Re: [Teas] Genart last call review of draft-ietf-teas-rsvp-te-scaling-rec-06

[Lou Berger <[e-mail]>]

Hi Pavan,

WRT if this document updates rfc2961:

I don't have a strong opinion on or objection to this document updating 
rfc2961.  To have this document be an update, I do think we and it need to 
be clear on what exactly is being updated in 2961. After rereading both 
it's unclear to me what you see is being updated. As best I can see, this 
document basically relates to 2961 in that it says (a) use the reliable 
message delivery defined in 2961 and (b) restates that 2205 refresh 
processing of path and resv messages still applies after a rapid retry 
period expires and (c) sending acks moves from recommended to required.

What did I miss?

FWIW I think (a) and (c) are requirements of this document not 2961 and (b) 
seems like an informative statement that the basic refresh processing rules 
of rfc2205 still apply.

Thanks
Lou


On October 1, 2017 9:14:15 AM Vishnu Pavan Beeram <[e-mail]> 
wrote:

> Elwyn, Hi!
>
> Please see inline for responses.
>
> Regards,
> -Pavan
>
> On Fri, Sep 29, 2017 at 1:34 PM, Elwyn Davies <[e-mail]> wrote:
>
>>
>>
>> Hi, Pavan.
>>
>> I've checked through the changes in -07 and I think all is good as regards
>> fixing the 'major issue', restucturing s2 and fixing the nits - thanks.
>>
>
> [Pavan] Great!
>
>
>> Looking at the IESG comments I think you have covered most of them  except
>> it would be good to put a pointer to Appendix A into the intro of s2.
>>
>> With reference to Appendix A(d), it would be helpful to s/periodic
>> retransmission interval/Periodic Retransmission Interval/ and possibly give
>> it a name (Rpri or some such)  in s2.3 and Appendix A(d).  Adding the name
>> of the interval after "retransmission of these on a slower timer" migt mak
>> it clearer also.
>>
>
> [Pavan] Ok. We'll add a pointer to the Appendix and also find a short form
> for the periodic retransmission interval.
>
>>
>> However,  I think you still need to address all three of the minor issues:
>> - Capability object:  A 'basic' implementation of RFC 2209/RFC3209 will
>> not include the RFC5063 extensions.
>>
>
> [Pavan] I think you meant RFC2205 and not RFC2209.
>
> I think you should therefore make it explicit that a prerequisite for your
>> extensions is an implementation of the Capability object as specified in
>> RFC5063 (my proposal for s3) , making it clear that this does not require
>> any of the other functionality of RFC 5063, especially no support for the S
>> bit in the Capabilities.
>>
>
> [Pavan] I'm not really sure that "Capability Object" needs a separate
> prerequisite section. I'll let the Document-Shepherd and our AD take a call
> on this. Please note that the document also talks about using Node-ID
> hellos from RFC4558. Would "Node-Hellos/RFC4558" also then need a separate
> prerequisite section? We added a separate section for RFC2961 because there
> is a need to explicitly clarify the usage of certain 2961 procedures. With
> "Capability Object" and "Node Hellos", there isn't anything (IMHO) that
> needs to be explicitly clarified. We could just add a statement in Section
> 4.1 saying that you don't need to set any other flags. Would that address
> your concern about the ambiguity regarding the "Graceful Restart" bits?
>
> OLD
>
>    An implementation supporting the RI-RSVP technique MUST set a new
>    flag "RI-RSVP Capable" in the CAPABILITY object signaled in Hello
>    messages.
>
> NEW
>
>    An implementation supporting the RI-RSVP technique MUST set a new
>    flag "RI-RSVP Capable" in the CAPABILITY object signaled in Hello
>    messages. This MAY be the only flag set in the object.
>
> -  Your response regarding what happens if a peer initially acknowledges
>> that it supports the new capabilities by setting the I/F bits in the
>> Capability and sends some messages with the Refresh-Reduction-Capable bit
