[dnssd] Feedback on draft-ietf-dnssd-requirements-03
RJ Atkinson <rja.lists@gmail.com> Wed, 06 August 2014 14:35 UTC
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From: RJ Atkinson <rja.lists@gmail.com>
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Date: Wed, 06 Aug 2014 10:35:29 -0400
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Subject: [dnssd] Feedback on draft-ietf-dnssd-requirements-03
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I apologise for the tardiness of this note. I have tried to organise this note following the sequence (e.g. pages, sections) of the I-D. Many of my comments are informed from Toronto WG time, numerous Toronto hallway discussions, and WG list discussions. I apologise that I often don't recall precisely who suggested which idea. Many of the ideas below arose from others and the note below is merely my formulation of an idea that originated in someone else's head. Yours, Ran Atkinson Section 1, paragraph 3: The 2nd sentence, which begins "Wireless networks...", is misleading at present. It could cause someone to erroneously believe that most types of wireless links and networks do not support multicasting efficiently. In fact, for most wireless link technologies, the link is natively broadcast (not only at the physical layer, but also at the link layer) making broadcast/multicast traffic much more efficient than unicast traffic. For MANET networking, the IETF has actually already defined mechanisms for handling IP multicasting well (e.g. RFC-6621). The paragraph could be edited a bit to make it clear that while there are wireless links with these issues, there are also many other wireless link technologies that work most efficiently with multicast/broadcast traffic. So, I propose to edit this paragraph to read instead: "mDNS in its present form is also not optimized for network technologies where multicast transmissions are relatively expensive. For most wireless link technologies, multicast and broadcast traffic is much more efficient than unicast traffic. However, some wireless networks, for example [IEEE.802.11], have a higher network overhead for multicast transmissions. For IEEE 802.11, this is a result of design choices made in the design of that MAC layer. Some wireless mesh networks, for example 6LoWPAN [RFC4944] are effectively multi-link subnets [RFC4903] where multicasts must be forwarded by intermediate nodes." Section 1.2: Consistent with Tim Chown's note from 29th July to the dnssd mailing list, please define these additional terms and also examine the whole I-D to use the newly defined terms to clarify intended meanings: - "discoverable service" - "reachable service" - "usable service" Section 2.1, paragraph 1: It would be helpful if the text more clearly indicated that the issues being summarised here are those from the Educause petition (as different from being generated within the IETF). We should give credit where due, and also differentiate them crisply from the Section 3 IETF requirements. Proposed Edit: s/The following is a summary of the technical issues/ The following is a summary of their technical issues/ Section 2.1, page 4: Another edit of the same type, for the same reason, as the above. Proposed Edit: s/The following is a summary of the technical requirements/ The following is a summary of their technical requirements/ Section 2.2, paragraph 1: As was true in Section 1, this section is unclear and seems to imply that non-efficient multicasting is typically true for a wireless technology, when actually the opposite is true for most wireless technologies. I propose to make slight edits to clarify this. Proposed Edit: s/In IEEE 802.11 networks however,/ However, unlike many other wireless link technologies, in IEEE 802.11 networks,/ Section 2.2, paragraph 2: All this talk of reliability might lead one to believe that wired Ethernet, wireless Ethernet, and IP are reliable. However, each is defined to provide an unreliable datagram service. Proposed new text to be appended to the end of this paragraph: "Of course, wired Ethernet, wireless Ethernet [IEEE 802.11], and the Internet Protocol (IP) are all defined to provide an unreliable datagram service." Section 3, Use case (C): For clarity and consistency, this should be edited: s/small business network/Small enterprise network/. Section 3, Use case (D): For clarity and consistency, this should be edited: s/Enterprise networks/Large enterprise networks/ Section 4, REQ3: Minor proposed edit to add clarifying examples: s/physical proximity/physical proximity (e.g. building)/ s/organisational structure/organisational structure (e.g. marketing, engineering)/ Section 4, REQ9: Optimising DNS-SD for any specific link-layer is objectionable, as I noted previously on the dnssd list. If optimisations are useful for particular link types (e.g. 802.11), then those optimisations ought to be confined to devices that implement 802.11 rather than impacting all deployed link types. Proposed Replacement Text: "SSD should operate efficiently in all networks." Section 4, REQ10: I don't know what this means and don't understand how it is trying to impact the WG's future engineering efforts. Section 4, Proposed New Requirement: I would like to make more explicit that any link-specific optimisations ought to be confined to devices that implement that type of link. Accordingly, I propose REQ15 below. Proposed New Text: "REQ15: Any link-specific optimisations for DNS-SD should be defined in separate specification documents and should be applicable only to devices that implement that specific link type." Section 6.3, paragraph 1: I find the first sentence of this paragraph awkward and its (very precise) meaning hard to understand. I think that many non-native readers of English will find this confusing. Please try to rephrase this, possibly making more clear the difference -- in a DNS context -- between "validity" and "veracity". It might be sufficient to add an example or two immediately after this first sentence. Section 6, page 9: Based on list discussion, I would suggest adding a new subsection immediately after sub-section 6.4 that discusses "Access Control". Some rapid candidate text follows; please edit to taste: "6.5 Access Control Access Control refers to the ability to restrict which users are able to use a particular service that might be advertised via DNS-SD. In this case, "use" of a service is different from the ability to "discover" or "reach" a service. [Ed: please recall to my suggested edit to Section 1.2] While access control to an advertised service is outside the scope of DNS-SD, we note that access control today often is provided by existing site infrastructure (e.g. router access control lists, firewalls) and/or by service-specific mechanisms (e.g. user authentication to the service). For example, many networked printers already support access controls via a user-id and password. At least one widely deployed DNS-SD + mDNS implementation supports such access controls for printers. So the reliance on existing service-specific security mechanisms (i.e. outside the scope of DNS-SD) does not create new security considerations." Section 6.5: The existing discussion is good, but the exact same issue arises with laptop computers, tablets, and so forth. Purely as an example, at the Toronto IETF a number of laptops were advertising on-link sharing of their music libraries via existing DNS-SD + mDNS. EOF