Re: Review of draft-ietf-6man-rfc4291bis-06

Mark Smith <> Fri, 13 January 2017 20:55 UTC

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From: Mark Smith <>
Date: Sat, 14 Jan 2017 07:54:48 +1100
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Subject: Re: Review of draft-ietf-6man-rfc4291bis-06
To: Randy Bush <>
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On 13 January 2017 at 11:49, Randy Bush <> wrote:
>>> to be clear, i have no problem with iids being 64-bit.  my issue is with
>>> unicast globals being classful in 2.4.4.
>> Randy I take your point, but this supposed conflict isn't new, it's not
>> introduced in 4291bis, it goes back to RFC3513.
> i know; and i have pushed back every cm of the way.  it took years to
> get the other classful insanity, tls/nla, removed.  the old cidr war
> continues.  this last bit of classfulness (excuse the word) too will
> pass.
>> Do you have a suggestion how to change this within the context of
>> advancing this to Internet Standard?
> yes.  simply remove the mandatory requirement for classful global
> unicast addresses.

I think people are combining together in this thread two separate things:

- the addressing structure

- how addresses are processed by routers when the router is forwarding a packet.

In IPv6 they're separate things, in classful IPv4 they weren't (if I
recall correctly).

I think unicast IPv6 could only be described as classful if the
structure of the address dictated how processing of addresses for
forwarding occurred. (You could describe the difference between IPv6
unicast and multicast forwarding to be classful as forwarding is
different for those two types of addresses.)

BCP198/RFC7608, "IPv6 Prefix Length Recommendation for Forwarding"
makes it very clear that forwarding is to occur based on the longest
match rule of an IPv6 address, with no consideration of what the
structure of the address happens to be for the purposes of device
configuration or anything else.


   IPv6 prefix length, as in IPv4, is a parameter conveyed and used in
   IPv6 routing and forwarding processes in accordance with the
   Classless Inter-domain Routing (CIDR) architecture.  The length of an
   IPv6 prefix may be any number from zero to 128, although subnets
   using stateless address autoconfiguration (SLAAC) for address
   allocation conventionally use a /64 prefix.  Hardware and software
   implementations of routing and forwarding should therefore impose no
   rules on prefix length, but implement longest-match-first on prefixes
   of any valid length."