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Internet IPv6 Maintenance IPv6 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 8504, and in turn RFC 6434 and its predecessor, RFC 4294. About This Document The latest revision of this draft can be found at . Status information for this document may be found at . Discussion of this document takes place on the IPv6 Maintenance Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

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 ). 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" .

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.

Description of IPv6 Nodes From "Internet Protocol, Version 6 (IPv6) Specification" , we have the following definitions:

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 when, and only when, they appear in all capitals, as shown here.

Abbreviations Used in This Document

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.

• Transmission of IPv6 Packets over Ethernet Networks
• Transmission of IPv6 Packets over Frame Relay Networks Specification
• Transmission of IPv6 Packets over IEEE 1394 Networks
• Transmission of IPv6, IPv4, and Address Resolution Protocol (ARP) Packets over Fibre Channel
• Transmission of IPv6 Packets over IEEE 802.15.4 Networks
• Transmission of IPv6 via the IPv6 Convergence Sublayer over IEEE 802.16 Networks
• IP version 6 over PPP

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

• Basic Transition Mechanisms for IPv6 Hosts and Routers (see )

IP Layer

Internet Protocol Version 6 - RFC 8200 The Internet Protocol version 6 is specified in . 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.

IPv6 Fragments 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 Section 4.5 of for more information. As recommended in Section 4.5 of , nodes MUST NOT generate atomic fragments, i.e., where the fragment is a whole datagram. As per , 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 .

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

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 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 due to security concerns and which MUST be treated as an unrecognized routing type. Further, 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. MUST be supported for processing IPv6 Hop-by-Hop options in IPv6 routers and hosts to allow for deployment of the option. 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 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 . For further background reading on this topic, see . allows for better visibility on EHs, including identifying root causes of performance degradation and packet drops.

Protecting a Node from Excessive Extension Header Options As per , 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 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.

Neighbor Discovery for IPv6 - RFC 4861 Neighbor Discovery is defined in ; the definition was updated by . 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 .

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. 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. 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. 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 , 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" includes additional recommendations on how to select from a set of available routers. SHOULD be supported.

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.

Path MTU Discovery and Packet Size

Path MTU Discovery - RFC 8201 The rules in and MUST be followed for packet fragmentation and reassembly. As described in , 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 . 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 ). An alternative to Path MTU Discovery defined in can be found in and , 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. A node MUST implement a PMTU discovery method and this MUST be enabled by default (see and for UDP Options), except in minimal IPv6 implementations.

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.

ICMP for the Internet Protocol Version 6 (IPv6) - RFC 4443 ICMPv6 MUST be supported. "Extended ICMP to Support Multi-Part Messages" MAY be supported.

Default Router Preferences and More-Specific Routes - RFC 4191 "Default Router Preferences and More-Specific Routes" 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 and MUST implement the Type C host role defined in RFC 4191.

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 deployed in multihomed environments MUST follow the guidance given in unless this is a constrained host.

Multicast Listener Discovery (MLD) for IPv6 - RFC 3810 Nodes that need to join multicast groups MUST support MLDv2 . 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 . Previous versions of this specification only required MLDv1 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, and deprecates the use of Any-Source Multicast (ASM) for interdomain multicast. Note that Neighbor Discovery (as used on most link types -- see ) depends on multicast and requires that nodes join Solicited Node multicast addresses.

Differentiated Services (Diffserv) The Differentiated Services (Diffserv) architecture, described in , and the definition of the Differentiated Services (DS) Field, specified in , define how the IPv6 Traffic Class field is used to classify and manage network traffic in order to provide different levels of service. Nodes SHOULD support Diffserv by implementing an interface for the upper layer, e.g. via an API, to set and access the Differentiated Services Code Point (DSCP) within the Traffic Class field.

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 by implementing an interface for the upper layer to access and by setting the ECN fields in the IP header. The benefits of using ECN are documented in .

Addressing and Address Configuration

IP Version 6 Addressing Architecture - RFC 4291 The IPv6 Addressing Architecture 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 . Implementations MUST also support the multicast flag updates documented in .

Host Address Availability Recommendations Hosts may be configured with addresses through a variety of methods, including Stateless Address Autoconfiguration (SLAAC), DHCPv6, or manual configuration. 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 for assigning multiple addresses to a host. A host SHOULD support assigning multiple addresses as described in . Nodes SHOULD support the capability to be assigned a prefix per host as documented in and . Routers SHOULD support the P flag in the Prefix Information Option where the network supports DHCPv6 prefix delegation, and hosts SHOULD process it, as specified in . Such an approach can offer improved host isolation, enhanced subscriber management, scalability, and ability to extend the network.

IPv6 Stateless Address Autoconfiguration - RFC 4862 Hosts MUST support IPv6 Stateless Address Autoconfiguration. It is RECOMMENDED, as described in , 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 to generate SLAAC-based addresses, rather than use . Addresses generated using the method described in 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 . 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 :

• 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].

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

Privacy Extensions for Address Configuration in IPv6 - RFC 8981 A node using Stateless Address Autoconfiguration 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, as that node moves around the network. Privacy Extensions for Stateless Address Autoconfiguration address this concern by allowing nodes to configure a 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 . RFC 8981 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 8981 can be used independently of traditional SLAAC or independently of SLAAC that is based on RFC 7217. Implementers of RFC 8981 should be aware that certain addresses are reserved and should not be chosen for use as temporary addresses. Consult "Reserved IPv6 Interface Identifiers" for more details.

Stateful Address Autoconfiguration (DHCPv6) - RFC 9915 DHCPv6 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 . 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 to minimize the disclosure of identifying information. describes operational considerations on the use of such anonymity profiles.

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 , as updated by , MUST be implemented.

Prefer IPv6-Only IPv6 nodes that support IPv6-only operation, as defined in , MAY forego obtaining an IPv4 address by using the IPv4 DHCP Option 108 specified in , if the node has provisions in place to support connecting to IPv4-only resources. A node without such provisions would be unable to reach IPv4-only resources.

DNS DNS is described in , , , and . 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 functionality, as in Section 5.3.1 of , with support for:

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AAAA type Resource Records ;

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reverse addressing in ip6.arpa using PTR records ; and

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Extension Mechanisms for DNS (EDNS(0)) to allow for DNS packet sizes larger than 512 octets; and

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Service Binding (SVCB) and HTTPS Resource Records , which convey transport parameters such as IPv6 hints for a service.

Those nodes are RECOMMENDED to support DNS security extensions . Discovery of encrypted DNS resolvers per SHOULD be implemented. A6 Resource Records are classified as Historic per . These were defined with Experimental status in . Nodes SHOULD support to perform local IPv6 address synthesis when in IPv6-only environments (see ). For a dual-stack node with addresses and routes configured for both IPv4 and IPv6, any IPv4-mapped IPv6 addresses encountered within the response of a DNS request nodes with the AAAA record MUST be discarded and returned as NXDOMAIN or the "ANY" record MUST be discarded. A IPv6-only node MUST NOT discard it if it's the only address within the response otherwise (when also a non IPv4-mapped IPv6-address is returned) the IPv4-mapped IPv6 address MUST be discarded.

Configuring Non-address Information

DHCP for Other Configuration Information DHCP specifies a mechanism for IPv6 nodes to obtain address configuration information (see ) 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 ) to obtain other configuration information. If an IPv6 node implements DHCP, it MUST implement the DNS options as most deployments will expect that these options are available.

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.

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 . Implementations MUST include support for the DNS RA option .

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.

Port Control Protocol (PCP) Hosts SHOULD support , Port Control Protocol , to allow an IPv6 host to control how incoming IPv6 packets are forwarded by simple firewalls on routers.

Service Discovery Protocols Multicast DNS (mDNS) and DNS-based Service Discovery (DNS-SD) are described in and , 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.