>> set, but then stops setting the Refresh-Reduction-Capable bit doesn't
>> really address the problem.   Would this mean that the receiver should
>> assume that the peer can no longer support the extensions?
>>
>
> [Pavan] Yes.
>
> Is this a permanent state or could the peer start setting the
>> Refresh-Reduction-Capable bit again and restore initial functionality - or
>> should this just not be allowed.
>>
>
> [Pavan] The peer can set the bit again and restore the functionality.
>
> I think you need to think through what happes in the various possible cases
>> and explain what an implementation should do in each case.
>>
>
> [Pavan] There are only two possibilities -- Is the functionality enabled on
> the peer or is it not? If the functionality is enabled, the implementation
> does everything that is specified as required for the given technique. If
> it is not enabled, then the implementation doesn't employ the technique and
> just behaves like it does today. We'll try and add some text to make this
> obvious.
>
>
>> - So, I have done my homework and checked back on what happens when there
>> is no acknowledgement of refreshes. The relevant parameter is the cleanup
>> time.  However, this leaves us with a problem.. the cleanup time is
>> typically set as a multiple of the refresh interval (9 times seems to be
>> the default) - indeed I see that the interface configuration on a Juniper
>> router (!) actually sets it by asking for the multiple rather than an
>> absolute value.  Wth the new dispensation in ths document, there are two
>> time periods involved:  I think you do need to respecify how to calculate a
>> sensible cleanup interval, and note that the retransmissions will then halt
>> after this interval.
>>
>
> [Pavan] I think you are confusing this with the "setup retry" timer (which
> comes into play when you signal the PATH setup of an LSP instance and don't
> get a RESV back). Please go through
> https://tools.ietf.org/html/draft-ravisingh-teas-rsvp-setup-retry-01 for a
> detailed account of setup retry timer, issues associated with it and
> recommended practices. The staged retransmission (Section 2.3) that comes
> into play when there is no ACK is different from what you are alluding to
> -- it is meant for any message seeking ACK (not just PATH). This is very
> specific to the exponential back-off procedure discussed in Section 6 of
> RFC2961. As per RFC2961, the rapid retransmissions stop after we reach a
> certain retry limit. In Section 2.3, we are clarifying what needs to be
> done after this Retry limit is reached --- the recommendation is to fall
> back on a not so rapid retransmission interval. As a I said in my previous
> email, this needs to be done until either an ACK is received or the
> corresponding state is torn down.
>
>
>> Does this last modification constitute an update of RFC 2209?  I am not
>> sure -consult your AD!
>>
>
> [Pavan] RFC2209 is an informational document that provides guidance on the
> various data-models and procedures needed for an implementation to be
> RFC2205 compliant. Most of the content in RFC2209 is outdated (imho). No
> one has had the inclination over the years to update this and we don't
> intend to do this either.
>
> [Pavan] Reading through the various questions/comments from the IESG, I'm
> convinced that this document needs to formally update RFC2961. We'll go
> ahead and do that if the shepherd and our AD have no objections.
>
>
>>
>> Regards,
>> Elwyn
>>
>> Sent from Samsung tablet.
>>
>> -------- Original message --------
>> From: Vishnu Pavan Beeram <[e-mail]>
>> Date: 28/09/2017 03:48 (GMT+00:00)
>> To: Elwyn Davies <[e-mail]>
>> Cc: [e-mail], [e-mail],
>> ietf <[e-mail]>, [e-mail]
>> Subject: Re: [Teas] Genart last call review of 
>> draft-ietf-teas-rsvp-te-scaling-rec-06
>>
>>
>> Elwyn, Hi!
>>
>> Thanks for the detailed review and the text suggestions. We just posted a
>> new revision (-07) to address the concerns listed below. Please go through
