Re: [trill] Routing directorate review of draft-ietf-trill-channel-tunnel

[Donald Eastlake <[e-mail]>]

Hi Jonathan,

Thanks for agreeing that the suggested changes resolve our comments.  I
think they are pretty much editorial/clarification so I'll go ahead and
post a revision incorporating them.

Donald
===============================
 Donald E. Eastlake 3rd   [phone] (cell)
 155 Beaver Street, Milford, MA 01757 USA
 [e-mail]

On Wed, May 4, 2016 at 7:29 AM, Jonathan Hardwick <
[e-mail]> wrote:

> Hi Donald,
>
> Thanks for the replies - I agree with the changes you propose.  Please see
> discussion below (look for [JEH]).
>
> Best regards
> Jon
>
> -----Original Message-----
> From: Donald Eastlake [mailto:[e-mail]]
> Sent: 01 May 2016 21:46
> To: Jonathan Hardwick <[e-mail]>
> Cc: <[e-mail]> ([e-mail]) <[e-mail]>;
> [e-mail]; [e-mail];
> [e-mail]; [e-mail]
> Subject: Re: Routing directorate review of draft-ietf-trill-channel-tunnel
>
> On Thu, Apr 28, 2016 at 9:26 AM, Jonathan Hardwick <
> [e-mail]> wrote:
> > Hello,
> >
> > I have been selected as the Routing Directorate reviewer for this
> > draft. The Routing Directorate seeks to review all routing or
> > routing-related drafts as they pass through IETF last call and IESG
> > review, and sometimes on special request. The purpose of the review is
> > to provide assistance to the Routing ADs. For more information about
> > the Routing Directorate, please see
> > http://trac.tools.ietf.org/area/rtg/trac/wiki/RtgDir
> >
> > Although these comments are primarily for the use of the Routing ADs,
> > it would be helpful if you could consider them along with any other
> > IETF Last Call comments that you receive, and strive to resolve them
> > through discussion or by updating the draft.
> >
> > Best regards
> > Jon
> > ===
> >
> > Document: draft-ietf-trill-channel-tunnel
> > Reviewer: Jon Hardwick
> > Review Date: 28 April 2016
> > Intended Status: Standards Track
> >
> >
> > Summary
> >
> > I have some concerns about this document and recommend that the
> > Routing ADs discuss these issues further with the authors.
> >
> >
> > Comments
> >
> > The draft is overall well written and the specification is quite easy
> > to understand,
>
> Thanks.
>
> >                      but I found some of the terminology and rationale
> > to be confusing.  I would prefer to see this clarified before the
> > document is published as RFC.  Note that this is the first TRILL
> > document I’ve reviewed, so my context comes largely from mailing list
> > searches and the shepherd’s report.
> >
> >
> > Major Comments
> >
> > The motivations for this draft are quite obscure from the perspective
> > of the outsider J which makes it hard for me to evaluate the proposed
> > mechanism.
> >
> > I think the problems that the draft solves should be more clearly
> > spelled out.  From the introduction:
> >
> >    This document updates [RFC7178] and specifies extensions to RBridge
> >    Channel that provide two additional facilities as follows:
> >
> >       (1) A standard method to tunnel a variety of payload types by
> >           encapsulating them in an RBridge Channel message.
> >
> >       (2) A method to provide security facilities for RBridge Channel
> >           messages.
> >
> > I think that number (1) requires more explanation because the RBridge
> > channel already provides a standard method for a variety of payload
> > types to be transmitted without needing the current draft.
> > What tunneling capability is this draft adding?
>
> Good point.
>
> The RBridge Channel facility does provide a "protocol number" which is, in
> essence, the "type" of its payload. However, there are three limitations of
> RBridge Channel: (1) No security; (2) No way to leverage the many existing
> defined Ethertypes as a payload type; and
>
> [JEH] OK, now I understand (2), thank you.  I thought maybe you'd allocate
> Chanel protocol numbers to match Ethertypes as needed, though I now see
> that this would be quite tedious process-wise (not to mention that
> Ethertype has 4 additional bits). [/JEH]
>
> (3) RBridge Channel can only send typed messages either (3a) between
> RBridges in a campus and (3b) between end stations and RBridges on the same
