[6lo] Draft applicability for 6775bis

[Erik Nordmark <[e-mail]>]

Here is an attempt at an applicability statement based on what we talked 
about today.
It is sufficiently strong?
Other RFCs or drafts that we should reference?

    Erik

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Applicability

The purpose of the ARO and EARO is to facilitate duplicate address 
detection for hosts and pre-populate NCEs in the routers to reduce the 
need for sending multicast neighbor solicitations and also to be able to 
support backbone routers.

In some cases the address registration can fail or be useless for 
reasons other than a duplicate address. Example are the router having 
run out of space, the host having a stale sequence number, or the host 
is using an address which does not match the prefix(es) for the link. In 
such cases the host will receive an error to help diagnose the issue and 
retry.

However, the ability to return errors to address registrations MUST NOT 
be used to restrict the ability of hosts to form and use addresses as 
specified in [RFC7934]. In particular, this is needed for enhanced 
privacy, which implies that each host will register a multiplicity of 
address as part mechanisms like [RFC4941]. This implies that a 6LR or 
6LBR which is intended to support N hosts MUST have space to register at 
least on the order of 10N IPv6 addresses.

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