| DOTS | T. Reddy, Ed. |
| Internet-Draft | McAfee |
| Intended status: Standards Track | M. Boucadair, Ed. |
| Expires: April 20, 2020 | Orange |
| P. Patil | |
| Cisco | |
| A. Mortensen | |
| Arbor Networks, Inc. | |
| N. Teague | |
| Iron Mountain Data Centers | |
| October 18, 2019 |
Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel Specification
draft-ietf-dots-signal-channel-38
This document specifies the DOTS signal channel, a protocol for signaling the need for protection against Distributed Denial-of-Service (DDoS) attacks to a server capable of enabling network traffic mitigation on behalf of the requesting client.
A companion document defines the DOTS data channel, a separate reliable communication layer for DOTS management and configuration purposes.
Please update these statements within the document with the RFC number to be assigned to this document:
Please update this statement with the RFC number to be assigned to the following documents:
Please update TBD/TBD1/TBD2 statements with the assignments made by IANA to DOTS Signal Channel Protocol.
Also, please update the "revision" date of the YANG modules.
This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet-Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 20, 2020.
Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License.
A distributed denial-of-service (DDoS) attack is a distributed attempt to make machines or network resources unavailable to their intended users. In most cases, sufficient scale for an effective attack can be achieved by compromising enough end-hosts and using those infected hosts to perpetrate and amplify the attack. The victim in this attack can be an application server, a host, a router, a firewall, or an entire network.
Network applications have finite resources like CPU cycles, the number of processes or threads they can create and use, the maximum number of simultaneous connections they can handle, the limited resources of the control plane, etc. When processing network traffic, such applications are supposed to use these resources to provide the intended functionality in the most efficient manner. However, a DDoS attacker may be able to prevent an application from performing its intended task by making the application exhaust its finite resources.
A TCP DDoS SYN-flood [RFC4987], for example, is a memory-exhausting attack while an ACK-flood is a CPU-exhausting attack. Attacks on the link are carried out by sending enough traffic so that the link becomes congested, thereby likely causing packet loss for legitimate traffic. Stateful firewalls can also be attacked by sending traffic that causes the firewall to maintain an excessive number of states that may jeopardize the firewall's operation overall, besides likely performance impacts. The firewall then runs out of memory, and can no longer instantiate the states required to process legitimate flows. Other possible DDoS attacks are discussed in [RFC4732].
In many cases, it may not be possible for network administrators to determine the cause(s) of an attack. They may instead just realize that certain resources seem to be under attack. This document defines a lightweight protocol that allows a DOTS client to request mitigation from one or more DOTS servers for protection against detected, suspected, or anticipated attacks. This protocol enables cooperation between DOTS agents to permit a highly-automated network defense that is robust, reliable, and secure. Note that "secure" means the support of the features defined in Section 2.4 of [RFC8612].
An example of a network diagram that illustrates a deployment of DOTS agents is shown in Figure 1. In this example, a DOTS server is operating on the access network. A DOTS client is located on the LAN (Local Area Network), while a DOTS gateway is embedded in the CPE (Customer Premises Equipment).
Network Resource CPE router Access network __________ +-----------+ +--------------+ +-------------+ / \ | |___| |____| |___ | Internet | |DOTS client| | DOTS gateway | | DOTS server | | | | | | | | | | | +-----------+ +--------------+ +-------------+ \__________/
Figure 1: Sample DOTS Deployment (1)
DOTS servers can also be reachable over the Internet, as depicted in Figure 2.
Network DDoS mitigation Resource CPE router __________ service +-----------+ +-------------+ / \ +-------------+ | |___| |____| |___ | | |DOTS client| |DOTS gateway | | Internet | | DOTS server | | | | | | | | | +-----------+ +-------------+ \__________/ +-------------+
Figure 2: Sample DOTS Deployment (2)
The DOTS server may (not) be co-located with the DOTS mitigator. In typical deployments, the DOTS server belongs to the same administrative domain as the mitigator. The DOTS client can communicate directly with a DOTS server or indirectly via a DOTS gateway.
The document adheres to the DOTS architecture [I-D.ietf-dots-architecture]. The requirements for DOTS signal channel protocol are documented in [RFC8612]. This document satisfies all the use cases discussed in [I-D.ietf-dots-use-cases].
This document focuses on the DOTS signal channel. This is a companion document of the DOTS data channel specification [I-D.ietf-dots-data-channel] that defines a configuration and a bulk data exchange mechanism supporting the DOTS signal channel.
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 [RFC2119][RFC8174] when, and only when, they appear in all capitals, as shown here.
(D)TLS is used for statements that apply to both Transport Layer Security [RFC5246][RFC8446] and Datagram Transport Layer Security [RFC6347]. Specific terms are used for any statement that applies to either protocol alone.
The reader should be familiar with the terms defined in [RFC8612].
The meaning of the symbols in YANG tree diagrams is defined in [RFC8340].
The DOTS signal channel is built on top of the Constrained Application Protocol (CoAP) [RFC7252], a lightweight protocol originally designed for constrained devices and networks. The many features of CoAP (expectation of packet loss, support for asynchronous Non-confirmable messaging, congestion control, small message overhead limiting the need for fragmentation, use of minimal resources, and support for (D)TLS) makes it a good candidate to build the DOTS signaling mechanism from.
The DOTS signal channel is layered on existing standards (Figure 3).
+---------------------+ | DOTS Signal Channel | +---------------------+ | CoAP | +----------+----------+ | TLS | DTLS | +----------+----------+ | TCP | UDP | +----------+----------+ | IP | +---------------------+
Figure 3: Abstract Layering of DOTS Signal Channel over CoAP over (D)TLS
In some cases, a DOTS client and server may have mutual agreement to use a specific port number, such as by explicit configuration or dynamic discovery [I-D.ietf-dots-server-discovery]. Absent such mutual agreement, the DOTS signal channel MUST run over port number TBD as defined in Section 9.1, for both UDP and TCP. In order to use a distinct port number (as opposed to TBD), DOTS clients and servers SHOULD support a configurable parameter to supply the port number to use.
[RFC7252] and the "coaps+tcp" URI scheme defined in Section 8.2 of [RFC8323] to identify DOTS server resources accessible using CoAP over UDP secured with DTLS and CoAP over TCP secured with TLS, respectively.
The signal channel uses the "coaps" URI scheme defined in Section 6 of
The DOTS signal channel can be established between two DOTS agents prior or during an attack. The DOTS signal channel is initiated by the DOTS client. The DOTS client can then negotiate, configure, and retrieve the DOTS signal channel session behavior with its DOTS peer (Section 4.5). Once the signal channel is established, the DOTS agents may periodically send heartbeats to keep the channel active (Section 4.7). At any time, the DOTS client may send a mitigation request message (Section 4.4) to a DOTS server over the active signal channel. While mitigation is active (because of the higher likelihood of packet loss during a DDoS attack), the DOTS server periodically sends status messages to the client, including basic mitigation feedback details. Mitigation remains active until the DOTS client explicitly terminates mitigation, or the mitigation lifetime expires. Also, the DOTS server may rely on the signal channel session loss to trigger mitigation for pre-configured mitigation requests (if any).
DOTS signaling can happen with DTLS over UDP and TLS over TCP. Likewise, DOTS requests may be sent using IPv4 or IPv6 transfer capabilities. A Happy Eyeballs procedure for DOTS signal channel is specified in Section 4.3.