> link. Earlier versions of this draft included mechanisms extensions in area
> 3, for example, for sending RBridge Channel messages between end stations
> and RBridges not on the same link; however, this added significant
> complexity and there appears to be no current need for such extensions so
> they were dropped, leaving only extensions in areas 1 and 2.
>
> [JEH] OK.  Number 3 does sound a bit more like tunnelling than 1 or 2.
> Helps to have the history, thanks. [/JEH]
>
> How about the following change on additional facility 1 in the draft:
>
> OLD
>       (1) A standard method to tunnel a variety of payload types by
>           encapsulating them in an RBridge Channel message.
> NEW
>       (1) A standard method to tunnel payloads whose type may be
>           indicated by Ethertype through encapsulation in RBridge  Channel
> messages.
>
> [JEH] Yes, looks good. [/JEH]
>
> > A significant amount of text in the draft discusses number (2), which
> > secures the channel payload, presumably to cover cases where the
> > payload has no in-built security mechanism.  This appears to be the
> > major purpose of the draft.  The draft achieves number (2) by adding a
> > security shim header between the RBridge channel header and the
> > payload.  One consideration in doing this is to remain backwards
> > compatible with RFC 7178, and it looks like the working group has
> > decided to achieve backwards compatibility by defining a new RBridge
> > channel protocol type called “channel tunnel” – where this effectively
> > means the RBridge channel payload contains an additional security shim
> > which in turn contains an identifier that determines the real payload
> > protocol type.
> >
> > I find the term “channel tunnel” misleading, as the draft does not
> > appear to add any additional tunnelling capability above and beyond
> > the tunnelling that can already be done using RFC 7178.  The draft
> > actually describes an RBridge channel with enhanced security, so a
> > term like “secure channel” would make more sense to me than “channel
> > tunnel”.
>
> OK, I understand why you think that term is misleading. While it seems
> quite reasonable to called the added fields a "shim", note that the
> facility currently called "Channel Tunnel" is quite closely integrated with
> the existing RFC 7178 RBridge Channel facility. For example, there is only
> one error reporting mechanism. Errors in the "Channel Tunnel" facility
> added by this draft are reported as if they were errors in the RBridge
> Channel messages to which the "shim" was added.
>
> I don't actually like your suggestion of "secure channel" as a new name.
> How about re-naming the facility being added by this draft as the "RBridge
> Channel Header Extension"?
>
> [JEH] OK, I like RBridge Channel Header Extension. [/JEH]
>
> I believe that RFC 7783 and only that RFC that references this draft using
> the term "Channel Tunnel" but this is a very minor informational passing
> reference. There are drafts in the publication requested state that
> reference this draft using the term "Channel Tunnel" but it seems that it
> would be relatively straightforward to change the name to "RBridge Channel
> Header Extension" or some other new name in those drafts and even easier to
> change it in drafts still under the control of the TRILL WG.
>
> [JEH] Thanks, this works for me. [/JEH]
>
> > Minor Comments
> >
> > Section 3.1 – “Any particular use of the Null Payload should specify
> > what VLAN or priority should be used when relevant.” – is unclear and
> > no context for this statement is given.  Should be used by what and
> > for what purpose?
>
> OK. How about:
>
>    Any particular use of the Null Payload should specify what VLAN or
>    FGL and what priority should be used in the inner data label of the
>    RBridge Channel message (or in an outer VLAN tag for the native
>    RBridge Channel message case) when those values are relevant.
>
> [JEH] Fine [/JEH]
>
> > Section 4.3 feels like a corollary to section 4.5 and so may be better
> > placed as a subsection of 4.5.
>
> The method of deriving keying material given in Section 4.3 is also used
> in DTLS security as mentioned in Section 4.6 so I think it should remain a
> separate section.
>
> [JEH] OK [/JEH]
