Re: [dtn] working group last call on draft-ietf-dtn-bpbis

["Templin, Fred L" <[e-mail]>]

Hi Stephen,

I am still going through your comments, but one question that I have
on one of your points for now:

    "4) it's not ok to omit
     security mechanism definition, (making [BPSEC] normative and
     waiting on that in the RFC editor queue would fix this, and is
    IMO needed),

Wouldn't that create a circular dependency? If not, what do you see
as a way forward that would not entail a prolonged blockage in the
RFC editor queue?

Thanks - Fred
[e-mail]

> -----Original Message-----
> From: dtn [mailto:[e-mail]] On Behalf Of Stephen Farrell
> Sent: Monday, January 23, 2017 7:33 PM
> To: Marc Blanchet <[e-mail]>; dtn <[e-mail]>
> Subject: Re: [dtn] working group last call on draft-ietf-dtn-bpbis
> 
> 
> Hiya,
> 
> I've done a review of bpbis-06 and have many comments. (Sorry:-)
> 
> Overall I don't think this is ready, and some more discussion
> of some of the issues is needed. Since I've not followed the
> list as closely as I'd have liked I may have missed some such
> discussion in which case pointing me at the relevant bit(s) of
> the archive would be a fine response.
> 
> I've tried to separate stuff into things that'd cause me to
> ballot DISCUSS in IESG evaluation (*), things that might not,
> and nitty things. I hope that helps, but don't take that
> categorisation too seriously:-)
> 
> Cheers,
> S.
> 
> (*) Note that I'll likely not still be on the IESG when this
> gets there (I escape in March) so the fact that I would ballot
> DISCUSS is not that relevant to what other ADs might do.
> 
> 
> Possibly major issues (DISCUSS like)
> ------------------------------------
> 
> (A) intro: The last bullet list of the things that are not
> specified here seems problematic for a PS and I think needs
> more discussion/work. I'm not sure if it's only the text that
> needs work, or if the missing specification is required now.
> Taking the bullets one at at time (numbers are in order of
> presentation): 1) This isn't clear enough, I'm not sure what's
> being omitted, 2) Omitting routing I think is fair, 3) It's
> also fair to omot RIB/FIB issues, 4) it's not ok to omit
> security mechanism definition, (making [BPSEC] normative and
> waiting on that in the RFC editor queue would fix this, and is
> IMO needed), 5) I'm not sure what's right here.  I think it'd
> be good to have some list discussion about this, as it'll
> certainly come up in IETF LC and IESG review and having list
> traffic at which to point will help backup whatever conclusions
> are reached.  In particular in 4.3, I don't think it's
> acceptable for the BIB and BCB to not have a normative
> reference. Similarly, the "TBD" for the other extension block
> types are not appropritate. (But those can likely be
> informative refs.)
> 
> (B) The spec is overly prescriptive in many places and ought be
> loosened up wherever possible. All we need is interop and not
> the kind of conformance at which this spec seems to aim (but
> maybe miss). For exmple the "retention constraint" stuff has
> absoluely no reason to be a MUST. As another, I think section
> 5.4 only needs a MUST in step 4 and all the rest are bogus and
> a bad plan.  Also in 3.1, the text here is often far too
> prescritpive and I suspect based on only a couple of
> implementation strategies.  There are many more examples.  I
> think it'd be a good plan to do an editing pass to get rid of
> as many of the extraneous and unnecessary constraints that are
> here.  Examples feature in other comments, but I've not tried
> to be exhaustive in spotting all instances of this.
> 
> (C) Many of the flags relaed to reporting provide ways in which
> the BP, if it became widely deployed (even if not planned to be
> widely used), could be a significant (D)DoS accelerator. Has
> anyone figured out the scale factors involved, (e.g. if N bogus
> blocks say report if this can't be processed) whether those
> might be significant and if so what potential countermeasures
> might apply? Absent such an analysis, or fixing the problem,
> I'd argue it'd seem irresponsible to standardise the BP.  I'd
> say for a PS, the minimum is that BPAs MUST default to not
> sending all these new bundles except when specifically
> configured to be so verbose.  This also affects 5.1 and maybe
> elsewhere which says an agent MUST emit admin bundles if asked.
