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Re: IPv6 prefix lengths - how long?

Mark Smith <markzzzsmith@gmail.com> Tue, 11 June 2019 00:32 UTC

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From: Mark Smith <markzzzsmith@gmail.com>
Date: Tue, 11 Jun 2019 10:32:28 +1000
Message-ID: <CAO42Z2yz1vZGz0bnhfyOuoqNGcP8RFfgYV0P0LGXW7of5SSzBA@mail.gmail.com>
Subject: Re: IPv6 prefix lengths - how long?
To: "Templin (US), Fred L" <Fred.L.Templin@boeing.com>
Cc: 6man WG <ipv6@ietf.org>
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On Tue., 11 Jun. 2019, 02:54 Templin (US), Fred L, <
Fred.L.Templin@boeing.com> wrote:

> Two points I pulled out of the many points that were made were that 1)
> prefixes that are
> overly long can be trivially enumerated by an attacker, and 2) prefixes
> should be aligned
> on nibble boundaries.
>
> I really resonate with point 1), and with Host Address Availability
> (RFC7934) we see that
> it is good to allow hosts (nodes) to configure many IPv6 addresses -
> perhaps even very
> many. I agree with the points that there are already vast numbers of /64s
> available for
> delegation, and /64 has many nice properties including RFC7934 support and
> intractable
> address enumeration. But, if we want to go longer than /64



Why do we want to go longer than /64?

The IPv6 address space is 2^96 times, or about 73 billion billion times
larger than IPv4s.

Plenty of people have done the maths to show that we are not going to run
out of IPv6 addresses.

Just a few months ago Brian worked out that every grain of sand on Earth
could have its own /64, and from memory, that was just within 2000::/3.

For a technical field, I'm becoming more and more amazed at how many people
trust their intuition completely ("IPv4 ran out in a few decades so IPv6
will too"), rather than saying to themselves, "my intuition may be correct,
do the facts support it?".

It's not engineering if people rely on intuition, because ever now and then
things are counter-intuitive.


and still satisfy those
> properties, how long would that be - /96?
>
> Point 2) I am not as sure on. Why is it important for prefixes to land on
> even nibble
> boundaries? I can easily delegate a /63 today for example, and I don't see
> anything
> wrong with that. Are we saying that that should be disallowed?
>
> Fred
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