Subject: [6lo] Alissa Cooper's Discuss on draft-ietf-6lo-6lobac-06: (with DISCUSS and COMMENT)

From: "Alissa Cooper" <[email-masked]>
Date: Wed, 30 Nov 2016 08:33:03 -0800

Alissa Cooper has entered the following ballot position for
draft-ietf-6lo-6lobac-06: Discuss

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DISCUSS:
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Section 12 says:

"For this reason, it is RECOMMENDED that a different (but stable) IID be
   generated for each globally scoped address in use according to, for
   example, [RFC3315], [RFC3972], [RFC4941], [RFC5535], or [RFC7217]."

I have a couple of questions about this recommendation that should be
easy to clear up. First, do you really mean "different" IID? EUI-64
identifiers are different from each other, but embedding one in an IID
still leaves you susceptible to address scanning attacks. Maybe what is
meant here is "semantically opaque" or "with maximum supportable entropy"
or something along those lines?

Second, what is meant by the word "stable" here? The mechanisms cited
offer a variety of different "stability" spans -- DHCP lease lifetime,
temporary address lifetime, lifetime of connection to a link, etc. So
it's not clear what is actually being recommended or if the cited
mechanisms all provide the desired property.

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COMMENT:
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I mostly understand why Sections 6 and 12 are specified as they are but
there are a couple of points of departure from
draft-ietf-6lo-privacy-considerations and draft-ietf-6man-default-iids
that I'd like to discuss.

(1) draft-ietf-6man-default-iids says that the choice of address
generation mechanism should be configurable when a mechanism is specified
to embed a link layer address in an IID. Is there a reason that doesn't
apply here? The document doesn't say anything about it for the link-local
case.

(2) draft-ietf-6lo-privacy-considerations says:

"Specifications should make sure that an IPv6 address can change
      over long periods of time.  For example, the interface identifier
      might change each time a device connects to the network (if
      connections are short), or might change each day (if connections
      can be long).  This is necessary to mitigate correlation over
      time."

This document doesn't seem to provide any guidance about supporting the
ability to change an IPv6 address within the life span of a long-lived
attachment to the same physical network. Some of the mechanisms cited in
Section 12 provide this and some do not. I appreciate that correlation of
activities over time isn't perceived to be a huge threat here, but aren't
there cases where being able to change an address despite remaining
attached to the same physical network would be desirable? That seems
worth some guidance for nodes that want to support it.