A DOTS client is entitled to access only to resources it creates. In particular, a DOTS client can not retrieve data related to mitigation requests created by other DOTS clients of the same DOTS client domain.
Messages exchanged between DOTS agents are serialized using Concise Binary Object Representation (CBOR) [RFC7049], a binary encoding scheme designed for small code and message size. CBOR-encoded payloads are used to carry signal channel-specific payload messages which convey request parameters and response information such as errors. In order to allow reusing data models across protocols, [RFC7951] specifies the JavaScript Object Notation (JSON) encoding of YANG-modeled data. A similar effort for CBOR is defined in [I-D.ietf-core-yang-cbor].
DOTS agents determine that a CBOR data structure is a DOTS signal channel object from the application context, such as from the port number assigned to the DOTS signal channel. The other method DOTS agents use to indicate that a CBOR data structure is a DOTS signal channel object is the use of the "application/dots+cbor" content type (Section 9.3).
This document specifies a YANG module for representing DOTS mitigation scopes, DOTS signal channel session configuration data, and DOTS redirected signaling (Section 5). All parameters in the payload of the DOTS signal channel are mapped to CBOR types as specified in Table 4.
In order to prevent fragmentation, DOTS agents must follow the recommendations documented in Section 4.6 of [RFC7252]. Refer to Section 7.3 for more details.
DOTS agents MUST support GET, PUT, and DELETE CoAP methods. The payload included in CoAP responses with 2.xx Response Codes MUST be of content type "application/dots+cbor". CoAP responses with 4.xx and 5.xx error Response Codes MUST include a diagnostic payload (Section 5.5.2 of [RFC7252]). The Diagnostic Payload may contain additional information to aid troubleshooting.
In deployments where multiple DOTS clients are enabled in a network (owned and operated by the same entity), the DOTS server may detect conflicting mitigation requests from these clients. This document does not aim to specify a comprehensive list of conditions under which a DOTS server will characterize two mitigation requests from distinct DOTS clients as conflicting, nor recommend a DOTS server behavior for processing conflicting mitigation requests. Those considerations are implementation- and deployment-specific. Nevertheless, the document specifies the mechanisms to notify DOTS clients when conflicts occur, including the conflict cause (Section 4.4).
In deployments where one or more translators (e.g., Traditional NAT [RFC3022], CGN [RFC6888], NAT64 [RFC6146], NPTv6 [RFC6296]) are enabled between the client's network and the DOTS server, DOTS signal channel messages forwarded to a DOTS server MUST NOT include internal IP addresses/prefixes and/or port numbers; external addresses/prefixes and/or port numbers as assigned by the translator MUST be used instead. This document does not make any recommendation about possible translator discovery mechanisms. The following are some (non-exhaustive) deployment examples that may be considered:
This document assumes that DOTS clients are provisioned with the reachability information of their DOTS server(s) using any of a variety of means (e.g., local configuration, or dynamic means such as DHCP [I-D.ietf-dots-server-discovery]). The description of such means is out of scope of this document.
Likewise, it is out of scope of this document to specify the behavior to be followed by a DOTS client to send DOTS requests when multiple DOTS servers are provisioned (e.g., contact all DOTS servers, select one DOTS server among the list). Such behavior is specified in other documents (e.g., [I-D.ietf-dots-multihoming]).
The DOTS server MUST support the use of the path-prefix of "/.well-known/" as defined in [RFC5785] and the registered name of "dots". Each DOTS operation is indicated by a path-suffix that indicates the intended operation. The operation path (Table 1) is appended to the path-prefix to form the URI used with a CoAP request to perform the desired DOTS operation.
| Operation | Operation Path | Details |
|---|---|---|
| Mitigation | /mitigate | Section 4.4 |
| Session configuration | /config | Section 4.5 |
[RFC8612] mentions that DOTS agents will have to support both connectionless and connection-oriented protocols. As such, the DOTS signal channel is designed to operate with DTLS over UDP and TLS over TCP. Further, a DOTS client may acquire a list of IPv4 and IPv6 addresses (Section 4.1), each of which can be used to contact the DOTS server using UDP and TCP. If no list of IPv4 and IPv6 addresses to contact the DOTS server is configured (or discovered), the DOTS client adds the IPv4/IPv6 addresses of its default router to the candidate list to contact the DOTS server.
The following specifies the procedure to follow to select the address family and the transport protocol for sending DOTS signal channel messages.
Such procedure is needed to avoid experiencing long connection delays. For example, if an IPv4 path to reach a DOTS server is functional, but the DOTS server's IPv6 path is non-functional, a dual-stack DOTS client may experience a significant connection delay compared to an IPv4-only DOTS client, in the same network conditions. The other problem is that if a middlebox between the DOTS client and DOTS server is configured to block UDP traffic, the DOTS client will fail to establish a DTLS association with the DOTS server and, as a consequence, will have to fall back to TLS over TCP, thereby incurring significant connection delays.
To overcome these connection setup problems, the DOTS client attempts to connect to its DOTS server(s) using both IPv6 and IPv4, and tries both DTLS over UDP and TLS over TCP following a DOTS Happy Eyeballs approach. To some extent, this approach is similar to the Happy Eyeballs mechanism defined in [RFC8305]. The connection attempts are performed by the DOTS client when it initializes, or in general when it has to select an address family and transport to contact its DOTS server. The results of the Happy Eyeballs procedure are used by the DOTS client for sending its subsequent messages to the DOTS server. The difference in behavior with respect to the Happy Eyeballs mechanism [RFC8305] are listed below:
When connection attempts are made during an attack, the DOTS client SHOULD use a "Connection Attempt Delay" [RFC8305] set to 100 ms.
In reference to Figure 4, the DOTS client proceeds with the connection attempts following the rules in [RFC8305]. In this example, it is assumed that the IPv6 path is broken and UDP traffic is dropped by a middlebox but has little impact to the DOTS client because there is no long delay before using IPv4 and TCP.
+-----------+ +-----------+
|DOTS client| |DOTS server|
+-----------+ +-----------+
| |
T0 |--DTLS ClientHello, IPv6 ---->X |
T1 |--DTLS ClientHello, IPv4 ---->X |
T2 |--TCP SYN, IPv6-------------->X |
T3 |--TCP SYN, IPv4--------------------------------------->|
|<-TCP SYNACK-------------------------------------------|
|--TCP ACK--------------------------------------------->|
|<------------Establish TLS Session-------------------->|
|----------------DOTS signal--------------------------->|
| |
Note:
* Retransmission messages are not shown.
* T1-T0=T2-T1=T3-T2= Connection Attempt Delay.
Figure 4: DOTS Happy Eyeballs (Sample Flow)
A single DOTS signal channel between DOTS agents can be used to exchange multiple DOTS signal messages. To reduce DOTS client and DOTS server workload, DOTS clients SHOULD re-use the (D)TLS session.
The following methods are used by a DOTS client to request, withdraw, or retrieve the status of mitigation requests:
Mitigation request and response messages are marked as Non-confirmable messages (Section 2.2 of [RFC7252]).
DOTS agents MUST NOT send more than one UDP datagram per round-trip time (RTT) to the peer DOTS agent on average following the data transmission guidelines discussed in Section 3.1.3 of [RFC8085].
Requests marked by the DOTS client as Non-confirmable messages are sent at regular intervals until a response is received from the DOTS server. If the DOTS client cannot maintain an RTT estimate, it MUST NOT send more than one Non-confirmable request every 3 seconds, and SHOULD use an even less aggressive rate whenever possible (case 2 in Section 3.1.3 of [RFC8085]).