IPv4 Support and Transition IPv6 nodes MAY support IPv4.

Transition Mechanisms

Basic Transition Mechanisms for IPv6 Hosts and Routers - RFC 4213 If an IPv6 node implements dual stack and tunneling, then MUST be supported.

Support for discovery of translation prefixes describes a Neighbor Discovery option to be used in Router Advertisements (RAs) to communicate prefixes of Network Address and Protocol Translation from IPv6 clients to IPv4 servers (NAT64) to hosts. In order to support migration to and operation of IPv6-mostly and IPv6-only network environments, nodes SHOULD support discovery of NAT64 prefixes as described in . provides guidance on NAT64 prefix discovery.

Application Support

Textual Representation of IPv6 Addresses Software that allows users and operators to input IPv6 addresses in text form SHOULD support "A Recommendation for IPv6 Address Text Representation" . Such software SHOULD also support entering the zone identifier of an IPv6 scoped address as specified in .

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" 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) . "Advanced Sockets Application Program Interface (API) for IPv6" provides access to advanced IPv6 features needed by diagnostic and other more specialized applications. "IPv6 Socket API for Source Address Selection" provides facilities that allow an application to override the default Source Address Selection rules of . "Socket Interface Extensions for Multicast Source Filters" provides support for expressing source filters on multicast group memberships. "Extension to Sockets API for Mobile IPv6" provides application support for accessing and enabling Mobile IPv6 features.

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. 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 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., ). Currently, the recommended automated key-management protocol to implement is IKEv2 . 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 for guidance on this area.

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

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 . IPv6 nodes implementing the IPsec Architecture MUST conform to the requirements in . 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 . IPv6 nodes implementing IKEv2 MUST conform to the requirements in and/or any future updates or replacements to .

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, defines basic requirements for customer edge routers.

IPv6 Router Alert Option - RFC 2711 The IPv6 Router Alert option is an optional IPv6 Hop-by-Hop Header that is used in conjunction with some protocols (e.g., RSVP or Multicast Listener Discovery (MLDv2) ). The Router Alert option will need to be implemented whenever such protocols that mandate its use are implemented. See . The Router Alert option has been deprecated for use by new protocols, per .

Neighbor Discovery for IPv6 - RFC 4861 Sending Router Advertisements and processing Router Solicitations MUST be supported. Routers SHOULD support to avoid packet loss. 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.

Stateful Address Autoconfiguration (DHCPv6) - RFC 9915 A single DHCP server ( or ) 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., ). 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, prefixes for delegation, 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 including support for DHCPv6-PD as defined in . Note that "Basic Requirements for IPv6 Customer Edge Routers" requires implementation of a DHCPv6 server function in IPv6 Customer Edge (CE) routers.

IPv6 Prefix Length Recommendation for Forwarding - BCP 198 Forwarding nodes MUST conform to BCP 198 ; thus, IPv6 implementations of nodes that may forward packets MUST conform to the rules specified in .

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 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 (the means by which IPv6 packets are transmitted over IEEE 802.15.4 networks and ND optimizations for that medium ). IPv6 nodes that are battery powered SHOULD implement the recommendations in .

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 , NETCONF , and RESTCONF .

Management Information Base (MIB) Modules The obsoleted status of various IPv6-specific MIB modules is clarified in . The following two MIB modules SHOULD be supported by nodes that support an SNMP agent.

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

Management Information Base for the Internet Protocol (IP) The IP MIB SHOULD be supported by nodes that support an SNMP agent.

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

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

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

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

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 above.

IANA Considerations This document has no IANA actions.

