RFC 5952, "A Recommendation for IPv6 Address Text Representation", August 2010Source of RFC: 6man (int)
Errata ID: 4900
Reported By: Michael Krzyzaniak
Date Reported: 2017-01-10
Section 4.2.2. says:
Handling One 16-Bit 0 Field The symbol "::" MUST NOT be used to shorten just one 16-bit 0 field. For example, the representation 2001:db8:0:1:1:1:1:1 is correct, but 2001:db8::1:1:1:1:1 is not correct.
It should say:
But Section 2.2. Zero Compression says: 'A special syntax is available to compress the zeros. The use of "::" indicates one or more groups of 16 bits of zeros.' It is possible to select whether or not to omit just one 16-bit 0 field. 2001:db8:aaaa:bbbb:cccc:dddd::1 2001:db8:aaaa:bbbb:cccc:dddd:0:1
In 2.2 :: for only one 16-bit 0 filed :: is used
4.2.2 says MUST NOT -RFC 2119 says
2. MUST NOT This phrase, or the phrase "SHALL NOT", mean that the
definition is an absolute prohibition of the specification.