Re: Alia Atlas' Discuss on draft-ietf-bfd-seamless-base-09: (with DISCUSS and COMMENT)
"Carlos Pignataro (cpignata)" <cpignata@cisco.com> Tue, 03 May 2016 16:24 UTC
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From: "Carlos Pignataro (cpignata)" <cpignata@cisco.com>
To: Alia Atlas <akatlas@gmail.com>
Subject: Re: Alia Atlas' Discuss on draft-ietf-bfd-seamless-base-09: (with DISCUSS and COMMENT)
Thread-Topic: Alia Atlas' Discuss on draft-ietf-bfd-seamless-base-09: (with DISCUSS and COMMENT)
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Date: Tue, 03 May 2016 16:23:46 +0000
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Hi Alia, Thank you. Yes, I will submit before the telechat, but will still wait a couple days for additional comments. Best, — Carlos. > On May 3, 2016, at 12:21 PM, Alia Atlas <akatlas@gmail.com> wrote: > > Hi Carlos, > > This all looks good to me. Thanks for the quick resolution! > I'll clear my discuss assuming that you will submit the updated version very very soon. > > Regards, > Alia > > On Tue, May 3, 2016 at 12:13 PM, Carlos Pignataro (cpignata) <cpignata@cisco.com <mailto:cpignata@cisco.com>> wrote: > 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 <akatlas@gmail.com <mailto:akatlas@gmail.com>> wrote: >> >> Hi Carlos, >> >> On Mon, May 2, 2016 at 6:34 PM, Carlos Pignataro (cpignata) <cpignata@cisco.com <mailto:cpignata@cisco.com>> 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 <akatlas@gmail.com <mailto:akatlas@gmail.com>> 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. >> >> >> > > >
- Alia Atlas' Discuss on draft-ietf-bfd-seamless-ba… Alia Atlas
- Alia Atlas' Discuss on draft-ietf-bfd-seamless-ba… Alia Atlas
- Re: Alia Atlas' Discuss on draft-ietf-bfd-seamles… Carlos Pignataro (cpignata)
- Re: Alia Atlas' Discuss on draft-ietf-bfd-seamles… Alia Atlas
- Re: Alia Atlas' Discuss on draft-ietf-bfd-seamles… Alia Atlas
- Re: Alia Atlas' Discuss on draft-ietf-bfd-seamles… Carlos Pignataro (cpignata)
- Re: Alia Atlas' Discuss on draft-ietf-bfd-seamles… Carlos Pignataro (cpignata)