-aware router sets a mark in the IP header in order to signal
       impending congestion, rather than dropping a packet.  The receiver of
       the packet echoes the congestion indication to the sender, which can
       then reduce its transmission rate as if it detected a dropped packet.

       Nodes SHOULD support ECN [RFC3168] by implementing an interface for
       the upper layer to access and by setting the ECN bits in the IP
       header.  The benefits of using ECN are documented in [RFC8087].

    6.  Addressing and Address Configuration

    6.1.  IP Version 6 Addressing Architecture - RFC 4291

       The IPv6 Addressing Architecture [RFC4291] MUST be supported.

       The current IPv6 Address Architecture is based on a 64-bit boundary
       for subnet prefixes.  The reasoning behind this decision is
       documented in [RFC7421].

       Implementations MUST also support the multicast flag updates
       documented in [RFC7371].

    6.2.  Host Address Availability Recommendations

       Hosts may be configured with addresses through a variety of methods,
       including Stateless Address Autoconfiguration (SLAAC), DHCPv6, or
       manual configuration.

    Chown, et al.             Best Current Practice                [Page 13]

    RFC 8504                 IPv6 Node Requirements             January 2019

       [RFC7934] recommends that networks provide general-purpose end hosts
       with multiple global IPv6 addresses when they attach, and it
       describes the benefits of and the options for doing so.  Routers
       SHOULD support [RFC7934] for assigning multiple addresses to a host.
       A host SHOULD support assigning multiple addresses as described in
       [RFC7934].

       Nodes SHOULD support the capability to be assigned a prefix per host
       as documented in [RFC8273].  Such an approach can offer improved host
       isolation and enhanced subscriber management on shared network
       segments.

    6.3.  IPv6 Stateless Address Autoconfiguration - RFC 4862

       Hosts MUST support IPv6 Stateless Address Autoconfiguration.  It is
       RECOMMENDED, as described in [RFC8064], that unless there is a
       specific requirement for Media Access Control (MAC) addresses to be
       embedded in an Interface Identifier (IID), nodes follow the procedure
       in [RFC7217] to generate SLAAC-based addresses, rather than use
       [RFC4862].  Addresses generated using the method described in
       [RFC7217] will be the same whenever a given device (re)appears on the
       same subnet (with a specific IPv6 prefix), but the IID will vary on
       each subnet visited.

       Nodes that are routers MUST be able to generate link-local addresses
       as described in [RFC4862].

       From RFC 4862:

          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.

       All nodes MUST implement Duplicate Address Detection.  Quoting from
       Section 5.4 of RFC 4862:

          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].

    Chown, et al.             Best Current Practice                [Page 14]

    RFC 8504                 IPv6 Node Requirements             January 2019

       "Optimistic Duplicate Address Detection (DAD) for IPv6" [RFC4429]
       specifies a mechanism to reduce delays associated with generating
       addresses via Stateless Address Autoconfiguration [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.

       [RFC7527] discusses enhanced DAD and describes an algorithm to
       automate the detection of looped-back IPv6 ND messages used by DAD.
       Nodes SHOULD implement this behavior where such detection is
       beneficial.

    6.4.  Privacy Extensions for Address Configuration in IPv6 - RFC 4941

       A node using Stateless Address Autoconfiguration [RFC4862] to form a
       globally unique IPv6 address that uses its MAC address to generate
       the IID will see that the IID remains the same on any visited
       network, even though the network prefix part changes.  Thus, it is
       possible for a third-party device to track the activities of the node
       they communicate with, as that node moves around the network.
       Privacy Extensions for Stateless Address Autoconfiguration [RFC4941]
       address this concern by allowing nodes to configure an additional
       temporary address where the IID is effectively randomly generated.
       Privacy addresses are then used as source addresses for new
       communications initiated by the node.

       General issues regarding privacy issues for IPv6 addressing are
       discussed in [RFC7721].

       RFC 4941 SHOULD be supported.  In some scenarios, such as dedicated
       servers in a data center, it provides limited or no benefit, or it
       may complicate network management.  Thus, devices implementing this
       specification MUST provide a way for the end user to explicitly
       enable or disable the use of such temporary addresses.

       Note that RFC 4941 can be used independently of traditional SLAAC or
       independently of SLAAC that is based on RFC 7217.

       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" [RFC5453] for more
       details.

    Chown, et al.             Best Current Practice                [Page 15]

    RFC 8504                 IPv6 Node Requirements             January 2019

    6.5.  Stateful Address Autoconfiguration (DHCPv6) - RFC 3315

       DHCPv6 [RFC3315] can be used to obtain and configure addresses.  In
       general, a network may provide for the configuration of addresses
       through SLAAC, 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 stateful address assignment.
       Consequently, all hosts SHOULD implement address configuration via
       DHCPv6.

       In the absence of observed Router Advertisement messages, IPv6 nodes
       MAY initiate DHCP to obtain IPv6 addresses and other configuration
       information, as described in Section 5.5.2 of [RFC4862].

       Where devices are likely to be carried by users and attached to
       multiple visited networks, DHCPv6 client anonymity profiles SHOULD be
       supported as described in [RFC7844] to minimize the disclosure of
       identifying information.  Section 5 of RFC 7844 describes operational
       considerations on the use of such anonymity profiles.

    6.6.  Default Address Selection for IPv6 - RFC 6724

       IPv6 nodes will invariably have multiple addresses configured
       simultaneously and thus will need to choose which addresses to use
       for which communications.  The rules specified in the Default Address
       Selection for IPv6 document [RFC6724] MUST be implemented.  [RFC8028]
       updates Rule 5.5 from [RFC6724]; implementations SHOULD implement
       this rule.

    7.  DNS

       DNS is described in [RFC1034], [RFC1035], [RFC3363], and [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 [RFC1034]
       functionality, as in Section 5.3.1 of [RFC1034], with support for:

       -  AAAA type Resource Records [RFC3596];

       -  reverse addressing in ip6.arpa using PTR records [RFC3596]; and

       -  Extension Mechanisms for DNS (EDNS(0)) [RFC6891] to allow for DNS
          packet sizes larger than 512 octets.

       Those nodes are RECOMMENDED to support DNS security extensions
       [RFC4033] [RFC4034] [RFC4035].

    Chown, et al.             Best Current Practice                [Page 16]

    RFC 8504                 IPv6 Node Requirements             January 2019

       A6 Resource Records [RFC2874] are classified as Historic per
       [RFC6563].  These were defined with Experimental status in [RFC3363].

    8.  Configuring Non-address Information

    8.1.  DHCP for Other Configuration Information

       DHCP [RFC3315] specifies a mechanism for IPv6 nodes to obtain address
       configuration information (see Section 6.5) 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.

       An IPv6 node can use the subset of DHCP (described in [RFC3736]) to
       obtain other configuration information.

       If an IPv6 node implements DHCP, it MUST implement the DNS options
       [RFC3646] as most deployments will expect that these options are
       available.

    8.2.  Router Advertisements and Default Gateway

       There is no defined DHCPv6 Gateway option.

       Nodes using the Dynamic Host Configuration Protocol for IPv6 (DHCPv6)
       are thus expected to determine their default router information and
       on-link prefix information from received Router Advertisements.

    8.3.  IPv6 Router Advertisement Options for DNS Configuration - RFC 8106

       Router Advertisement options have historically been limited to those
       that are critical to basic IPv6 functionality.  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; thus, a Standards Track
       document has been published to provide this capability [RFC8106].

       Implementations MUST include support for the DNS RA option [RFC8106].