References Normative References This RFC is the revised basic definition of The Domain Name System. It obsoletes RFC-882. This memo describes the domain style names and their used for host address look up and electronic mail forwarding. It discusses the clients and servers in the domain name system and the protocol used between them. This RFC is the revised specification of the protocol and format used in the implementation of the Domain Name System. It obsoletes RFC-883. This memo documents the details of the domain name client - server communication. This document defines the IP header field, called the DS (for differentiated services) field. [STANDARDS-TRACK] This document defines an architecture for implementing scalable service differentiation in the Internet. This memo provides information for the Internet community. This document specifies the protocol used by an IPv6 router to discover the presence of multicast listeners (that is, nodes wishing to receive multicast packets) on its directly attached links, and to discover specifically which multicast addresses are of interest to those neighboring nodes. [STANDARDS-TRACK] This memo describes a new IPv6 Hop-by-Hop Option type that alerts transit routers to more closely examine the contents of an IP datagram. [STANDARDS-TRACK] This memo discusses the 'interfaces' group of MIB-II, especially the experience gained from the definition of numerous media-specific MIB modules for use in conjunction with the 'interfaces' group for managing various sub-layers beneath the internetwork-layer. It specifies clarifications to, and extensions of, the architectural issues within the MIB-II model of the 'interfaces' group. [STANDARDS-TRACK] This memo specifies the incorporation of ECN (Explicit Congestion Notification) to TCP and IP, including ECN's use of two bits in the IP header. [STANDARDS-TRACK] This document describes an architecture for describing Simple Network Management Protocol (SNMP) Management Frameworks. The architecture is designed to be modular to allow the evolution of the SNMP protocol standards over time. The major portions of the architecture are an SNMP engine containing a Message Processing Subsystem, a Security Subsystem and an Access Control Subsystem, and possibly multiple SNMP applications which provide specific functional processing of management data. This document obsoletes RFC 2571. [STANDARDS-TRACK] This document defines the changes that need to be made to the Domain Name System (DNS) to support hosts running IP version 6 (IPv6). The changes include a resource record type to store an IPv6 address, a domain to support lookups based on an IPv6 address, and updated definitions of existing query types that return Internet addresses as part of additional section processing. The extensions are designed to be compatible with existing applications and, in particular, DNS implementations themselves. [STANDARDS-TRACK] This document updates RFC 2710, and it specifies Version 2 of the ulticast Listener Discovery Protocol (MLDv2). MLD is used by an IPv6 router to discover the presence of multicast listeners on directly attached links, and to discover which multicast addresses are of interest to those neighboring nodes. MLDv2 is designed to be interoperable with MLDv1. MLDv2 adds the ability for a node to report interest in listening to packets with a particular multicast address only from specific source addresses or from all sources except for specific source addresses. [STANDARDS-TRACK] The Domain Name System Security Extensions (DNSSEC) add data origin authentication and data integrity to the Domain Name System. This document introduces these extensions and describes their capabilities and limitations. This document also discusses the services that the DNS security extensions do and do not provide. Last, this document describes the interrelationships between the documents that collectively describe DNSSEC. [STANDARDS-TRACK] This document is part of a family of documents that describe the DNS Security Extensions (DNSSEC). The DNS Security Extensions are a collection of resource records and protocol modifications that provide source authentication for the DNS. This document defines the public key (DNSKEY), delegation signer (DS), resource record digital signature (RRSIG), and authenticated denial of existence (NSEC) resource records. The purpose and format of each resource record is described in detail, and an example of each resource record is given. This document obsoletes RFC 2535 and incorporates changes from all updates to RFC 2535. [STANDARDS-TRACK] This document is part of a family of documents that describe the DNS Security Extensions (DNSSEC). The DNS Security Extensions are a collection of new resource records and protocol modifications that add data origin authentication and data integrity to the DNS. This document describes the DNSSEC protocol modifications. This document defines the concept of a signed zone, along with the requirements for serving and resolving by using DNSSEC. These techniques allow a security-aware resolver to authenticate both DNS resource records and authoritative DNS error indications. This document obsoletes RFC 2535 and incorporates changes from all updates to RFC 2535. [STANDARDS-TRACK] This document specifies IPv4 compatibility mechanisms that can be implemented by IPv6 hosts and routers. Two mechanisms are specified, dual stack and configured tunneling. Dual stack implies providing complete implementations of both versions of the Internet Protocol (IPv4 and IPv6), and configured tunneling provides a means to carry IPv6 packets over unmodified IPv4 routing infrastructures. This document obsoletes RFC 2893. [STANDARDS-TRACK] This specification defines the addressing architecture of the IP Version 6 (IPv6) protocol. The document includes the IPv6 addressing model, text representations of IPv6 addresses, definition of IPv6 unicast addresses, anycast addresses, and multicast addresses, and an IPv6 node's required addresses. This document obsoletes RFC 3513, "IP Version 6 Addressing Architecture". [STANDARDS-TRACK] This document defines a portion of the Management Information Base (MIB) for use with network management protocols in the Internet community. In particular, it describes managed objects related to the forwarding of Internet Protocol (IP) packets in an IP version-independent manner. This document obsoletes RFC 2096. [STANDARDS-TRACK] This memo defines a portion of the Management Information Base (MIB) for use with network management protocols in the Internet community. In particular, it describes managed objects used for implementations of the Internet Protocol (IP) in an IP version independent manner. This memo obsoletes RFCs 2011, 2465, and 2466. [STANDARDS-TRACK] This document describes an updated version of the "Security Architecture for IP", which is designed to provide security services for traffic at the IP layer. This document obsoletes RFC 2401 (November 1998). [STANDARDS-TRACK] This document describes an updated version of the Encapsulating Security Payload (ESP) protocol, which is designed to provide a mix of security services in IPv4 and IPv6. ESP is used to provide confidentiality, data origin authentication, connectionless integrity, an anti-replay service (a form of partial sequence integrity), and limited traffic flow confidentiality. This document obsoletes RFC 2406 (November 1998). [STANDARDS-TRACK] The original IPv6 conceptual sending algorithm does not do load sharing among equivalent IPv6 routers, and suggests schemes that can be problematic in practice. This document updates the conceptual sending algorithm in RFC 2461 so that traffic to different destinations can be distributed among routers in an efficient fashion. [STANDARDS-TRACK] This document describes the format of a set of control messages used in ICMPv6 (Internet Control Message Protocol). ICMPv6 is the Internet Control Message Protocol for Internet Protocol version 6 (IPv6). [STANDARDS-TRACK] IP version 4 (IPv4) addresses in the 232/8 (232.0.0.0 to 232.255.255.255) range are designated as source-specific multicast (SSM) destination addresses and are reserved for use by source-specific applications and protocols. For IP version 6 (IPv6), the address prefix FF3x::/32 is reserved for source-specific multicast use. This document defines an extension to the Internet network service that applies to datagrams sent to SSM addresses and defines the host and router requirements to support this extension. [STANDARDS-TRACK] This memo discusses the strategy for address assignment of the existing 32-bit IPv4 address space with a view toward conserving the address space and limiting the growth rate of global routing state. This document obsoletes the original Classless Inter-domain Routing (CIDR) spec in RFC 1519, with changes made both to clarify the concepts it introduced and, after more than twelve years, to update the Internet community on the results of deploying the technology described. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document specifies the Neighbor Discovery protocol for IP Version 6. IPv6 nodes on the same link use Neighbor Discovery to discover each other's presence, to determine each other's link-layer addresses, to find routers, and to maintain reachability information about the paths to active neighbors. [STANDARDS-TRACK] This document specifies the steps a host takes in deciding how to autoconfigure its interfaces in IP version 6. The autoconfiguration process includes generating a link-local address, generating global addresses via stateless address autoconfiguration, and the Duplicate Address Detection procedure to verify the uniqueness of the addresses on a link. [STANDARDS-TRACK] The functionality provided by IPv6's Type 0 Routing Header can be exploited in order to achieve traffic amplification over a remote path for the purposes of generating denial-of-service traffic. This document updates the IPv6 specification to deprecate the use of IPv6 Type 0 Routing Headers, in light of this security concern. [STANDARDS-TRACK] Interface identifiers in IPv6 unicast addresses are used to identify interfaces on a link. They are required to be unique within a subnet. Several RFCs have specified interface identifiers or identifier ranges that have a special meaning attached to them. An IPv6 node autoconfiguring an interface identifier in these ranges will encounter unexpected consequences. Since there is no centralized repository for such reserved identifiers, this document aims to create one. [STANDARDS-TRACK] The fragmentation and reassembly algorithm specified in the base IPv6 specification allows fragments to overlap. This document demonstrates the security issues associated with allowing overlapping fragments and updates the IPv6 specification to explicitly forbid overlapping fragments. [STANDARDS-TRACK] This document describes lightweight IGMPv3 and MLDv2 protocols (LW- IGMPv3 and LW-MLDv2), which simplify the standard (full) versions of IGMPv3 and MLDv2. The interoperability with the full versions and the previous versions of IGMP and MLD is also taken into account. [STANDARDS-TRACK] IPv6 specifies a model of a subnet that is different than the IPv4 subnet model. The subtlety of the differences has resulted in incorrect implementations that do not interoperate. This document spells out the most important difference: that an IPv6 address isn't automatically associated with an IPv6 on-link prefix. This document also updates (partially due to security concerns caused by incorrect implementations) a part of the definition of "on-link" from RFC 4861. [STANDARDS-TRACK] As IPv6 deployment increases, there will be a dramatic increase in the need to use IPv6 addresses in text. While the IPv6 address architecture in Section 2.2 of RFC 4291 describes a flexible model for text representation of an IPv6 address, this flexibility has been causing problems for operators, system engineers, and users. This document defines a canonical textual representation format. It does not define a format for internal storage, such as within an application or database. It is expected that the canonical format will be followed by humans and systems when representing IPv6 addresses as text, but all implementations must accept and be able to handle any legitimate RFC 4291 format. [STANDARDS-TRACK] The Network Configuration Protocol (NETCONF) defined in this document provides mechanisms to install, manipulate, and delete the configuration of network devices. It uses an Extensible Markup Language (XML)-based data encoding for the configuration data as well as the protocol messages. The NETCONF protocol operations are realized as remote procedure calls (RPCs). This document obsoletes RFC 4741. [STANDARDS-TRACK] This document specifies the IPv6 Flow Label field and the minimum requirements for IPv6 nodes labeling flows, IPv6 nodes forwarding labeled packets, and flow state establishment methods. Even when mentioned as examples of possible uses of the flow labeling, more detailed requirements for specific use cases are out of the scope for this document. The usage of the Flow Label field enables efficient IPv6 flow classification based only on IPv6 main header fields in fixed positions. [STANDARDS-TRACK] In IPv6, optional internet-layer information is encoded in separate headers that may be placed between the IPv6 header and the transport-layer header. There are a small number of such extension headers currently defined. This document describes the issues that can arise when defining new extension headers and discusses the alternate extension mechanisms in IPv6. It also provides a common format for defining any new IPv6 extension headers, if they are needed. [STANDARDS-TRACK] This document describes two algorithms, one for source address selection and one for destination address selection. The algorithms specify default behavior for all Internet Protocol version 6 (IPv6) implementations. They do not override choices made by applications or upper-layer protocols, nor do they preclude the development of more advanced mechanisms for address selection. The two algorithms share a common context, including an optional mechanism for allowing administrators to provide policy that can override the default behavior. In dual-stack implementations, the destination address selection algorithm can consider both IPv4 