Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel Configuration Attributes for Robust Block Transmission

The Constrained Application Protocol (CoAP) , although inspired by HTTP, was designed to use UDP instead of TCP. The message layer of CoAP over UDP includes support for reliable delivery, simple congestion control, and flow control. The block-wise transfer introduced the CoAP Block1 and Block2 options to handle data records that cannot fit in a single IP packet, so not having to rely on IP fragmentation. The block-wise transfer was further updated by for use over TCP, TLS, and WebSockets. The CoAP Block1 and Block2 options work well in environments where there are no or minimal packet losses. These options operate synchronously where each individual block has to be requested and can only ask for (or send) the next block when the request for the previous block has completed. Packet, and hence block transmission rate, is controlled by Round-Trip Times (RTTs). There is a requirement for these blocks of data to be transmitted at higher rates under network conditions where there may be asymmetrical transient packet loss (e.g., responses may get dropped). An example is when a network is subject to a Distributed Denial of Service (DDoS) attack and there is a need for DDoS mitigation agents relying upon CoAP to communicate with each other (e.g., ). As a reminder, recommends the use of Confirmable (CON) responses to handle potential packet loss. However, such a recommendation does not work with a flooded pipe DDoS situation because the returning ACK packets may not get through. The block-wise transfer specified in covers the general case, but falls short in situations where packet loss is highly asymmetrical. The mechanism specified in provides roughly similar features to the Block1/Block2 options, but provides additional properties that are tailored towards the intended DDoS Open Threat Signaling (DOTS) transmission. Concretely, primarily targets applications such as DOTS that can't use Confirmable responses to handle potential packet loss and that support application-specific mechanisms to assess whether the remote peer is able to handle the messages sent by a CoAP endpoint (e.g., DOTS heartbeats in Section 4.7 of ). includes guards to prevent a CoAP agent from overloading the network by adopting an aggressive sending rate. These guards are followed in addition to the existing CoAP congestion control as specified in Section 4.7 of (mainly, PROBING_RATE). Table 1 lists the additional CoAP parameters that are used for the guards (Section 7.2 of ). Note that NON in this table refers to Non-confirmable.

PROBING_RATE and other transmission parameters are negotiated between DOTS peers as discussed in Section 4.5.2 of . Nevertheless, negotiating the parameters listed in Table 1 is not supported in . This document defines new DOTS signal channel attributes, corresponding to the parameters in Table 1, that are used to customize the configuration of robust block transmission in a DOTS context.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here. Readers should be familiar with the terms and concepts defined in and . The terms "payload" and "body" are defined in . The term "payload" is thus used for the content of a single CoAP message (i.e., a single block being transferred), while the term "body" is used for the entire resource representation that is being transferred in a block-wise fashion. The meaning of the symbols in YANG tree diagrams are defined in and .

Section 7.2 of defines the following parameters that are used for congestion control purposes: is the maximum number of payloads that can be transmitted at any one time. is the maximum number of times a request for the retransmission of missing payloads can occur without a response from the remote peer. By default, NON_MAX_RETRANSMIT has the same value as MAX_RETRANSMIT (Section 4.8 of ). is the maximum period of delay between sending sets of MAX_PAYLOADS payloads for the same body. NON_TIMEOUT has the same value as ACK_TIMEOUT (Section 4.8 of ). is the initial actual delay between sending the first two MAX_PAYLOADS_SETs of the same body. It is a random duration between NON_TIMEOUT and (NON_TIMEOUT * ACK_RANDOM_FACTOR). is the maximum time to wait for a missing payload before requesting retransmission. By default, NON_RECEIVE_TIMEOUT has a value of twice NON_TIMEOUT. is used to limit the potential wait needed when using PROBING_RATE. is used for expiring partially received bodies. These parameters are used together with PROBING_RATE parameter which in CoAP indicates the average data rate that must not be exceeded by a CoAP endpoint in sending to a peer endpoint that does not respond. The single body of blocks will be subjected to PROBING_RATE (Section 4.7 of ), not the individual packets. If the wait time between sending bodies that are not being responded to based on PROBING_RATE exceeds NON_PROBING_WAIT, then the wait time is limited to NON_PROBING_WAIT. This document augments the "ietf-dots-signal-channel" DOTS signal YANG module defined in Section 5.3 of with the following additional attributes that can be negotiated between DOTS peers to enable robust and faster transmission: This attribute echoes the MAX_PAYLOADS parameter in .This is an optional attribute. If the attribute is supplied in both ‘idle-config’ and ‘mitigating-config’, then it MUST convey the same value. If the attribute is only provided as part of ‘idle-config’ (or ‘mitigating-config’), then the other definition (i.e., ‘mitigating-config’ (or ‘idle-config’)) MUST be updated to the same value. This attribute echoes the NON_MAX_RETRANSMIT parameter in . The default value of this attribute is 'max-retransmit'. Note that DOTS uses a default value of '3' instead of '4' used for the generic CoAP use (Section 4.5.2 of ) for max-transmit. This is an optional attribute. This attribute, expressed in seconds, echoes the NON_TIMEOUT parameter in . The default value of this attribute is 'ack-timeout'.This attribute is also used to compute the NON_TIMEOUT_RANDOM parameter.This is an optional attribute. This attribute, expressed in seconds, echoes the NON_RECEIVE_TIMEOUT parameter in . The default value of this attribute is twice 'non-timeout'.This is an optional attribute. This attribute, expressed in seconds, echoes the NON_PROBING_WAIT parameter in . This is an optional attribute. This attribute, expressed in seconds, echoes the NON_PARTIAL_TIMEOUT parameter in . The default value of this attribute is 247 seconds.This is an optional attribute. The tree structure of the "ietf-dots-robust-trans" module () is shown in .

