Re: [trill] RtgDir review: draft-ietf-trill-directory-assisted-encap-02

Donald Eastlake <> Wed, 17 January 2018 23:23 UTC

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From: Donald Eastlake <>
Date: Wed, 17 Jan 2018 18:23:37 -0500
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To: Ben Niven-Jenkins <>
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Subject: Re: [trill] RtgDir review: draft-ietf-trill-directory-assisted-encap-02
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Hi Ben,

Thanks for the further review and comments. See below.

Version -08 has been uploaded with the goal of resolving these comments.

On Wed, Jan 17, 2018 at 8:48 AM, Ben Niven-Jenkins
<> wrote:
> Hi Donald,
> Apologies for not responding sooner, I have reviewed the latest version (-07) and still have a couple of comments, see inline below. I have also included at the bottom of this email some additional editorial nits I found when reading -07. I have trimmed previous comment and responses from you that are now covered in the document.
> On 10 Jan 2018, at 20:05, Donald Eastlake <> wrote:
> ...
> On Thu, Oct 26, 2017 at 10:29 PM, Donald Eastlake <> wrote:
>> Hi Ben,
>> Thanks for your review. It appears that is was not responded to in a
>> timely fashion. Apologies on behalf of the authors.
>> (Your review was of the -02 version. The current version is -05.)
>> On Sun, Apr 24, 2016 at 4:28 AM, Ben Niven-Jenkins
>> <> 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. The purpose of the review is to provide assistance to the
>> > Routing ADs. For more information about the Routing Directorate,
>> > please see
>> >
>> > 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.
>> >
>> >
>> > Document: draft-ietf-trill-directory-assisted-encap-02.txt
>> > Reviewer: Ben Niven-Jenkins
>> > Review Date: 21 April 2016
>> > Intended Status: Proposed Standard
>> >
>> > Summary:
>> > I have significant concerns about this document and recommend that
>> > the Routing ADs discuss these issues further with the authors.
>> Hopefully the changes made between the version -02 you reviewed and
>> the current -05 have made some improvements and, based on your
>> comments and WG LC comments, further improvements can be made.
> I think the -07 is almost good to go, the only outstanding concern I have is with regards to the security considerations section, see below.


>> > Comments:
>> > Overall this is not the easiest document to read although some of
>> > that might be due to my lack of background in TRILL and its
>> > terminology.
>> >
>> > Major Issues:
>> >
>> > 1) The document has an Intended Status of Proposed Standard, however
>> > it does not contain any RFC2119 keywords and does not seem to make
>> > any normative statements about required behaviour which I would have
>> > expected in a Proposed Standard.
>> Well, in version -05 there is at least one keyword instance.
>> Furthermore, I don't know that such keywords need to always be used
>> when an implementation requirement level is being specified. That
>> said, we could see if additional RFC 2119 keywords are warranted.
> I noted this as a flag to the ADs because the lack of RFC2119 key words seemed unusual to me. If the ADs are happy for this to be proposed standard then I am happy with it being a proposed standard.


>> > 2) Section 4: If I understand correctly the TRILL-EN spoofs the
>> > Ingress RBridge edge node's nickname in the source address field of
>> > the TRILL header. Is this likely to introduce problems? E.g. if
>> > RBridges will accept & forward frames that have their own source
>> > address in, does it perpetuate routing loops or present security
>> > considerations that the document should discuss?
>> TRILL goes to great lengths to avoid loops and has a hop count in the
>> TRILL header so that, should there be a transient loop, a TRILL packet
>> in that loop (i.e., an encapsulated frame) will be discarded. In the
>> potentially more dangerous case of multi-destination packets, as
>> compared with known unicast, where copies could multiply due to forks
>> in the distribution tree, a Reverse Path Forwarding Check is used to
>> discard packets that appear to be on the wrong link or when there is
>> disagreement about the distribution tree.
>> Security Considerations should probably say more on this.
>> > Section 8 on Security Considerations also looks very light on
>> > text. If you are allowing TRILL-ENs to spoof RBridge source
>> > addresses (which I think you are, see comment above) I think you
>> > should have a discussion about that somewhere in the document.
>> I agree that some further discussion is needed in the Security
>> Considerations section.
> I don’t see any discussion on TRILL-ENs spoofing ingress bridge nicknames in section 7 on security considerations. I see the security consideration section of the referenced RFC6325 states "RBridges do not prevent nodes from impersonating other nodes” although RFC6325 doesn’t appear to discuss the security considerations related to allowing such impersonation.
> I think it would be valuable for the security considerations section of draft-ietf-trill-directory-assisted-encap to explicitly call out that TRILL-ENs spoof ingress bridge nicknames and explain why that is not an issue (the text you use above is sufficient for that purpose IMO).
> I leave it up to you & the chairs/ADs to decide if my suggestion is overkill and that the existing reference to RFC6325 is sufficient for a reader skilled in the art of TRILL.

A paragraph has been added to the Security Considerations to cover this.

>> > Minor Issues:
>> >
>> > 1) Section 3. I am not sure what Figure 2 is trying to convey and it
>> > is not referred to by the main text. Is it required?
>> Figure 2 is intended to show the header of a pre-encapsulated frame
>> going from a TRILL-EN to an edge TRILL switch. If it is retained in
>> the draft, there should be clarifying text that references it.
> I still don’t see any reference to figure 2 in the text (or to figure 1 for that matter).

References have been added.

>> > However, Section 4 says
>> >
>> >    The TRILL-EN learns this nickname by listening
>> >    to the TRILL IS-IS Hellos from the Ingress RBridge.
>> >
>> > which makes me think if the TRILL-EN is running IS-IS for hellos, is
>> > pushing the directory such an obstacle?
>> That text refers to snooping on IS-IS messages, not running IS-IS.
> Ah, I see. IMO explicitly using the term “snooping" rather than “listening” here (and in section 1) would make this unambiguous. I leave it up to you whether to make that change or not.

"listening" has been changed to "snooping".

>> > 4) Section 7 on Manageability Considerations only states that in
>> > order for the solution to work requires the availability of a
>> > directory service, which seems a bit redundant when the entire
>> > document is about "Directory Assisted TRILL Encapsulation”. Is this
>> > section required?
>> I agree that the Manageability Considerations section should have
>> some material added concerning configuration or be dropped.
> I see this section now includes "TRILL-EN have the same configuration options as any pull directory client.” Is there a suitable document you could informatively reference here that describes/discusses the configuration options for a pull directory client?

A reference to the appropriate section of RFC 8171 has been added.

> Minor nit: should the sentence start “TRILL-ENs”?


> Other editorial nits I found reading -07:
> Section 3, para 2 says "If a destination is not known to be attached to one or more RBridge edge nodes”. I struggled to parse this without reading it multiple times, I think what you mean to say is "If it is not known whether a destination is attached to one or more RBridge edge nodes”?

That seems to be better wording.

> Section 3, para 4: s/don’t/doesn’t/
> Section 3, para 8: s/and perform/and performs/
> Section 5.1, para 2: s/data frames with TRILL header/data frames with TRILL headers/
> Section 7, para 1: s/TRIL-ENs/TRILL-ENs/

The above editorial fixes have been made.

 Donald E. Eastlake 3rd   +1-508-333-2270 (cell)
 155 Beaver Street, Milford, MA 01757 USA

> Regards
> Ben