JSON encoding of YANG modelled data [RFC7951] is used to illustrate the various methods defined in the following sub-sections. Also, the examples use the Labels defined in Sections 9.6.2, 9.6.3, 9.6.4, and 9.6.5.
When a DOTS client requires mitigation for some reason, the DOTS client uses the CoAP PUT method to send a mitigation request to its DOTS server(s) (Figures 5 and 6).
If a DOTS client is entitled to solicit the DOTS service, the DOTS server enables mitigation on behalf of the DOTS client by communicating the DOTS client's request to a mitigator (which may be co-located with the DOTS server) and relaying the feedback of the thus-selected mitigator to the requesting DOTS client.
Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw"
Uri-Path: "mid=123"
Content-Format: "application/dots+cbor"
{
...
}
Figure 5: PUT to Convey DOTS Mitigation Requests
The order of the Uri-Path options is important as it defines the CoAP resource. In particular, 'mid' MUST follow 'cuid'.
The additional Uri-Path parameters to those defined in Section 4.2 are as follows:
'cuid' and 'mid' MUST NOT appear in the PUT request message body (Figure 6). The schema in Figure 6 uses the types defined in Section 6. Note that this figure (and other similar figures depicting a schema) are non-normative sketches of the structure of the message.
{
"ietf-dots-signal-channel:mitigation-scope": {
"scope": [
{
"target-prefix": [
"string"
],
"target-port-range": [
{
"lower-port": number,
"upper-port": number
}
],
"target-protocol": [
number
],
"target-fqdn": [
"string"
],
"target-uri": [
"string"
],
"alias-name": [
"string"
],
"lifetime": number,
"trigger-mitigation": true|false
}
]
}
}
Figure 6: PUT to Convey DOTS Mitigation Requests (Message Body Schema)
The parameters in the CBOR body (Figure 6) of the PUT request are described below:
In deployments where server-domain DOTS gateways are enabled, identity information about the origin source client domain ('cdid') SHOULD be propagated to the DOTS server. That information is meant to assist the DOTS server to enforce some policies such as grouping DOTS clients that belong to the same DOTS domain, limiting the number of DOTS requests, and identifying the mitigation scope. These policies can be enforced per-client, per-client domain, or both. Also, the identity information may be used for auditing and debugging purposes.
Figure 7 shows an example of a request relayed by a server-domain DOTS gateway.
Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cdid=7eeaf349529eb55ed50113"
Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw"
Uri-Path: "mid=123"
Content-Format: "application/dots+cbor"
{
...
}
Figure 7: PUT for DOTS Mitigation Request as Relayed by a DOTS Gateway
A server-domain DOTS gateway SHOULD add the following Uri-Path parameter:
A DOTS gateway SHOULD add the CoAP Hop-Limit Option [I-D.ietf-core-hop-limit].
Because of the complexity to handle partial failure cases, this specification does not allow for including multiple mitigation requests in the same PUT request. Concretely, a DOTS client MUST NOT include multiple entries in the 'scope' array of the same PUT request.
FQDN and URI mitigation scopes may be thought of as a form of scope alias, in which the addresses associated with the domain name or URI (as resolved by the DOTS server) represent the scope of the mitigation. Particularly, the IP addresses to which the host subcomponent of authority component of an URI resolves represent the 'target-prefix', the URI scheme represents the 'target-protocol', the port subcomponent of authority component of an URI represents the 'target-port-range'. If the optional port information is not present in the authority component, the default port defined for the URI scheme represents the 'target-port'.
In the PUT request at least one of the attributes 'target-prefix', 'target-fqdn','target-uri', or 'alias-name' MUST be present.
Attributes and Uri-Path parameters with empty values MUST NOT be present in a request and render the entire request invalid.
Figure 8 shows a PUT request example to signal that TCP port numbers 80, 8080, and 443 used by 2001:db8:6401::1 and 2001:db8:6401::2 servers are under attack. The presence of 'cdid' indicates that a server-domain DOTS gateway has modified the initial PUT request sent by the DOTS client. Note that 'cdid' MUST NOT appear in the PUT request message body.
Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cdid=7eeaf349529eb55ed50113"
Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw"
Uri-Path: "mid=123"
Content-Format: "application/dots+cbor"
{
"ietf-dots-signal-channel:mitigation-scope": {
"scope": [
{
"target-prefix": [
"2001:db8:6401::1/128",
"2001:db8:6401::2/128"
],
"target-port-range": [
{
"lower-port": 80
},
{
"lower-port": 443
},
{
"lower-port": 8080
}
],
"target-protocol": [
6
],
"lifetime": 3600
}
]
}
}
Figure 8: PUT for DOTS Mitigation Request (An Example)
The corresponding CBOR encoding format for the payload is shown in Figure 9.
A1 # map(1)
01 # unsigned(1)
A1 # map(1)
02 # unsigned(2)
81 # array(1)
A3 # map(3)
06 # unsigned(6)
82 # array(2)
74 # text(20)
323030313A6462383A363430313A3A312F313238
74 # text(20)
323030313A6462383A363430313A3A322F313238
07 # unsigned(7)
83 # array(3)
A1 # map(1)
08 # unsigned(8)
18 50 # unsigned(80)
A1 # map(1)
08 # unsigned(8)
19 01BB # unsigned(443)
A1 # map(1)
08 # unsigned(8)
19 1F90 # unsigned(8080)
0A # unsigned(10)
81 # array(1)
06 # unsigned(6)
0E # unsigned(14)
19 0E10 # unsigned(3600)
Figure 9: PUT for DOTS Mitigation Request (CBOR)
In both DOTS signal and data channel sessions, the DOTS client MUST authenticate itself to the DOTS server (Section 8). The DOTS server MAY use the algorithm presented in Section 7 of [RFC7589] to derive the DOTS client identity or username from the client certificate. The DOTS client identity allows the DOTS server to accept mitigation requests with scopes that the DOTS client is authorized to manage.
The DOTS server couples the DOTS signal and data channel sessions using the DOTS client identity and optionally the 'cdid' parameter value, so the DOTS server can validate whether the aliases conveyed in the mitigation request were indeed created by the same DOTS client using the DOTS data channel session. If the aliases were not created by the DOTS client, the DOTS server MUST return 4.00 (Bad Request) in the response.
The DOTS server couples the DOTS signal channel sessions using the DOTS client identity and optionally the 'cdid' parameter value, and the DOTS server uses 'mid' and 'cuid' Uri-Path parameter values to detect duplicate mitigation requests. If the mitigation request contains the 'alias-name' and other parameters identifying the target resources (such as 'target-prefix', 'target-port-range', 'target-fqdn', or 'target-uri'), the DOTS server appends the parameter values in 'alias-name' with the corresponding parameter values in 'target-prefix', 'target-port-range', 'target-fqdn', or 'target-uri'.
The DOTS server indicates the result of processing the PUT request using CoAP response codes. CoAP 2.xx codes are success. CoAP 4.xx codes are some sort of invalid requests (client errors). COAP 5.xx codes are returned if the DOTS server is in an error state or is currently unavailable to provide mitigation in response to the mitigation request from the DOTS client.
Figure 10 shows an example response to a PUT request that is successfully processed by a DOTS server (i.e., CoAP 2.xx response codes). This version of the specification forbids 'cuid' and 'cdid' (if used) to be returned in a response message body.