These attributes are mapped to CBOR types as specified in and Section 6 of . DOTS clients follow the procedure specified in Section 4.5 of to negotiate, configure, and retrieve the DOTS signal channel session behavior (including Q-Block parameters) with DOTS peers. 'non-probing-wait' ideally should be left having some jitter and so should not be hard-coded with an explicit value. It is suggested to use a base value (using NON_TIMEOUT instead of NON_TIMEOUT_RANDOM) and, then, the jitter (ACK_RANDOM_FACTOR - 1) is added to each time the value is checked. If any of the signal channel session configuration parameters is updated, the 'non-probing-wait' and 'non-partial-timeout' values should be recalculated according to the definition algorithms in Section 7.2 of unless explicit values are provided as part of the negotiated configuration. An example of a PUT message to configure Q-Block parameters is depicted in . In this example, a non-default value is configured for the 'max-payloads' attribute, while default values are used for 'non-max-retransmit', 'non-timeout', and 'non-receive-timeout' in both idle and mitigation times. Given that 'non-probing-wait' and 'non-partial-wait' are not explicitly configured in this example, these attributes will be computed following the algorithms in Section 7.2 of . The meaning of the other attributes is detailed in Section 4.5 of .

The payload of the message depicted in is CBOR-encoded as indicated by the Content-Format set to "application/dots+cbor" (Section 10.3 of ). However, and for the sake of better readability, the example uses JSON encoding of YANG-modeled data following the mapping table in and Section 6 of : use the JSON names and types defined in . These conventions are inherited from .

The YANG/JSON mapping parameters to CBOR are listed in Table 2. Note: Implementers must check that the mapping output provided by their YANG-to-CBOR encoding schemes is aligned with the content of Table 2.

This module uses the data structure extension defined in .