>> the new diffs (https://www.ietf.org/rfcdiff?url2=draft-ietf-teas-rsvp-te-
>> scaling-rec-07) and let us know if additional changes are required.
>>
>> Please see inline for further responses (prefixed VPB).
>>
>> Regards,
>> -Pavan
>>
>> On Fri, Sep 22, 2017 at 6:06 PM, Elwyn Davies <[e-mail]>
>> wrote:
>>
>>> Reviewer: Elwyn Davies
>>> Review result: Not Ready
>>>
>>> I am the assigned Gen-ART reviewer for this draft. The General Area
>>> Review Team (Gen-ART) reviews all IETF documents being processed
>>> by the IESG for the IETF Chair.  Please treat these comments just
>>> like any other last call comments.
>>>
>>> For more information, please see the FAQ at
>>>
>>> <https://trac.ietf.org/trac/gen/wiki/GenArtfaq>.
>>>
>>> Document: draft-ietf-teas-rsvp-te-scaling-rec-06
>>> Reviewer: Elwyn Davies
>>> Review Date: 2017-09-22
>>> IETF LC End Date: 2017-09-22
>>> IESG Telechat date: 2017-09-28
>>>
>>> Summary: Not ready, primarily because the title and presentation give the
>>> impression that the content is really a BCP when it isn't.  This conceals
>>> the
>>> considerable amount of tweaking of RFC 2961 functionality and addition of
>>> new
>>> RSVP Capabilities described in the document.  There are also a couple of
>>> minor
>>> issues that need to be sorted out.
>>>
>>> Major issues:
>>> Title and way proposals are presented:  The document defines two new
>>> 'capabilities' for RSVP-TE and is indeed (as specified in the document
>>> header)
>>> correctly intended for Standards Track status.  However the title and the
>>> whole
>>> of the meat of the document in Section 2 presents the proposals as
>>> 'recommendations' which says to me that I am expecting a BCP where a
>>> profile of
>>> available options from existing standards is recommended as the best
>>> choice for
>>> implementation and deployment.  In my opinion, the title would be better
>>> as
>>> something like "Additional Capabilities Designed to Improve the
>>> Scalability of
>>> RSVP-TE Deployments".  Whilst the proposals are based on the techniques
>>> in RFC
>>> 2961, the document *requires* the implementor to conform to rules that
>>> were
>>> optional and constrains configurable values to different ranges in order
>>> to be
>>> able to deliver the capabilities defined in the document as well as
>>> defining
>>> new RSVP extensions modifying some of the behaviour defined in RFC 2961.
>>> Thus
>>> although some of the rules could be met by choosing particular values
>>> within
>>> the RFC 2961 set, the use of MUST, tweaking of functionality and
>>> variation of
>>> ranges takes it well beyond a set of recommendations for RFC 2961 options
>>> selections.  In view of this Section 1 needs to be written as an
>>> introduction
>>> to the definitions of the new capabilities rather than advocacy for
>>> selection
>>> of RFC 2961 options and the implication that the techniques mentioned in
>>> the
>>> last paragraph of s1 are just a matter of selecting a profile of option
>>> values.
>>>  In actuality new protocol values are introduced and ss2.2 and 2.3 define
>>> novel
>>> extensions to RSVP beyond what is available for RFC 2961 and requiring
>>> modification to basic RFC 2961 functionality..
>>>
>>>
>> [VPB] We changed the title to "Techniques to Improve the Scalability of
>> RSVP-TE Deployments". We also tweaked the text in the introduction section
>> as suggested. Please see if the new set of diffs address the comment above.
>>
>> Minor issues:
>>> Interaction with RFC 5063:  The document does not explicitly state that an
>>> implementation would need to support (at least) the extra capability obect
>>> defined in s4.2 of RFC 5063.  Some words about interaction with RFC 5063
>>> are
>>> probably required in that s4.2.1 of RFC 5063 rather assumes that if there
>>> is a
>>> capability object, by default its S bit will be set.
>>>
>>
>> [VPB] The CAPABILITY object in RFC5063 is meant for generic use and can be