{
"ietf-dots-signal-channel:mitigation-scope": {
"scope": [
{
"mid": 123,
"lifetime": 3600
}
]
}
}
Figure 10: 2.xx Response Body
If the request is missing a mandatory attribute, does not include 'cuid' or 'mid' Uri-Path options, includes multiple 'scope' parameters, or contains invalid or unknown parameters, the DOTS server MUST reply with 4.00 (Bad Request). DOTS agents can safely ignore comprehension-optional parameters they don't understand (Section 9.6.1.1).
A DOTS server that receives a mitigation request with a lifetime set to '0' MUST reply with a 4.00 (Bad Request).
If the DOTS server does not find the 'mid' parameter value conveyed in the PUT request in its configuration data, it MAY accept the mitigation request by sending back a 2.01 (Created) response to the DOTS client; the DOTS server will consequently try to mitigate the attack. A DOTS server could reject mitigation requests when it is near capacity or needs to rate-limit a particular client, for example.
The relative order of two mitigation requests, having the same 'trigger-mitigation' type, from a DOTS client is determined by comparing their respective 'mid' values. If two mitigation requests with the same 'trigger-mitigation' type have overlapping mitigation scopes, the mitigation request with the highest numeric 'mid' value will override the other mitigation request. Two mitigation requests from a DOTS client have overlapping scopes if there is a common IP address, IP prefix, FQDN, URI, or alias-name. To avoid maintaining a long list of overlapping mitigation requests (i.e., requests with the same 'trigger-mitigation' type and overlapping scopes) from a DOTS client and avoid error-prone provisioning of mitigation requests from a DOTS client, the overlapped lower numeric 'mid' MUST be automatically deleted and no longer available at the DOTS server. For example, if the DOTS server receives a mitigation request which overlaps with an existing mitigation with a higher numeric 'mid', the DOTS server rejects the request by returning 4.09 (Conflict) to the DOTS client. The response includes enough information for a DOTS client to recognize the source of the conflict as described below in the 'conflict-information' subtree with only the relevant nodes listed:
If the DOTS server receives a mitigation request which overlaps with an active mitigation request, but both having distinct 'trigger-mitigation' types, the DOTS server SHOULD deactivate (absent explicit policy/configuration otherwise) the mitigation request with 'trigger-mitigation' set to false. Particularly, if the mitigation request with 'trigger-mitigation' set to false is active, the DOTS server withdraws the mitigation request (i.e., status code is set to '7' as defined in Table 2) and transitions the status of the mitigation request to '8'.
Upon DOTS signal channel session loss with a peer DOTS client, the DOTS server SHOULD withdraw (absent explicit policy/configuration otherwise) any active mitigation requests overlapping with mitigation requests having 'trigger-mitigation' set to false from that DOTS client, as the loss of the session implicitly activates these preconfigured mitigation requests and they take precedence. Note that active-but-terminating period is not observed for mitigations withdrawn at the initiative of the DOTS server.
DOTS clients may adopt various strategies for setting the scopes of immediate and pre-configured mitigation requests to avoid potential conflicts. For example, a DOTS client may tweak pre-configured scopes so that the scope of any overlapping immediate mitigation request will be a subset of the pre-configured scopes. Also, if an immediate mitigation request overlaps with any of the pre-configured scopes, the DOTS client sets the scope of the overlapping immediate mitigation request to be a subset of the pre-configured scopes, so as to get a broad mitigation when the DOTS signal channel collapses and maximize the chance of recovery.
If the request is conflicting with an existing mitigation request from a different DOTS client, the DOTS server may return 2.01 (Created) or 4.09 (Conflict) to the requesting DOTS client. If the DOTS server decides to maintain the new mitigation request, the DOTS server returns 2.01 (Created) to the requesting DOTS client. If the DOTS server decides to reject the new mitigation request, the DOTS server returns 4.09 (Conflict) to the requesting DOTS client. For both 2.01 (Created) and 4.09 (Conflict) responses, the response includes enough information for a DOTS client to recognize the source of the conflict as described below:
Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cuid=7eeaf349529eb55ed50113"
Uri-Path: "mid=12"
(1) Request with a conflicting 'cuid'
{
"ietf-dots-signal-channel:mitigation-scope": {
"scope": [
{
"conflict-information": {
"conflict-cause": "cuid-collision"
}
}
]
}
}
(2) Message body of the 4.09 (Conflict) response
from the DOTS server
Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cuid=f30d281ce6b64fc5a0b91e"
Uri-Path: "mid=12"
(3) Request with a new 'cuid'
Figure 11: Example of Generating a New 'cuid'
As an active attack evolves, DOTS clients can adjust the scope of requested mitigation as necessary, by refining the scope of resources requiring mitigation. This can be achieved by sending a PUT request with a new 'mid' value that will override the existing one with overlapping mitigation scopes.
For a mitigation request to continue beyond the initial negotiated lifetime, the DOTS client has to refresh the current mitigation request by sending a new PUT request. This PUT request MUST use the same 'mid' value, and MUST repeat all the other parameters as sent in the original mitigation request apart from a possible change to the lifetime parameter value. In such case, the DOTS server MAY update the mitigation request, and a 2.04 (Changed) response is returned to indicate a successful update of the mitigation request. If this is not the case, the DOTS server MUST reject the request with a 4.00 (Bad Request).
A GET request is used by a DOTS client to retrieve information (including status) of DOTS mitigations from a DOTS server.
'cuid' is a mandatory Uri-Path parameter for GET requests.
Uri-Path parameters with empty values MUST NOT be present in a request.
The same considerations for manipulating 'cdid' parameter by server-domain DOTS gateways specified in Section 4.4.1 MUST be followed for GET requests.
The 'c' Uri-Query option is used to control selection of configuration and non-configuration data nodes. Concretely, the 'c' (content) parameter and its permitted values defined in the following table [I-D.ietf-core-comi] can be used to retrieve non-configuration data (attack mitigation status), configuration data, or both. The DOTS server MAY support this optional filtering capability. It can safely ignore it if not supported. If the DOTS client supports the optional filtering capability, it SHOULD use "c=n" query (to get back only the dynamically changing data) or "c=c" query (to get back the static configuration values) when the DDoS attack is active to limit the size of the response.
| Value | Description |
|---|---|
| c | Return only configuration descendant data nodes |
| n | Return only non-configuration descendant data nodes |
| a | Return all descendant data nodes |
The DOTS client can use Block-wise transfer [RFC7959] to get the list of all its mitigations maintained by a DOTS server, it can send Block2 Option in a GET request with NUM = 0 to aid in limiting the size of the response. If the representation of all the active mitigation requests associated with the DOTS client does not fit within a single datagram, the DOTS server MUST use the Block2 Option with NUM = 0 in the GET response. The Size2 Option may be conveyed in the response to indicate the total size of the resource representation. The DOTS client retrieves the rest of the representation by sending additional GET requests with Block2 Options containing NUM values greater than zero. The DOTS client MUST adhere to the block size preferences indicated by the DOTS server in the response. If the DOTS server uses the Block2 Option in the GET response and the response is for a dynamically changing resource (e.g., "c=n" or "c=a" query), the DOTS server MUST include the ETag Option in the response. The DOTS client MUST include the same ETag value in subsequent GET requests to retrieve the rest of the representation.
The following examples illustrate how a DOTS client retrieves active mitigation requests from a DOTS server. In particular:
These two examples assume the default of "c=a"; that is, the DOTS client asks for all data to be reported by the DOTS server.