> In 5.6, step 2: again the SHOULD needs to be qualified in order
> to not have the BP be a fine DoS accelerator (given
> non-singletons). Step 3's SHOULD for this is even worse as a
> bad actor could include many such blocks.  In 5.13 - I think
> that is too many custody signals. If one envisages DTNs with
> custodians located at links that are particularly subject to
> disruption, then those may be few in number and having all
> other nodes/routers emit custody signals for each bundle not
> taken into custody seems hugely inefficient and unnecessary.
> There may be more examples.  FWIW, my guess is that if all the
> current reporting is kept, then the IESG will require some kind
> of applicability statement about the kind of network in which
> the BP can safely be deployed. For me, fixing the problem is a
> better approach than constraining it via an applicability
> statement.
> 
> A bit less major (maybe not DISCUSS-worthy)
> -------------------------------------------
> 
> (1) 3.1's definition of a bundle correctly says that bundles
> are better when they include all the meta-data that might be
> useful. If considered naively, that conflicts with modern
> approaches to privacy where we want to ensure that meta-data is
> only seen by those (nodes) that need to see meta-data, as one
> form of data minimisation. OTOH, one could argue that such
> bundles will ensure that meta-data and payloads enjoy the same
> security services, which is a good thing. In any case, I think
> it'd be useful to have a discussion about the privacy aspects
> of the BP, esp the ways in which those may be different from
> other protocols. For example, would we expect report-to URIs to
> commonly allow re-identification of a person? I don't recall
> we've ever really discussed such issues.
> 
> (2) 3.1, destination: I think this ought be clear that delivery
> to some node in the endpoint represents success, i.e.  that the
> BP does not force successful delivery to all or failure as a
> binary choice.
> 
> (3) What bad things would follow if 3.2 was deleted?  It may be
> that I'm too familiar with DTN (and hence not a good judge if
> this section is useful or not) but I didn't find it useful.
> Also - is 3.2 normative? If not, I'm even happier to see it go.
> If it is, then I gotta wonder if it conflicts with other text
> later. And I see there are a few 2119 MUSTs in there so I guess
> you do mean it to be normative or did they sneak in in by
> accident whilst editing? (As can happen.) If not deleting this
> section, I'd argue to find all the bits of text in it that are
> needed and move them all elsewhere and then delete the section.
> 
> (4) 3.2: The idea that the EID fully determines the MRG seems
> just wrong to me. While that might be a nice theory, I figure
> it's way more likely that the routing scheme determines how
> many copies of a bundle are rx'd at how many instances of the
> destination EID. What'd be bad about losing that concept and
> letting (the determinants of) the MRG be unspecified here?
> 
> (5) 3.2, "Custody of a bundle MAY be taken only if the
> destination of the bundle is a singleton endpoint." That's
> plain wrong. Not all custodians can know about the desitnation
> being a singleton or not. And before you say it, I don't
> believe in the flag in 4.1.3 that allows an origin to specify
> this - I've never seen a real example of when that's useful -
> the only nearby case I recall was where the developer (me:-)
> knew we wanted distibution to all nodes in a multi-member
> endpoint but with best effort in terms of getting to them all
> and with custody and less frequent application layer re-tx's to
> ensure we got to as many as possible.  This also affects 5.2.
> 
> (6) 3.3, I'm not sure this is useful either. What'd break if it
> were deleted? (But then I never liked those bits of DTNRG's
> work either;-)
> 
> (7) Including some examples and an RFC 7942 implementation
> status section would be a good thing, if easily done. That
> would help progression and increase confidence in the
> correctness of the spec.
