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.