Re: Alia Atlas' Discuss on draft-ietf-bfd-seamless-base-09: (with DISCUSS and COMMENT)

["Carlos Pignataro (cpignata)" <[e-mail]>]

Hi, Alia,

Thanks for the response!

We are on the exact same page regarding items #1 and #2.

For item #3, we really want to modularize the specs and not tie the -base to the transports. Note that we mention “UDP” but also “associated channel type”.

For #3, here’s the change I implemented:

    S-BFD packet MUST be demultiplexed with lower layer information
-   (e.g., dedicated destination UDP port, associated channel type).
-   Following procedure SHOULD be executed on both initiator and
-   reflector.
+   (e.g., dedicated destination UDP port [I-D.ietf-bfd-seamless-ip],
+   associated channel type [I-D.ietf-pals-seamless-vccv]).  Following
+   procedure SHOULD be executed on both initiator and reflector.

And please find attached full diffs addressing all the Discuss points.

Thanks!

— Carlos.



> On May 3, 2016, at 10:53 AM, Alia Atlas <[e-mail]> wrote:
> 
> Hi Carlos,
> 
> On Mon, May 2, 2016 at 6:34 PM, Carlos Pignataro (cpignata) <[e-mail] <mailto:[e-mail]>> wrote:
> Hi, Alia,
> 
> Thanks for your review and for bringing up these issues — please see inline.
> 
> > On May 2, 2016, at 5:24 PM, Alia Atlas <[e-mail] <mailto:[e-mail]>> wrote:
> >
> > Alia Atlas has entered the following ballot position for
> > draft-ietf-bfd-seamless-base-09: Discuss
> >
> > 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-bfd-seamless-base/ <https://datatracker.ietf.org/doc/draft-ietf-bfd-seamless-base/>
> >
> >
> >
> > ----------------------------------------------------------------------
> > DISCUSS:
> > ----------------------------------------------------------------------
> >
> > a) In Sec 7.2.3:  "If the SBFDReflector is generating a response S-BFD
> > control packet for a local entity that is in
> >      service, then "state" in response BFD control packets MUST be set
> > to UP."
> >    So far, it looked like the SBFDReflector only sends BFD control
> > packets in response to receiving such packets
> >    from SBFDInitiators.   This paragraph (not just copied) does not
> > clearly describe the desired behavior.  If the
> >   monitored local entity is "temporarily out of service", does the
> > SBFDReflector respond back to the SBFDInitiator
> >   with 2 BFD control packets - one indicating UP (as a MUST) and then
> > the next indicating ADMINDOWN?  Is the
> >   SBFDReflector expected to store a list of active SBFDInitiators and
> > proactively send BFD control packets indicating
> >   ADMINDOWN?   Please clarify in non-trivial detail.
> 
> The way in which that particular bullet in that subsection is written can be a bit confusing.
> 
> First, you are right that the SBFDReflector only sends packets in response to S-BFD control packets from the SBFDInitiators. This is clearly spelled out in Section 5, and in other places that explain how the reflector is stateless.
> 
> The SBFDReflector only response and does not stores a list of SBFDInitiators to proactively send S-BFD packets (see Section 5). Further, it does not respond with two packets. (UP and ADMINDOWN).
> 
> I think this can be rewritten to better explain what happens, as follows:
> 
> OLD:
>    o  If the SBFDReflector wishes to communicate to some or all
>       SBFDInitiators that monitored local entity is "temporarily out of
>       service", then S-BFD control packets with "state" set to ADMINDOWN
>       are sent to those SBFDInitiators.  The SBFDInitiators, upon
>       reception of such packets, MUST NOT conclude loss of reachability
>       to corresponding remote entity, and MUST back off packet
>       transmission interval for the remote entity to an interval no
>       faster than 1 second.  If the SBFDReflector is generating a
>       response S-BFD control packet for a local entity that is in
>       service, then "state" in response BFD control packets MUST be set
>       to UP.
> 
> NEW:
>    o  If the SBFDReflector, upon receiving an S-BFD control packet from
>       an SBFDInitiators, wishes to communicate to those
>       SBFDInitiators that a monitored local entity is "temporarily out of
>       service", then an S-BFD control packet with "state" set to ADMINDOWN
>       is sent in response to those SBFDInitiators.  The SBFDInitiators, upon
>       reception of such packets, MUST NOT conclude loss of reachability
>       to corresponding remote entity, and MUST back off packet
>       transmission interval for the remote entity to an interval no
>       faster than 1 second.  If, on the other hand, the SBFDReflector is generating a
>       response S-BFD control packet for a local entity that is in
>       service, then "state" in response BFD control packets MUST be set
>       to UP.
> 
> Is that more clear?
> 
> Slightly - but what about:
> 
> "When the SBFDReflector receives an S-BFD control packet from an SBFDInitiator,
> then the SBFDReflector needs to determine what state to send in the response S-BFD
> control packet.  If the monitored local entity is in service, then the "state" MUST be
> set to UP.  However, if the monitored local entity is "temporarily out of service" for
> rapidly processing S-BFD packets, for instance due to an overload, then the "state"
> SHOULD be set to ADMINDOWN.  The SBFDReflector SHOULD send a response
> S-BFD control packet.
> 
> When an SBFDInitiator receives a response S-BFD control packet, if the state specified
> is ADMINDOWN, the SBFDInitiator MUST NOT conclude loss of  reachability
