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

Alexandre Petrescu <alexandre.petrescu@gmail.com> Sat, 15 June 2019 15:17 UTC

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Subject: Re: Is 1111 1110 10 equal to 0xfe80 or...
To: James R Cutler <james.cutler@consultant.com>
Cc: "Mudric, Dusan (Dusan)" <dmudric@avaya.com>, "ipv6@ietf.org" <ipv6@ietf.org>
References: <DM6PR15MB2506E62560613C85F74A1FF8BB100@DM6PR15MB2506.namprd15.prod.outlook.com> <cb14591f-3abe-55e6-5bf8-f55afb68cae0@gmail.com> <1CB66B2D-08CE-4EA4-8901-F3A2967A2113@consultant.com>
From: Alexandre Petrescu <alexandre.petrescu@gmail.com>
Message-ID: <f31b310b-3ec6-e9df-f9c7-c4e2c60d26db@gmail.com>
Date: Sat, 15 Jun 2019 17:17:19 +0200
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Le 09/06/2019 à 17:56, James R Cutler a écrit :
>> On Jun 9, 2019, at 11:50 AM, Alexandre Petrescu 
>> <alexandre.petrescu@gmail.com <mailto: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 <mailto:fredbaker.ietf@gmail.com>> To: 
>>>> Alexandre Petrescu
>>>> <alexandre.petrescu@gmail.com <mailto:alexandre.petrescu@gmail.com>> 
>>>> Cc: IPv6 <ipv6@ietf.org <mailto:ipv6@ietf.org>> Subject:
>>>> Re: Is 1111 1110 10 equal to 0xfe80 or 0x3fa? Message-ID:
>>>> <A722E202-7671-4111-BA92-8A67B3D3B924@gmail.com 
>>>> <mailto: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.

What is a nub?

Alex

>>
>> Alex
>>
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>>
>>
> James R. Cutler
> James.cutler@consultant.com <mailto:James.cutler@consultant.com>
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> 
> 
> 
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