> 
> (8) 4.1.6: Was sub-second timing discussed by the WG?  I'm not
> terribly pushed on that myself, but it'd be a shame to do an
> interop breaking change in the BP without discussing that
> topic. A reason to think about this is that there may be
> inter-VM (or intra-data-centre) reasons to consider the BP with
> sub-second timing as interesting.  It'd be a shame to make that
> impossible just to make it slightly simpler to represent time.
> 
> (9) 4.2.2, creation time rules: I don't see why it'd be a
> problem if node-id=X, creation-time=0,counter=0,lifetime=2s is
> used in two bundles emitted 3 seconds apart. Why does that
> justify a MUST NOT in the spec?
> 
> (10) 4.2.2: The "30 seconds" rule also seems wrong to me, as is
> the "MUST NEVER" (not a 2119 term btw) for re-use of the seq
> no, which is unrealistic.  As an example of that last: what do
> you expect to happen with a node that usually knows the wall
> clock time, but, at this moment, knows that it does not? E.g.
> previous logs have some real dates, but current clock is
> 1970-01-01 or whatever. I think this is fixable but the current
> language is too prescriptive. Best might be to weaken the
> language here and to see what implementations do in the real
> world.
> 
> (11) 4.3.1: Is the SHALL here right? I would have thought a
> SHOULD is better to allow for legacy interop with 5050 via
> gateways, in which case there may be no node ID. That might be
> better off handled in some generic fashion though, and not
> piecemeal with each mention of node ID.
> 
> (12) 4.3.2: I don't believe it is correct to drop a bundle due
> to the lack of a previous node block, which is what sems to be
> implied here. Not all routing schemes need this and so it ought
> not be a MUST. Maybe a SHOULD is enough, but even if you say
> "MUST insert this" then I would like to argue that "receivers
> can decide to not care" be stated explicitly e.g.  by saying
> that bundles MUST NOT be rejected solely due to the lack of
> this EB.
> 
> (13) I'm not sure if you have all the right "watch out for the
> null EID node ID" text needed. (I didn't go back over
> everything, but it'd seem wrong e.g. in an current custodian
> AR.
> 
> (14) 5.4: "The bundle protocol agent MUST determine which
> node(s) to forward the bundle to." That's ungrammatical and
> close to BS - what if I want to multicast or broadcast the
> bundle or use some other opportunistic CLA? Or a sneakernet
> where nobody knows who'll be next hop.
> 
> (15) 5.4: The text about the flow label should be deleted as it
> says nothing. If includng this, then the flow label spec may
> need to be a normative ref (arguably).
> 
> (16) 5.4 - I think this is badly misleading. There will be many
> cases where a bundle cannot be forwarded now but may be
> forwarded later. Am I wrong in reading this section as
> precluding that?
> 
> (17) 5.6, step 4 says one MUST handle "custody transfer
> redundancy" but that term seems undefined.
> 
> (18) 5.6 (step 5) points back to 5.3 which points to 5.7 or
> 5.4. I don't think such GOTOs are a good idea really.  I
> suggest removing lots of this and adding in some informative
> (i.e. non-normative) pseudo code (or real code) as an appendix.
> 
> (19) I think some rules related to custody and fragmentation
> may be missing. For example, if bundle A is multicast and
> reaches two nodes on different paths who take custody
> (custodians C1/C2) and who both fragment but differently (into
> F11/F12 and F21/F22 resp) with eventually a custody ack for F21
> reaching C1.  Assume F21 is longer than F11, what is C1 to do
> with F11 when a custody timer expires?  Ought it re-transmit or
> consider that the custody ack for F21 matched F11 sufficiently
> well?  I'm not sure what'd be right here, if such cases can
> happen.  I'd be fine with the spec admitting that some such
> corner cases exist, or maybe it's easy enough to figure out,
> not sure.
