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9. IANA Considerations

9. IANA Considerations​

The IANA has assigned RR type code 41 for OPT.

[RFC2671] specified a number of IANA subregistries within "DOMAIN NAME SYSTEM PARAMETERS":

  • DNS EDNS(0) Options
  • EDNS Version Number
  • EDNS Header Flags

Additionally, two entries were generated in existing registries:

  • EDNS Extended Label Type in the DNS Label Types registry
  • Bad OPT Version in the DNS RCODES registry

IANA has updated references to [RFC2671] in these entries and subregistries to this document.

[RFC2671] created the DNS Label Types registry. This registry is to remain open.

The registration procedure for the DNS Label Types registry is Standards Action.

This document assigns option code 65535 in the DNS EDNS0 Options registry to "Reserved for future expansion".

The current status of the IANA registry for EDNS Option Codes at the time of publication of this document is:

  • 0-4 assigned, per references in the registry
  • 5-65000 Available for assignment, unassigned
  • 65001-65534 Local/Experimental use
  • 65535 Reserved for future expansion

[RFC2671] expands the RCODE space from 4 bits to 12 bits. This allows more than the 16 distinct RCODE values allowed in [RFC1035]. IETF Review is required to add a new RCODE.

This document assigns EDNS Extended RCODE 16 to "BADVERS" in the DNS RCODES registry.

[RFC2671] called for the recording of assignment of extended label types 0bxx111111 as "Reserved for future extended label types"; the IANA registry currently contains "Reserved for future expansion". This request implied, at that time, a request to open a new registry for extended label types, but due to the possibility of ambiguity, new text registrations were instead made within the general DNS Label Types registry, which also registers entries originally defined by [RFC1035]. There is therefore no Extended Label Types registry, with all label types registered in the DNS Label Types registry.

This document deprecates Binary Labels. Therefore, the status for the DNS Label Types registration "Binary Labels" is now "Historic".

IETF Standards Action is required for assignments of new EDNS(0) flags. Flags SHOULD be used only when necessary for DNS resolution to function. For many uses, an EDNS Option Code may be preferred.

IETF Standards Action is required to create new entries in the EDNS Version Number registry. Within the EDNS Option Code space, Expert Review is required for allocation of an EDNS Option Code. Per this document, IANA maintains a registry for the EDNS Option Code space.

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