    Chown, et al.             Best Current Practice                [Page 17]

    RFC 8504                 IPv6 Node Requirements             January 2019

    8.4.  DHCP Options versus Router Advertisement Options for Host
          Configuration

       In IPv6, there are two main protocol mechanisms for propagating
       configuration information to hosts: RAs and DHCP.  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.  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.

       One issue with having multiple ways to configure 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 Wi-Fi hotspot), problems can arise.  To maximize
       interoperability in such environments, hosts would need to implement
       multiple configuration mechanisms to ensure interoperability.

    9.  Service Discovery Protocols

       Multicast DNS (mDNS) and DNS-based Service Discovery (DNS-SD) are
       described in [RFC6762] and [RFC6763], respectively.  These protocols,
       often collectively referred to as the 'Bonjour' protocols after their
       naming by Apple, provide the means for devices to discover services
       within a local link and, in the absence of a unicast DNS service, to
       exchange naming information.

       Where devices are to be deployed in networks where service discovery
       would be beneficial, e.g., for users seeking to discover printers or
       display devices, mDNS and DNS-SD SHOULD be supported.

    10.  IPv4 Support and Transition

       IPv6 nodes MAY support IPv4.

    Chown, et al.             Best Current Practice                [Page 18]

    RFC 8504                 IPv6 Node Requirements             January 2019

    10.1.  Transition Mechanisms

    10.1.1.  Basic Transition Mechanisms for IPv6 Hosts and Routers -
             RFC 4213

       If an IPv6 node implements dual stack and tunneling, then [RFC4213]
       MUST be supported.

    11.  Application Support

    11.1.  Textual Representation of IPv6 Addresses - RFC 5952

       Software that allows users and operators to input IPv6 addresses in
       text form SHOULD support "A Recommendation for IPv6 Address Text
       Representation" [RFC5952].

    11.2.  Application Programming Interfaces (APIs)

       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.

       "Basic Socket Interface Extensions for IPv6" [RFC3493] provides IPv6
       functionality used by typical applications.  Implementers should note
       that RFC 3493 has been picked up and further standardized by the
       Portable Operating System Interface (POSIX) [POSIX].

       "Advanced Sockets Application Program Interface (API) for IPv6"
       [RFC3542] provides access to advanced IPv6 features needed by
       diagnostic and other more specialized applications.

       "IPv6 Socket API for Source Address Selection" [RFC5014] provides
       facilities that allow an application to override the default Source
       Address Selection rules of [RFC6724].

       "Socket Interface Extensions for Multicast Source Filters" [RFC3678]
       provides support for expressing source filters on multicast group
       memberships.

       "Extension to Sockets API for Mobile IPv6" [RFC4584] provides
       application support for accessing and enabling Mobile IPv6 [RFC6275]
       features.

    Chown, et al.             Best Current Practice                [Page 19]

    RFC 8504                 IPv6 Node Requirements             January 2019

    12.  Mobility

       Mobile IPv6 [RFC6275] and associated specifications [RFC3776]
       [RFC4877] allow a node to change its point of attachment within the
       Internet, while maintaining (and using) a permanent address.  All
       communication using the permanent address continues to proceed as
       expected even as the node moves around.  The definition of Mobile IP
       includes requirements for the following types of nodes:

          - mobile nodes

          - correspondent nodes with support for route optimization

          - home agents

          - all IPv6 routers

       At the present time, Mobile IP has seen only limited implementation
       and no significant deployment, partly because it originally assumed
       an IPv6-only environment rather than a mixed IPv4/IPv6 Internet.
       Additional work has been done to support mobility in mixed-mode IPv4
       and IPv6 networks [RFC5555].

       More usage and deployment experience is needed with mobility before
       any specific approach can be recommended for broad implementation in
       all hosts and routers.  Consequently, Mobility Support in IPv6
       [RFC6275], Mobile IPv6 Support for Dual Stack Hosts and Routers
       [RFC5555], and associated standards (such as Mobile IPv6 with IKEv2
       and IPsec [RFC4877]) are considered a MAY at this time.

       IPv6 for 3GPP [RFC7066] lists a snapshot of required IPv6
       functionalities at the time the document was published that would
       need to be implemented, going above and beyond the recommendations in
       this document.  Additionally, a 3GPP IPv6 Host MAY implement
       [RFC7278] to deliver IPv6 prefixes on the LAN link.

    13.  Security

       This section describes the security specification for IPv6 nodes.

       Achieving security in practice is a complex undertaking.  Operational
       procedures, protocols, key distribution mechanisms, certificate
       management approaches, etc., are all components that impact the level
       of security actually achieved in practice.  More importantly,
       deficiencies or a poor fit in any one individual component can
       significantly reduce the overall effectiveness of a particular
       security approach.

    Chown, et al.             Best Current Practice                [Page 20]

    RFC 8504                 IPv6 Node Requirements             January 2019

       IPsec can provide either end-to-end security between nodes or channel
       security (for example, via a site-to-site IPsec VPN), making it
       possible to provide secure communication for all (or a subset of)
       communication flows at the IP layer between pairs of Internet nodes.
       IPsec has two standard operating modes: Tunnel-mode and Transport-
       mode.  In Tunnel-mode, IPsec provides network-layer security and
       protects an entire IP packet by encapsulating the original IP packet
       and then prepending a new IP header.  In Transport-mode, IPsec
       provides security for the transport layer (and above) by
       encapsulating only the transport-layer (and above) portion of the IP
       packet (i.e., without adding a second IP header).

       Although IPsec can be used with manual keying in some cases, such
       usage has limited applicability and is not recommended.

       A range of security technologies and approaches proliferate today
       (e.g., IPsec, Transport Layer Security (TLS), Secure SHell (SSH), TLS
       VPNS, etc.).  No single approach has emerged as an ideal technology
       for all needs and environments.  Moreover, IPsec is not viewed as the
       ideal security technology in all cases and is unlikely to displace
       the others.

       Previously, IPv6 mandated implementation of IPsec and recommended the
       key-management approach of IKE.  RFC 6434 updated that recommendation
       by making support of the IPsec architecture [RFC4301] a SHOULD for
       all IPv6 nodes, and this document retains that recommendation.  Note
       that the IPsec Architecture requires the implementation of both
       manual and automatic key management (e.g., Section 4.5 of RFC 4301).
       Currently, the recommended automated key-management protocol to
       implement is IKEv2 [RFC7296].

       This document recognizes that there exists a range of device types
       and environments where approaches to security other than IPsec can be
       justified.  For example, special-purpose devices may support only a
       very limited number or type of applications, and an application-
       specific security approach may be sufficient for limited management
       or configuration capabilities.  Alternatively, some devices may run
       on extremely constrained hardware (e.g., sensors) where the full
       IPsec Architecture is not justified.

       Because most common platforms now support IPv6 and have it enabled by
       default, IPv6 security is an issue for networks that are ostensibly
       IPv4 only; see [RFC7123] for guidance on this area.

    Chown, et al.             Best Current Practice                [Page 21]

    RFC 8504                 IPv6 Node Requirements             January 2019

    13.1.  Requirements

       "Security Architecture for the Internet Protocol" [RFC4301] SHOULD be
       supported by all IPv6 nodes.  Note that the IPsec Architecture
       requires the implementation of both manual and automatic key
       management (e.g., Section 4.5 of [RFC4301]).  Currently, the default
       automated key-management protocol to implement is IKEv2.  As required
       in [RFC4301], IPv6 nodes implementing the IPsec Architecture MUST
       implement ESP [RFC4303] and MAY implement AH [RFC4302].

