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

神明達哉 <jinmei@wide.ad.jp> Mon, 15 April 2019 19:02 UTC

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From: 神明達哉 <jinmei@wide.ad.jp>
Date: Mon, 15 Apr 2019 12:02:19 -0700
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To: Alexandre Petrescu <alexandre.petrescu@gmail.com>
Cc: Pascal Thubert <pthubert@cisco.com>, "<int-dir@ietf.org>" <int-dir@ietf.org>, draft-ietf-ipwave-ipv6-over-80211ocb.all@ietf.org, its@ietf.org, IETF Discussion <ietf@ietf.org>
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Subject: Re: [Int-dir] side note RFC 4291 2nd par sec. 2.1 LL on loopback
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At Mon, 15 Apr 2019 09:42:53 +0200,
Alexandre Petrescu <alexandre.petrescu@gmail.com> 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:

   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

--
JINMEI, Tatuya

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