and IPv6 addresses -- depending on the available source addresses, the algorithm might prefer IPv6 addresses over IPv4 addresses, or vice versa. Default address selection as defined in this specification applies to all IPv6 nodes, including both hosts and routers. This document obsoletes RFC 3484. [STANDARDS-TRACK] As networked devices become smaller, more portable, and more ubiquitous, the ability to operate with less configured infrastructure is increasingly important. In particular, the ability to look up DNS resource record data types (including, but not limited to, host names) in the absence of a conventional managed DNS server is useful. Multicast DNS (mDNS) provides the ability to perform DNS-like operations on the local link in the absence of any conventional Unicast DNS server. In addition, Multicast DNS designates a portion of the DNS namespace to be free for local use, without the need to pay any annual fee, and without the need to set up delegations or otherwise configure a conventional DNS server to answer for those names. The primary benefits of Multicast DNS names are that (i) they require little or no administration or configuration to set them up, (ii) they work when no infrastructure is present, and (iii) they work during infrastructure failures. This document specifies how DNS resource records are named and structured to facilitate service discovery. Given a type of service that a client is looking for, and a domain in which the client is looking for that service, this mechanism allows clients to discover a list of named instances of that desired service, using standard DNS queries. This mechanism is referred to as DNS-based Service Discovery, or DNS-SD. The IETF work in IPv6 over Low-power Wireless Personal Area Network (6LoWPAN) defines 6LoWPANs such as IEEE 802.15.4. This and other similar link technologies have limited or no usage of multicast signaling due to energy conservation. In addition, the wireless network may not strictly follow the traditional concept of IP subnets and IP links. IPv6 Neighbor Discovery was not designed for non- transitive wireless links, as its reliance on the traditional IPv6 link concept and its heavy use of multicast make it inefficient and sometimes impractical in a low-power and lossy network. This document describes simple optimizations to IPv6 Neighbor Discovery, its addressing mechanisms, and duplicate address detection for Low- power Wireless Personal Area Networks and similar networks. The document thus updates RFC 4944 to specify the use of the optimizations defined here. [STANDARDS-TRACK] The Port Control Protocol allows an IPv6 or IPv4 host to control how incoming IPv6 or IPv4 packets are translated and forwarded by a Network Address Translator (NAT) or simple firewall, and also allows a host to optimize its outgoing NAT keepalive messages. The Domain Name System's wire protocol includes a number of fixed fields whose range has been or soon will be exhausted and does not allow requestors to advertise their capabilities to responders. This document describes backward-compatible mechanisms for allowing the protocol to grow. This document updates the Extension Mechanisms for DNS (EDNS(0)) specification (and obsoletes RFC 2671) based on feedback from deployment experience in several implementations. It also obsoletes RFC 2673 ("Binary Labels in the Domain Name System") and adds considerations on the use of extended labels in the DNS. The IPv6 specification allows packets to contain a Fragment Header without the packet being actually fragmented into multiple pieces (we refer to these packets as "atomic fragments"). Such packets are typically sent by hosts that have received an ICMPv6 "Packet Too Big" error message that advertises a Next-Hop MTU smaller than 1280 bytes, and are currently processed by some implementations as normal "fragmented traffic" (i.e., they are "reassembled" with any other queued fragments that supposedly correspond to the same original packet). Thus, an attacker can cause hosts to employ atomic fragments by forging ICMPv6 "Packet Too Big" error messages, and then launch any fragmentation-based attacks against such traffic. This document discusses the generation of the aforementioned atomic fragments and the corresponding security implications. Additionally, this document formally updates RFC 2460 and RFC 5722, such that IPv6 atomic fragments are processed independently of any other fragments, thus completely eliminating the aforementioned attack vector. Various IPv6 extension headers have been standardised since the IPv6 standard was first published. This document updates RFC 2460 to clarify how intermediate nodes should deal with such extension headers and with any that are defined in the future. It also specifies how extension headers should be registered by IANA, with a corresponding minor update to RFC 2780. IPv6 Neighbor Discovery includes Neighbor Unreachability Detection. That function is very useful when a host has an alternative neighbor -- for instance, when there are multiple default routers -- since it allows the host to switch to the alternative neighbor in a short time. By default, this time is 3 seconds after the node starts probing. However, if there are no alternative neighbors, this timeout behavior is far too impatient. This document specifies relaxed rules for Neighbor Discovery retransmissions that allow an implementation to choose different timeout behavior based on whether or not there are alternative neighbors. This document updates RFC 4861. The IPv6 specification allows IPv6 Header Chains of an arbitrary size. The specification also allows options that can, in turn, extend each of the headers. In those scenarios in which the IPv6 Header Chain or options are unusually long and packets are fragmented, or scenarios in which the fragment size is very small, the First Fragment of a packet may fail to include the entire IPv6 Header Chain. This document discusses the interoperability and security problems of such traffic, and updates RFC 2460 such that the First Fragment of a packet is required to contain the entire IPv6 Header Chain. This document specifies a method for generating IPv6 Interface Identifiers to be used with IPv6 Stateless Address Autoconfiguration (SLAAC), such that an IPv6 address configured using this method is stable within each subnet, but the corresponding Interface Identifier changes when the host moves from one network to another. This method is meant to be an alternative to generating Interface Identifiers based on hardware addresses (e.g., IEEE LAN Media Access Control (MAC) addresses), such that the benefits of stable addresses can be achieved without sacrificing the security and privacy of users. The method specified in this document applies to all prefixes a host may be employing, including link-local, global, and unique-local prefixes (and their corresponding addresses). This document describes version 2 of the Internet Key Exchange (IKE) protocol. IKE is a component of IPsec used for performing mutual authentication and establishing and maintaining Security Associations (SAs). This document obsoletes RFC 5996, and includes all of the errata for it. It advances IKEv2 to be an Internet Standard. IPv6 Loopback Suppression and Duplicate Address Detection (DAD) are discussed in Appendix A of RFC 4862. That specification mentions a hardware-assisted mechanism to detect looped back DAD messages. If hardware cannot suppress looped back DAD messages, a software solution is required. Several service provider communities have expressed a need for automated detection of looped back Neighbor Discovery (ND) messages used by DAD. This document includes mitigation techniques and outlines the Enhanced DAD algorithm to automate the detection of looped back IPv6 ND messages used by DAD. For network loopback tests, the Enhanced DAD algorithm allows IPv6 to self-heal after a loopback is placed and removed. Further, for certain access networks, this document automates resolving a specific duplicate address conflict. This document updates RFCs 4429, 4861, and 4862. When an interface on a host is initialized, the host transmits Router Solicitations in order to minimize the amount of time it needs to wait until the next unsolicited multicast Router Advertisement is received. In certain scenarios, these Router Solicitations transmitted by the host might be lost. This document specifies a mechanism for hosts to cope with the loss of the initial Router Solicitations. IPv6 prefix length, as in IPv4, is a parameter conveyed and used in IPv6 routing and forwarding processes in accordance with the Classless Inter-domain Routing (CIDR) architecture. The length of an IPv6 prefix may be any number from zero to 128, although subnets using stateless address autoconfiguration (SLAAC) for address allocation conventionally use a /64 prefix. Hardware and software implementations of routing and forwarding should therefore impose no rules on prefix length, but implement longest-match-first on prefixes of any valid length. This document describes expected IPv6 host behavior in a scenario that has more than one prefix, each allocated by an upstream network that is assumed to implement BCP 38 ingress filtering, when the host has multiple routers to choose from. It also applies to other scenarios such as the usage of stateful firewalls that effectively act as address-based filters. Host behavior in choosing a first-hop router may interact with source address selection in a given implementation. However, the selection of the source address for a packet is done before the first-hop router for that packet is chosen. Given that the network or host is, or appears to be, multihomed with multiple provider-allocated addresses, that the host has elected to use a source address in a given prefix, and that some but not all neighboring routers are advertising that prefix in their Router Advertisement Prefix Information Options, this document specifies to which router a host should present its transmission. It updates RFC 4861. This document describes an HTTP-based protocol that provides a programmatic interface for accessing data defined in YANG, using the datastore concepts defined in the Network Configuration Protocol (NETCONF). This document changes the recommended default Interface Identifier (IID) generation scheme for cases where Stateless Address Autoconfiguration (SLAAC) is used to generate a stable IPv6 address. It recommends using the mechanism specified in RFC 7217 in such cases, and recommends against embedding stable link-layer addresses in IPv6 IIDs. It formally updates RFC 2464, RFC 2467, RFC 2470, RFC 2491, RFC 2492, RFC 2497, RFC 2590, RFC 3146, RFC 3572, RFC 4291, RFC 4338, RFC 4391, RFC 5072, and RFC 5121. This document does not change any existing recommendations concerning the use of temporary addresses as specified in RFC 4941. This document specifies IPv6 Router Advertisement (RA) options (called "DNS RA options") to allow IPv6 routers to advertise a list of DNS Recursive Server Addresses and a DNS Search List to IPv6 hosts. This document, which obsoletes RFC 6106, defines a higher default value of the lifetime of the DNS RA options to reduce the likelihood of expiry of the options on links with a relatively high rate of packet loss. This document specifies version 6 of the Internet Protocol (IPv6). It obsoletes RFC 2460. This document describes Path MTU Discovery (PMTUD) for IP version 6. It is largely derived from RFC 1191, which describes Path MTU Discovery for IP version 4. It obsoletes RFC 1981. This document replaces RFC 7321, "Cryptographic Algorithm Implementation Requirements and Usage Guidance for Encapsulating Security Payload (ESP) and Authentication Header (AH)". The goal of this document is to enable ESP and AH to benefit from cryptography that is up to date while making IPsec interoperable. The IPsec series of protocols makes use of various cryptographic algorithms in order to provide security services. The Internet Key Exchange (IKE) protocol is used to negotiate the IPsec Security Association (IPsec SA) parameters, such as which algorithms should be used. To ensure interoperability between different implementations, it is necessary to specify a set of algorithm implementation requirements and usage guidance to ensure that there is at least one algorithm that all implementations support. This document updates RFC 7296 and obsoletes RFC 4307 in defining the current algorithm implementation requirements and usage guidance for IKEv2, and does minor cleaning up of the IKEv2 IANA registry. This document does not update the algorithms used for packet encryption using IPsec Encapsulating Security Payload (ESP). This document defines a YANG data model for the management of network interfaces. It is expected that interface-type-specific data models augment the generic interfaces data model defined in this document. The data model includes definitions for configuration and system state (status information and counters for the collection of statistics). The YANG data model in this document conforms to the Network Management Datastore Architecture (NMDA) defined in RFC 8342. This document obsoletes RFC 7223. This document defines a YANG data model for management of IP implementations. The data model includes configuration and system state. The YANG data model in this document conforms to the Network Management Datastore Architecture defined in RFC 8342. This document obsoletes RFC 7277. This document specifies a Neighbor Discovery option to be used in Router Advertisements (RAs) to communicate prefixes of Network Address and Protocol Translation from IPv6 clients to IPv4 servers (NAT64) to hosts. This document recommends deprecation of the use of Any-Source Multicast (ASM) for interdomain multicast. It recommends the use of Source-Specific Multicast (SSM) for interdomain multicast applications and recommends that hosts and routers in these deployments fully support SSM. The recommendations in this document do not preclude the continued use of ASM within a single organization or domain and are especially easy to adopt in existing deployments of intradomain ASM using PIM Sparse Mode (PIM-SM). This document specifies Datagram Packetization Layer Path MTU Discovery (DPLPMTUD). This is a robust method for Path MTU Discovery (PMTUD) for datagram Packetization Layers (PLs). It