Subject: [6lo] IID length in draft-ietf-6lo-btle-06.txt - why64?

From: Alexandre Petrescu <[email-masked]>
Date: Fri, 16 Jan 2015 10:32:15 +0100

Hello,

I wonder why is the length of the IID in draft-ietf-6lo-btle-06.txt set 
to 64 since the BTLE MAC address is just 48bit?

Is there a problem if we set the IID length to 48?

Because if we do, then we may have an advantage in using longer than 64 
prefix lengths in the BTLE subnet - e.g. /65.  This is helpful in 
networks at the very edge of the Internet - typically the prefix 
arriving from the Internet to the 6LBR is is of length 64.  With such a 
prefix arriving to the 6LBR it is practically impossible to create 
another prefix of length also 64 beyond 6LBR, in the BTLE subnet.  Hence 
we'd need a prefix length of /65 in the BTLE subnet.  But a /65 in BTLE 
is impossible if the IID is of length 64.

Let me illustrate this by way of comparison:

                          6LN
                           \              ____________
            /65 impossible  \       /64  /            \
                    6LN ---- 6LBR ----- |  Internet   |
                            /            \____________/
                           /
                          6LN

             - with IID of length 64 -

--------------------------------------------------------------

                          6LN
                           \              ____________
              /65 possible  \       /64  /            \
                    6LN ---- 6LBR ----- |  Internet   |
                            /            \____________/
                           /
                          6LN

             - with IID of length 48 -

Alex
PS:  fyi a soon-to-be-RFC on the topic draft-ietf-6man-why64-08
      "Analysis of the 64-bit Boundary in IPv6 Addressing"

---

From: James Woodyatt <[email-masked]>
Date: Tue, 20 Jan 2015 10:50:10 -0800

[as an individual contributor]

On Fri, Jan 16, 2015 at 1:32 AM, Alexandre Petrescu <
[email-masked]> wrote:

>
> I wonder why is the length of the IID in draft-ietf-6lo-btle-06.txt set to
> 64 since the BTLE MAC address is just 48bit?
> [...]

Sections 4.1 and 4.2 in that draft are a good catalog of existing problems—
in my opinion, the most obviously relevant ones, in order of decreasing
importance, would be NAT64, IKE, CGA and Mobile IP. Not to mention the
predictable outcome that future IETF and external standards will come to
expect on-link network prefixes always to be 64 bits, so it's therefore
important to keep 6BLE from becoming a divergence in that respect.

-- 
james woodyatt <[email-masked]>
Nest Labs, Communications Engineering

---

From: Carsten Bormann <[email-masked]>
Date: Wed, 21 Jan 2015 02:02:44 +0100

On 2015-01-20 19:50, James Woodyatt wrote:
> Not to mention the predictable outcome that future IETF and external
> standards will come to expect on-link network prefixes always to be 64
> bits, so it's therefore important to keep 6BLE from becoming a
> divergence in that respect.

A very strong +1 from me.

Grüße, Carsten