Header: GET (Code=0.01) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "mitigate" Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw" Observe: 0
Figure 12: GET to Retrieve all DOTS Mitigation Requests
Header: GET (Code=0.01) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "mitigate" Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw" Uri-Path: "mid=12332" Observe: 0
Figure 13: GET to Retrieve a Specific DOTS Mitigation Request
If the DOTS server does not find the 'mid' Uri-Path value conveyed in the GET request in its configuration data for the requesting DOTS client, it MUST respond with a 4.04 (Not Found) error response code. Likewise, the same error MUST be returned as a response to a request to retrieve all mitigation records (i.e., 'mid' Uri-Path is not defined) of a given DOTS client if the DOTS server does not find any mitigation record for that DOTS client. As a reminder, a DOTS client is identified by its identity (e.g., client certificate, 'cuid') and optionally the 'cdid'.
Figure 14 shows a response example of all active mitigation requests associated with the DOTS client as maintained by the DOTS server. The response indicates the mitigation status of each mitigation request.
{
"ietf-dots-signal-channel:mitigation-scope": {
"scope": [
{
"mid": 12332,
"mitigation-start": "1507818434",
"target-prefix": [
"2001:db8:6401::1/128",
"2001:db8:6401::2/128"
],
"target-protocol": [
17
],
"lifetime": 1756,
"status": "attack-successfully-mitigated",
"bytes-dropped": "134334555",
"bps-dropped": "43344",
"pkts-dropped": "333334444",
"pps-dropped": "432432"
},
{
"mid": 12333,
"mitigation-start": "1507818393",
"target-prefix": [
"2001:db8:6401::1/128",
"2001:db8:6401::2/128"
],
"target-protocol": [
6
],
"lifetime": 1755,
"status": "attack-stopped",
"bytes-dropped": "0",
"bps-dropped": "0",
"pkts-dropped": "0",
"pps-dropped": "0"
}
]
}
}
Figure 14: Response Body to a GET Request
The mitigation status parameters are described below:
| Parameter Value | Description |
|---|---|
| 1 | Attack mitigation setup is in progress (e.g., changing the network path to redirect the inbound traffic to a DOTS mitigator). |
| 2 | Attack is being successfully mitigated (e.g., traffic is redirected to a DDoS mitigator and attack traffic is dropped). |
| 3 | Attack has stopped and the DOTS client can withdraw the mitigation request. This status code will be transmitted for immediate mitigation requests till the mitigation is withdrawn or the lifetime expires. For mitigation requests with pre-configured scopes (i.e., 'trigger-mitigation' set to 'false'), this status code will be transmitted 4 times and then transition to "8". |
| 4 | Attack has exceeded the mitigation provider capability. |
| 5 | DOTS client has withdrawn the mitigation request and the mitigation is active but terminating. |
| 6 | Attack mitigation is now terminated. |
| 7 | Attack mitigation is withdrawn (by the DOTS server). If a mitigation request with 'trigger-mitigation' set to false is withdrawn because it overlaps with an immediate mitigation request, this status code will be transmitted 4 times and then transition to "8" for the mitigation request with pre-configured scopes. |
| 8 | Attack mitigation will be triggered for the mitigation request only when the DOTS signal channel session is lost. |
The Observe Option defined in [RFC7641] extends the CoAP core protocol with a mechanism for a CoAP client to "observe" a resource on a CoAP server: The client retrieves a representation of the resource and requests this representation be updated by the server as long as the client is interested in the resource. DOTS implementations MUST use the Observe Option for both 'mitigate' and 'config' (Section 4.2).
A DOTS client conveys the Observe Option set to '0' in the GET request to receive asynchronous notifications of attack mitigation status from the DOTS server.
Unidirectional mitigation notifications within the bidirectional signal channel enables asynchronous notifications between the agents. [RFC7641] indicates that (1) a notification can be sent in a Confirmable or a Non-confirmable message, and (2) the message type used is typically application-dependent and may be determined by the server for each notification individually. 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. This overrides the behavior defined in Section 4.5 of [RFC7641] to send a Confirmable message instead of a Non-confirmable message at least every 24 hour for the following reasons: First, the DOTS signal channel uses a heartbeat mechanism to determine if the DOTS client is alive. Second, Confirmable messages are not suitable during an attack.
Due to the higher likelihood of packet loss during a DDoS attack, the DOTS server periodically sends attack mitigation status to the DOTS client and also notifies the DOTS client whenever the status of the attack mitigation changes. If the DOTS server cannot maintain an RTT estimate, it MUST NOT send more than one asynchronous notification every 3 seconds, and SHOULD use an even less aggressive rate whenever possible (case 2 in Section 3.1.3 of [RFC8085]).
When conflicting requests are detected, the DOTS server enforces the corresponding policy (e.g., accept all requests, reject all requests, accept only one request but reject all the others, ...). It is assumed that this policy is supplied by the DOTS server administrator or it is a default behavior of the DOTS server implementation. Then, the DOTS server sends notification message(s) to the DOTS client(s) at the origin of the conflict (refer to the conflict parameters defined in Section 4.4.1). A conflict notification message includes information about the conflict cause, scope, and the status of the mitigation request(s). For example,
Upon receipt of a conflict notification message indicating that a mitigation request is deactivated because of a conflict, a DOTS client MUST NOT resend the same mitigation request before the expiry of 'retry-timer'. It is also recommended that DOTS clients support means to alert administrators about mitigation conflicts.
A DOTS client that is no longer interested in receiving notifications from the DOTS server can simply "forget" the observation. When the DOTS server sends the next notification, the DOTS client will not recognize the token in the message and thus will return a Reset message. This causes the DOTS server to remove the associated entry. Alternatively, the DOTS client can explicitly deregister itself by issuing a GET request that has the Token field set to the token of the observation to be cancelled and includes an Observe Option with the value set to '1' (deregister). The latter is RECOMMENDED.
Figure 15 shows an example of a DOTS client requesting a DOTS server to send notifications related to a mitigation request. Note that for mitigations with pre-configured scopes (i.e., 'trigger-mitigation' set to 'false'), the state will need to transition from 3 (attack-stopped) to 8 (attack-mitigation-signal-loss).
+-----------+ +-----------+
|DOTS client| |DOTS server|
+-----------+ +-----------+
| |
| GET /<mid> |
| Token: 0x4a | Registration
| Observe: 0 |
+----------------------------------------->|
| |
| 2.05 Content |
| Token: 0x4a | Notification of
| Observe: 12 | the current state
| status: "attack-mitigation-in-progress" |
| |
|<-----------------------------------------+
| 2.05 Content |
| Token: 0x4a | Notification upon
| Observe: 44 | a state change
| status: "attack-successfully-mitigated" |
| |
|<-----------------------------------------+
| 2.05 Content |
| Token: 0x4a | Notification upon
| Observe: 60 | a state change
| status: "attack-stopped" |
|<-----------------------------------------+
| |
...
Figure 15: Notifications of Attack Mitigation Status
The DOTS client can send the GET request at frequent intervals without the Observe Option to retrieve the configuration data of the mitigation request and non-configuration data (i.e., the attack status). DOTS clients MAY be configured with a policy indicating the frequency of polling DOTS servers to get the mitigation status. This frequency MUST NOT be more than one UDP datagram per RTT as discussed in Section 3.1.3 of [RFC8085].
If the DOTS server has been able to mitigate the attack and the attack has stopped, the DOTS server indicates as such in the status. In such case, the DOTS client recalls the mitigation request by issuing a DELETE request for this mitigation request (Section 4.4.4).
