[dnsext] A contradiction in RFC 5155

["Roy Arends" <roy@nominet.org.uk>]

Dear DNSEXT WG,

During an NSEC3 interoperability test we found a contradiction in RFC 
5155:

A NSEC3 record, that matches an Empty Non-Terminal, effectively has no 
type associated with it. This NSEC3 record has an empty type bit map. 
Section 3.2.1 contains the statement:

   Blocks with no types present MUST NOT be included.

However, the same section contains a regular expression:

   Type Bit Maps Field = ( Window Block # | Bitmap Length | Bitmap )+

The plus sign in the regular expression indicates that there is one or 
more of the preceding element. This means that there must be at least one 
window block. If this window block has no types, it contradicts with the 
first statement. Therefore, the correct text in RFC 5155 3.2.1 should be:

   Type Bit Maps Field = ( Window Block # | Bitmap Length | Bitmap )*

I suggest we add this to dnssec-bis updates (
draft-ietf-dnsext-dnssec-bis-updates-07), and we get this one character 
error in RFC5155 ERRATA posted on the rfc-editors site. 

If the suggested change is not satisfactory, I want better text by 
November 26th. At that point I'll brief the RFC editor and ask the chairs 
and the dnssec-bis editors to add it to dnssec-bis updates.

With Kind Regards,

Roy Arends
Senior Researcher
Nominet UK

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