Re: Objection to draft-ietf-6man-rfc4291bis-07.txt - /63 and /65 RAs on linux

Philip Homburg <pch-ipv6-ietf-3@u-1.phicoh.com> Fri, 03 March 2017 22:54 UTC

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Subject: Re: Objection to draft-ietf-6man-rfc4291bis-07.txt - /63 and /65 RAs on linux
From: Philip Homburg <pch-ipv6-ietf-3@u-1.phicoh.com>
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Date: Fri, 03 Mar 2017 23:54:54 +0100
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Cc: Alexandre Petrescu <alexandre.petrescu@gmail.com>
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> > If "what to put between /10 and /64" is for (auto)configuring
> > link-local addresses, yes, I assume it's 0s.  But not "silently" -
> > it's based on Section 2.5.6 of RFC4291.
> 
> That section 2.5.6 does not say whether the 0s are part of the plen
> or part of the IID.
> 
> It is your reading, with an inclined view to make everything work,
> that makes it read so.
> 
> But read it with an inquiring view: is the 0 part of the IID or of
> the plen?  The section does not answer.

Section 5.3 of RFC 4862 spells it out in great detail:
   A link-local address is formed by combining the well-known link-local
   prefix FE80::0 [RFC4291] (of appropriate length) with an interface
   identifier as follows:

   1.  The left-most 'prefix length' bits of the address are those of
       the link-local prefix.

   2.  The bits in the address to the right of the link-local prefix are
       set to all zeroes.

   3.  If the length of the interface identifier is N bits, the right-
       most N bits of the address are replaced by the interface
       identifier.

   If the sum of the link-local prefix length and N is larger than 128,
   autoconfiguration fails and manual configuration is required.  The
   length of the interface identifier is defined in a separate link-
   type-specific document, which should also be consistent with the
   address architecture [RFC4291] (see Section 2).  These documents will
   carefully define the length so that link-local addresses can be
   autoconfigured on the link.

   A link-local address has an infinite preferred and valid lifetime; it
   is never timed out.