[core] draft-ietf-core-groupcomm-bis-15 telechat Intdir review

[Brian Haberman via Datatracker <[e-mail]>]

Document: draft-ietf-core-groupcomm-bis
Title: Group Communication for the Constrained Application Protocol (CoAP)
Reviewer: Brian Haberman
Review result: Almost Ready

I am an assigned INT directorate reviewer for draft-ietf-core-groupcomm-bis.
These comments were written primarily for the benefit of the Internet Area
Directors. Document editors and shepherd(s) should treat these comments just
like they would treat comments from any other IETF contributors and resolve
them along with any other Last Call comments that have been received. For more
details on the INT Directorate, see
https://datatracker.ietf.org/group/intdir/about/

I was asked to look at this document from the multicast address perspective, so
these comments focus on that area of the document driven by the DISCUSS
comments related to multicast addressing.

# Use of ff35:30:2001:db8:f1:0:8000:1 - FF35::/32 is an SSM range per RFC 3306
and RFC 4607. But, the referenced multicast address does not fall in that range
since it has values in the last 8 bits of the prefix. This makes it an IPv6
multicast address with an embedded IPv6 unicast prefix.

# The above confusion probably stems from a lack of explanatory text around the
multicast prefixes mentioned in the document. Given that, I would recommend the
following:

## The mention of "one-to-many" and ASM in section 1.1 may be confusing. The
purpose of the first sentence appears to be to indicate that this document only
defines CoAP group communication over multicast-capable transport protocols.
But, even that does not limit things to ASM. It seems like this document is
defining how many-to-many communication is carried out over multicast-capable
transport protocols.

## In the 2nd paragraph of section 1.1, I would suggest replacing "CoAP group
requests" with "CoAP group messages" as it seems like responses can be sent to
multicast groups as well.

## Section 2.2.2

### I would suggest providing supporting text for the use of FF1x::16 and
FF3x::/16. This should include references to RFCs 3306, 3956, and 7371
(possibly).

### The text essentially says that assignment of multicast addresses is done by
an administrator. I would suggest adding text to guide administrators in the
selection of multicast prefixes, multicast scopes, and possible group IPs. This
would benefit from a reference to RFC 3307. Please note that 3307 is in the
process of being updated by draft-ietf-pim-updt-ipv6-dyn-mcast-addr-grp-id.