>> used even when there are no Graceful Restart extensions in play (even when
>> no GR flags are set). As far as we can tell, there is nothing in RFC5063
>> that precludes this. We added a reference to RFC5063 when the new
>> Capability flags are introduced. Would this be sufficient to address this
>> concern?
>>
>>
>>>
>>> Behaviour if a node stops setting Refresh-Reduction-Capable bit:  The
>>> last para
>>> of s2 in RFC 2961 discusses behaviour if a node stops setting this bit in
>>> messages.  What would happen with the extensions defined in this document
>>> if
>>> this happened while either of the extensions is in use?  As a matter of
>>> interest, if a peer offers the capabilities defined in this draft, is it
>>> possible or sensible for it to stop setting the Refresh-Reduction-Capable
>>> bit
>>> without stopping offering the extensions?
>>>
>>
>> [VPB]  If a peer sets the I or F bit in the CAPABILITY object but does not
>> set the Refresh-Reduction-capable bit, then the corresponding functionality
>> ("RI-RSVP" or "Per-Peer Flow-Control") is not activated for that peer. In
>> other words, resetting the Refresh-Reduction-Capable bit immediately makes
>> the node incapable of supporting the two capabilities discussed in this
>> document. This is covered in Sections 3.1 and 4.1 ( -07 version).
>>
>>
>>> s2.1.3, para 2: As specified, it appears that the 'slower timer'
>>> transmission
>>> of Path and Resv messages can go on indefinitely if no ack arrives.  What
>>> puts
>>> an end to this repetition?  [It may be that I have forgotten how basic
>>> RSVP
>>> works, but since this is altering the behaviour it would be good to
>>> explain how
>>> it terminates, and whether this requires any additional modification to
>>> timers.]
>>>
>>
>> [VPB]  There is nothing new about Path and Resv messages getting
>> transmitted indefinitely (this is normal soft-state signaling behavior) --
>> all that this section does is discuss how these transmissions are paced in
>> the absence of an ack. The slower timer transmission will go on until
>> either an ack is received (at which point the regular "refresh interval"
>> comes into play) or the corresponding LSP instance state is torn down.
>>
>>
>>> Nits/editorial comments:
>>> Abstract: RSVP-TE is not a 'well-known' abbreviation: s/RSVP-TE/RSVP
>>> Traffic
>>> Engineering (RSVP-TE)/
>>>
>>
>>> Abstract and s1, first para:  This para is not future proof.  Suggest:
>>> OLD:
>>>    The scale at which RSVP-TE [RFC3209] Label Switched Paths (LSPs) get
>>>    deployed is growing continually and there is considerable onus on
>>>    RSVP-TE implementations across the board to keep up with this
>>>    increasing demand in scale.
>>> NEW:
>>>    At the time of writing, networks which utilise RSVP Traffic Engineering
>>>    (RSVP-TE) [RFC3209] Label Switched Paths (LSPs) are encountering
>>> limitations
>>>    in the ability of implementations to support the growth in the number
>>> of LSPs
>>>    deployed.  This document defines two additional RSVP-TE extensions that
>>>    are intended to reduce the number of messages needed to maintain
>>> RSVP-TE
>>>    soft state in routers and hence allow implementations to support larger
>>>    scale deployments.
>>> ENDS
>>> Note:  Omit reference from Abstract.
>>>
>>>
>> [VPB] Fixed in -07
>>
>> s1, para 2: s/under certain/beyond a certain/
>>>
>>
>> [VPB] Fixed in -07
>>
>>
>>> s1, para 3: s/makes a set of concrete implementation
>>> recommendations/defines
>>> two extensions/; s/- push higher/by increasing/; s/maintain LSP
>>> state./maintain
>>> LSP state by reducing the number of messages needed./
>>>
>>> Abstract, para 2 and s1, last para:  [Omit reference from Abstract]
>>> OLD:
>>>    This document advocates the use of a couple of techniques - "Refresh-
>>>    Interval Independent RSVP (RI-RSVP)" and "Per-Peer Flow-Control" -
>>>    for significantly cutting down the amount of processing cycles
>>>    required to maintain LSP state.