allows a PL, or a datagram application that uses a PL, to discover whether a network path can support the current size of datagram. This can be used to detect and reduce the message size when a sender encounters a packet black hole. It can also probe a network path to discover whether the maximum packet size can be increased. This provides functionality for datagram transports that is equivalent to the PLPMTUD specification for TCP, specified in RFC 4821, which it updates. It also updates the UDP Usage Guidelines to refer to this method for use with UDP datagrams and updates SCTP. The document provides implementation notes for incorporating Datagram PMTUD into IETF datagram transports or applications that use datagram transports. This specification updates RFC 4960, RFC 4821, RFC 6951, RFC 8085, and RFC 8261. This document specifies a DHCPv4 option to indicate that a host supports an IPv6-only mode and is willing to forgo obtaining an IPv4 address if the network provides IPv6 connectivity. It also updates RFC 2563 to specify DHCPv4 server behavior when the server receives a DHCPDISCOVER not containing the Auto-Configure option but containing the new option defined in this document. This document describes an extension to IPv6 Stateless Address Autoconfiguration that causes hosts to generate temporary addresses with randomized interface identifiers for each prefix advertised with autoconfiguration enabled. Changing addresses over time limits the window of time during which eavesdroppers and other information collectors may trivially perform address-based network-activity correlation when the same address is employed for multiple transactions by the same host. Additionally, it reduces the window of exposure of a host as being accessible via an address that becomes revealed as a result of active communication. This document obsoletes RFC 4941. Neighbor Discovery (RFC 4861) is used by IPv6 nodes to determine the link-layer addresses of neighboring nodes as well as to discover and maintain reachability information. This document updates RFC 4861 to allow routers to proactively create a Neighbor Cache entry when a new IPv6 address is assigned to a node. It also updates RFC 4861 and recommends that nodes send unsolicited Neighbor Advertisements upon assigning a new IPv6 address. These changes will minimize the delay and packet loss when a node initiates connections to an off-link destination from a new IPv6 address. This document specifies the "SVCB" ("Service Binding") and "HTTPS" DNS resource record (RR) types to facilitate the lookup of information needed to make connections to network services, such as for HTTP origins. SVCB records allow a service to be provided from multiple alternative endpoints, each with associated parameters (such as transport protocol configuration), and are extensible to support future uses (such as keys for encrypting the TLS ClientHello). They also enable aliasing of apex domains, which is not possible with CNAME. The HTTPS RR is a variation of SVCB for use with HTTP (see RFC 9110, "HTTP Semantics"). By providing more information to the client before it attempts to establish a connection, these records offer potential benefits to both performance and privacy. This document specifies new DHCP and IPv6 Router Advertisement options to discover encrypted DNS resolvers (e.g., DNS over HTTPS, DNS over TLS, and DNS over QUIC). Particularly, it allows a host to learn an Authentication Domain Name together with a list of IP addresses and a set of service parameters to reach such encrypted DNS resolvers. This document specifies procedures for processing IPv6 Hop-by-Hop options in IPv6 routers and hosts. It modifies the procedures specified in the IPv6 Protocol Specification (RFC 8200) to make processing of the IPv6 Hop-by-Hop Options header practical with the goal of making IPv6 Hop-by-Hop options useful to deploy and use at IPv6 routers and hosts. This document updates RFC 8200. This document specifies new IP Flow Information Export (IPFIX) Information Elements (IEs) to solve issues with existing ipv6ExtensionHeaders and tcpOptions IPFIX IEs, especially the ability to export any observed IPv6 extension headers or TCP options. This document defines the P flag in the Prefix Information Option (PIO) of IPv6 Router Advertisements (RAs). The flag is used to indicate that the network prefers that clients use the deployment model in RFC 9663 instead of using individual addresses in the on-link prefix assigned using Stateless Address Autoconfiguration (SLAAC) or DHCPv6 address assignment. This document updates RFC 4862 to indicate that the Autonomous flag in a PIO needs to be ignored if the PIO has the P flag set. It also updates RFC 4861 to specify that the P flag indicates DHCPv6 prefix delegation support for clients. This document describes how the zone identifier of an IPv6 scoped address, defined in the IPv6 Scoped Address Architecture specification (RFC 4007), should be entered into a user interface. This document obsoletes RFC 6874 and updates RFCs 4007, 7622, and 8089. This document specifies how a UDP Options sender implements Datagram Packetization Layer Path MTU Discovery (DPLPMTUD) as a robust method for Path MTU Discovery (PMTUD). This method uses the UDP Options packetization layer. It allows an application to discover the largest size of datagram that can be sent across a network path. It also provides a way to allow the application to periodically verify the current Maximum Packet Size (MPS) supported by a path and to update this when required. This document specifies the Dynamic Host Configuration Protocol for IPv6 (DHCPv6), an extensible mechanism for configuring nodes with network configuration parameters, IP addresses, and prefixes. Parameters can be provided statelessly or in combination with stateful assignment of one or more IPv6 addresses and/or IPv6 prefixes. DHCPv6 can operate either in place of or in addition to stateless address autoconfiguration (SLAAC). This document obsoletes RFC 8415. It incorporates verified errata and obsoletes the assignment of temporary addresses (the IA_TA option) and the server unicast capability (the Server Unicast option and UseMulticast status code). Energy Sciences Network Jisc Tachyon Dynamics This document updates the default address selection algorithm for Internet Protocol Version 6 (IPv6), originally specified in RFC 6724, based on accumulated operational experience. It introduces the concept of "known-local" Unique Local Address (ULA) prefixes within the fd00::/8 block and specifies that ULA-to-ULA communications using such prefixes should be preferred over both IPv4-to-IPv4 and GUA-to- GUA (Global Unicast Address) communications in local use scenarios. The document defines mechanisms for nodes to identify and incorporate known-local prefixes into their address selection policy tables. It introduces a requirement to implement Rule 5.5 of RFC 6724 and reduces the default precedence for 6to4 addresses. These updates enhance the supportability of typical deployment environments, including automatic and unmanaged configurations, and promote consistent IPv6-over-IPv4 precedence behavior for both ULA and GUA within local networks. The document acknowledges that certain atypical deployment models may require explicit configuration to achieve intended operational outcomes. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References This memo describes version 1 of RSVP, a resource reservation setup protocol designed for an integrated services Internet. RSVP provides receiver-initiated setup of resource reservations for multicast or unicast data flows, with good scaling and robustness properties. [STANDARDS-TRACK] This document specifies the frame format for transmission of IPv6 packets and the method of forming IPv6 link-local addresses and statelessly autoconfigured addresses on Ethernet networks. It also specifies the content of the Source/Target Link-layer Address option used in Router Solicitation, Router Advertisement, Neighbor Solicitation, Neighbor Advertisement and Redirect messages when those messages are transmitted on an Ethernet. [STANDARDS-TRACK] This document describes a general architecture for IPv6 over NBMA networks. [STANDARDS-TRACK] This memo describes mechanisms for the transmission of IPv6 packets over Frame Relay networks. [STANDARDS-TRACK] This document defines changes to the Domain Name System to support renumberable and aggregatable IPv6 addressing. [STANDARDS-TRACK] This memo catalogs several known Transmission Control Protocol (TCP) implementation problems dealing with Path Maximum Transmission Unit Discovery (PMTUD), including the long-standing black hole problem, stretch acknowlegements (ACKs) due to confusion between Maximum Segment Size (MSS) and segment size, and MSS advertisement based on PMTU. This memo provides information for the Internet community. This document describes the frame format for transmission of IPv6 packets and the method of forming IPv6 link-local addresses and statelessly autoconfigured addresses on IEEE1394 networks. [STANDARDS-TRACK] This document clarifies and updates the standards status of RFCs that define direct and reverse map of IPv6 addresses in DNS. This document moves the A6 and Bit label specifications to experimental status. The de facto standard Application Program Interface (API) for TCP/IP applications is the "sockets" interface. Although this API was developed for Unix in the early 1980s it has also been implemented on a wide variety of non-Unix systems. TCP/IP applications written using the sockets API have in the past enjoyed a high degree of portability and we would like the same portability with IPv6 applications. But changes are required to the sockets API to support IPv6 and this memo describes these changes. These include a new socket address structure to carry IPv6 addresses, new address conversion functions, and some new socket options. These extensions are designed to provide access to the basic IPv6 features required by TCP and UDP applications, including multicasting, while introducing a minimum of change into the system and providing complete compatibility for existing IPv4 applications. Additional extensions for advanced IPv6 features (raw sockets and access to the IPv6 extension headers) are defined in another document. This memo provides information for the Internet community. This document provides sockets Application Program Interface (API) to support "advanced" IPv6 applications, as a supplement to a separate specification, RFC 3493. The expected applications include Ping, Traceroute, routing daemons and the like, which typically use raw sockets to access IPv6 or ICMPv6 header fields. This document proposes some portable interfaces for applications that use raw sockets under IPv6. There are other features of IPv6 that some applications will need to access: interface identification (specifying the outgoing interface and determining the incoming interface), IPv6 extension headers, and path Maximum Transmission Unit (MTU) information. This document provides API access to these features too. Additionally, some extended interfaces to libraries for the "r" commands are defined. The extension will provide better backward compatibility to existing implementations that are not IPv6-capable. This memo provides information for the Internet community. This document describes Dynamic Host Configuration Protocol for IPv6 (DHCPv6) options for passing a list of available DNS recursive name servers and a domain search list to a client. The Internet Group Management Protocol (IGMPv3) for IPv4 and the Multicast Listener Discovery (MLDv2) for IPv6 add the capability for applications to express source filters on multicast group memberships, which allows receiver applications to determine the set of senders (sources) from which to accept multicast traffic. This capability also simplifies support of one-to-many type multicast applications. This document specifies new socket options and functions to manage source filters for IP Multicast group memberships. It also defines the socket structures to provide input and output arguments to these new application program interfaces (APIs). These extensions are designed to provide access to the source filtering features, while introducing a minimum of change into the system and providing complete compatibility for existing multicast applications. This document describes an optional extension to Router Advertisement messages for communicating default router preferences and more-specific routes from routers to hosts. This improves the ability of hosts to pick an appropriate router, especially when the host is multi-homed and the routers are on different links. The preference values and specific routes advertised to hosts require administrative configuration; they are not automatically derived from routing tables. [STANDARDS-TRACK] 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 memo provides information for the Internet community. This document describes an updated version of the IP Authentication Header (AH), which is designed to provide authentication services in IPv4 and IPv6. This document obsoletes RFC 2402 (November 1998). [STANDARDS-TRACK] This document specifies the way of encapsulating IPv6, IPv4, and Address Resolution Protocol (ARP) packets over Fibre Channel. This document also specifies the method of forming IPv6 link-local addresses and statelessly autoconfigured IPv6 addresses on Fibre Channel networks, and a mechanism to perform IPv4 address resolution over Fibre Channel networks. This document obsoletes RFC 2625 and RFC 3831. [STANDARDS-TRACK] Optimistic Duplicate Address Detection is an interoperable modification of the existing IPv6 Neighbor Discovery (RFC 2461) and Stateless Address Autoconfiguration (RFC 2462) processes. The intention is to minimize address configuration delays in the successful case, to reduce disruption as far as possible in the failure case, and to remain interoperable with unmodified hosts and routers. [STANDARDS-TRACK] This document describes data structures and API support for Mobile IPv6 as an extension to the Advanced Socket API for IPv6. Just as the Advanced Sockets API for IPv6 gives access to various extension headers and the ICMPv6 protocol, this document specifies the same level of access for Mobile IPv6 components. It specifies a mechanism