    13.2.  Transforms and Algorithms

       The current set of mandatory-to-implement algorithms for the IPsec
       Architecture are defined in Cryptographic Algorithm Implementation
       Requirements for ESP and AH [RFC8221].  IPv6 nodes implementing the
       IPsec Architecture MUST conform to the requirements in [RFC8221].
       Preferred cryptographic algorithms often change more frequently than
       security protocols.  Therefore, implementations MUST allow for
       migration to new algorithms, as RFC 8221 is replaced or updated in
       the future.

       The current set of mandatory-to-implement algorithms for IKEv2 are
       defined in Cryptographic Algorithm Implementation Requirements for
       ESP and AH [RFC8247].  IPv6 nodes implementing IKEv2 MUST conform to
       the requirements in [RFC8247] and/or any future updates or
       replacements to [RFC8247].

    14.  Router-Specific Functionality

       This section defines general host considerations for IPv6 nodes that
       act as routers.  Currently, this section does not discuss detailed
       routing-specific requirements.  For the case of typical home routers,
       [RFC7084] defines basic requirements for customer edge routers.

    14.1.  IPv6 Router Alert Option - RFC 2711

       The IPv6 Router Alert option [RFC2711] is an optional IPv6 Hop-by-Hop
       Header that is used in conjunction with some protocols (e.g., RSVP
       [RFC2205] or Multicast Listener Discovery (MLDv2) [RFC3810]).  The
       Router Alert option will need to be implemented whenever such
       protocols that mandate its use are implemented.  See Section 5.11.

    14.2.  Neighbor Discovery for IPv6 - RFC 4861

       Sending Router Advertisements and processing Router Solicitations
       MUST be supported.

    Chown, et al.             Best Current Practice                [Page 22]

    RFC 8504                 IPv6 Node Requirements             January 2019

       Section 7 of [RFC6275] includes some mobility-specific extensions to
       Neighbor Discovery.  Routers SHOULD implement Sections 7.3 and 7.5,
       even if they do not implement home agent functionality.

    14.3.  Stateful Address Autoconfiguration (DHCPv6) - RFC 3315

       A single DHCP server ([RFC3315] or [RFC4862]) can provide
       configuration information to devices directly attached to a shared
       link, as well as to devices located elsewhere within a site.
       Communication between a client and a DHCP server located on different
       links requires the use of DHCP relay agents on routers.

       In simple deployments, consisting of a single router and either a
       single LAN or multiple LANs attached to the single router, together
       with a WAN connection, a DHCP server embedded within the router is
       one common deployment scenario (e.g., [RFC7084]).  There is no need
       for relay agents in such scenarios.

       In more complex deployment scenarios, such as within enterprise or
       service provider networks, the use of DHCP requires some level of
       configuration, in order to configure relay agents, DHCP servers, etc.
       In such environments, the DHCP server might even be run on a
       traditional server, rather than as part of a router.

       Because of the wide range of deployment scenarios, support for DHCP
       server functionality on routers is optional.  However, routers
       targeted for deployment within more complex scenarios (as described
       above) SHOULD support relay agent functionality.  Note that "Basic
       Requirements for IPv6 Customer Edge Routers" [RFC7084] requires
       implementation of a DHCPv6 server function in IPv6 Customer Edge (CE)
       routers.

    14.4.  IPv6 Prefix Length Recommendation for Forwarding - BCP 198

       Forwarding nodes MUST conform to BCP 198 [RFC7608]; thus, IPv6
       implementations of nodes that may forward packets MUST conform to the
       rules specified in Section 5.1 of [RFC4632].

    15.  Constrained Devices

       The focus of this document is general IPv6 nodes.  In this section,
       we briefly discuss considerations for constrained devices.

       In the case of constrained nodes, with limited CPU, memory, bandwidth
       or power, support for certain IPv6 functionality may need to be
       considered due to those limitations.  While the requirements of this
       document are RECOMMENDED for all nodes, including constrained nodes,
       compromises may need to be made in certain cases.  Where such

    Chown, et al.             Best Current Practice                [Page 23]

    RFC 8504                 IPv6 Node Requirements             January 2019

       compromises are made, the interoperability of devices should be
       strongly considered, particularly where this may impact other nodes
       on the same link, e.g., only supporting MLDv1 will affect other
       nodes.

       The IETF 6LowPAN (IPv6 over Low-Power Wireless Personal Area Network)
       WG produced six RFCs, including a general overview and problem
       statement [RFC4919] (the means by which IPv6 packets are transmitted
       over IEEE 802.15.4 networks [RFC4944] and ND optimizations for that
       medium [RFC6775]).

       IPv6 nodes that are battery powered SHOULD implement the
       recommendations in [RFC7772].

    16.  IPv6 Node Management

       Network management MAY be supported by IPv6 nodes.  However, for IPv6
       nodes that are embedded devices, network management may be the only
       possible way of controlling these nodes.

       Existing network management protocols include SNMP [RFC3411], NETCONF
       [RFC6241], and RESTCONF [RFC8040].

    16.1.  Management Information Base (MIB) Modules

       The obsoleted status of various IPv6-specific MIB modules is
       clarified in [RFC8096].

       The following two MIB modules SHOULD be supported by nodes that
       support an SNMP agent.

    16.1.1.  IP Forwarding Table MIB

       The IP Forwarding Table MIB [RFC4292] SHOULD be supported by nodes
       that support an SNMP agent.

    16.1.2.  Management Information Base for the Internet Protocol (IP)

       The IP MIB [RFC4293] SHOULD be supported by nodes that support an
       SNMP agent.

    16.1.3.  Interface MIB

       The Interface MIB [RFC2863] SHOULD be supported by nodes that support
       an SNMP agent.

    Chown, et al.             Best Current Practice                [Page 24]

    RFC 8504                 IPv6 Node Requirements             January 2019

    16.2.  YANG Data Models

       The following YANG data models SHOULD be supported by nodes that
       support a NETCONF or RESTCONF agent.

    16.2.1.  IP Management YANG Model

       The IP Management YANG Model [RFC8344] SHOULD be supported by nodes
       that support NETCONF or RESTCONF.

    16.2.2.  Interface Management YANG Model

       The Interface Management YANG Model [RFC8343] SHOULD be supported by
       nodes that support NETCONF or RESTCONF.

    17.  Security Considerations

       This document does not directly affect the security of the Internet,
       beyond the security considerations associated with the individual
       protocols.

       Security is also discussed in Section 13 above.

    18.  IANA Considerations

       This document has no IANA actions.

    19.  References

    19.1.  Normative References

       [RFC1034]  Mockapetris, P., "Domain names - concepts and facilities",
                  STD 13, RFC 1034, DOI 10.17487/RFC1034, November 1987,
                  <https://www.rfc-editor.org/info/rfc1034>.

       [RFC1035]  Mockapetris, P., "Domain names - implementation and
                  specification", STD 13, RFC 1035, DOI 10.17487/RFC1035,
                  November 1987, <https://www.rfc-editor.org/info/rfc1035>.

       [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
                  Requirement Levels", BCP 14, RFC 2119,
                  DOI 10.17487/RFC2119, March 1997,
                  <https://www.rfc-editor.org/info/rfc2119>.

       [RFC2710]  Deering, S., Fenner, W., and B. Haberman, "Multicast
                  Listener Discovery (MLD) for IPv6", RFC 2710,
                  DOI 10.17487/RFC2710, October 1999,
                  <https://www.rfc-editor.org/info/rfc2710>.

    Chown, et al.             Best Current Practice                [Page 25]

    RFC 8504                 IPv6 Node Requirements             January 2019

       [RFC2711]  Partridge, C. and A. Jackson, "IPv6 Router Alert Option",
                  RFC 2711, DOI 10.17487/RFC2711, October 1999,
                  <https://www.rfc-editor.org/info/rfc2711>.

