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

Greg Mirsky <gregimirsky@gmail.com> Mon, 06 March 2017 22:58 UTC

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From: Greg Mirsky <gregimirsky@gmail.com>
Date: Mon, 6 Mar 2017 14:58:08 -0800
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To: "Mirja Kuehlewind (IETF)" <ietf@kuehlewind.net>
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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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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>; wrote:

> Hi Greg,
>
> two quick replies below.
>
> Mirja
>
> > Am 03.03.2017 um 20:10 schrieb Greg Mirsky <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>; wrote:
> > Hi Greg,
> >
> > see inline.
> >
> > Mirja
> >
> >
> > > Am 03.03.2017 um 03:47 schrieb Greg Mirsky <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>;
> 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
> > > 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/
> > >
> > >
> > >
> > > ----------------------------------------------------------------------
> > > 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
> > >
> >
> >
>
>