2.1. Zone-File Presentation Format

The presentation format <RDATA> of the record (RFC 1035, Section 5.1) has the form:

SvcPriority TargetName SvcParams

The SVCB record is defined specifically within the Internet ("IN") Class (RFC 1035, Section 3.2.4).

SvcPriority is a number in the range 0-65535, TargetName is a <domain-name> (RFC 1035, Section 5.1), and the SvcParams are a whitespace-separated list with each SvcParam consisting of a SvcParamKey=SvcParamValue pair or a standalone SvcParamKey. SvcParamKeys are registered by IANA (Section 14.3).

Each SvcParamKey SHALL appear at most once in the SvcParams. In presentation format, SvcParamKeys are lowercase alphanumeric strings. Key names contain 1-63 characters from the ranges "a"-"z", "0"-"9", and "-". In ABNF (RFC 5234):

alpha-lc      = %x61-7A   ; a-z
SvcParamKey   = 1*63(alpha-lc / DIGIT / "-")
SvcParam      = SvcParamKey ["=" SvcParamValue]
SvcParamValue = char-string ; See Appendix A.
value         = *OCTET ; Value before key-specific parsing

The SvcParamValue is parsed using the character-string decoding algorithm (Appendix A), producing a value. The value is then validated and converted into wire format in a manner specific to each key.

When the optional "=" and SvcParamValue are omitted, the value is interpreted as empty.

Arbitrary keys can be represented using the unknown-key presentation format "keyNNNNN" where NNNNN is the numeric value of the key type without leading zeros. A SvcParam in this form SHALL be parsed as specified above, and the decoded value SHALL be used as its wire-format encoding.

For some SvcParamKeys, the value corresponds to a list or set of items. Presentation formats for such keys SHOULD use a comma-separated list (Appendix A.1).

SvcParams in presentation format MAY appear in any order, but keys MUST NOT be repeated.