       [RFC2863]  McCloghrie, K. and F. Kastenholz, "The Interfaces Group
                  MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000,
                  <https://www.rfc-editor.org/info/rfc2863>.

       [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,
                  <https://www.rfc-editor.org/info/rfc3168>.

       [RFC3315]  Droms, R., Ed., Bound, J., Volz, B., Lemon, T., Perkins,
                  C., and M. Carney, "Dynamic Host Configuration Protocol
                  for IPv6 (DHCPv6)", RFC 3315, DOI 10.17487/RFC3315, July
                  2003, <https://www.rfc-editor.org/info/rfc3315>.

       [RFC3411]  Harrington, D., Presuhn, R., and B. Wijnen, "An
                  Architecture for Describing Simple Network Management
                  Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
                  DOI 10.17487/RFC3411, December 2002,
                  <https://www.rfc-editor.org/info/rfc3411>.

       [RFC3596]  Thomson, S., Huitema, C., Ksinant, V., and M. Souissi,
                  "DNS Extensions to Support IP Version 6", STD 88,
                  RFC 3596, DOI 10.17487/RFC3596, October 2003,
                  <https://www.rfc-editor.org/info/rfc3596>.

       [RFC3736]  Droms, R., "Stateless Dynamic Host Configuration Protocol
                  (DHCP) Service for IPv6", RFC 3736, DOI 10.17487/RFC3736,
                  April 2004, <https://www.rfc-editor.org/info/rfc3736>.

       [RFC3810]  Vida, R., Ed. and L. Costa, Ed., "Multicast Listener
                  Discovery Version 2 (MLDv2) for IPv6", RFC 3810,
                  DOI 10.17487/RFC3810, June 2004,
                  <https://www.rfc-editor.org/info/rfc3810>.

       [RFC4033]  Arends, R., Austein, R., Larson, M., Massey, D., and
                  S. Rose, "DNS Security Introduction and Requirements",
                  RFC 4033, DOI 10.17487/RFC4033, March 2005,
                  <https://www.rfc-editor.org/info/rfc4033>.

       [RFC4034]  Arends, R., Austein, R., Larson, M., Massey, D., and
                  S. Rose, "Resource Records for the DNS Security
                  Extensions", RFC 4034, DOI 10.17487/RFC4034, March 2005,
                  <https://www.rfc-editor.org/info/rfc4034>.

    Chown, et al.             Best Current Practice                [Page 26]

    RFC 8504                 IPv6 Node Requirements             January 2019

       [RFC4035]  Arends, R., Austein, R., Larson, M., Massey, D., and
                  S. Rose, "Protocol Modifications for the DNS Security
                  Extensions", RFC 4035, DOI 10.17487/RFC4035, March 2005,
                  <https://www.rfc-editor.org/info/rfc4035>.

       [RFC4213]  Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms
                  for IPv6 Hosts and Routers", RFC 4213,
                  DOI 10.17487/RFC4213, October 2005,
                  <https://www.rfc-editor.org/info/rfc4213>.

       [RFC4291]  Hinden, R. and S. Deering, "IP Version 6 Addressing
                  Architecture", RFC 4291, DOI 10.17487/RFC4291, February
                  2006, <https://www.rfc-editor.org/info/rfc4291>.

       [RFC4292]  Haberman, B., "IP Forwarding Table MIB", RFC 4292,
                  DOI 10.17487/RFC4292, April 2006,
                  <https://www.rfc-editor.org/info/rfc4292>.

       [RFC4293]  Routhier, S., Ed., "Management Information Base for the
                  Internet Protocol (IP)", RFC 4293, DOI 10.17487/RFC4293,
                  April 2006, <https://www.rfc-editor.org/info/rfc4293>.

       [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
                  Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
                  December 2005, <https://www.rfc-editor.org/info/rfc4301>.

       [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
                  RFC 4303, DOI 10.17487/RFC4303, December 2005,
                  <https://www.rfc-editor.org/info/rfc4303>.

       [RFC4311]  Hinden, R. and D. Thaler, "IPv6 Host-to-Router Load
                  Sharing", RFC 4311, DOI 10.17487/RFC4311, November 2005,
                  <https://www.rfc-editor.org/info/rfc4311>.

       [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
                  Control Message Protocol (ICMPv6) for the Internet
                  Protocol Version 6 (IPv6) Specification", STD 89,
                  RFC 4443, DOI 10.17487/RFC4443, March 2006,
                  <https://www.rfc-editor.org/info/rfc4443>.

       [RFC4607]  Holbrook, H. and B. Cain, "Source-Specific Multicast for
                  IP", RFC 4607, DOI 10.17487/RFC4607, August 2006,
                  <https://www.rfc-editor.org/info/rfc4607>.

       [RFC4632]  Fuller, V. and T. Li, "Classless Inter-domain Routing
                  (CIDR): The Internet Address Assignment and Aggregation
                  Plan", BCP 122, RFC 4632, DOI 10.17487/RFC4632, August
                  2006, <https://www.rfc-editor.org/info/rfc4632>.

    Chown, et al.             Best Current Practice                [Page 27]

    RFC 8504                 IPv6 Node Requirements             January 2019

       [RFC4861]  Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
                  "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
                  DOI 10.17487/RFC4861, September 2007,
                  <https://www.rfc-editor.org/info/rfc4861>.

       [RFC4862]  Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
                  Address Autoconfiguration", RFC 4862,
                  DOI 10.17487/RFC4862, September 2007,
                  <https://www.rfc-editor.org/info/rfc4862>.

       [RFC4941]  Narten, T., Draves, R., and S. Krishnan, "Privacy
                  Extensions for Stateless Address Autoconfiguration in
                  IPv6", RFC 4941, DOI 10.17487/RFC4941, September 2007,
                  <https://www.rfc-editor.org/info/rfc4941>.

       [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,
                  <https://www.rfc-editor.org/info/rfc5095>.

       [RFC5453]  Krishnan, S., "Reserved IPv6 Interface Identifiers",
                  RFC 5453, DOI 10.17487/RFC5453, February 2009,
                  <https://www.rfc-editor.org/info/rfc5453>.

       [RFC5722]  Krishnan, S., "Handling of Overlapping IPv6 Fragments",
                  RFC 5722, DOI 10.17487/RFC5722, December 2009,
                  <https://www.rfc-editor.org/info/rfc5722>.

       [RFC5790]  Liu, H., Cao, W., and H. Asaeda, "Lightweight Internet
                  Group Management Protocol Version 3 (IGMPv3) and Multicast
                  Listener Discovery Version 2 (MLDv2) Protocols", RFC 5790,
                  DOI 10.17487/RFC5790, February 2010,
                  <https://www.rfc-editor.org/info/rfc5790>.

       [RFC5942]  Singh, H., Beebee, W., and E. Nordmark, "IPv6 Subnet
                  Model: The Relationship between Links and Subnet
                  Prefixes", RFC 5942, DOI 10.17487/RFC5942, July 2010,
                  <https://www.rfc-editor.org/info/rfc5942>.

       [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
                  Address Text Representation", RFC 5952,
                  DOI 10.17487/RFC5952, August 2010,
                  <https://www.rfc-editor.org/info/rfc5952>.

       [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
                  and A. Bierman, Ed., "Network Configuration Protocol
                  (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
                  <https://www.rfc-editor.org/info/rfc6241>.

    Chown, et al.             Best Current Practice                [Page 28]

    RFC 8504                 IPv6 Node Requirements             January 2019

       [RFC6437]  Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
                  "IPv6 Flow Label Specification", RFC 6437,
                  DOI 10.17487/RFC6437, November 2011,
                  <https://www.rfc-editor.org/info/rfc6437>.