for applications to retrieve and set information for Mobility Header messages, Home Address destination options, and Routing Header Type 2 extension headers. It also specifies the common data structures and definitions that might be used by certain advanced Mobile IPv6 socket applications. This memo provides information for the Internet community. This document describes a robust method for Path MTU Discovery (PMTUD) that relies on TCP or some other Packetization Layer to probe an Internet path with progressively larger packets. This method is described as an extension to RFC 1191 and RFC 1981, which specify ICMP-based Path MTU Discovery for IP versions 4 and 6, respectively. [STANDARDS-TRACK] This document redefines selected ICMP messages to support multi-part operation. A multi-part ICMP message carries all of the information that ICMP messages carried previously, as well as additional information that applications may require. Multi-part messages are supported by an ICMP extension structure. The extension structure is situated at the end of the ICMP message. It includes an extension header followed by one or more extension objects. Each extension object contains an object header and object payload. All object headers share a common format. This document further redefines the above mentioned ICMP messages by specifying a length attribute. All of the currently defined ICMP messages to which an extension structure can be appended include an "original datagram" field. The "original datagram" field contains the initial octets of the datagram that elicited the ICMP error message. Although the original datagram field is of variable length, the ICMP message does not include a field that specifies its length. Therefore, in order to facilitate message parsing, this document allocates eight previously reserved bits to reflect the length of the "original datagram" field. The proposed modifications change the requirements for ICMP compliance. The impact of these changes on compliant implementations is discussed, and new requirements for future implementations are presented. This memo updates RFC 792 and RFC 4443. [STANDARDS-TRACK] In networks supporting IPv6, the Internet Control Message Protocol version 6 (ICMPv6) plays a fundamental role with a large number of functions, and a correspondingly large number of message types and options. ICMPv6 is essential to the functioning of IPv6, but there are a number of security risks associated with uncontrolled forwarding of ICMPv6 messages. Filtering strategies designed for the corresponding protocol, ICMP, in IPv4 networks are not directly applicable, because these strategies are intended to accommodate a useful auxiliary protocol that may not be required for correct functioning. This document provides some recommendations for ICMPv6 firewall filter configuration that will allow propagation of ICMPv6 messages that are needed to maintain the functioning of the network but drop messages that are potential security risks. This memo provides information for the Internet community. This document describes the assumptions, problem statement, and goals for transmitting IP over IEEE 802.15.4 networks. The set of goals enumerated in this document form an initial set only. This memo provides information for the Internet community. This document describes the frame format for transmission of IPv6 packets and the method of forming IPv6 link-local addresses and statelessly autoconfigured addresses on IEEE 802.15.4 networks. Additional specifications include a simple header compression scheme using shared context and provisions for packet delivery in IEEE 802.15.4 meshes. [STANDARDS-TRACK] The IPv6 default address selection document (RFC 3484) describes the rules for selecting source and destination IPv6 addresses, and indicates that applications should be able to reverse the sense of some of the address selection rules through some unspecified API. However, no such socket API exists in the basic (RFC 3493) or advanced (RFC 3542) IPv6 socket API documents. This document fills that gap partially by specifying new socket-level options for source address selection and flags for the getaddrinfo() API to specify address selection based on the source address preference in accordance with the socket-level options that modify the default source address selection algorithm. The socket API described in this document will be particularly useful for IPv6 applications that want to choose between temporary and public addresses, and for Mobile IPv6 aware applications that want to use the care-of address for communication. It also specifies socket options and flags for selecting Cryptographically Generated Address (CGA) or non-CGA source addresses. This memo provides information for the Internet community. The Point-to-Point Protocol (PPP) provides a standard method of encapsulating network-layer protocol information over point-to-point links. PPP also defines an extensible Link Control Protocol, and proposes a family of Network Control Protocols (NCPs) for establishing and configuring different network-layer protocols. This document defines the method for sending IPv6 packets over PPP links, the NCP for establishing and configuring the IPv6 over PPP, and the method for forming IPv6 link-local addresses on PPP links. It also specifies the conditions for performing Duplicate Address Detection on IPv6 global unicast addresses configured for PPP links either through stateful or stateless address autoconfiguration. This document obsoletes RFC 2472. [STANDARDS-TRACK] IEEE Std 802.16 is an air interface specification for fixed and mobile Broadband Wireless Access Systems. Service-specific convergence sublayers to which upper-layer protocols interface are a part of the IEEE 802.16 MAC (Medium Access Control). The Packet convergence sublayer (CS) is used for the transport of all packet- based protocols such as Internet Protocol (IP) and IEEE 802.3 LAN/MAN CSMA/CD Access Method (Ethernet). IPv6 packets can be sent and received via the IP-specific part of the Packet CS. This document specifies the addressing and operation of IPv6 over the IP-specific part of the Packet CS for hosts served by a network that utilizes the IEEE Std 802.16 air interface. It recommends the assignment of a unique prefix (or prefixes) to each host and allows the host to use multiple identifiers within that prefix, including support for randomly generated interface identifiers. [STANDARDS-TRACK] This document specifies Mobile IPv6, a protocol that allows nodes to remain reachable while moving around in the IPv6 Internet. Each mobile node is always identified by its home address, regardless of its current point of attachment to the Internet. While situated away from its home, a mobile node is also associated with a care-of address, which provides information about the mobile node's current location. IPv6 packets addressed to a mobile node's home address are transparently routed to its care-of address. The protocol enables IPv6 nodes to cache the binding of a mobile node's home address with its care-of address, and to then send any packets destined for the mobile node directly to it at this care-of address. To support this operation, Mobile IPv6 defines a new IPv6 protocol and a new destination option. All IPv6 nodes, whether mobile or stationary, can communicate with mobile nodes. This document obsoletes RFC 3775. [STANDARDS-TRACK] This document provides a summary of issues related to the use of A6 records, discusses the current status, and moves RFC 2874 to Historic status, providing clarity to implementers and operators. This document is not an Internet Standards Track specification; it is published for informational purposes. This document analyzes the security implications of employing IPv6 fragmentation with Neighbor Discovery (ND) messages. It updates RFC 4861 such that use of the IPv6 Fragmentation Header is forbidden in all Neighbor Discovery messages, thus allowing for simple and effective countermeasures for Neighbor Discovery attacks. Finally, it discusses the security implications of using IPv6 fragmentation with SEcure Neighbor Discovery (SEND) and formally updates RFC 3971 to provide advice regarding how the aforementioned security implications can be mitigated. This document discusses the security implications of native IPv6 support and IPv6 transition/coexistence technologies on "IPv4-only" networks and describes possible mitigations for the aforementioned issues. This document updates the IPv6 multicast addressing architecture by redefining the reserved bits as generic flag bits. The document also provides some clarifications related to the use of these flag bits. This document updates RFCs 3956, 3306, and 4291. The IPv6 unicast addressing format includes a separation between the prefix used to route packets to a subnet and the interface identifier used to specify a given interface connected to that subnet. Currently, the interface identifier is defined as 64 bits long for almost every case, leaving 64 bits for the subnet prefix. This document describes the advantages of this fixed boundary and analyzes the issues that would be involved in treating it as a variable boundary. This document discusses privacy and security considerations for several IPv6 address generation mechanisms, both standardized and non-standardized. It evaluates how different mechanisms mitigate different threats and the trade-offs that implementors, developers, and users face in choosing different addresses or address generation mechanisms. IPv6 specifies the Fragment Header, which is employed for the fragmentation and reassembly mechanisms. The Fragment Header contains an "Identification" field that, together with the IPv6 Source Address and the IPv6 Destination Address of a packet, identifies fragments that correspond to the same original datagram, such that they can be reassembled together by the receiving host. The only requirement for setting the Identification field is that the corresponding value must be different than that employed for any other fragmented datagram sent recently with the same Source Address and Destination Address. Some implementations use a simple global counter for setting the Identification field, thus leading to predictable Identification values. This document analyzes the security implications of predictable Identification values, and provides implementation guidance for setting the Identification field of the Fragment Header, such that the aforementioned security implications are mitigated. Frequent Router Advertisement messages can severely impact host power consumption. This document recommends operational practices to avoid such impact. Some DHCP options carry unique identifiers. These identifiers can enable device tracking even if the device administrator takes care of randomizing other potential identifications like link-layer addresses or IPv6 addresses. The anonymity profiles are designed for clients that wish to remain anonymous to the visited network. The profiles provide guidelines on the composition of DHCP or DHCPv6 messages, designed to minimize disclosure of identifying information. This document 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. The goal of this document is to describe the potential benefits of applications using a transport that enables Explicit Congestion Notification (ECN). The document outlines the principal gains in terms of increased throughput, reduced delay, and other benefits when ECN is used over a network path that includes equipment that supports Congestion Experienced (CE) marking. It also discusses challenges for successful deployment of ECN. It does not propose new algorithms to use ECN nor does it describe the details of implementation of ECN in endpoint devices (Internet hosts), routers, or other network devices. In 2005-2006, the IPv6 MIB update group published updated versions of the IP-MIB, UDP-MIB, TCP-MIB, and IP-FORWARD-MIB modules, which use the InetAddressType/InetAddress construct to handle IPv4 and IPv6 in the same table. This document contains versions of the obsoleted IPV6-MIB, IPV6-TC, IPV6-ICMP-MIB, IPV6-TCP-MIB, and IPV6-UDP-MIB modules for the purpose of updating MIB module repositories. This document obsoletes RFCs 2452, 2454, 2465, and 2466 (i.e., the RFCs containing these MIBs) and reclassifies them as Historic. This document outlines an approach utilizing existing IPv6 protocols to allow hosts to be assigned a unique IPv6 prefix (instead of a unique IPv6 address from a shared IPv6 prefix). Benefits of using a unique IPv6 prefix over a unique service-provider IPv6 address include improved host isolation and enhanced subscriber management on shared network segments. This document discusses an IPv6 deployment scenario when individual nodes connected to large broadcast networks (such as enterprise networks or public Wi-Fi networks) are allocated unique prefixes via DHCPv6 Prefix Delegation (DHCPv6-PD), as specified in RFC 8415. This document deprecates the IPv6 Router Alert option. Protocols that use the IPv6 Router Alert option may continue to do so, even in future versions. However, new protocols that are standardized in the future must not use the IPv6 Router Alert option. This document updates RFC 2711. On networks providing IPv4-IPv6 translation (RFC 7915), hosts and other endpoints need to know the IPv6 prefix(es) used for translation (the NAT64 prefix (RFC 6052)). This document provides guidelines for NAT64 prefix discovery, specifically recommending obtaining the NAT64 prefix from the Router Advertisement option (RFC 8781) when available. Széchenyi István University The IPv6 Company University of New Hampshire, Interoperability Lab (UNH-IOL) QA Cafe This document specifies requirements for an IPv6 Customer Edge (CE) router. Specifically, the current version of this document focuses on the basic provisioning of an IPv6 CE router and the provisioning of IPv6 hosts attached to it. The document obsoletes RFC 7084. The IPv6 Company This document defines the terminology regarding the usage of expressions such as "IPv6-Only" and "IPv6-Mostly", in order to avoid confusions when using them in IETF and other documents. The goal is that a reference to "IPv6-Only" describes the actual functionality being used in a given scope, not the installed protocol support. IEEE National Institute of Standards and Technology