A DOTS client SHOULD react to the status of the attack as per the information sent by the DOTS server rather than performing its own detection that the attack has been mitigated. This ensures that the DOTS client does not recall a mitigation request prematurely because it is possible that the DOTS client does not sense the DDoS attack on its resources, but the DOTS server could be actively mitigating the attack because the attack is not completely averted.
While DDoS mitigation is in progress, due to the likelihood of packet loss, a DOTS client MAY periodically transmit DOTS mitigation efficacy updates to the relevant DOTS server. A PUT request is used to convey the mitigation efficacy update to the DOTS server. This PUT request is treated as a refresh of the current mitigation.
The PUT request used for efficacy update MUST include all the parameters used in the PUT request to carry the DOTS mitigation request (Section 4.4.1) unchanged apart from the 'lifetime' parameter value. If this is not the case, the DOTS server MUST reject the request with a 4.00 (Bad Request).
The If-Match Option (Section 5.10.8.1 of [RFC7252]) with an empty value is used to make the PUT request conditional on the current existence of the mitigation request. If UDP is used as transport, CoAP requests may arrive out-of-order. For example, the DOTS client may send a PUT request to convey an efficacy update to the DOTS server followed by a DELETE request to withdraw the mitigation request, but the DELETE request arrives at the DOTS server before the PUT request. To handle out-of-order delivery of requests, if an If-Match Option is present in the PUT request and the 'mid' in the request matches a mitigation request from that DOTS client, the request is processed by the DOTS server. If no match is found, the PUT request is silently ignored by the DOTS server.
An example of an efficacy update message, which includes an If-Match Option with an empty value, is depicted in Figure 16.
Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "mitigate"
Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw"
Uri-Path: "mid=123"
If-Match:
Content-Format: "application/dots+cbor"
{
"ietf-dots-signal-channel:mitigation-scope": {
"scope": [
{
"target-prefix": [
"2001:db8:6401::1/128",
"2001:db8:6401::2/128"
],
"target-port-range": [
{
"lower-port": 80
},
{
"lower-port": 443
},
{
"lower-port": 8080
}
],
"target-protocol": [
6
],
"attack-status": "under-attack"
}
]
}
}
Figure 16: An Example of Efficacy Update
The 'attack-status' parameter is a mandatory attribute when performing an efficacy update. The various possible values contained in the 'attack-status' parameter are described in Table 3.
| Parameter value | Description |
|---|---|
| 1 | The DOTS client determines that it is still under attack. |
| 2 | The DOTS client determines that the attack is successfully mitigated (e.g., attack traffic is not seen). |
The DOTS server indicates the result of processing a PUT request using CoAP response codes. The response code 2.04 (Changed) is returned if the DOTS server has accepted the mitigation efficacy update. The error response code 5.03 (Service Unavailable) is returned if the DOTS server has erred or is incapable of performing the mitigation. As specified in [RFC7252], 5.03 uses Max-Age option to indicate the number of seconds after which to retry.
DELETE requests are used to withdraw DOTS mitigation requests from DOTS servers (Figure 17).
'cuid' and 'mid' are mandatory Uri-Path parameters for DELETE requests.
The same considerations for manipulating 'cdid' parameter by DOTS gateways, as specified in Section 4.4.1, MUST be followed for DELETE requests. Uri-Path parameters with empty values MUST NOT be present in a request.
Header: DELETE (Code=0.04) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "mitigate" Uri-Path: "cuid=dz6pHjaADkaFTbjr0JGBpw" Uri-Path: "mid=123"
Figure 17: Withdraw a DOTS Mitigation
If the DELETE request does not include 'cuid' and 'mid' parameters, the DOTS server MUST reply with a 4.00 (Bad Request).
Once the request is validated, the DOTS server immediately acknowledges a DOTS client's request to withdraw the DOTS signal using 2.02 (Deleted) response code with no response payload. A 2.02 (Deleted) Response Code is returned even if the 'mid' parameter value conveyed in the DELETE request does not exist in its configuration data before the request.
If the DOTS server finds the 'mid' parameter value conveyed in the DELETE request in its configuration data for the DOTS client, then to protect against route or DNS flapping caused by a DOTS client rapidly removing a mitigation, and to dampen the effect of oscillating attacks, the DOTS server MAY allow mitigation to continue for a limited period after acknowledging a DOTS client's withdrawal of a mitigation request. During this period, the DOTS server status messages SHOULD indicate that mitigation is active but terminating (Section 4.4.2).
The initial active-but-terminating period SHOULD be sufficiently long to absorb latency incurred by route propagation. The active-but-terminating period SHOULD be set by default to 120 seconds. If the client requests mitigation again before the initial active-but-terminating period elapses, the DOTS server MAY exponentially increase (the base of the exponent is 2) the active-but-terminating period up to a maximum of 300 seconds (5 minutes).
Once the active-but-terminating period elapses, the DOTS server MUST treat the mitigation as terminated, as the DOTS client is no longer responsible for the mitigation.
If a mitigation is triggered due to a signal channel loss, the DOTS server relies upon normal triggers to stop that mitigation (typically, receipt of a valid DELETE request, expiry of the mitigation lifetime, or scrubbing the traffic to the attack target). In particular, the DOTS server MUST NOT consider the signal channel recovery as a trigger to stop the mitigation.
A DOTS client can negotiate, configure, and retrieve the DOTS signal channel session behavior with its DOTS peers. The DOTS signal channel can be used, for example, to configure the following:
When the DOTS signal channel is established over a reliable transport (e.g., TCP), there is no need for the reliability mechanisms provided by CoAP over UDP since the underlying TCP connection provides retransmissions and deduplication [RFC8323]. As a reminder, CoAP over reliable transports does not support Confirmable or Non-confirmable message types. As such, the transmission-related parameters (missing-hb-allowed and acceptable signal loss ratio) are negotiated only for DOTS over unreliable transports.
The same or distinct configuration sets may be used during times when a mitigation is active ('mitigating-config') and when no mitigation is active ('idle-config'). This is particularly useful for DOTS servers that might want to reduce heartbeat frequency or cease heartbeat exchanges when an active DOTS client has not requested mitigation. If distinct configurations are used, DOTS agents MUST follow the appropriate configuration set as a function of the mitigation activity (e.g., if no mitigation request is active (also referred to as 'idle' time), 'idle-config'-related values must be followed). Additionally, DOTS agents MUST automatically switch to the other configuration upon a change in the mitigation activity (e.g., if an attack mitigation is launched after an 'idle' time, the DOTS agent switches from 'idle-config' to 'mitigating-config'-related values).
The specification allows for a flexible retry configuration when an unreliable transport is in use. For example, a server may be tweaked to return the following configuration to be used when a mitigation is active:
CoAP Requests and responses are indicated for reliable delivery by marking them as Confirmable messages. DOTS signal channel session configuration requests and responses are marked as Confirmable messages. As explained in Section 2.1 of [RFC7252], a Confirmable message is retransmitted using a default timeout and exponential back-off between retransmissions, until the DOTS server sends an Acknowledgement message (ACK) with the same Message ID conveyed from the DOTS client.
