Re: Exception to "MUST NOT"

["Jiwoong Lee" <porce at ktf.com>]

----- Original Message ----- 
From: "Harald Tveit Alvestrand" <harald at alvestrand.no>
Sent: Thursday, September 27, 2001 6:41 PM
Subject: Re: Exception to "MUST NOT"


> --On 27. september 2001 09:32 +0900 Jiwoong Lee <porce at ktf.com> wrote:
> 
> >> MUST NOT means that you never do it, and any implementation that does it
> >> is  nonconformant to the spec.
> >> If you find that you have to do it in some case, you have found a bug in
> >> the spec.
> >
> > Somecases. However, ICMPv6 example case, described in the first mail of
> > this thread, has not been found but already described in the spec; which
> > is not a bug at all.
> 
> could you give the RFC or draft name, and quote the text you are worried 
> about?

Yes. Please have a look on section 2.4 of RFC 2463 (ICMPv6)

    ...

    (e) An ICMPv6 error message MUST NOT be sent as a result of
        receiving:
    ...

         (e.2) a packet destined to an IPv6 multicast address (there are
               two exceptions to this rule: (1) the Packet Too Big
               Message - Section 3.2 - to allow Path MTU discovery to
               work for IPv6 multicast, and (2) the Parameter Problem
               Message, Code 2 - Section 3.4 - reporting an unrecognized
               IPv6 option that has the Option Type highest-order two
               bits set to 10), or

         (e.3) a packet sent as a link-layer multicast, (the exception
               from e.2 applies to this case too), or

         (e.4) a packet sent as a link-layer broadcast, (the exception
               from e.2 applies to this case too), or
    ...


Jiwoong