       [RFC6564]  Krishnan, S., Woodyatt, J., Kline, E., Hoagland, J., and
                  M. Bhatia, "A Uniform Format for IPv6 Extension Headers",
                  RFC 6564, DOI 10.17487/RFC6564, April 2012,
                  <https://www.rfc-editor.org/info/rfc6564>.

       [RFC6724]  Thaler, D., Ed., Draves, R., Matsumoto, A., and T. Chown,
                  "Default Address Selection for Internet Protocol Version 6
                  (IPv6)", RFC 6724, DOI 10.17487/RFC6724, September 2012,
                  <https://www.rfc-editor.org/info/rfc6724>.

       [RFC6762]  Cheshire, S. and M. Krochmal, "Multicast DNS", RFC 6762,
                  DOI 10.17487/RFC6762, February 2013,
                  <https://www.rfc-editor.org/info/rfc6762>.

       [RFC6763]  Cheshire, S. and M. Krochmal, "DNS-Based Service
                  Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
                  <https://www.rfc-editor.org/info/rfc6763>.

       [RFC6775]  Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and
                  C. Bormann, "Neighbor Discovery Optimization for IPv6 over
                  Low-Power Wireless Personal Area Networks (6LoWPANs)",
                  RFC 6775, DOI 10.17487/RFC6775, November 2012,
                  <https://www.rfc-editor.org/info/rfc6775>.

       [RFC6891]  Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
                  for DNS (EDNS(0))", STD 75, RFC 6891,
                  DOI 10.17487/RFC6891, April 2013,
                  <https://www.rfc-editor.org/info/rfc6891>.

       [RFC6946]  Gont, F., "Processing of IPv6 "Atomic" Fragments",
                  RFC 6946, DOI 10.17487/RFC6946, May 2013,
                  <https://www.rfc-editor.org/info/rfc6946>.

       [RFC7045]  Carpenter, B. and S. Jiang, "Transmission and Processing
                  of IPv6 Extension Headers", RFC 7045,
                  DOI 10.17487/RFC7045, December 2013,
                  <https://www.rfc-editor.org/info/rfc7045>.

       [RFC7048]  Nordmark, E. and I. Gashinsky, "Neighbor Unreachability
                  Detection Is Too Impatient", RFC 7048,
                  DOI 10.17487/RFC7048, January 2014,
                  <https://www.rfc-editor.org/info/rfc7048>.

    Chown, et al.             Best Current Practice                [Page 29]

    RFC 8504                 IPv6 Node Requirements             January 2019

       [RFC7112]  Gont, F., Manral, V., and R. Bonica, "Implications of
                  Oversized IPv6 Header Chains", RFC 7112,
                  DOI 10.17487/RFC7112, January 2014,
                  <https://www.rfc-editor.org/info/rfc7112>.

       [RFC7217]  Gont, F., "A Method for Generating Semantically Opaque
                  Interface Identifiers with IPv6 Stateless Address
                  Autoconfiguration (SLAAC)", RFC 7217,
                  DOI 10.17487/RFC7217, April 2014,
                  <https://www.rfc-editor.org/info/rfc7217>.

       [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and
                  T. Kivinen, "Internet Key Exchange Protocol Version 2
                  (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
                  2014, <https://www.rfc-editor.org/info/rfc7296>.

       [RFC7527]  Asati, R., Singh, H., Beebee, W., Pignataro, C., Dart, E.,
                  and W. George, "Enhanced Duplicate Address Detection",
                  RFC 7527, DOI 10.17487/RFC7527, April 2015,
                  <https://www.rfc-editor.org/info/rfc7527>.

       [RFC7559]  Krishnan, S., Anipko, D., and D. Thaler, "Packet-Loss
                  Resiliency for Router Solicitations", RFC 7559,
                  DOI 10.17487/RFC7559, May 2015,
                  <https://www.rfc-editor.org/info/rfc7559>.

       [RFC7608]  Boucadair, M., Petrescu, A., and F. Baker, "IPv6 Prefix
                  Length Recommendation for Forwarding", BCP 198, RFC 7608,
                  DOI 10.17487/RFC7608, July 2015,
                  <https://www.rfc-editor.org/info/rfc7608>.

       [RFC8021]  Gont, F., Liu, W., and T. Anderson, "Generation of IPv6
                  Atomic Fragments Considered Harmful", RFC 8021,
                  DOI 10.17487/RFC8021, January 2017,
                  <https://www.rfc-editor.org/info/rfc8021>.

       [RFC8028]  Baker, F. and B. Carpenter, "First-Hop Router Selection by
                  Hosts in a Multi-Prefix Network", RFC 8028,
                  DOI 10.17487/RFC8028, November 2016,
                  <https://www.rfc-editor.org/info/rfc8028>.

       [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
                  Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
                  <https://www.rfc-editor.org/info/rfc8040>.

    Chown, et al.             Best Current Practice                [Page 30]

    RFC 8504                 IPv6 Node Requirements             January 2019

       [RFC8064]  Gont, F., Cooper, A., Thaler, D., and W. Liu,
                  "Recommendation on Stable IPv6 Interface Identifiers",
                  RFC 8064, DOI 10.17487/RFC8064, February 2017,
                  <https://www.rfc-editor.org/info/rfc8064>.

       [RFC8106]  Jeong, J., Park, S., Beloeil, L., and S. Madanapalli,
                  "IPv6 Router Advertisement Options for DNS Configuration",
                  RFC 8106, DOI 10.17487/RFC8106, March 2017,
                  <https://www.rfc-editor.org/info/rfc8106>.

       [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
                  2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
                  May 2017, <https://www.rfc-editor.org/info/rfc8174>.

       [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
                  (IPv6) Specification", STD 86, RFC 8200,
                  DOI 10.17487/RFC8200, July 2017,
                  <https://www.rfc-editor.org/info/rfc8200>.

       [RFC8201]  McCann, J., Deering, S., Mogul, J., and R. Hinden, Ed.,
                  "Path MTU Discovery for IP version 6", STD 87, RFC 8201,
                  DOI 10.17487/RFC8201, July 2017,
                  <https://www.rfc-editor.org/info/rfc8201>.

       [RFC8221]  Wouters, P., Migault, D., Mattsson, J., Nir, Y., and
                  T. Kivinen, "Cryptographic Algorithm Implementation
                  Requirements and Usage Guidance for Encapsulating Security
                  Payload (ESP) and Authentication Header (AH)", RFC 8221,
                  DOI 10.17487/RFC8221, October 2017,
                  <https://www.rfc-editor.org/info/rfc8221>.

       [RFC8247]  Nir, Y., Kivinen, T., Wouters, P., and D. Migault,
                  "Algorithm Implementation Requirements and Usage Guidance
                  for the Internet Key Exchange Protocol Version 2 (IKEv2)",
                  RFC 8247, DOI 10.17487/RFC8247, September 2017,
                  <https://www.rfc-editor.org/info/rfc8247>.

       [RFC8343]  Bjorklund, M., "A YANG Data Model for Interface
                  Management", RFC 8343, DOI 10.17487/RFC8343, March 2018,
                  <https://www.rfc-editor.org/info/rfc8343>.

       [RFC8344]  Bjorklund, M., "A YANG Data Model for IP Management",
                  RFC 8344, DOI 10.17487/RFC8344, March 2018,
                  <https://www.rfc-editor.org/info/rfc8344>.