>>> NEW:
>>>    This document defines two RSVP Capabilities [RFC5063] "Refresh-
>>>    Interval Independent RSVP (RI-RSVP)" and "Per-Peer Flow-Control"
>>>    that will cut down the number of messsages and processing cycles
>>>    required to maintain LSP state.
>>> ENDS
>>>
>>
>> [VPB] Fixed in -07
>>
>>
>>> s1, last para: Add new penultimate sentence:
>>>    Note that the "Per-Peer Flow-Control" capability requires the "RI-RSVP"
>>>    capability as a prerequisite.
>>>
>>
>> [VPB] Fixed in -07
>>
>>
>>> s1, last para: s/RECOMMENDED/recommended/ - this isn't a recommendation
>>> about
>>> the protocol on the wire.
>>>
>>
>> [VPB] Fixed in -07
>>
>>
>>> Subdivision of s2:  The issues regarding the nature of the document would
>>> be
>>> helped by altering s2 into four top level sections, thus: s2: Requirement
>>> for
>>> RFC 2961 Refresh Overhead Reduction Support and Specific Option Choices
>>> (from
>>> s2.1) s3: Requirement for RFC 5063 Capability Object support (see Minor
>>> Issues
>>> above) s4: Refresh-Interval Independent RSVP Capability (from s2.3) s5:
>>> Per-Peer RSVP Flow Control Capability (from s2.4) Subsequent major
>>> sections
>>> then renumbered as s6 onwards. References to s2.x will need to be updated
>>> throughout.
>>>
>>
>> [VPB] We subdivided s2 into 3 top level sections. We did not add a
>> separate section for discussing RFC5063 Capability Object support.
>>
>>
>>> s2.1 (would be introduction of new s2):
>>> OLD:
>>>    The implementation recommendations discussed in this section are
>>>    based on the proposals made in [RFC2961] and act as prerequisites for
>>>    implementing the techniques discussed in Sections 2.2 and 2.3.
>>>
>>> NEW:
>>>    The Capabilities defined in Sections 4 and 5 of this document are
>>> based on
>>>    proposals made in [RFC2961].  Implementations of these Capabilities
>>> will
>>>    need to support the RSVP messages and techniques defined in [RFC2961]
>>> as set
>>>    out in Section 2.1 [was 2.1.1] with
>>>    some minor modifications and alterations to recommended time intervals
>>> and
>>>    iteration counts as defined in the remainder of this section.
>>> ENDS
>>>
>>>
>> [VPB] Fixed in -07
>>
>> s2.1.1, title and para 1 [will be s2.1]:
>>> OLD:
>>> 2.1.1.  Basic Prerequisites
>>>
>>>    An implementation that supports the techniques discussed in Sections
>>>    2.2 and 2.3 must meet certain basic prerequisites.
>>> NEW:
>>> 2.1.  Required Functionality from RFC 2961 to be Implemented
>>>
>>>    An implementation that supports the capabiities discussed in Sections
>>>    4 and 5 must provide a large subset of the functionality described
>>>    in [RFC2961] as follows:
>>> ENDS
>>>
>>
>> [VPB] Fixed in -07
>>
>>
>>> s2.1.2, para 2 [will be s2.2]: s/techniques discussed in Sections 2.2 and
>>> 2.3/Capabilities defined in Sections 4 and 5/
>>>
>>
>> [VPB] Fixed in -07
>>
>>
>>> s2.1.2, para 2: s/MESSAGE ID/MESSAGE_ID/
>>>
>>
>> [VPB] Fixed in -07
>>
>>
>>> s2.2, para 1: s/improvement on transmission overhead/improvement of
>>> transmission overhead/
>>>
>>
>> [VPB] Fixed in -07
>>
>>
>>> s2.2, para 1: s/proposes sufficient recommendations/sets out additional
>>> requirements/
>>>
>>
>> [VPB] Fixed in -07
>>
>>
>>> s2.2, last bullet: Add a reference to the proposed new Section 3 that
>>> discusses
>>> the Capability object.
>>>
>>
>> [VPB] Added a direct reference to RFC5063
>>
>>
>>> s2.2.1, last para: s/set Refresh-Reduction-Capable bit in common
>>> header/set the
>>> Refresh-Reduction-Capable bit in the common header/
>>>
>>
>> [VPB] Fixed in -07
>>
>>
>>> s2.3, para 1: s/set of recommendations/functionality/;
>>> s/provide/provides/;
>>> s/RSVP-TE control plane congestion/a significant portion of the RSVP-TE
>>> control
>>> message load/
>>>
>>
>> [VPB] Fixed in -07
>>
>>
>>> s2.3.2: s/MESSAGE ID/MESSAGE_ID/
>>>
>>
>> [VPB] Fixed in -07
>>
>>
>>>
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>>>
>>
>>