[pim] Gorry Fairhurst's Discuss on draft-ietf-pim-zeroconf-m cast-addr-alloc-ps-07: (with DISCUSS and COMMENT)

Gorry Fairhurst has entered the following ballot position for
draft-ietf-pim-zeroconf-mcast-addr-alloc-ps-07: Discuss

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DISCUSS:
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(1) The documents says it defines requirements.
I saw in the abstract this statement:
"The document presents explicit requirements covering discovery", but yet from
a standards perspective it does not - there are no formal requirements based on
RFC-2119 keywords derived. That may well be suitable for an Informational
document, and I expect the declaration of keywords can also be removed, and
this sentence could be rewritten as guidance for future work rather than
requirements?

(2) From the TSV_ART review:
The document appears to be about selecting multicast IP addresses to avoid link
address collisions, rather than IP address collisions. That should be made more
clear in the title, abstract, intro, and throughout. The current text is easily
misread as focusing on IP address collisions until section 2.

Can this be clarified in the document?

(3) The TSV_ART review suggested:
The document jumps between link and network issues without enough context for
the reader to distinguish between the two. Collisions should be referred to
throughout as link address collisions, not just address collisions, and address
assignment should be referred to as IP address assignment.

Sec 5 should more clearly relate the way 32 IP addresses could map to the same
MAC address, i.e., this is because only the lower 23 bits are used of the 28
bits in the IP multicast address range. It would be very useful if the reason
for this mapping were discussed in this doc – i.e., why did we not just use all
28 bits?

Can this be clarified in the document?


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COMMENT:
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Thank you Joe Touch for his TSV-ART review, I'd like to pick-up on the issues
discussed there, so include them here:

(i) It also appears that the limited number of (host) hardware address filters
has been overlooked; i.e., if a device is capable of filtering only 4 multicast
addresses in hardware, the device would more efficiently support 7 addresses if
at least 3 DID collide, rather than ensuring that none collide.  When no
addresses collide and the number of filters is exceeded, the network interface
is driven into promiscuous mode that requires software filtering – i.e., it
completely undermines the goal of this doc.

(ii) The protocol requirements need some refinement. Resistance to failure is
NOT the same as robustness to a single point of failure; the tag phrase and the
definition need to be adjusted to align. Item 3 is “multicast self-assignment
protocol coexistence”, i.e., this isn’t about interoperation with other
protocols in general. Item 7 (collision detection and resolution) is not a
requirement; it is an approach to satisfying other requirements, such as 1, 2,
and 5. It would help if the tag phrases were similar (they seem to be phrases
defining properties, except for #6, which should be “supports host-level
multiplexing” – check this throughout for all lists).

(iii) The Note needs revision; the collisions arise after *rejoining
disconnected networks caused by* a temporary network partition. I.e., it is the
rejoining that causes the problem, not the partitioning. The second list should
describe goals of a design; it seems odd to include “cross-platform
availability”, as this seems to conflate deployment with OS capabilities; it is
difficult to appreciate what OS properties could ever interfere with these
mechanisms. An example would help as would rephrasing this as “OS independence”.

... Please see additional comments in the review that may also be helpful.



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