    Chown, et al.             Best Current Practice                [Page 31]

    RFC 8504                 IPv6 Node Requirements             January 2019

    19.2.  Informative References

       [RFC793]   Postel, J., "Transmission Control Protocol", STD 7,
                  RFC 793, DOI 10.17487/RFC0793, September 1981,
                  <https://www.rfc-editor.org/info/rfc793>.

       [RFC2205]  Braden, R., Ed., Zhang, L., Berson, S., Herzog, S., and
                  S. Jamin, "Resource ReSerVation Protocol (RSVP) -- Version
                  1 Functional Specification", RFC 2205,
                  DOI 10.17487/RFC2205, September 1997,
                  <https://www.rfc-editor.org/info/rfc2205>.

       [RFC2464]  Crawford, M., "Transmission of IPv6 Packets over Ethernet
                  Networks", RFC 2464, DOI 10.17487/RFC2464, December 1998,
                  <https://www.rfc-editor.org/info/rfc2464>.

       [RFC2491]  Armitage, G., Schulter, P., Jork, M., and G. Harter, "IPv6
                  over Non-Broadcast Multiple Access (NBMA) networks",
                  RFC 2491, DOI 10.17487/RFC2491, January 1999,
                  <https://www.rfc-editor.org/info/rfc2491>.

       [RFC2590]  Conta, A., Malis, A., and M. Mueller, "Transmission of
                  IPv6 Packets over Frame Relay Networks Specification",
                  RFC 2590, DOI 10.17487/RFC2590, May 1999,
                  <https://www.rfc-editor.org/info/rfc2590>.

       [RFC2874]  Crawford, M. and C. Huitema, "DNS Extensions to Support
                  IPv6 Address Aggregation and Renumbering", RFC 2874,
                  DOI 10.17487/RFC2874, July 2000,
                  <https://www.rfc-editor.org/info/rfc2874>.

       [RFC2923]  Lahey, K., "TCP Problems with Path MTU Discovery",
                  RFC 2923, DOI 10.17487/RFC2923, September 2000,
                  <https://www.rfc-editor.org/info/rfc2923>.

       [RFC3146]  Fujisawa, K. and A. Onoe, "Transmission of IPv6 Packets
                  over IEEE 1394 Networks", RFC 3146, DOI 10.17487/RFC3146,
                  October 2001, <https://www.rfc-editor.org/info/rfc3146>.

       [RFC3363]  Bush, R., Durand, A., Fink, B., Gudmundsson, O., and
                  T. Hain, "Representing Internet Protocol version 6 (IPv6)
                  Addresses in the Domain Name System (DNS)", RFC 3363,
                  DOI 10.17487/RFC3363, August 2002,
                  <https://www.rfc-editor.org/info/rfc3363>.

    Chown, et al.             Best Current Practice                [Page 32]

    RFC 8504                 IPv6 Node Requirements             January 2019

       [RFC3493]  Gilligan, R., Thomson, S., Bound, J., McCann, J., and
                  W. Stevens, "Basic Socket Interface Extensions for IPv6",
                  RFC 3493, DOI 10.17487/RFC3493, February 2003,
                  <https://www.rfc-editor.org/info/rfc3493>.

       [RFC3542]  Stevens, W., Thomas, M., Nordmark, E., and T. Jinmei,
                  "Advanced Sockets Application Program Interface (API) for
                  IPv6", RFC 3542, DOI 10.17487/RFC3542, May 2003,
                  <https://www.rfc-editor.org/info/rfc3542>.

       [RFC3646]  Droms, R., Ed., "DNS Configuration options for Dynamic
                  Host Configuration Protocol for IPv6 (DHCPv6)", RFC 3646,
                  DOI 10.17487/RFC3646, December 2003,
                  <https://www.rfc-editor.org/info/rfc3646>.

       [RFC3678]  Thaler, D., Fenner, B., and B. Quinn, "Socket Interface
                  Extensions for Multicast Source Filters", RFC 3678,
                  DOI 10.17487/RFC3678, January 2004,
                  <https://www.rfc-editor.org/info/rfc3678>.

       [RFC3776]  Arkko, J., Devarapalli, V., and F. Dupont, "Using IPsec to
                  Protect Mobile IPv6 Signaling Between Mobile Nodes and
                  Home Agents", RFC 3776, DOI 10.17487/RFC3776, June 2004,
                  <https://www.rfc-editor.org/info/rfc3776>.

       [RFC3971]  Arkko, J., Ed., Kempf, J., Zill, B., and P. Nikander,
                  "SEcure Neighbor Discovery (SEND)", RFC 3971,
                  DOI 10.17487/RFC3971, March 2005,
                  <https://www.rfc-editor.org/info/rfc3971>.

       [RFC3972]  Aura, T., "Cryptographically Generated Addresses (CGA)",
                  RFC 3972, DOI 10.17487/RFC3972, March 2005,
                  <https://www.rfc-editor.org/info/rfc3972>.

       [RFC4191]  Draves, R. and D. Thaler, "Default Router Preferences and
                  More-Specific Routes", RFC 4191, DOI 10.17487/RFC4191,
                  November 2005, <https://www.rfc-editor.org/info/rfc4191>.

       [RFC4294]  Loughney, J., Ed., "IPv6 Node Requirements", RFC 4294,
                  DOI 10.17487/RFC4294, April 2006,
                  <https://www.rfc-editor.org/info/rfc4294>.

       [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
                  DOI 10.17487/RFC4302, December 2005,
                  <https://www.rfc-editor.org/info/rfc4302>.

    Chown, et al.             Best Current Practice                [Page 33]

    RFC 8504                 IPv6 Node Requirements             January 2019

       [RFC4338]  DeSanti, C., Carlson, C., and R. Nixon, "Transmission of
                  IPv6, IPv4, and Address Resolution Protocol (ARP) Packets
                  over Fibre Channel", RFC 4338, DOI 10.17487/RFC4338,
                  January 2006, <https://www.rfc-editor.org/info/rfc4338>.

       [RFC4380]  Huitema, C., "Teredo: Tunneling IPv6 over UDP through
                  Network Address Translations (NATs)", RFC 4380,
                  DOI 10.17487/RFC4380, February 2006,
                  <https://www.rfc-editor.org/info/rfc4380>.

       [RFC4429]  Moore, N., "Optimistic Duplicate Address Detection (DAD)
                  for IPv6", RFC 4429, DOI 10.17487/RFC4429, April 2006,
                  <https://www.rfc-editor.org/info/rfc4429>.

       [RFC4584]  Chakrabarti, S. and E. Nordmark, "Extension to Sockets API
                  for Mobile IPv6", RFC 4584, DOI 10.17487/RFC4584, July
                  2006, <https://www.rfc-editor.org/info/rfc4584>.

       [RFC4821]  Mathis, M. and J. Heffner, "Packetization Layer Path MTU
                  Discovery", RFC 4821, DOI 10.17487/RFC4821, March 2007,
                  <https://www.rfc-editor.org/info/rfc4821>.

       [RFC4877]  Devarapalli, V. and F. Dupont, "Mobile IPv6 Operation with
                  IKEv2 and the Revised IPsec Architecture", RFC 4877,
                  DOI 10.17487/RFC4877, April 2007,
                  <https://www.rfc-editor.org/info/rfc4877>.

       [RFC4884]  Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
                  "Extended ICMP to Support Multi-Part Messages", RFC 4884,
                  DOI 10.17487/RFC4884, April 2007,
                  <https://www.rfc-editor.org/info/rfc4884>.

       [RFC4890]  Davies, E. and J. Mohacsi, "Recommendations for Filtering
                  ICMPv6 Messages in Firewalls", RFC 4890,
                  DOI 10.17487/RFC4890, May 2007,
                  <https://www.rfc-editor.org/info/rfc4890>.