>
> > Section 4.6 “The PType indicates the nature of the application_data.”
> > - is potentially open to misinterpretation.  At face value it sounds
> > like you are leaking some potentially sensitive information about the
> > “nature” of the encrypted payload.  I think all you are actually
> > saying is that it indicates whether the payload is an Ethertype, an
> > Ethernet frame etc.  Suggest instead “In this case, the PType value in
> > the RBridge Channel Tunnel Protocol Specific Data applies to the
> > decrypted application_data.”
>
> OK.
>
> > Section 5.2 “with a payload type (PType) indicating a nested RBridge
> > Channel message” – strictly all the PType can indicate is that the
> > payload is Ethertyped; on its own it cannot indicate a nested RBridge
> > Chanel message.  Suggest “and it contains a nested RBridge Chanel
> > message”.
>
> OK.
>
> > Section 6.2
> >
> > “Section xxx of [RFC 7178]” should be “Section 3.2 of [RFC 7178]”.
>
> Right. Sorry about that.
>
> > Don’t you also need a new IANA registry for the “Rbridge Channel Error
> > Subcodes” listed in table 5.2?
>
> My opinion is that, for the first document in which you specify a field
> and some values, it is a judgment call whether you should create an IANA
> registry or not.  If you expect multiple groups to start requesting values
> to multiple purposes, then creating a registry from the start is the way to
> go. On the other hand, if a field is internal to a particular protocol and
> you don't expect any new field values to be assigned until there is a
> significant extension of that protocol, I don't see any problem in
> deferring the registry creation to the second document. This is the second
> document assigning values for RBridge Channel Error Codes so it creates a
> registry for them. It does not create a registry for SubERR field values.
>
> [JEH] OK, just checking, and happy to defer to your judgment here. [/JEH]
>
> > Nits
> >
> > Section 3.2
> >
> > “as describe in” -> “as described in”
>
> OK.
>
> > Section 4
> >
> > “not to met” -> “not to meet”
>
> OK.
>
> > 2nd paragraph – this sentence is quite long and hard to parse.
>
> You're right. Looking at the sentence, it seems fairly easy to simplify
> and split into two sentences. How about the following
> replacement:
>
>    The Channel Tunnel DTLS based security specified in Section 4.6
>    below is intended for pairwise (known unicast) use. That is, the
>    case where the M bit in the TRILL Header is zero and any
>    Outer.MacDA is individually addressed.
>
> [JEH] Looks good. [/JEH]
>
> > Section 4.2 & Section 5.1
> >
> > “As show in” - > “As shown in”
>
> OK.
>
> > Section 4.3
> >
> > “The use Derived Material” -> “The use of the Derived Material”
>
> OK.
>
> > Does Derived Material really need to be capitalized in this section?
>
> Well, it is capitalized in the equation. Seems to me reasonable to
> capitalize in both cases to indicate that a specific type of Derived
> Material is being talked about.
>
> [JEH] OK. [/JEH]
>
> > Section 4.5
> >
> > “can reasonable be” -> “can reasonably be”
>
> OK.
>
> > Section 4.6
> >
> > “minimum MTU Sz” -> “minimum MTU size”
>
> Sz is a standard TRILL symbol widely used in TRILL documents and defined
> in Section 1.1 of this draft. I would prefer to make the following change
> in Section 4.6: "the TRILL campus wide minimum MTU Sz" -> "Sz".
>
> [JEH] OK - sorry, I missed the definition! [/JEH]
>
> > “Actual application_data sent with Channel Tunnel” -> “Actual
> > application_data sent within the Channel Tunnel”
>
> OK.
>
> > Why do you say “application_data” not “application data”?
>
> "application_data" is the name of the field type in DTLS.
>
> [JEH] OK. [/JEH]
>
> > Appendix Z should presumably be removed prior to IETF last call.
>
> While I'm not sure how much help it would be to IESG members or IETF
> participants in reviewing the draft, I don't see any reason for Appendix Z
> to be removed until RFC publication. But at least a notation asked the RFC
> Editor to delete it should be added.
>
> [JEH] OK - please add the RFC editor note. [/JEH]
>
> Thanks,
> Donald
> =============================
>  Donald E. Eastlake 3rd   [phone] (cell)
>  155 Beaver Street, Milford, MA 01757 USA  [e-mail]
>