Re: [Int-dir] side note RFC 4291 2nd par sec. 2.1 LL on loopback

[Alexandre Petrescu <[e-mail]>]

Le 15/04/2019 à 21:02, 神明達哉 a écrit :
> At Mon, 15 Apr 2019 09:42:53 +0200,
> Alexandre Petrescu <[e-mail] 
> <mailto:[e-mail]>> wrote:
> 
>  > That RFC4291 section 2.1 says:
>  > >    All interfaces are required to have at least one Link-Local unicast
>  > >    address (see Section 2.8 for additional required addresses).
>  >
>  > Sidenote: I think the loopback interface does not have a link-local
>  > address.  Probably it is not all interfaces that must have at least 
> one ll(
> 
> Indeed, there's some subtle point here.  RFC4007 somewhat tries to
> clarifies it:

Well,  RFC4007 predates RFC4291, so it is little meaningful to say it 
clarifies it.

Maybe we can say that RFC4291 must be updated given all these issues.

> 
>     The IPv6 unicast loopback address, ::1, is treated as having link-
>     local scope within an imaginary link to which a virtual "loopback
>     interface" is attached.
> 
> that is, (with the assumption that the loopback interface is
> configured with ::1) the loopback interface does not (necessarily)
> have an 'fe80' address, but it still has a link-local scope address.
> If and when 6man resumes the work of rfc4291bis we should probably
> make this clarification.
> 
> BTW, whether a loopback interface has an fe80 address is actually
> implementation dependent.  BSDs usually assign ::1 on a loopback
> interface while also generating an fe80 address on it:
> 
> % ifconfig lo0
> lo0: flags=8049<UP,LOOPBACK,RUNNING,MULTICAST> metric 0 mtu 16384
>      options=600003<RXCSUM,TXCSUM,RXCSUM_IPV6,TXCSUM_IPV6>
>      inet6 ::1 prefixlen 128
>      inet6 fe80::1%lo0 prefixlen 64 scopeid 0x2

Ah?  It self-forms that fe80 address without a sysadmin requesting it?

In other OSs like linux, windows, there is no fe80::1 unless the 
sysadmin adds it.

In that sense, this is an additional reason (together with the 
RFC4291-violating fe80:1::1 potentially breaking in BSD) to think that 
RFC4291 and co. are mostly for BSDs.

This is not a happy situation to be in.

Alex

> 
> --
> JINMEI, Tatuya