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

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.

Alex

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