Changes from RFC 8504 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 obsoleted RFCs including 3315 and 3736 (both to 9915) and 4941 to 8981. RFC 793 has been obsoleted by 9293 but the latter does not include the the robustness principle for which RFC 793 is cited in this document.
2. Added support for Gratuitous Neighbor Discovery Creating Neighbor Cache Entries on First‑Hop Routers, RFC 9131.
3. Type C host from RFC 4191 was updated from a SHOULD to MUST.
4. Removed the Mobility Section due to lack of known deployment.
5. Removed the SEND Section due to limited use.
6. Removed the text allowing a host to disallow unknown destination options or hop-by-hop options.
7. Added Discovery of translation prefixes section (10.1.2) which includes RFC 8781 and 9872.
8. Added Discovery of encrypted DNS resolver, RFC 9463.
9. Added requirement to support PMTUD (RFC 8201) and PLPMTUD (RFC 4821, 8899, and 9869).
10. Added Hop-by-Hop Options processing (RFC 9673) as a MUST.
11. Added Port Control Protocol (PCP) to allow for IPv6 host to control incoming IPv6 packets with simple firewalls.
12. Added RFC 9663 for using DHCPv6 Prefix Delegation to allocate IPv6 prefixes to hosts.
13. Added a SHOULD requirement for RFC 8781 for discovery of IPv6 prefix for IPv6 address synthesis.
14. Added DHCPv4 Option 108 for allowing hosts to specify support for IPv6-only networks.
15. Added additional text for supporting IPv4-mapped DNS entries.
16. Added RFC 9740 for better visibility with extension headers in networks.
17. Added a Differentiated Services (Diffserv) section (RFC 2474 and RFC 2475), including a SHOULD requirement for an API to set and access the DSCP.
18. Added SVCB and HTTPS Resource Records (RFC 9460) to the list of stub-resolver support, noting their use for conveying IPv6 hints.
19. Added RFC 8815, noting the deprecation of Any-Source Multicast (ASM) for interdomain multicast.
20. Added RFC 9762 for support of the P flag in the Prefix Information Option, used to signal the availability of DHCPv6 prefix delegation.
21. Updated the Default Address Selection for IPv6 requirement to reference draft-ietf-6man-rfc6724-update, which updates RFC 6724.
22. Added RFC 9844 for entering the zone identifier of an IPv6 scoped address in user interfaces.
23. Updated the reference for basic requirements for IPv6 customer edge routers from RFC 7084 to draft-ietf-v6ops-rfc7084bis.
24. Added RFC 9805, noting that the IPv6 Router Alert option is deprecated for use by new protocols.
25. RFC 8028 was updated from a SHOULD to a MUST for hosts in multihomed environments, with an exception for constrained hosts.
26. Updated the reference for overlapping fragment handling from RFC 5722 to Section 4.5 of RFC 8200.
27. Removed Teredo (RFC 4380) due to lack of current deployment.
28. Split the fragment and Flow Label text from the Internet Protocol Version 6 section into new IPv6 Fragments and IPv6 Flow Label sections.
29. Remove quoted text from 8200 in Path MTU Discovery.
30. Added a reference to draft-ietf-v6ops-ipv6-only in the Prefer IPv6-Only section for the definition of IPv6-only operation.

