Re: [MBONED] Spencer Dawkins' No Objection on draft-ietf-mboned-mtrace-v2-22: (with COMMENT)

[Kerry Meyer <[e-mail]>]

Hi Spencer,

Please see inline below for responses to some of your comments and questions.

             Kerry

> On Jan 24, 2018, at 8:44 AM, Spencer Dawkins <[e-mail]> wrote:
> 
> Spencer Dawkins has entered the following ballot position for
> draft-ietf-mboned-mtrace-v2-22: No Objection
> 
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> 
> 
> Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html
> for more information about IESG DISCUSS and COMMENT positions.
> 
> 
> The document, along with other ballot positions, can be found here:
> https://datatracker.ietf.org/doc/draft-ietf-mboned-mtrace-v2/
> 
> 
> 
> ----------------------------------------------------------------------
> COMMENT:
> ----------------------------------------------------------------------
> 
> I support Mirja's Discuss ballot point on IANA.
> 
> In addition, I have a few comments.
> 
> I'm looking in the Introduction for an unambiguous statement as to whether this
> mechanism can be initiated by a source, and I'm not seeing one. Just based on
> the Introduction, I'm guessing not, but the Introduction starts by mentioning
> that it's difficult to trace from the source, so I'm confused.
> 

It is fine for a source to initiate a trace by sending an mtrace Query to a given receiver. This results in an upstream (reverse) hop-by-hop trace that will yield the correct result. The introductory comment is intended to contrast the requirements of doing this type of tracing for multicast (which uses Reverse Path Forwarding to make routing determinations) versus the unicast form of traceroute, which works as required by doing hop by hop downstream tracing toward the destination.

Would it be helpful if the following introductory sentence were rephrased to clarify this point?

*********

Current:

Given a multicast distribution tree, tracing from a multicast source
 to a receiver is difficult, since we do not know on which branch of
 the multicast tree the receiver lies.  

*********
Proposed:

Given a multicast distribution tree, tracing hop-by-hop downstream from a multicast source
to a given multicast receiver is difficult because there is no efficient and deterministic way to
determine the branch of the multicast routing tree on which that receiver lies.  

********* 

> In section 3, I'm seeing
> 
>   If an
>   implementation receives an unknown TLV type for the first TLV in a
>   message (i.e., the header TLV), it SHOULD ignore and silently discard
>   the entire packet.  If an implementation receives an unknown TLV type
>   for a subsequent TLV within a message, it SHOULD ignore and silently
>   discard the entire packet.
> 
> and trying to understand why these two cases are listed separately. I'm also
> trying to understand why they're SHOULDs, but please help me understand the
> differences you have in mind.
> 

These sentences initially specified different actions.  when the actions were edited
to specify the same thing for both, they should have been combined . We will
combine them and will also modify the SHOULD to MUST.

> I share the question about mixing IPv4 and IPv6.
> 
Please clarify: What is your question regarding mixing of IPv4 and IPv6? 

> Is the last sentence in
> 
>   Upstream Router Address: 32 bits
>      This field specifies the address of the upstream router from which
>      this router expects packets from this source.  This may be a
>      multicast group (e.g., ALL-[protocol]-ROUTERS group) if the
>      upstream router is not known because of the workings of the
>      multicast routing protocol.  However, it should be 0 if the
>      incoming interface address is unknown or unnumbered.
> 
> normative?
> 
> 
Are you suggesting that the “may” and “should” in the preceding
paragraph would be more appropriately stated as MAY and SHOULD?
(Please confirm.) If so, we will change these terms accordingly.