[Roll] AD review of draft-ietf-roll-p2p-measurement-06
"Adrian Farrel" <adrian@olddog.co.uk> Wed, 05 December 2012 14:22 UTC
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From: Adrian Farrel <adrian@olddog.co.uk>
To: draft-ietf-roll-p2p-measurement.all@tools.ietf.org
Date: Wed, 05 Dec 2012 14:22:34 -0000
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Subject: [Roll] AD review of draft-ietf-roll-p2p-measurement-06
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Hi, I have done my usual AD review of your document as part of processing the publication request. This review should be considered alongside my review of draft-ietf-roll-p2p-rpl as the documents are closely linked. I have a number of questions and minor issues that I would like to resolve before advancing the documents. As usual, all of my comments are up for discussion, but I think that a new revision will be needed, so I have moved the document into "Revised I-D Needed" state in the data tracker and will wait for your emails and/or a new revision. Many thanks for your work, Adrian --- As with draft-ietf-roll-p2p-rpl, I would like some discussion in the Introduction about why this Experimental and what you expect to discover. I think the text is easier for this document... This document provides a mechanism that can be used to determine whether and how to establish a new point-to-point route in an LLN. This utility of the mechanism described in this document is, therefore, dependent on the existence of a protocol mechanism for establishing P2P routes. [I-D.ietf-roll-p2p-rpl] is targeted at publication as an Experimental RFC for reasons described in that document. It makes sense, therefore, for this document also to be targeted as Experimental. As experience is gained using the mechanisms described in [I-D.ietf-roll-p2p-rpl] it is hoped that the mechanisms described in this document will also be used, and feedback will be provided to the ROLL working group on the utility and benefits of this document. --- I think that "quality" is the wrong word. "Quality" is usually associated with measures like packet loss, delay, and jitter. I don't think you are measuring those things, and while I understand why you say "quality of a route", I think you need some other phrase. I think this more like... A Mechanism to Record the end-to-end Metrics of a Point-to-point Route in a Low Power and Lossy Network In the Introduction, you have some nice words... to measure the aggregated values of the routing metrics along the existing route --- Abstract I'm confused :-) The document title is very specific to P2P routes. But the Abstract (deliberately?) does not mention P2P. Section 1 seems to imply that I could run the mechanisms on any route from origin to target to see if it is good enough - and that would include routes created using normal RPL. But section 2 explicitly constrains the mechanism to P2P routes. Furthermore, the redefined terminology in 1.1 (see below for my objection to that!) seem to suggest measuring from an arbitrary origin to an arbitrary target regardless of whether a P2P route exists. Can you: - unconfuse me - make sure that the abstract and introduction explain the real situation - make sure the document title is accurate - make sure that the document is consistent - be careful with terminology (just because you run the mechanism from A to B in a point-to-point sort of way, doesn't mean that there is a P2P route from A to B) --- 1.1 Did you really need to redefine these terms instead of use new terms for new concepts? Given how close the two documents are, it's a shame to confuse things. --- 3.1 I was going to say... Seems like the H flag is not needed since leaving it clear is semantically equivalent to setting RPLInstanceID=0b10000000 Not very important, but you increase the chances of a malformed message, and you use your last bit that could be reserved for future use. ...but then I read the text lower down about how a transit router can change the H flag under special circumstances. Now I am confused because if the H flag setting is changed, surely the rule governing the RPLInstanceID is broken. --- 3.1 Some of the flag settings that have no meaning dependent on other flag settings are described as "MUST be set to zero" which is fine. But should you also say they should be ignored? --- 3.1 I found the description of what goes in the Metric Container Options inadequate. There should at least be a forward pointer to some section that describes how this piece of the MO object is constructed, but some text would help as well. --- Section 4 The Origin MUST discard the MO message if: That reads a bit odd. Didn't the Origin just build the message? Why would it build a message and then discard it? Why not just not build a bad message? --- Section 5 An Intermediate Router MUST discard the packet with no further processing if the received MO is not a Measurement Request. For clarity and consistency with other paragraphs, can you add... i.e., if the T flag is not set to one. --- Section 7 The Origin MUST discard the packet with no further processing ... ... if the Origin has no recollection of sending a Measurement Request with the sequence number listed in the received MO. Trying to decide why that is a "MUST". I guess there are some security/bug considerations. But are you unduly limiting the Origin implementation to be required to keep track of the MOs that it sends? --- Section 7 The Origin MUST examine the routing metric objects inside the Metric Container options to evaluate the quality of the measured P2P route. If a routing metric object contains local metric values recorded by routers on the route, the Origin MUST aggregate these local values into an end-to-end value as per the aggregation rules for the metric. That is going too far in the use of "MUST". The Origin can do anything it likes with the Measurement Reply including discard it, hash it and use it as a random number, or process it according to policy! I think what you need is... The Origin can use the routing metric objects inside the Metric Container to evaluate the metrics for the measured P2P route. If a routing metric object contains local metric values recorded by routers on the route, the Origin can make use of these local values by aggregating them into an end-to-end metric according to the aggregation rules for the specific metric. An Origin is then free to interpret the metrics for the route according to its local policy. --- Section 8 Question. Can I use this mechanism to find out stuff about the network that should/would otherwise be private? And could I, as an outside node do that? For example, if I sit next to the network and ping every possible P2P route, can I find out which nodes are almost out of battery, and which nodes are key nodes in the topology? Knowing this would help me attack the network. What are the protections? --- 11.2 You have used [I-D.ietf-roll-p2p-rpl] as a normative reference (at least for the terminology).
- [Roll] AD review of draft-ietf-roll-p2p-measureme… Adrian Farrel
- Re: [Roll] AD review of draft-ietf-roll-p2p-measu… JP Vasseur (jvasseur)