Message transmission parameters are defined in Section 4.8 of [RFC7252]. The DOTS server can either piggyback the response in the acknowledgement message or, if the DOTS server cannot respond immediately to a request carried in a Confirmable message, it simply responds with an Empty Acknowledgement message so that the DOTS client can stop retransmitting the request. Empty Acknowledgement messages are explained in Section 2.2 of [RFC7252]. When the response is ready, the server sends it in a new Confirmable message which in turn needs to be acknowledged by the DOTS client (see Sections 5.2.1 and 5.2.2 of [RFC7252]). Requests and responses exchanged between DOTS agents during 'idle' time are marked as Confirmable messages.
A GET request is used to obtain acceptable (e.g., minimum and maximum values) and current configuration parameters on the DOTS server for DOTS signal channel session configuration. This procedure occurs between a DOTS client and its immediate peer DOTS server. As such, this GET request MUST NOT be relayed by a DOTS gateway.
Figure 18 shows how to obtain acceptable configuration parameters for the DOTS server.
Header: GET (Code=0.01) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "config"
Figure 18: GET to Retrieve Configuration
The DOTS server in the 2.05 (Content) response conveys the current, minimum, and maximum attribute values acceptable by the DOTS server (Figure 19).
{
"ietf-dots-signal-channel:signal-config": {
"mitigating-config": {
"heartbeat-interval": {
"max-value": number,
"min-value": number,
"current-value": number
},
"missing-hb-allowed": {
"max-value": number,
"min-value": number,
"current-value": number
},
"max-retransmit": {
"max-value": number,
"min-value": number,
"current-value": number
},
"ack-timeout": {
"max-value-decimal": "string",
"min-value-decimal": "string",
"current-value-decimal": "string"
},
"ack-random-factor": {
"max-value-decimal": "string",
"min-value-decimal": "string",
"current-value-decimal": "string"
}
},
"idle-config": {
"heartbeat-interval": {
"max-value": number,
"min-value": number,
"current-value": number
},
"missing-hb-allowed": {
"max-value": number,
"min-value": number,
"current-value": number
},
"max-retransmit": {
"max-value": number,
"min-value": number,
"current-value": number
},
"ack-timeout": {
"max-value-decimal": "string",
"min-value-decimal": "string",
"current-value-decimal": "string"
},
"ack-random-factor": {
"max-value-decimal": "string",
"min-value-decimal": "string",
"current-value-decimal": "string"
}
}
}
}
Figure 19: GET Configuration Response Body Schema
The parameters in Figure 19 are described below:
Figure 20 shows an example of acceptable and current configuration parameters on a DOTS server for DOTS signal channel session configuration. The same acceptable configuration is used during mitigation and idle times.
{
"ietf-dots-signal-channel:signal-config": {
"mitigating-config": {
"heartbeat-interval": {
"max-value": 240,
"min-value": 15,
"current-value": 30
},
"missing-hb-allowed": {
"max-value": 9,
"min-value": 3,
"current-value": 5
},
"max-retransmit": {
"max-value": 15,
"min-value": 2,
"current-value": 3
},
"ack-timeout": {
"max-value-decimal": "30.00",
"min-value-decimal": "1.00",
"current-value-decimal": "2.00"
},
"ack-random-factor": {
"max-value-decimal": "4.00",
"min-value-decimal": "1.10",
"current-value-decimal": "1.50"
}
},
"idle-config": {
"heartbeat-interval": {
"max-value": 240,
"min-value": 15,
"current-value": 30
},
"missing-hb-allowed": {
"max-value": 9,
"min-value": 3,
"current-value": 5
},
"max-retransmit": {
"max-value": 15,
"min-value": 2,
"current-value": 3
},
"ack-timeout": {
"max-value-decimal": "30.00",
"min-value-decimal": "1.00",
"current-value-decimal": "2.00"
},
"ack-random-factor": {
"max-value-decimal": "4.00",
"min-value-decimal": "1.10",
"current-value-decimal": "1.50"
}
}
}
}
Figure 20: Example of a Configuration Response Body
A PUT request (Figures 21 and 22) is used to convey the configuration parameters for the signal channel (e.g., heartbeat interval, maximum retransmissions). Message transmission parameters for CoAP are defined in Section 4.8 of [RFC7252]. The RECOMMENDED values of transmission parameter values are ack-timeout (2 seconds), max-retransmit (3), ack-random-factor (1.5). In addition to those parameters, the RECOMMENDED specific DOTS transmission parameter values are 'heartbeat-interval' (30 seconds) and 'missing-hb-allowed' (5).
Section 4.2 of [RFC7252] defines a “CoAP Ping” mechanism. Concretely, the DOTS agent sends an Empty Confirmable message and the peer DOTS agent will respond by sending a Reset message.
When a Confirmable "CoAP Ping" is sent, and if there is no response, the "CoAP Ping" is retransmitted max-retransmit number of times by the CoAP layer using an initial timeout set to a random duration between ack-timeout and (ack-timeout*ack-random-factor) and exponential back-off between retransmissions. By choosing the recommended transmission parameters, the "CoAP Ping" will timeout after 45 seconds. If the DOTS agent does not receive any response from the peer DOTS agent for 'missing-hb-allowed' number of consecutive "CoAP Ping" Confirmable messages, it concludes that the DOTS signal channel session is disconnected. A DOTS client MUST NOT transmit a "CoAP Ping" while waiting for the previous "CoAP Ping" response from the same DOTS server.
If the DOTS agent wishes to change the default values of message transmission parameters, it SHOULD follow the guidance given in Section 4.8.1 of [RFC7252]. The DOTS agents MUST use the negotiated values for message transmission parameters and default values for non-negotiated message transmission parameters.
The signal channel session configuration is applicable to a single DOTS signal channel session between DOTS agents, so the 'cuid' Uri-Path MUST NOT be used.
Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "config"
Uri-Path: "sid=123"
Content-Format: "application/dots+cbor"
{
...
}
Figure 21: PUT to Convey the DOTS Signal Channel Session Configuration Data
The additional Uri-Path parameter to those defined in Table 1 is as follows:
{
"ietf-dots-signal-channel:signal-config": {
"mitigating-config": {
"heartbeat-interval": {
"current-value": number
},
"missing-hb-allowed": {
"current-value": number
},
"max-retransmit": {
"current-value": number
},
"ack-timeout": {
"current-value-decimal": "string"
},
"ack-random-factor": {
"current-value-decimal": "string"
}
},
"idle-config": {
"heartbeat-interval": {
"current-value": number
},
"missing-hb-allowed": {
"current-value": number
},
"max-retransmit": {
"current-value": number
},
"ack-timeout": {
"current-value-decimal": "string"
},
"ack-random-factor": {
"current-value-decimal": "string"
}
}
}
}
Figure 22: PUT to Convey the DOTS Signal Channel Session Configuration Data (Message Body Schema)
The meaning of the parameters in the CBOR body (Figure 22) is defined in Section 4.5.1.
At least one of the attributes 'heartbeat-interval', 'missing-hb-allowed', 'max-retransmit', 'ack-timeout', and 'ack-random-factor' MUST be present in the PUT request. Note that 'heartbeat-interval', 'missing-hb-allowed', 'max-retransmit', 'ack-timeout', and 'ack-random-factor', if present, do not need to be provided for both 'mitigating-config', and 'idle-config' in a PUT request.
The PUT request with a higher numeric 'sid' value overrides the DOTS signal channel session configuration data installed by a PUT request with a lower numeric 'sid' value. To avoid maintaining a long list of 'sid' requests from a DOTS client, the lower numeric 'sid' MUST be automatically deleted and no longer available at the DOTS server.