file "ietf-dots-robust-trans@2022-01-04.yang" module ietf-dots-robust-trans { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-dots-robust-trans"; prefix dots-robust; import ietf-dots-signal-channel { prefix dots-signal; reference "RFC 9132: Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel Specification"; } import ietf-yang-structure-ext { prefix sx; reference "RFC 8791: YANG Data Structure Extensions"; } organization "IETF DDoS Open Threat Signaling (DOTS) Working Group"; contact "WG Web: WG List: Author: Mohamed Boucadair ; Author: Jon Shallow "; description "This module contains YANG definitions for the configuration of parameters that can be negotiated between a DOTS client and a DOTS server for robust block transmission. Copyright (c) 2022 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Revised BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info). This version of this YANG module is part of RFC XXXX; see the RFC itself for full legal notices."; revision 2022-01-04 { description "Initial revision."; reference "RFC XXXX: Distributed Denial-of-Service Open Threat Signaling (DOTS) Configuration Attributes for Robust Block Transmission"; } grouping robust-transmission-attributes { description "A set of DOTS signal channel session configuration that are negotiated between DOTS agents when making use of Q-Block1 and Q-Block2 options."; container max-payloads { description "Indicates the maximum number of payloads that can be transmitted at any one time."; choice direction { description "Indicates the communication direction in which the data nodes can be included."; case server-to-client-only { description "These data nodes appear only in a message sent from the server to the client."; leaf max-value { type uint16; description "Maximum acceptable max-payloads value."; } leaf min-value { type uint16; description "Minimum acceptable max-payloads value."; } } } leaf current-value { type uint16; default "10"; description "Current max-payloads value."; reference "RFC 9177: Constrained Application Protocol (CoAP) Block-Wise Transfer Options Supporting Robust Transmission, Section 7.2"; } } container non-max-retransmit { description "Indicates the maximum number of times a request for the retransmission of missing payloads can occur without a response from the remote peer."; choice direction { description "Indicates the communication direction in which the data nodes can be included."; case server-to-client-only { description "These data nodes appear only in a message sent from the server to the client."; leaf max-value { type uint16; description "Maximum acceptable non-max-retransmit value."; } leaf min-value { type uint16; description "Minimum acceptable non-max-retransmit value."; } } } leaf current-value { type uint16; default "3"; description "Current non-max-retransmit value."; reference "RFC 9177: Constrained Application Protocol (CoAP) Block-Wise Transfer Options Supporting Robust Transmission, Section 7.2"; } } container non-timeout { description "Indicates the maximum period of delay between sending sets of MAX_PAYLOADS payloads for the same body."; choice direction { description "Indicates the communication direction in which the data nodes can be included."; case server-to-client-only { description "These data nodes appear only in a message sent from the server to the client."; leaf max-value-decimal { type decimal64 { fraction-digits 2; } units "seconds"; description "Maximum ack-timeout value."; } leaf min-value-decimal { type decimal64 { fraction-digits 2; } units "seconds"; description "Minimum ack-timeout value."; } } } leaf current-value-decimal { type decimal64 { fraction-digits 2; } units "seconds"; default "2.00"; description "Current ack-timeout value."; reference "RFC 9177: Constrained Application Protocol (CoAP) Block-Wise Transfer Options Supporting Robust Transmission, Section 7.2"; } } container non-receive-timeout { description "Indicates the time to wait for a missing payload before requesting retransmission."; choice direction { description "Indicates the communication direction in which the data nodes can be included."; case server-to-client-only { description "These data nodes appear only in a message sent from the server to the client."; leaf max-value-decimal { type decimal64 { fraction-digits 2; } units "seconds"; description "Maximum non-receive-timeout value."; } leaf min-value-decimal { type decimal64 { fraction-digits 2; } units "seconds"; description "Minimum non-receive-timeout value."; } } } leaf current-value-decimal { type decimal64 { fraction-digits 2; } units "seconds"; default "4.00"; description "Current non-receive-timeout value."; reference "RFC 9177: Constrained Application Protocol (CoAP) Block-Wise Transfer Options Supporting Robust Transmission, Section 7.2"; } } container non-probing-wait { description "Is used to limit the potential wait needed when using probing-rate."; choice direction { description "Indicates the communication direction in which the data nodes can be included."; case server-to-client-only { description "These data nodes appear only in a message sent from the server to the client."; leaf max-value-decimal { type decimal64 { fraction-digits 2; } units "seconds"; description "Maximum non-probing-wait value."; } leaf min-value-decimal { type decimal64 { fraction-digits 2; } units "seconds"; description "Minimum non-probing-wait value."; } } } leaf current-value-decimal { type decimal64 { fraction-digits 2; } units "seconds"; description "Current non-probing-wait value."; reference "RFC 9177: Constrained Application Protocol (CoAP) Block-Wise Transfer Options Supporting Robust Transmission, Section 7.2"; } } container non-partial-wait { description "Is used for expiring partially received bodies."; choice direction { description "Indicates the communication direction in which the data nodes can be included."; case server-to-client-only { description "These data nodes appear only in a message sent from the server to the client."; leaf max-value-decimal { type decimal64 { fraction-digits 2; } units "seconds"; description "Maximum non-partial-wait value."; } leaf min-value-decimal { type decimal64 { fraction-digits 2; } units "seconds"; description "Minimum non-partial-wait value."; } } } leaf current-value-decimal { type decimal64 { fraction-digits 2; } units "seconds"; default "247.00"; description "Current non-partial-wait value."; reference "RFC 9177: Constrained Application Protocol (CoAP) Block-Wise Transfer Options Supporting Robust Transmission, Section 7.2"; } } } sx:augment-structure "/dots-signal:dots-signal" + "/dots-signal:message-type" + "/dots-signal:signal-config" + "/dots-signal:mitigating-config" { description "Indicates DOTS configuration attributes to use for robust transmission when a mitigation is active."; uses robust-transmission-attributes; } sx:augment-structure "/dots-signal:dots-signal" + "/dots-signal:message-type" + "/dots-signal:signal-config" + "/dots-signal:idle-config" { description "Indicates DOTS configuration parameters to use for robust transmission when no mitigation is active."; uses robust-transmission-attributes; } } ]]>



    
      
        This specification registers the following parameters in the IANA
        "DOTS Signal Channel CBOR Key Values" registry .

        
            Note to the RFC Editor: Please replace TBA1-TBA6 with the CBOR
            keys that are assigned from the 32768-49151 range. Please update
            Table 2 accordingly.
          

        
            
          
      

      
        This document requests IANA to register the following URI in the
        "ns" subregistry within the "IETF XML Registry" :

        
            
          

        This document requests IANA to register the following YANG module
        in the "YANG Module Names" subregistry 
        within the "YANG Parameters" registry.

        
            
          
      
    

    
      The security considerations for the DOTS signal channel protocol are
      discussed in Section 11 of .

      CoAP-specific security considerations are discussed in Section 11 of
      .

      Consistent with Section 5 of , the
      "ietf-dots-robust-trans" module is not intended to be used via
      NETCONF/RESTCONF. It serves as an abstract representation in DOTS signal
      channel messages. The "ietf-dots-robust-trans" module does not introduce
      any new vulnerabilities beyond those specified above.
    

    
      Thanks to Tiru Reddy, Meiling Chen, and Kaname Nishizuka for the
      review.

      Thanks to Michal Vaško for the yangdoctors review.

      Thanks to Valery Smyslov for shepherding the document, Paul Wouters
      for the AD review, Paul Kyzivat for the artart directorate review, Tim
      Evens for the Gen-ART review, and Jean-Michel Combes for the int-dir
      review.

      Thanks to John Scudder, Lars Eggert, Éric Vyncke, Roman
      Danyliw, Rob Wilton, and Martin Duke for the comments during the IESG
      review.