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

[Spencer Dawkins at IETF <[e-mail]>]

Hi, Kerry,

On Wed, Feb 7, 2018 at 6:06 PM, Kerry Meyer <[e-mail]> wrote:

> 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
>
> When responding, please keep the subject line intact and reply to all
> email addresses included in the To and CC lines. (Feel free to cut this
> introductory paragraph, however.)
>
>
> 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.
>

That helps. Thanks.


>
> *********
>
> 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.
>

Thanks!


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

Sorry, I should have bounded your search space. I meant the question in
Alia's ballot, which was

"I do not understand the rationale for forbidding some addresses being IPv4
and some IPv6.
Presumably, some could even be unnumbered interfaces.  Many networks are
dual-stack or
may have IPv4 in one part of the network and IPv6 in another part.  What is
the reason for
ruling this out as a valid situation?  I do see that the encodings are
problematic if partly IPv4
and partly IPv6 - but I do not see a reason that IPv4 addresses could not
be sent as mapped into IPv6."

but I'll let you two talk that one out.


>
> 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.
>

That would help, but what I was asking was whether that was true by
definition, and not just an interoperation requirement.

If the incoming interface address is unknown or unnumbered, is there a
reason why the Upstream Router Address would not be zero?

Thanks!

Spencer