Re: appropriate length of fe80:: prefix and new IP-over-foo drafts

[Alexandre Petrescu <[e-mail]>]

Le 31/01/2019 à 12:17, Fernando Gont a écrit :
> On 31/1/19 07:24, Alexandre Petrescu wrote:
>>
>>
>> Le 30/01/2019 à 23:14, Brian E Carpenter a écrit :
>>> Section 5.3 "Creation of Link-Local Addresses" of RFC4862 refers to
>>> an interface identifier of N bits and an fe80::0 prefix "of
>>> appropriate length", which according to the addressing architecture
>>> is 128-N. But N is undefined by RFC4862 and cannot be derived from an
>>> RA because all this happens as soon as the interface is enabled.
>>> Therefore N must be predefined.
>>>
>>> As pioneered by RFC2464**, all ipv6-over-foo documents must therefore
>>> specify N for their link type. So far, everybody has specified 64, as
>>> far as I know. Is there a reason to do otherwise for the two drafts
>>> mentioned below?
>>
>> One of the two drafts involves a Network ID of length 24.
>>
>> The question is why not use 24 for InterfaceID?  Just because Ethernet
>> had it that way?
> 
> You can certainly do that with OpenBSD. ;-)

In linux too I can add (and we actually do) link-local addresses with 
prefix length 32.

I do not understand why there is insistance that it must be 64.

Alex

>