[Dots] Mirja Kühlewind's Discuss on draft-ietf-dots-signal-channel-31: (with DISCUSS and COMMENT)
Mirja Kühlewind via Datatracker <noreply@ietf.org> Wed, 01 May 2019 14:42 UTC
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Date: Wed, 01 May 2019 07:42:31 -0700
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Subject: [Dots] Mirja Kühlewind's Discuss on draft-ietf-dots-signal-channel-31: (with DISCUSS and COMMENT)
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Mirja Kühlewind has entered the following ballot position for draft-ietf-dots-signal-channel-31: Discuss When responding, please keep the subject line intact and reply to all email addresses included in the To and CC lines. (Feel free to cut this introductory paragraph, however.) Please refer to https://www.ietf.org/iesg/statement/discuss-criteria.html for more information about IESG DISCUSS and COMMENT positions. The document, along with other ballot positions, can be found here: https://datatracker.ietf.org/doc/draft-ietf-dots-signal-channel/ ---------------------------------------------------------------------- DISCUSS: ---------------------------------------------------------------------- 1) Port usage (see section 3): The port request for DOTS was reviewed by the port expert team. Some members of the team were concerned about the assignment of a separate port number for DOTS as Coap is used and already has a designated port number. I believe that Coap is used as a transport in the case and DOTS provides a separate service compared to what Coap is usually used for, however, it is not clear why DOTS needs a designated port. Section 3 says that the port can either be preconfigured or dynamically detected, therefore it is not clear why a fixed port is needed (see also section 7.1. of RFC7605). In the port review process the authored argued that a port is needed to differentiate the DOTS service in the network. However, this is not an endorsed usage for port numbers (see section 6.2. of RFC7605). Further, I believe assigning a fixed port might actually add an attack vector for DOTS, either by DDoSing the respective port at the DOTS server, or any attempt to block DOTS traffic on the network from the DOTS client to the DOTS server. 2) Section 4.3 says: "In reference to Figure 4, the DOTS client sends two TCP SYNs and two DTLS ClientHello messages at the same time over IPv6 and IPv4." However, RFC8305 explicitly states that connection attempts SHOULD NOT be made simultaneously (see sec 5). Further Figure 4 shows a different order of request as recommended in the text (text says: "UDP over IPv6, UDP over IPv4, TCP over IPv6, and finally TCP over IPv4"). Also why are the UDP connection attempts repeated? I guess that is meant to be the retransmission of the DTLS Hello? However, usually you should receive the TCP SYNACK before you retransmit or in the best case even before you start the next connection attempt. Therefore that should be not displayed like this in the figure or needs further explanation. 3) Why are these statements SHOULDs and not MUSTs (see section 4.4)? "DOTS agents SHOULD follow the data transmission guidelines discussed in Section 3.1.3 of [RFC8085] and control transmission behavior by not sending more than one UDP datagram per round-trip time (RTT) to the peer DOTS agent on average." and "If the DOTS client cannot maintain an RTT estimate, it SHOULD NOT send more than one Non-confirmable request every 3 seconds" as well as in section 4.4.2.1: "If the DOTS server cannot maintain an RTT estimate, it SHOULD NOT send more than one asynchronous notification every 3 seconds" and again in section 4.4.2.2: "The frequency of polling the DOTS server to get the mitigation status SHOULD follow the transmission guidelines in Section 3.1.3 of [RFC8085]. However, most of the communication pattern used by DOTS rely on a request/reply pattern and Coap specifies for this case that only one request can be outstanding at a time (until the reply is received or message is assumed to be lost) (see section 4.7 and 4.2 of RFC7252) which therefore will be used in this case. Only migration updates are send without reply, and here a MUST would be more appropriate. Please also note that if there can only be one request outstanding (before a reply is received) it is also not possible that requests are received out of order (see e.g. 4.4.3: "If UDP is used as transport, CoAP requests may arrive out-of-order."). 4) draft-ietf-core-hop-limit is used in section 10: "The presence of DOTS gateways may lead to infinite forwarding loops, which is undesirable. To prevent and detect such loops, this document uses the Hop-Limit Option." This sounds like it should be required (and normative language should be used) and therefore draft-ietf-core-hop-limit should also be a normative reference. Also draft-ietf-core-comi should probably another normative reference. 