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Internet Engineering Task Force DNS SRv6 A Domain Name System (DNS) Resource Record (RR) Type is specified for storing IPv6 Segment Routing (SRv6) Information in the DNS.

Introduction The Domain Name System (DNS) is a hierarchical, distributed, highly available database with a variety of security features used for bi-directional mapping between domain names and addresses, for email routing, and for other information . This data is formatted into resource records (RRs) whose content type and structure are indicated by the RR Type field. General familiarity with the DNS and its terminology is assumed in this document.

IPv6 Segment Routing Internet Protocol versions 4 (IPv4,) and 6 (IPv5, ) have long provided header options to include an ordered sequence of addresses in a packet header so the packet travels in order through the nodes specified by that sequence of addresses. This is sometimes referred to as "source routing" because the route or path the packet follows is set at least in part when a sequence of addresses is added to the packet, usually at the packet's source, rather than being dynamically determined as the packet proceeds through the network. IPv6 Segment Routing (SRv6, ) extends "source routing" by generalizing the IPv6 sized "address" quantities in a sequence to be "instructions". specifies a particular Segment Routing Header (SRH) that may be use used as part of the headers of an IPv6 packet to indicate an IPv6 Segment Routing sequence of addresses/instructions. And further specifies the structuring of an IPv6 address size quantity such that it is composed of addressing information followed by a function designation which is optionally further followed by arguments to that function. Thus, segment routing might encode a series of operations to be performed on a packet. Furthermore, because a sequence of SRv6 instructions may start with the same constant addressing prefix, methods of compression have been suggested to represent this addressing prefix less often and pack an increased number of quantities into a Segment Routing Header where each quantity may consist optionally of additional address information and/or function designation and/or function arguments. In many ways, the data returned for an SRV6 DNS RR is like an address. For example, it would be reasonable for an application using SRv6 to do a type SRV DNS query followed by an SRV6 query at the resulting domain name. Furthermore, as a fall back, if no SRV6 RR is present in the DNS at a domain name, an application could try querying for the AAAA IPv6 address RR type.

Terminology 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. The following acronyms are used in this document:

• DNS - Domain Name System
• IANA - Internet Assigned Number Authority
• RR - DNS Resource Record
• SRv6 - IPv6 Segment Routing
• SRV6 - Mnemonic for the SRv6 RR Type

SRV6 RR Type RDATA The SRV6 RR type enables the storage and retrieval of an ordered sequence of SRv6 quantities each of which is the size of IPv6 addresses. The RDATA for this type of RR is simple a sequence of such quantities preceded by 16 bits that are available for future definition as flags (see Figure 1) and will be 2+(N*16) bytes long where N is the number of such quantities present. The RR Type Code for the SRV6 RR is TBD1. The Flags field is for future flexibility and MUST be sent as zero and ignored on receipt.

SRV6 RRTYPE Data

Acknowledgements The suggestions and comments of the following persons are gratefully acknowledged: tbd

IANA Considerations IANA is request to assign an SRV6 RR Type (TBD1) as in the template in Appendix A.

Security Considerations tbd

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. 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. This document specifies version 6 of the Internet Protocol (IPv6). It obsoletes RFC 2460. Segment Routing (SR) leverages the source routing paradigm. A node steers a packet through an ordered list of instructions, called "segments". A segment can represent any instruction, topological or service based. A segment can have a semantic local to an SR node or global within an SR domain. SR provides a mechanism that allows a flow to be restricted to a specific topological path, while maintaining per-flow state only at the ingress node(s) to the SR domain. SR can be directly applied to the MPLS architecture with no change to the forwarding plane. A segment is encoded as an MPLS label. An ordered list of segments is encoded as a stack of labels. The segment to process is on the top of the stack. Upon completion of a segment, the related label is popped from the stack. SR can be applied to the IPv6 architecture, with a new type of routing header. A segment is encoded as an IPv6 address. An ordered list of segments is encoded as an ordered list of IPv6 addresses in the routing header. The active segment is indicated by the Destination Address (DA) of the packet. The next active segment is indicated by a pointer in the new routing header. The Segment Routing over IPv6 (SRv6) Network Programming framework enables a network operator or an application to specify a packet processing program by encoding a sequence of instructions in the IPv6 packet header. Each instruction is implemented on one or several nodes in the network and identified by an SRv6 Segment Identifier in the packet. This document defines the SRv6 Network Programming concept and specifies the base set of SRv6 behaviors that enables the creation of interoperable overlays with underlay optimization. Informative References 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 describes a DNS RR which specifies the location of the server(s) for a specific protocol and domain. [STANDARDS-TRACK] Extending the Domain Name System (DNS) with new Resource Record (RR) types currently requires changes to name server software. This document specifies the changes necessary to allow future DNS implementations to handle new RR types transparently. [STANDARDS-TRACK] The Domain Name System (DNS) is defined in literally dozens of different RFCs. The terminology used by implementers and developers of DNS protocols, and by operators of DNS systems, has sometimes changed in the decades since the DNS was first defined. This document gives current definitions for many of the terms used in the DNS in a single document. This document obsoletes RFC 7719 and updates RFC 2308. Segment Routing can be applied to the IPv6 data plane using a new type of Routing Extension Header called the Segment Routing Header (SRH). This document describes the SRH and how it is used by nodes that are Segment Routing (SR) capable.

SRV6 RR Type Template