> 
> (20) 5.10.1, I've always wondered why custody timer expiry is
> covered here, and not really considered a part of DTN routing.
> It seems to me to make more sense to couple custody timing and
> routing. If that resonated with folks, I think the change would
> be to make the timer-related text here into an illustrative
> example and to say that such things are better considered
> together with routing and/or by chunks of code that are
> somewhat more topology/disruption-aware of the situation in the
> particular DTN.
> 
> (21) section 9 seems woefully incomplete - why is it ok to say
> "will be required" at WGLC? Surely the WG should at least have
> discussed the set of registries needed and the registration
> rules for those? E.g. do we sill want CCSDS to be able to add
> entries to some of those registries as we did with 5050?  And
> has the WG considered how do all the things in this draft
> relate to the set of IANA registries related to the BP? [1,2]
> (In the case of [3], section 4.1.5.1 really probably does need
> to say something.)
> 
>   [1] https://www.iana.org/assignments/bundle/bundle.xhtml
>   [2]
> https://www.iana.org/assignments/uri-schemes/uri-schemes.xhtml#uri-schemes-1
> 
> Seemingly more minor or nitty things
> ------------------------------------
> 
> - abstract: "This Internet Draft" is no longer appropriate
> language.
> 
> - abstract: I think this ought capture the fact that this
> version is not interoperable with 5050. That's not a bad thing,
> but worth noting here.
> 
> - intro: I don't think the "sales" language is needed or
> appropriate in the first couple of paras. It should be entirely
> ok to say "we've learned stuff and fixed stuff."
> 
> - intro: "Custodial forwarding" is too terse at this point but
> also hard to explain briefly, is really a mechanism and not a
> capabililty, and maybe not such a highlight, so I'd delete that
> bullet
> 
> - intro: "[TUT]" is quite outdated and using dtnrg.org for the
> reference isn't wise (particularly at the moment when we're
> seeing SERVFAIL from the relevant NS;-)
> 
> - intro: this is a bit self-serving, but maybe a reference to
> the architectural retrospective [3] that Kevin and I wrote
> might be useful here, though I've not checked if it touches on
> enough of the issues behind the differences between 5050 and
> this.
> 
>    [3] https://ieeexplore.ieee.org/document/4530739
> 
> - Figure 1: I wonder if it'd be worth pointing out that the BP
> does not have to run over a layer 4 that runs over a layer 3
> etc. The figure and this text does give that impression that a
> "proper" transport is needed, which isn't the case.
> (Tactically, I'm not sure if the text as-is, or something more
> correct, would make getting a new RFC easier or harder - I
> guess it'll depend on the reader;-)
> 
> - Figure 2: Few if any of the applications I've used with the
> BP had an administrative element. That's maybe down to the
> experimental nature of the work we've done but I don't think
> it's correct to imply that all applications using the BP need
> to be able to handle admin records, if that's what you're
> implying. (I'm not sure.) I'd say indicating that that's an
> optional thing would be right.
> 
> - 3.1, singleton: not sure if it's clear enough that all
> endpoints are sets, so this may puzzle folks. Maybe add e.g.
> "remember that endpoints are sets," not sure.
> 
> - 3.1, forwarding: the text is odd - "sustained effort" is not
> mandatory, and what "that node" is meant here?
> 
> - 4: The first two SHALL statements are odd in that there's no
> way in which one could implement this spec and not conform to
> those I think. In cases like that it's fine to avoid 2119
> language. Not a big deal though, as the current IESG don't get
> anal about that, though some ADs in the past have done;-)
> 
> - 4: last item MUST be break stop code. Is a decoder supposed
> to barf a bundle if this is not true? More generally, same
> question applies for all MUSTs stated only in terms of what the
> encoding must match.
> 
> - 4.1.1: why >1 CRC type? That seems bogus. None or strong
> seems better to me. (And I'd go for a crypto hash for strong.)
