Re: [mpls] Mirja Kühlewind's No Objection on draft-ietf-mpls-residence-time-14: (with COMMENT)

Mirja Kühlewind <ietf@kuehlewind.net> Tue, 07 March 2017 13:32 UTC

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To: Greg Mirsky <gregimirsky@gmail.com>
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Subject: Re: [mpls] =?utf-8?q?Mirja_K=C3=BChlewind=27s_No_Objection_on_draft-i?= =?utf-8?q?etf-mpls-residence-time-14=3A_=28with_COMMENT=29?=
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Still not convinced because you can just use an new RTM TLV for this case.

On 06.03.2017 23:58, Greg Mirsky wrote:
> Hi Mirja,
> we use sub-TLV in Figure 2 as future proofing approach in case someone may
> need to define different sub-TLV that MUST precede the PTP packet.
> Would you agree that it is reasonable design choice?
>
> Regards,
> Greg
>
> On Fri, Mar 3, 2017 at 11:19 AM, Mirja Kuehlewind (IETF) <ietf@kuehlewind.net
> <mailto:ietf@kuehlewind.net>> wrote:
>
>     Hi Greg,
>
>     two quick replies below.
>
>     Mirja
>
>     > Am 03.03.2017 um 20:10 schrieb Greg Mirsky <gregimirsky@gmail.com
>     <mailto:gregimirsky@gmail.com>>:
>     >
>     > Hi Mirja,
>     > thank you for your comments and very helpful discussion. My notes
>     in-lined and now tagged with GIM2>>
>     >
>     > Regards,
>     > Greg
>     >
>     > On Fri, Mar 3, 2017 at 1:46 AM, Mirja Kuehlewind (IETF)
>     <ietf@kuehlewind.net <mailto:ietf@kuehlewind.net>> wrote:
>     > Hi Greg,
>     >
>     > see inline.
>     >
>     > Mirja
>     >
>     >
>     > > Am 03.03.2017 um 03:47 schrieb Greg Mirsky <gregimirsky@gmail.com
>     <mailto:gregimirsky@gmail.com>>:
>     > >
>     > > Hi Mirja,
>     > > thank your for the review and the comments, most helpful.
>     > > Please find my answers in-line tagged GIM>>.
>     > >
>     > > Regards,
>     > > Greg
>     > >
>     > > On Wed, Mar 1, 2017 at 8:48 AM, Mirja Kühlewind <ietf@kuehlewind.net
>     <mailto:ietf@kuehlewind.net>> wrote:
>     > > Mirja Kühlewind has entered the following ballot position for
>     > > draft-ietf-mpls-residence-time-14: 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
>     <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-mpls-residence-time/
>     <https://datatracker.ietf.org/doc/draft-ietf-mpls-residence-time/>
>     > >
>     > >
>     > >
>     > > ----------------------------------------------------------------------
>     > > COMMENT:
>     > > ----------------------------------------------------------------------
>     > >
>     > > High level comment:
>     > > Maybe extend the security section a bit and describe what can happen in
>     > > the worse case if the value has been modified to a too high or too low
>     > > value; and maybe even given some guidance on performing additional checks
>     > > to figure out if a given value is reasonable for a given path or not.
>     > >
>     > > Questions:
>     > > - Can you explain why PTPType, Port ID, and Sequence ID are needed in the
>     > > PTP Sub-TLV format if those values are already in the PTP packet itself
>     > > that follows?
>     > > GIM>> We propose to copy these values as they uniquely identify PTP
>     control message as these are required for two-step mode and suggesting
>     inspection of the PTP payload would cause layer violation.
>     >
>     > I see. Maybe add a sentence that these field are use to identify the
>     packet. However, when you copy them, you also have to inspect the payload
>     and that’s the same layer violation. Also not sure if duplicating
>     information in the packet is the best approach. Why don’t use just add an
>     own identifier to the packet instead?
>     > GIM2>> Will the following, when added at the very end of Section 3.1, work:
>     >    Tuple of PTPType, Port ID, and Sequence ID uniquely identifies PTP
>     >    control packet encapsulated in RTM message and are used in two-step
>     >    RTM mode Section 2.1.1.
>     >
>     > GIM2>> The RTM message created by egress or the first on the LSP
>     two-step RTM node. Thus other RTM nodes don't need to look into PTP
>     control message but use the PTP sub-TLV. Creating new identifier is
>     certainly an alternative but I believe that will require more state
>     coordination between LERs on the same RTM LSP. Re-using existing
>     characteristic information, in my view, is simpler solution.
>
>     Yes the new text helps. I don’t see why there is any more coordination
>     needed if you use an identifier. If you are in two-step mode, you simply
>     remember the identifier of the packet that you use to measurement