       [RFC4919]  Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
                  over Low-Power Wireless Personal Area Networks (6LoWPANs):
                  Overview, Assumptions, Problem Statement, and Goals",
                  RFC 4919, DOI 10.17487/RFC4919, August 2007,
                  <https://www.rfc-editor.org/info/rfc4919>.

       [RFC4944]  Montenegro, G., Kushalnagar, N., Hui, J., and D. Culler,
                  "Transmission of IPv6 Packets over IEEE 802.15.4
                  Networks", RFC 4944, DOI 10.17487/RFC4944, September 2007,
                  <https://www.rfc-editor.org/info/rfc4944>.

    Chown, et al.             Best Current Practice                [Page 34]

    RFC 8504                 IPv6 Node Requirements             January 2019

       [RFC5014]  Nordmark, E., Chakrabarti, S., and J. Laganier, "IPv6
                  Socket API for Source Address Selection", RFC 5014,
                  DOI 10.17487/RFC5014, September 2007,
                  <https://www.rfc-editor.org/info/rfc5014>.

       [RFC5072]  Varada, S., Ed., Haskins, D., and E. Allen, "IP Version 6
                  over PPP", RFC 5072, DOI 10.17487/RFC5072, September 2007,
                  <https://www.rfc-editor.org/info/rfc5072>.

       [RFC5121]  Patil, B., Xia, F., Sarikaya, B., Choi, JH., and
                  S. Madanapalli, "Transmission of IPv6 via the IPv6
                  Convergence Sublayer over IEEE 802.16 Networks", RFC 5121,
                  DOI 10.17487/RFC5121, February 2008,
                  <https://www.rfc-editor.org/info/rfc5121>.

       [RFC5555]  Soliman, H., Ed., "Mobile IPv6 Support for Dual Stack
                  Hosts and Routers", RFC 5555, DOI 10.17487/RFC5555, June
                  2009, <https://www.rfc-editor.org/info/rfc5555>.

       [RFC6275]  Perkins, C., Ed., Johnson, D., and J. Arkko, "Mobility
                  Support in IPv6", RFC 6275, DOI 10.17487/RFC6275, July
                  2011, <https://www.rfc-editor.org/info/rfc6275>.

       [RFC6563]  Jiang, S., Conrad, D., and B. Carpenter, "Moving A6 to
                  Historic Status", RFC 6563, DOI 10.17487/RFC6563, March
                  2012, <https://www.rfc-editor.org/info/rfc6563>.

       [RFC6980]  Gont, F., "Security Implications of IPv6 Fragmentation
                  with IPv6 Neighbor Discovery", RFC 6980,
                  DOI 10.17487/RFC6980, August 2013,
                  <https://www.rfc-editor.org/info/rfc6980>.

       [RFC7066]  Korhonen, J., Ed., Arkko, J., Ed., Savolainen, T., and S.
                  Krishnan, "IPv6 for Third Generation Partnership Project
                  (3GPP) Cellular Hosts", RFC 7066, DOI 10.17487/RFC7066,
                  November 2013, <https://www.rfc-editor.org/info/rfc7066>.

       [RFC7084]  Singh, H., Beebee, W., Donley, C., and B. Stark, "Basic
                  Requirements for IPv6 Customer Edge Routers", RFC 7084,
                  DOI 10.17487/RFC7084, November 2013,
                  <https://www.rfc-editor.org/info/rfc7084>.

       [RFC7123]  Gont, F. and W. Liu, "Security Implications of IPv6 on
                  IPv4 Networks", RFC 7123, DOI 10.17487/RFC7123, February
                  2014, <https://www.rfc-editor.org/info/rfc7123>.

    Chown, et al.             Best Current Practice                [Page 35]

    RFC 8504                 IPv6 Node Requirements             January 2019

       [RFC7278]  Byrne, C., Drown, D., and A. Vizdal, "Extending an IPv6
                  /64 Prefix from a Third Generation Partnership Project
                  (3GPP) Mobile Interface to a LAN Link", RFC 7278,
                  DOI 10.17487/RFC7278, June 2014,
                  <https://www.rfc-editor.org/info/rfc7278>.

       [RFC7371]  Boucadair, M. and S. Venaas, "Updates to the IPv6
                  Multicast Addressing Architecture", RFC 7371,
                  DOI 10.17487/RFC7371, September 2014,
                  <https://www.rfc-editor.org/info/rfc7371>.

       [RFC7421]  Carpenter, B., Ed., Chown, T., Gont, F., Jiang, S.,
                  Petrescu, A., and A. Yourtchenko, "Analysis of the 64-bit
                  Boundary in IPv6 Addressing", RFC 7421,
                  DOI 10.17487/RFC7421, January 2015,
                  <https://www.rfc-editor.org/info/rfc7421>.

       [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,
                  <https://www.rfc-editor.org/info/rfc7721>.

       [RFC7739]  Gont, F., "Security Implications of Predictable Fragment
                  Identification Values", RFC 7739, DOI 10.17487/RFC7739,
                  February 2016, <https://www.rfc-editor.org/info/rfc7739>.

       [RFC7772]  Yourtchenko, A. and L. Colitti, "Reducing Energy
                  Consumption of Router Advertisements", BCP 202, RFC 7772,
                  DOI 10.17487/RFC7772, February 2016,
                  <https://www.rfc-editor.org/info/rfc7772>.

       [RFC7844]  Huitema, C., Mrugalski, T., and S. Krishnan, "Anonymity
                  Profiles for DHCP Clients", RFC 7844,
                  DOI 10.17487/RFC7844, May 2016,
                  <https://www.rfc-editor.org/info/rfc7844>.

       [RFC7934]  Colitti, L., Cerf, V., Cheshire, S., and D. Schinazi,
                  "Host Address Availability Recommendations", BCP 204,
                  RFC 7934, DOI 10.17487/RFC7934, July 2016,
                  <https://www.rfc-editor.org/info/rfc7934>.

       [RFC8087]  Fairhurst, G. and M. Welzl, "The Benefits of Using
                  Explicit Congestion Notification (ECN)", RFC 8087,
                  DOI 10.17487/RFC8087, March 2017,
                  <https://www.rfc-editor.org/info/rfc8087>.

    Chown, et al.             Best Current Practice                [Page 36]

    RFC 8504                 IPv6 Node Requirements             January 2019

       [RFC8096]  Fenner, B., "The IPv6-Specific MIB Modules Are Obsolete",
                  RFC 8096, DOI 10.17487/RFC8096, April 2017,
                  <https://www.rfc-editor.org/info/rfc8096>.

       [RFC8273]  Brzozowski, J. and G. Van de Velde, "Unique IPv6 Prefix
                  per Host", RFC 8273, DOI 10.17487/RFC8273, December 2017,
                  <https://www.rfc-editor.org/info/rfc8273>.

       [POSIX]    IEEE, "Information Technology -- Portable Operating System
                  Interface (POSIX(R)) Base Specifications, Issue 7", IEEE
                  Std 1003.1-2017, DOI: 10.1109/IEEESTD.2018.8277153,
                  January 2018,
                  <https://ieeexplore.ieee.org/document/8277153>.

       [USGv6]    National Institute of Standards and Technology, "A Profile
                  for IPv6 in the U.S. Government - Version 1.0",
                  NIST SP500-267, July 2008,
                  <https://www.nist.gov/programs-projects/usgv6-program>.

    Chown, et al.             Best Current Practice                [Page 37]

    RFC 8504                 IPv6 Node Requirements             January 2019

    Appendix A.  Changes from RFC 6434

       There have been many editorial clarifications as well as significant
       additions and updates.  While this section highlights some of the
       changes, readers should not rely on this section for a comprehensive
       list of all changes.