> I assume the WG discussed this and found that there are real
> use-cases for each of those specified. While those don't need
> to be in the spec, can someone tell me what they are as I'm not
> at all sure, e.g. why a 16 bit CRC is useful as an option.
> 
> - 4.1.3: "enables anonymous bundle transmission" - that's
> overstated, chances are that something in the CLA will be
> identifying, or allow re-identification, so I think what you
> want to say is that omitting the source EID helps with, but
> does not ensure, nymity.
> 
> - 4.1.5.1: RFC3986 is the correct reference here, so the spec
> text is correct as-is. It may however be worth taking a look at
> the whatwg web page that has sometimes claimed to supercede
> 3986 for the browser-related things in which whatwg have an
> interest.  That's just in case there're some useful error
> handling considerations on the whatwg web page, (on the day you
> look at it;-). It's also the case that since BP EIDs are URIs,
> it's possible that strings that comply with today's or
> yesterday's whatwg web page may end up in the BP, so it'd be
> good to know if any of those (that are not valid according to
> 3986) might cause a problem with the CBOR encoding.
> 
> - 4.1.5.2: Danger, metaphysics! "Every node MUST be a member of
> at least one singleton endpoint." This entire section is
> over-thought.  I think all you need to say is that nodes the
> emit bundles need to have an EID they can use as a source EID
> for as long as necessary.
> 
> - 4.2.1: this entire section is duplicative. That's a bad idea.
> 
> - 4.2.2: 2nd para is badly written - that'd encourage coders to
> use the values 8,9,10 and 11 in ways that might be unwise.
> 
> - 4.2.2: wrt "anonymous" see earlier comment
> 
> - 4.2.2: description of creation time is duplicative, except
> the earlier text didn't cover relative time.
> 
> - 4.3.3: Is "Bundle Age Block" a good name? BAB used to mean
> another type of block, so that could confuse maybe. (That said,
> I forget how long we're had this name.)
> 
> - 4.3.4: Do you need to say that the hop limit MUST NOT be
> changed, once a hop count EB is added. Also, can any node add
> one of these, if one was not prevsiously present?
> 
> - 5: It's not necessary to say that new RFCs can supercede
> this.  That's just standard IEFF process.
> 
> - 5.2: mentions "dispatch pending" as if I should know what
> that is - is all the retention constraint stuff sufficiently
> explained I wonder? (Personally I don't think you need to
> mandate all this stuff and you cannot tell if an implementation
> has done it or not so I'd not bother trying to be so
> prescriptive.)
> 
> - 5.4: "at the last possible moment... MUST..." that's a bit
> silly as it seems to require BP code inside a NIC which is not
> how this'll usually be implemented.
> 
> - 5.5: I'm not convinced that the MUSTs here are right for all
> DTNs. I reckon that 5.5 could just as well say "MAY delete" and
> the BP would be fine. That might also provide some additional
> flexibility for some rounting schemes. That said, I won't press
> on this - if this doesn't resonate with folks now, and later
> turns out to be useful, I don't think we'd have such a hard
> time modifying BPAs where needed.
> 
> - 5.6: Again, this is overly prescriptive.
> 
> - 5.6, step 4: I wonder if an implementer will get all this
> right.
> 
> - 5.9: Badly implemented, re-assembly can create a memory
> consumption DoS vector, perhaps esp. if attempted on a
> non-destination node. It'd be better to warn about that. And
> maybe change from MAY for in-path reassembly to SHOULD NOT.
> 
> - 5.11: does this mean that a custodian MUST ignore a custody
> signal destined for some other custodian?
> 
> - Figure 6: I don't get when reason codes 5 to 8 would really
> be used. Are they in fact needed?  (They seem a bit
> implementation specific to me, but I've not gone looking.)
> 
> - section 8: First sentence is bogus.
> 
> - section 8: [SECO] isn't a good reference. It's outdated and I
> doubt will be picked up.
> 
>