>     together with your measurement and wait for the next packet with the same
>     identifier. I don’t think that’s any different than using the PTP
>     information as identifier. Anyway that’s not an big issue.
>
>     >
>     > >
>     > > - Why is it necessary to define PTP sub-TLV (and have a registry for one
>     > > value only)? Are you expecting to see more values here? What would those
>     > > values be?
>     > > GIM>> We may have another protocols or applications to use RTM and these the most likely will have their specific set of parameters to uniquely identify control session for two-step mode. One obvious case would be NTP when on-path support is defined. But since we don't know which parameters will uniquely identify cotrol session we don't request code point allocation.
>     >
>     > My understanding was that a new protocol would be a different RTM TLV in the registry in section 7.2. That’s fine. I don’t understand why your PTP sub-TLV needs ANOTHER TLV scheme: figure 2 and registry in sec 7.3.
>     > GIM2>> RTM TLV differentiates  between different encapsulation types, e.g. Ethernet, IPv4 or IPv6 but sub-TLV doesn't have to. Do you see this as a problem?
>
>     I still don’t fully understand this. You can use the same sub-TLV even if
>     that sub-TLV is not extensible. All I’m saying is that I don’t understand
>     why the sub-TLV in figure 2 has again a type and a value. I don’t think
>     those two field are needed.
>
>     >
>     > > - Similar to Spencer's question: Why don't you also define a Sub-TLV
>     > > format for NTP?
>     > > GIM>>Hope that above answer addresses this question.
>     >
>     > Actually not really. Why don’t you know which parameters to use?
>     >
>     > > - sec 4.3: "RTM (capability) - is a three-bit long bit-map field with
>     > > values
>     > >       defined as follows:
>     > >       *  0b001..."
>     > >   Maybe I don't understand what a bit-map field is here but these are
>     > > more then 3 bits...?
>     > > GIM>> '0b' identifies binary format as '0x' identifies hexadecimal
>     format of notation.
>     > Ah sorry, fully overview that.
>     >
>     > > - also sec 4.3.: "Value contains variable number of bit-map fields so
>     > > that overall
>     > >       number of bits in the fields equals Length * 8."
>     > >   However there is no field 'Value' in the figure...
>     > > GIM>> Thank you for pointing. I'll update Figure 4 and Figure 5 to
>     add Value tag on the field immediately following RTM field.
>     >
>     > There are more questions here:
>     >
>     > > Also the following
>     > > explanation about future bit-maps is really confusing to me; why don't
>     > > you just say that the rest as indicated by the length field must be
>     > > padded with zeros...?
>     > GIM2>> The description follows RFC 7794 Section 2.1
>     > > - Should section 4.8 maybe be a subsection of 4.7? This part confused me
>     > > a bit because the example seems to be generic but the rest is RSVP-TE
>     > > specific, right? Maybe move the example as a separate section before or
>     > > after the whole section 4...?
>     > GIM2>> Thank you, I agree it is more logical flow. With the change
>     suggested by Ben it will look like this:
>     >    4.  Control Plane Theory of Operation . . . . . . . . . . . . . .  10
>     >      4.1.  RTM Capability  . . . . . . . . . . . . . . . . . . . . .  10
>     >      4.2.  RTM Capability Sub-TLV  . . . . . . . . . . . . . . . . .  11
>     >      4.3.  RTM Capability Advertisement in Routing Protocols . . . .  11
>     >        4.3.1.  RTM Capability Advertisement in OSPFv2  . . . . . . .  11
>     >        4.3.2.  RTM Capability Advertisement in OSPFv3  . . . . . . .  13
>     >        4.3.3.  RTM Capability Advertisement in IS-IS . . . . . . . .  13
>     >        4.3.4.  RTM Capability Advertisement in BGP-LS  . . . . . . .  13
>     >      4.4.  RSVP-TE Control Plane Operation to Support RTM  . . . . .  14
>     >        4.4.1.  RTM_SET TLV . . . . . . . . . . . . . . . . . . . . .  15
>     >
>     > >
>     > > Nits:
>     > > - Maybe change to title to: Residence Time Measurement (RTM) in MPLS
>     > > network
>     > > - There are (still) some not spelled out abbreviations (LDP, PW);
>     > > GIM>> Since both are used only once - expanded
>     > > in turn
>     > > others are extended twice (e.g. PTP)...
>     > > GIM>>  Cleaned.
>     > > - In figure 1, I would rename 'Value' to 'Sub-TLV' and maybe also
>     > > indicate it as optional in the figure: Sub-TLV (optional)
>     > > GIM>> Agree
>     > >
>     >
>     >
>
>