/Client

The SVCB RR has two modes:

• 1) AliasMode (Section 2.4.2), which aliases a name to another name and 2) ServiceMode (Section 2.4.3), which provides connection information bound to a service endpoint domain.

Placing both forms in a single RR type allows clients to fetch the relevant information with a single query (Section 2.3).

/AliasMode

1. history

The SVCB RR has two required fields and one optional field.  The fields are:

   SvcPriority (Section 2.4.1):  The priority of this record (relative
      to others, with lower values preferred).  A value of 0 indicates
      AliasMode.

   TargetName:  The domain name of either the alias target (for
      AliasMode) or the alternative endpoint (for ServiceMode).

   SvcParams (optional):  A list of key=value pairs describing the
      alternative endpoint at TargetName (only used in ServiceMode and
      otherwise ignored).  SvcParams are described in Section 2.1.

2.1. Zone-File Presentation Format

• The presentation format <RDATA> of the record ([RFC1035], Section 5.1) has the form:

  SvcPriority TargetName SvcParams The SVCB record is defined specifically within the Internet ("IN") Class ([RFC1035], Section 3.2.4).

2.2. RDATA Wire Format

The RDATA for the SVCB RR consists of:

• a 2-octet field for SvcPriority as an integer in network byte order.

• the uncompressed, fully qualified TargetName, represented as a

  • sequence of length-prefixed labels per Section 3.1 of [RFC1035].

• the SvcParams, consuming the remainder of the record (so smaller

  • than 65535 octets and constrained by the RDATA and DNS message sizes).

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