       1.   Restructured sections.

       2.   Added 6LoWPAN to link layers as it has some deployment.

       3.   Removed the Downstream-on-Demand (DoD) IPv6 Profile as it hasn't
            been updated.

       4.   Updated MLDv2 support to a MUST since nodes are restricted if
            MLDv1 is used.

       5.   Required DNS RA options so SLAAC-only devices can get DNS; RFC
            8106 is a MUST.

       6.   Required RFC 3646 DNS Options for DHCPv6 implementations.

       7.   Added RESTCONF and NETCONF as possible options to network
            management.

       8.   Added a section on constrained devices.

       9.   Added text on RFC 7934 to address availability to hosts
            (SHOULD).

       10.  Added text on RFC 7844 for anonymity profiles for DHCPv6
            clients.

       11.  Added mDNS and DNS-SD as updated service discovery.

       12.  Added RFC 8028 as a SHOULD as a method for solving a multi-
            prefix network.

       13.  Added ECN RFC 3168 as a SHOULD.

       14.  Added reference to RFC 7123 for security over IPv4-only
            networks.

       15.  Removed Jumbograms (RFC 2675) as they aren't deployed.

       16.  Updated obsoleted RFCs to the new version of the RFC, including
            RFCs 2460, 1981, 7321, and 4307.

    Chown, et al.             Best Current Practice                [Page 38]

    RFC 8504                 IPv6 Node Requirements             January 2019

       17.  Added RFC 7772 for power consumptions considerations.

       18.  Added why /64 boundaries for more detail -- RFC 7421.

       19.  Added a unique IPv6 prefix per host to support currently
            deployed IPv6 networks.

       20.  Clarified RFC 7066 was a snapshot for 3GPP.

       21.  Updated RFC 4191 as a MUST and the Type C Host as a SHOULD as
            they help solve multi-prefix problems.

       22.  Removed IPv6 over ATM since there aren't many deployments.

       23.  Added a note in Section 6.6 for Rule 5.5 from RFC 6724.

       24.  Added MUST for BCP 198 for forwarding IPv6 packets.

       25.  Added a reference to RFC 8064 for stable address creation.

       26.  Added text on the protection from excessive extension header
            options.

       27.  Added text on the dangers of 1280 MTU UDP, especially with
            regard to DNS traffic.

       28.  Added text to clarify RFC 8200 behavior for unrecognized
            extension headers or unrecognized ULPs.

       29.  Removed dated email addresses from design team acknowledgements
            for [RFC4294].

    Appendix B.  Changes from RFC 4294 to RFC 6434

       There have been many editorial clarifications as well as significant
       additions and updates.  While this section highlights some of the
       changes, readers should not rely on this section for a comprehensive
       list of all changes.

       1.   Updated the Introduction to indicate that this document is an
            applicability statement and is aimed at general nodes.

       2.   Significantly updated the section on mobility protocols; added
            references and downgraded previous SHOULDs to MAYs.

       3.   Changed the Sub-IP Layer section to just list relevant RFCs, and
            added some more RFCs.

    Chown, et al.             Best Current Practice                [Page 39]

    RFC 8504                 IPv6 Node Requirements             January 2019

       4.   Added a section on SEND (it is a MAY).

       5.   Revised the section on Privacy Extensions [RFC4941] to add more
            nuance to the recommendation.

       6.   Completely revised the IPsec/IKEv2 section, downgrading the
            overall recommendation to a SHOULD.

       7.   Upgraded recommendation of DHCPv6 to a SHOULD.

       8.   Added a background section on DHCP versus RA options, added a
            SHOULD recommendation for DNS configuration via RAs (RFC 6106),
            and cleaned up the DHCP recommendations.

       9.   Added the recommendation that routers implement Sections 7.3 and
            7.5 of [RFC6275].

       10.  Added a pointer to subnet clarification document [RFC5942].

       11.  Added text that "IPv6 Host-to-Router Load Sharing" [RFC4311]
            SHOULD be implemented.

       12.  Added reference to [RFC5722] (Overlapping Fragments), and made
            it a MUST to implement.

       13.  Made "A Recommendation for IPv6 Address Text Representation"
            [RFC5952] a SHOULD.

       14.  Removed the mention of delegation name (DNAME) from the
            discussion about [RFC3363].

       15.  Numerous updates to reflect newer versions of IPv6 documents,
            including [RFC3596], [RFC4213], [RFC4291], and [RFC4443].

       16.  Removed discussion of "Managed" and "Other" flags in RAs.  There
            is no consensus at present on how to process these flags, and
            discussion of their semantics was removed in the most recent
            update of Stateless Address Autoconfiguration [RFC4862].

       17.  Added many more references to optional IPv6 documents.

       18.  Made "A Recommendation for IPv6 Address Text Representation"
            [RFC5952] a SHOULD.

       19.  Updated the MLD section to include reference to Lightweight MLD
            [RFC5790].

    Chown, et al.             Best Current Practice                [Page 40]

    RFC 8504                 IPv6 Node Requirements             January 2019

       20.  Added a SHOULD recommendation for "Default Router Preferences
            and More-Specific Routes" [RFC4191].

       21.  Made "IPv6 Flow Label Specification" [RFC6437] a SHOULD.

    Acknowledgments

       o  Acknowledgments (Current Document)

          The authors would like to thank Brian Carpenter, Dave Thaler, Tom
          Herbert, Erik Kline, Mohamed Boucadair, and Michayla Newcombe for
          their contributions and many members of the 6man WG for the inputs
          they gave.

       o  Authors and Acknowledgments from RFC 6434

          RFC 6434 was authored by Ed Jankiewicz, John Loughney, and Thomas
          Narten.

          The authors of RFC 6434 thank Hitoshi Asaeda, Brian Carpenter, Tim
          Chown, Ralph Droms, Sheila Frankel, Sam Hartman, Bob Hinden, Paul
          Hoffman, Pekka Savola, Yaron Sheffer, and Dave Thaler for their
          comments.  In addition, the authors thank Mark Andrews for
          comments and corrections on DNS text and Alfred Hoenes for
          tracking the updates to various RFCs.

       o  Authors and Acknowledgments from RFC 4294

          RFC 4294 was written by the IPv6 Node Requirements design team,
          which had the following members: Jari Arkko, Marc Blanchet, Samita
          Chakrabarti, Alain Durand, Gerard Gastaud, Jun-ichiro Itojun
          Hagino, Atsushi Inoue, Masahiro Ishiyama, John Loughney, Rajiv
          Raghunarayan, Shoichi Sakane, Dave Thaler, and Juha Wiljakka.

          The authors of RFC 4294 thank Ran Atkinson, Jim Bound, Brian
          Carpenter, Ralph Droms, Christian Huitema, Adam Machalek, Thomas
          Narten, Juha Ollila, and Pekka Savola for their comments.

    Chown, et al.             Best Current Practice                [Page 41]

    RFC 8504                 IPv6 Node Requirements             January 2019

    Authors' Addresses

       Tim Chown
       Jisc
       Lumen House, Library Avenue
       Harwell Oxford, Didcot  OX11 0SG
       United Kingdom

       Email: tim.chown@jisc.ac.uk

       John Loughney
       Intel
       Santa Clara, CA
       United States of America

       Email: john.loughney@gmail.com

       Timothy Winters
       University of New Hampshire, Interoperability Lab (UNH-IOL)
       Durham, NH
       United States of America

       Email: twinters@iol.unh.edu

    Chown, et al.             Best Current Practice                [Page 42]