A proposal for draft-ietf-6man-rfc4291bis-07

David Farmer <farmer@umn.edu> Thu, 02 March 2017 22:43 UTC

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From: David Farmer <farmer@umn.edu>
Date: Thu, 2 Mar 2017 16:43:49 -0600
Message-ID: <CAN-Dau17q_BrUuzfvB1mLDt6p5UxYikphWaHpa8VQ2L-3kx-DA@mail.gmail.com>
Subject: A proposal for draft-ietf-6man-rfc4291bis-07
To: 6man WG <ipv6@ietf.org>
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I've been thinking about this, really hard, and listening to what others
are saying. I think we want to say the following;

1. IPv6 unicast routing is 128 bits in length [BCP198], AKA not classful!
2. Subnet Prefixes of 64 bits are RECOMMENDED
3. IIDs are REQUIRED to be 64 bits
4. Say nothing that would imply you cannot configure a prefix length longer
than 64 bits in length, at least manually.
5. Avoid all explicit exceptions, like RFC6164, etc...

How about in the current draft remove the 2nd paragraph of 2.4, then add
the following paragraph at the end of section 2.4

   IPv6 unicast routing is based on prefixes of any length up to 128
   bits [BCP198]. However, subnet prefixes of 64 bits in length are
   recommended in normal use. Furthermore, subnet prefixes and
   Interface IDs both of 64 bits in length are required when a unicast
   address is formed from a subnet prefix and an Interface ID. Otherwise,
   when a subnet prefix of another length is used then a unicast address
   is assumed to have no internal structure and is treated as a single
   128 bit quantity. The rationale for the 64 bit boundary in IPv6
   addresses can be found in [RFC7421].

Then in the 4th paragraph of 2.4.1

   As noted in Section 2.4, when a unicast address is formed from a
   subnet prefix and an Interface ID, both are required to be 64 bits
   in length.

I think this accomplishes the 5 goals above and is not inconsistent with at
least the intent of RFC4291. If you read section 2.5 of the RFC4291, I
think my new paragraph is only more clearly restating what is said there

Note that SLACC and other things that use IIDs have 64 bits required for
the IID and subnet prefix length.  But, it should also be noted that host
are not required to have any knowledge of an addresses structure including
its own addresses, therefore IIDs are in fact optional.   Additionally, 64
bit prefix lengths are recommend for everything, including manual config
and DHCP, but manual config and DHCP are allowed other prefix lengths as
well.   Also, the exception for unicast addresses that begin with 000 is no
longer really necessary.

Rotten tomatoes and eggs now please. :)


David Farmer               Email:farmer@umn.edu
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University of Minnesota
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