Changes from RFC 6434 to RFC 8504 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.
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 .

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.
4. Added a section on SEND (it is a MAY).
5. Revised the section on Privacy Extensions 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 .
10. Added a pointer to subnet clarification document .
11. Added text that "IPv6 Host-to-Router Load Sharing" SHOULD be implemented.
12. Added reference to (Overlapping Fragments), and made it a MUST to implement.
13. Made "A Recommendation for IPv6 Address Text Representation" a SHOULD.
14. Removed the mention of delegation name (DNAME) from the discussion about .
15. Numerous updates to reflect newer versions of IPv6 documents, including , , , and .
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 .
17. Added many more references to optional IPv6 documents.
18. Made "A Recommendation for IPv6 Address Text Representation" a SHOULD.
19. Updated the MLD section to include reference to Lightweight MLD .
20. Added a SHOULD recommendation for "Default Router Preferences and More-Specific Routes" .
21. Made "IPv6 Flow Label Specification" a SHOULD.

Acknowledgments

• Acknowledgements from (Current Documents) The authors would like to thank Mohamed Boucadair, Nick Buraglio, Brian Carpenter, Jeremy Duncan, and Klaus Frank, Fernando Gont, and Bob Hinden, for their contributions and many members of the 6man WG for the inputs they gave.
• Acknowledgments from RFC 8504 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.
• 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.
• 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.