Network Time Protocol Last Extension Field

NTPv4 is defined by RFC 5905, and it and earlier versions of the NTP Protocol have supported symmetric private key MAC authentication. MACs pre-date the Extension Fields introduced in RFC 5905, and as the number of Extension Fields grows there is an increasing chance of ambiguity when deciding if the "next" set of data is an Extension Field or a MAC. This proposal defines a new Extension Field which is used to signifiy that it is the last Extension Field in the packet. If present, any subsequent data SHOULD be considered to be a legacy MAC.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119.

Now that multiple extension fields are a possibility, and the chance that additional packet data could be an Extension Field or an old-style MAC, having a means to indicate that there are no more Extension Fields in an NTP packet, and any subsequent data MUST be something else, almost certainly an old-style MAC, is a valuable facility.

Field Type: TBD (Recommendation for IANA: 0x2008 (Last Extension Field, MAC OPTIONAL)) Field Length: 4 Payload: None. Example:

The author wishes to acknowledge the contributions of Joey Saccadonuts.

This memo requests IANA to allocate NTP Extension Field Types 0x0007 (I-Do), 0x2007 (I-Do, MAC OPTIONAL), 0x4007 (I-Do Response), and 0x6007 (I-Do Response, MAC OPTIONAL) for this proposal.

Additional information TBD