Re: Is 1111 1110 10 equal to 0xfe80 or...

> On Jun 9, 2019, at 11:50 AM, Alexandre Petrescu <alexandre.petrescu@gmail.com> wrote:
> 
> 
> 
> Le 07/06/2019 à 21:29, Mudric, Dusan (Dusan) a écrit :
>>> Message: 3 Date: Fri, 7 Jun 2019 10:53:28 -0700 From: Fred Baker
>>> <fredbaker.ietf@gmail.com> To: Alexandre Petrescu
>>> <alexandre.petrescu@gmail.com> Cc: IPv6 <ipv6@ietf.org> Subject:
>>> Re: Is 1111 1110 10 equal to 0xfe80 or 0x3fa? Message-ID:
>>> <A722E202-7671-4111-BA92-8A67B3D3B924@gmail.com> Content-Type:
>>> text/plain; charset="us-ascii"
>>> If I have prefix fe80::/10, as described in RFC 4291, the next bit
>>> is bit 11. Doing the same subdivision of the prefix is fe80::/11
>>> and fea0::/11.
>> [Dusan] The hexadecimal definition for LL address is not
>> syntactically correct. The binary 10 bit prefix 1111111010 cannot be
>> presented as hexadecimal FE80::/10. It is rather a range FE80::/10 -
>> FEBF::/10.
> 
> I fully agree.  That is what we should be talking about: a range.  The fe80::/10 to febf::/10 is the prefix of link local addresses.
> 
> The difficulty (not able to say just one hextet fe80, but a range from one hextet to another) is due  to the IPv6 notation, the textual representation of IPv6 addresses.
> 
> It is still strange to say that the bit pattern 1111 1110 10 can not be represented in hexa.  Or maybe there is a need of a new base.
> 
>> In this notation, FE80::/10 = FEBF::/10,  because the
>> first 10 bits are equal and other 6 should be ignored.
> 
> I agree.
> 
>> 111 1111010
>> can be defined as FE80::/10 only if every time it is also mentioned
>> that the trailing 6 bits are all zero.
> 
> I agree.  And the trailing 6 bits are not all zero.  RFC 4291 makes them to be 0, but IANA allocation does not make them to be 0.
> 
>> But, it is very common to say
>> FE80::/10 is LL prefix, without mentioning the 6 trailing bits to be
>> zeros.
> 
> I agree.  Whoever I spoke to about LL was saying they are FE80.
> 
> On another hand, there is a similar difficulty with fc and fd in ULA addresses.  In the v6ops WG, and in the ULA RFC, there seems to be a clearer idea about the ULA notation.
> 
> In private I am also told to get mind around around CIDR notation.

	Aye, there’s the nub.
> 
> Alex
> 
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> 
James R. Cutler
James.cutler@consultant.com
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