Re: [ippm] Robert Wilton's Discuss on draft-ietf-ippm-rfc8321bis-02: (with DISCUSS)

[Giuseppe Fioccola <[e-mail]>]

Hi Robert,
Thanks for your revision,
Please see my reply inline tagged as [GF].
I will address your comments in the next version.

Best Regards,

Giuseppe

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Subject: Robert Wilton's Discuss on draft-ietf-ippm-rfc8321bis-02: (with DISCUSS)

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----------------------------------------------------------------------
DISCUSS:
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Sorry, another discuss, but hopefully a trivial one to resolve.

I found this text to be a unclear regarding passive vs hybrid:

   Therefore, the Alternate-Marking Method could be considered Hybrid or
   Passive, depending on the case.  In the case where the marking method
   is obtained by changing existing field values of the packets the
   technique is Hybrid.  In the case where the marking field is
   dedicated, reserved, and included in the protocol specification, the
   Alternate-Marking technique can be considered as Passive.

Please can you clarify the third sentence, to clarify that the marking is done
at source, or at least outside the controlled domain?  I.e., I presume that
even if there were some reserved bits in the protocol header for colouring
packets, that were then written at the edge of the controlled domain, then this
would be a active rather than passive measurement?

[GF]: I think it is better to further clarify this point. If you look at RFC7799:
"Passive Methods of Measurement are:

   o  based solely on observations of an undisturbed and unmodified
      packet stream of interest (in other words, the method of
      measurement MUST NOT add, change, or remove packets or fields or
      change field values anywhere along the path).

   o  dependent on the existence of one or more packet streams to supply
      the stream of interest.

   o  dependent on the presence of the packet stream of interest at one
      or more designated Observation Points."

By assuming that there are reserved bits in the protocol header, if the change in value of these marking bits at the domain edges (and not along the path) is still considered a modification to the packet stream, AltMark cannot be considered Passive.
Therefore, AltMark can be considered Hybrid Type I in any case. 
Note that, according to RFC7799, Hybrid Type I methods imply "Augmentation or modification of the stream of interest, or employment of methods that modify the treatment of the stream" 
I can eventually revise the text and state that Alternate-Marking Method can only be considered Hybrid.


Thanks,
Rob