5)Section 4.5.2: You give recommendations for min and max in a note, however, these values should be specified normatively and in best with a MUST. 6) Section 4.7: "the DOTS agent sends a heartbeat over the signal channel to maintain its half of the channel. The DOTS agent similarly expects a heartbeat from its peer DOTS agent" and "DOTS servers MAY trigger their heartbeat requests immediately after receiving heartbeat probes from peer DOTS clients." Actually heartbeat should only be send in one direction (as the other end will send an ack) and the protocol should clearly specify which endpoint is responsible for triggering the ping. 7) sec 7.3:"To avoid DOTS signal message fragmentation and the subsequent decreased probability of message delivery, DOTS agents MUST ensure that the DTLS record MUST fit within a single datagram." This should be handled by the DTLS record layer and not by DOTS that works on top of DTLS (actually Coap), therefor it seems straight to have a normative requirement here in the DOTS spec. Also note that the calculation provided is not valid for early data (0-RTT) as the hello messages could be transmitted in the same datagram. 8) Also sec 7.3: "If the path MTU is not known to the DOTS server, an IP MTU of 1280 bytes SHOULD be assumed." Actually this is only true for IPv6. The later note mentions that the situation is different from IPV4, however, it should probably be made clear from the beginning that 1280 can only be assumed for IPv6. 9) sec 9.6: What's the registration policy for the newly created registries? 10) The document should more explicitly provide more guidance about when a client should start a session and what should be done (from the client side) if a session is detected as inactive (other than during migration which is discussed a bit in 4.7). Is the assumption to have basically permanently an active session or connect for migration and configuration requests separately at a time? ---------------------------------------------------------------------- COMMENT: ---------------------------------------------------------------------- 1) I really recommend to add subsections to section 4.4.1. 2) section 4.4.1: "The lifetime of the deactivated mitigation request will be updated to (retry-timer + 45 seconds), so the DOTS client can refresh the deactivated mitigation request after retry-timer seconds before expiry of lifetime and check if the conflict is resolved." This wording is not fully clear to me. If the life time of a deactivated request in updated, isn't it active again? And if it is active and another request is sent, isn't that request rejected again. Can you please further clarify. 3) section 4.4.2: "lifetime: The remaining lifetime of the mitigation request, in seconds." Shouldn't lifetime we rather a timestamp because there is some unknown transmission delay between the time when the reply is generated and the reply is received, and as such a lifetime in seconds is quite meaningless for the client. 4) section 4.4.2.1: " For DOTS server application, the message type MUST always be set to Non-confirmable even if the underlying COAP library elects a notification to be sent in a Confirmable message." I'm not sure I understand this sentence. Can you please further explain? 5) section 4.4.4: "For example, if there is a financial relationship between the DOTS client and server domains, the DOTS client stops incurring cost at this point." I find this sentence a bit problematic given the active-but-terminating period is defined by server. Wouldn't that mean the server can make me pay for undefined period of time? Also the max of 300 sec doesn't seem to be a MUST...? 6) In section Section 4.5 you talk about Caop Ping/Pong. However, these terms are not used in RFC7252. Maybe clarify that empty confirmable messages are used and provide a pointer to section 4.2. of RFC7252 right here (instead of only later). 7) High-level question: Given this doc specifies a YANG model, why are configuration are not retrieved and changed using NETCONF or RESTCONF?
- [Dots] Mirja Kühlewind's Discuss on draft-ietf-do… Mirja Kühlewind via Datatracker
- Re: [Dots] Mirja Kühlewind's Discuss on draft-iet… mohamed.boucadair
- Re: [Dots] Mirja Kühlewind's Discuss on draft-iet… Konda, Tirumaleswar Reddy
- Re: [Dots] Mirja Kühlewind's Discuss on draft-iet… Mirja Kuehlewind
- Re: [Dots] Mirja Kühlewind's Discuss on draft-iet… mohamed.boucadair
- Re: [Dots] Mirja Kühlewind's Discuss on draft-iet… mohamed.boucadair
- Re: [Dots] Mirja Kühlewind's Discuss on draft-iet… Benjamin Kaduk
- Re: [Dots] Mirja Kühlewind's Discuss on draft-iet… Konda, Tirumaleswar Reddy
- Re: [Dots] Mirja Kühlewind's Discuss on draft-iet… Benjamin Kaduk
- Re: [Dots] Mirja Kühlewind's Discuss on draft-iet… Konda, Tirumaleswar Reddy
- Re: [Dots] Mirja Kühlewind's Discuss on draft-iet… Benjamin Kaduk
- Re: [Dots] Mirja Kühlewind's Discuss on draft-iet… Konda, Tirumaleswar Reddy
- Re: [Dots] Mirja Kühlewind's Discuss on draft-iet… Mirja Kuehlewind
- Re: [Dots] Mirja Kühlewind's Discuss on draft-iet… mohamed.boucadair
- Re: [Dots] Mirja Kühlewind's Discuss on draft-iet… Mirja Kuehlewind