> to corresponding remote entity, and MUST back off packet transmission interval for the
> remote entity to an interval no faster than 1 second. "
> 
> Either wording or a mixture is just fine.
> 
> >
> > b) Appendix A:  The looping problem is nicely defined but the text still
> > discusses three potential solutions; clearly the
> > use of the D bit has been chosen.   It would be much nicer to have the
> > justification in line, but for this discuss - the
> > unselected alternatives don't belong.
> >
> 
> Sorry I’m not sure I understand fully your point. Are you suggesting we mention in the actual reason for the D-bit procedures outside the Appendix (although the procedures for the D bit are explained in Section 6.2, 7.2.2, 7.2.3, 7.3.2, and 7.2.2), while still leave the Appendix as-is?
> 
> If so we can do that, but want to confirm.
> 
> I'm suggesting that you mention the reason for the D-bit procedures outside the Appendix and remove the Appendix.  Alternately, keep the Appendix but remove discussion of the other ways the problem could have been solved and add a reference from the D-bit procedures to the Appendix.
> 
> Once this is an RFC, it doesn't matter what the other possible and unselected design choices were.
> 
> > c) Sec 7.2.1: "   S-BFD packet MUST be demultiplexed with lower layer
> > information
> >   (e.g., dedicated destination UDP port, associated channel type)."
> >  Where precisely is this defined or described?  Is there an allocation
> > for a dedicated UDP
> > port for S-BFD?  I don't see any normative reference to such.  In
> > particular, since the format
> > for an S-BFD control packet is exactly the same as for BFD and since only
> > this demultiplexing
> > with lower layer information is used to tell the difference between S-BFD
> > and BFD packets,
> > this document requires more specifics.
> >
> 
> This is similar to RFC 5880 and RFC 5881. The actual S-BFD applications specify this. For example, bfd-seamless-ip defines the UDP port. We purposely do not want to have the specification (either explicitly or normatively pointed to) from this document, as this is just the base specification.
> 
> Why?  Unlike RFC 5880, this document mentions UDP ports as an example of a demultiplexer.
> While I do understand that BFD can run with different transports, it is useful to clearly articulate
> one use transport that has enough information to be actually implemented.   In this case, that's
> just a normative reference to another document progressing at the same time.
> 
> I can't get too worked up about normative vs. informative references in general - the guideline I
> use is whether an implementor would need to read the reference to properly implement the
> functionality.
> 
> If you feel extremely strongly that the reference must be informative, I'm not going to dig in my
> heels - but PLEASE put a reference by the mention of the UDP port.
> 
> 
> >
> > ----------------------------------------------------------------------
> > COMMENT:
> > ----------------------------------------------------------------------
> >
> > 1) In the last paragraph of Sec 4.2: "  Even when following the separate
> > discriminator pool approach,
> >   collision is still possible between one S-BFD application to another
> >   S-BFD application, that may be using different values and algorithms
> >   to derive S-BFD discriminator values.  If the two applications are
> >   using S-BFD for a same purpose (e.g., network reachability), then the
> >   colliding S-BFD discriminator value can be shared.  If the two
> >   applications are using S-BFD for a different purpose, then the
> >   collision must be addressed.  How such collisions are addressed is
> >   outside the scope of this document."
> >
> >  Sec 4.1 talks about the need for the S-BFD Discriminator to be unique
> > within an Administrative Domain.
> >  I don't see any details of that addressed here.   What is addressed
> > here seems to be the case for multiple
> >  S-BFD discriminators applying to the same node - which is specifically
> > discouraged at the end of Sec 3.
> >  Rather than simply describing the issue as "outside the scope of this
> > document", please either describe it
> >  as "future work and multiple S-BFD discriminators is discouraged" or
> > add a reference.
> >
> 
> Good point, will do.
> 
> > 2) In Sec 6.1: "bfd.SessionType:" is defined but the only possible values
> > are for SBFD.   Is it possible for a BFD
> > session to still use the same bfd structure?  I don't see a value for
> > SessionType there; I'd expect to see at least
> > a value for the original BFD session and possible an undefined or
> > unspecified value for future proofing.
> >
> >
> 
> Traditional BFD does not use this state variable. That’s why we don’t need to define a value for BFD. However, future specs can when it is relevant (e.g, using BFD for various types as opposed to S-BFD), as for example bfd-multipoint.
> 
> Right - I understand that.  I'm thinking a bit from the implementation perspective.  If I have the same data-structures and similar logic for BFD and S-BFD, then there'll be a bfd.SessionType even for BFD sessions that don't need it.  Clarifying a value of "Unused" or "Classical BFD" gives clarity that one
> of the S-BFD options doesn't need to be chosen.
> 
> This is just a comment.  It's up to your best judgement.
> 
> Thanks,
> Alia
> 
> 
> Please let us know your thoughts on the responses above, and we can send out diffs.
> 
> Thanks!
> 
> — Carlos.
> 
> 
>