[6tisch] Comments on draft-ietf-6tisch-msf-02 - Re: draft-ietf-6tisch-msf-02.txt is published
Yasuyuki Tanaka <yasuyuki.tanaka@inria.fr> Mon, 18 March 2019 14:50 UTC
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From: Yasuyuki Tanaka <yasuyuki.tanaka@inria.fr>
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Subject: [6tisch] Comments on draft-ietf-6tisch-msf-02 - Re: draft-ietf-6tisch-msf-02.txt is published
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Hi, Thank you, Tengfei and the other authors, for updating the draft! I'm sharing my comments on the latest version. https://tools.ietf.org/html/draft-ietf-6tisch-msf-02 [Security Consideration on autonomous SHARED cell allocation] > 4.5. Step 4 - Installing Autonomous Cells for each neighbor in neighbor > table > > Because it has learnt the link-layer keying material used in the > network, the joined node can now decrypt any packets sent by its > neighbors. Once a new neighbor is added to the neighbor table, a new > autonomous SHARED cell MUST be added to that neighbor. As per the second sentence in this section, a JP MUST allocate an autonomous SHARED cell to a pledge during its secure joining process. Tengfei's email says no action required on the JP side, but the JP need to have a neighbor table entry (neighbor cache entry) for the JP in order to send back a join response, doesn't it? I may miss something. tengfei> [Resolved. During join process, only pledge required to tengfei> install autonomous SHARED cell to JP, no action required from tengfei> JP side.] If this is the case, I would propose to add some note in Security Considerations section where we mention risks of this kind allocation, and may suggest a mitigation technique such as "on-demand allocation". Basically this is the same comment as the first one in the following email: https://mailarchive.ietf.org/arch/msg/6tisch/9jcaTddi6vLO5zHqTDNk6yqrNao [Join request packets can still increment NumCellUsed?] tengfei> non-trusted packet shouldn't be accounted for for adapting tengfei> traffic tengfei> ==================== tengfei> Mention that the untrusted packet (e.g. join tengfei> request/response) shouldn't be counted for adapting the tengfei> traffic. Issues link: tengfei> https://github.com/twatteyne/draft-ietf-6tisch-msf/issues/15 tengfei> tengfei> [Resolved. clarified in adapting traffic section.] I think this issue hasn't been resolved yet by the latest draft. I expect text describing how to handle packets having code point AF42 or AF43. https://tools.ietf.org/html/draft-ietf-6tisch-minimal-security-09#section-6.1 [EB / DIO transmission rules] I would propose to remove the third and fourth paragraphs mainly for these two reasons: - This is an implementation-specific optimization - This is irrevalnt to the scheduling function itself > 2. Interface to the Minimal 6TiSCH Configuration > > (snip) > > Because the minimal cell is SHARED, the back-off algorithm defined in > [IEEE802154-2015] is used to resolve collisions. To ensure there is > enough bandwidth available on the minimal cell, a node implementing > MSF SHOULD enforce the following rules for broadcast frames: > > 1. send EBs on a portion of the minimal cells not exceeding > 1/(3(N+1)), where N is the number of neighbors of the node. > 2. send any other broadcast packets on a portion of the minimal > cells not exceeding 1/(3(N+1)), where N is the number of > neighbors of the node. For example, the broadcast DIO and DIS, > IPv6 Neighbor Discovery (ND)[RFC4861] and any other application > layer broadcast packets. > > The RECOMMENDED behavior for sending EBs is to have a node send EBs > with a probability of 1/(3(N+1)). The RECOMMENDED behavior for > sending DIOs is to use a Trickle timer with rate-limiting. There is > no recommendation behavior for sending any other broadcast. However, > the traffic portion of all broadcast packets on minimal cell, except > EBs, MUST not exceed 1/(3(N+1)). Here is Xavi's comment on this: xavi> here we place a SHOULD and not a MUST. We want to make sure the xavi> network works as if there is over-use of the minimal cell xavi> collapses. We think this should be said here so an adopter is xavi> aware of the limitations and implements a working measure. https://mailarchive.ietf.org/arch/msg/6tisch/3SrQj7LXzfFZUSEYasWcwGSrFRM I'd like to hear what others think :-) Aside from that, it's unclear how to implement "Trickle timer with rate-limiting", and having such a modification to Trickle is discouraged by RFC6206: https://tools.ietf.org/html/rfc6206#section-6.7 [SAX Configuration] How can a mote know what values should be used for l_bit and r_bit? Do we assume they are configured offline? Or they can be advertised in EBs? > Appendix B. Example of Implementation of SAX hash function > > (snip) > > For interoperability purpose, the values of h0, l_bit and r_bit in > Step 1 and 2 are configured as: > > o h0 = 0 > o l_bit = 0 > o r_bit = 1 > > The appropriate values of l_bit and r_bit could vary depending on the > the set of motes' EUI64 address. How to find those values is out of > the scope of this specification. Additionally, it'd be nice to have test vectors of the SAX computation with the set of parameters (h0=0, l_bit=0, r_bit=1) for interoperability. [Autonomous Cell] We need a clearer description on the two types of the autonomous cell: > 3. Autonomous Cells > > MSF nodes MUST initialize Slotframe 1 with a set of default cells for > unicast communication with their neighbors. These cells are referred > to as 'autonomous cells', because they are maintained autonomously by > each node. To distinguish from the autonomous cells, the cell > scheduled by 6P transaction is defined as 'managed cells'. How to > schedule managed cells is detailed in Section 5. For autonomous > cells, each node has: > > o One cell at a [slotOffset,channelOffset] computed as a hash of the > node's EUI64 (detailed next). The cell options for this cell are > TX=1, RX=1, SHARED=0. > o One cell at a [slotOffset,channelOffset] computed as a hash of the > EUI64 of the Join Proxy or each neighbor in the IPv6 neighbor > table (detailed in Section 4.4 and Section 4.5). The cell options > for this cell are TX=1, RX=1, SHARED=1. - put the labels of "autonomous non-SHARED cell" and "autonomous SHARED cell" to the itemization: the first one is "autonomous non-SHARED cell", the second one is "autonomous SHARED cell" - tell what to set to NodeAddr (neighbor addresses) of these cells; I presume NodeAddr is not set for the autonomous non-SHARED cell, and the MAC address of the neighbor is set for the autonomous SHARED cell I'd like to have some explanation why we can set SHARED=0 for the autonomous non-SHARED cell whose slot offset and channel offset are actually shared with its neighbors. [Editorial] s/time offset/slot offset/ s/Joining Request/Join Request/ --- That's all. Thanks! Yatch
- [6tisch] draft-ietf-6tisch-msf-02.txt is published Tengfei Chang
- [6tisch] Comments on draft-ietf-6tisch-msf-02 - R… Yasuyuki Tanaka
- Re: [6tisch] Comments on draft-ietf-6tisch-msf-02… Tengfei Chang
- Re: [6tisch] Comments on draft-ietf-6tisch-msf-02… Yasuyuki Tanaka
- Re: [6tisch] Comments on draft-ietf-6tisch-msf-02… Tengfei Chang