Figure 23 shows a PUT request example to convey the configuration parameters for the DOTS signal channel. In this example, the heartbeat mechanism is disabled when no mitigation is active, while the heartbeat interval is set to '91' when a mitigation is active.
Header: PUT (Code=0.03)
Uri-Path: ".well-known"
Uri-Path: "dots"
Uri-Path: "config"
Uri-Path: "sid=123"
Content-Format: "application/dots+cbor"
{
"ietf-dots-signal-channel:signal-config": {
"mitigating-config": {
"heartbeat-interval": {
"current-value": 91
},
"missing-hb-allowed": {
"current-value": 3
},
"max-retransmit": {
"current-value": 3
},
"ack-timeout": {
"current-value-decimal": "2.00"
},
"ack-random-factor": {
"current-value-decimal": "1.50"
}
},
"idle-config": {
"heartbeat-interval": {
"current-value": 0
},
"max-retransmit": {
"current-value": 3
},
"ack-timeout": {
"current-value-decimal": "2.00"
},
"ack-random-factor": {
"current-value-decimal": "1.50"
}
}
}
}
Figure 23: PUT to Convey the Configuration Parameters
The DOTS server indicates the result of processing the PUT request using CoAP response codes:
A DOTS client may issue a GET message with 'sid' Uri-Path parameter to retrieve the negotiated configuration. The response does not need to include 'sid' in its message body.
Max-Age Option (Section 5.10.5 of [RFC7252]) SHOULD be returned by a DOTS server to associate a validity time with a configuration it sends. This feature allows the update of the configuration data if a change occurs at the DOTS server side. For example, the new configuration may instruct a DOTS client to cease heartbeats or reduce heartbeat frequency.
It is NOT RECOMMENDED to return a Max-Age Option set to 0.
Returning a Max-Age Option set to 2**32-1 is equivalent to associating an infinite lifetime with the configuration.
If a non-zero value of Max-Age Option is received by a DOTS client, it MUST issue a GET request with 'sid' Uri-Path parameter to retrieve the current and acceptable configuration before the expiry of the value enclosed in the Max-Age option. This request is considered by the client and the server as a means to refresh the configuration parameters for the signal channel. When a DDoS attack is active, refresh requests MUST NOT be sent by DOTS clients and the DOTS server MUST NOT terminate the (D)TLS session after the expiry of the value returned in Max-Age Option.
If Max-Age Option is not returned in a response, the DOTS client initiates GET requests to refresh the configuration parameters each 60 seconds (Section 5.10.5 of [RFC7252]). To prevent such overload, it is RECOMMENDED that DOTS servers return a Max-Age Option in GET responses. Considerations related to which value to use and how such value is set, are implementation- and deployment-specific.
If an Observe Option set to 0 is included in the configuration request, the DOTS server sends notifications of any configuration change (Section 4.2 of [RFC7641]).
If a DOTS server detects that a misbehaving DOTS client does not contact the DOTS server after the expiry of Max-Age and retrieve the signal channel configuration data, it MAY terminate the (D)TLS session. A (D)TLS session is terminated by the receipt of an authenticated message that closes the connection (e.g., a fatal alert (Section 6 of [RFC8446])).
A DELETE request is used to delete the installed DOTS signal channel session configuration data (Figure 24).
Header: DELETE (Code=0.04) Uri-Path: ".well-known" Uri-Path: "dots" Uri-Path: "config" Uri-Path: "sid=123"
Figure 24: Delete Configuration
The DOTS server resets the DOTS signal channel session configuration back to the default values and acknowledges a DOTS client's request to remove the DOTS signal channel session configuration using 2.02 (Deleted) response code.
Upon bootstrapping or reboot, a DOTS client MAY send a DELETE request to set the configuration parameters to default values. Such a request does not include any 'sid'.
Redirected DOTS signaling is discussed in detail in Section 3.2.2 of [I-D.ietf-dots-architecture].
If a DOTS server wants to redirect a DOTS client to an alternative DOTS server for a signal session, then the response code 5.03 (Service Unavailable) will be returned in the response to the DOTS client.
The DOTS server can return the error response code 5.03 in response to a request from the DOTS client or convey the error response code 5.03 in a unidirectional notification response from the DOTS server.
The DOTS server in the error response conveys the alternate DOTS server's FQDN, and the alternate DOTS server's IP address(es) values in the CBOR body (Figure 25).
{
"ietf-dots-signal-channel:redirected-signal": {
"alt-server": "string",
"alt-server-record": [
"string"
]
}
Figure 25: Redirected Server Error Response Body Schema
The parameters are described below:
The DOTS server returns the Time to live (TTL) of the alternate DOTS server in a Max-Age Option. That is, the time interval that the alternate DOTS server may be cached for use by a DOTS client. A Max-Age Option set to 2**32-1 is equivalent to receiving an infinite TTL. This value means that the alternate DOTS server is to be used until the alternate DOTS server redirects the traffic with another 5.03 response which encloses an alternate server.
A Max-Age Option set to '0' may be returned for redirecting mitigation requests. Such value means that the redirection applies only for the mitigation request in progress. Returning short TTL in a Max-Age Option may adversely impact DOTS clients on slow links. Returning short values should be avoided under such conditions.
If the alternate DOTS server TTL has expired, the DOTS client MUST use the DOTS server(s), that was provisioned using means discussed in Section 4.1. This fall back mechanism is triggered immediately upon expiry of the TTL, except when a DDoS attack is active.
Requests issued by misbehaving DOTS clients which do not honor the TTL conveyed in the Max-Age Option or react to explicit re-direct messages can be rejected by DOTS servers.
Figure 26 shows a 5.03 response example to convey the DOTS alternate server 'alt-server.example' together with its IP addresses 2001:db8:6401::1 and 2001:db8:6401::2.
{
"ietf-dots-signal-channel:redirected-signal": {
"alt-server": "alt-server.example",
"alt-server-record": [
"2001:db8:6401::1",
"2001:db8:6401::2"
]
}
Figure 26: Example of Redirected Server Error Response Body
When the DOTS client receives 5.03 response with an alternate server included, it considers the current request as failed, but SHOULD try re-sending the request to the alternate DOTS server. During a DDoS attack, the DNS server may be the target of another DDoS attack, alternate DOTS server's IP addresses conveyed in the 5.03 response help the DOTS client skip DNS lookup of the alternate DOTS server, at the cost of trusting the first DOTS server to provide accurate information. The DOTS client can then try to establish a UDP or a TCP session with the alternate DOTS server. The DOTS client MAY implement a method to construct IPv4-embedded IPv6 addresses [RFC6052]; this is required to handle the scenario where an IPv6-only DOTS client communicates with an IPv4-only alternate DOTS server.
If the DOTS client has been redirected to a DOTS server to which it has already communicated with within the last five (5) minutes, it MUST ignore the redirection and try to contact other DOTS servers listed in the local configuration or discovered using dynamic means such as DHCP or SRV procedures [I-D.ietf-dots-server-discovery]. It is RECOMMENDED that DOTS clients support means to alert administrators about redirect loops.
To provide an indication of signal health and distinguish an 'idle' signal channel from a 'disconnected' or 'defunct' session, the DOTS agent sends a heartbeat over the signal channel to maintain its half of the channel (also, aligned with the "consents" recommendation in Section 6 of [RFC8085]). The DOTS agent similarly expects a heartbeat from its peer DOTS agent, and may consider a session terminated in the prolonged absence of a peer agent heartbeat. Concretely, while the communication between the DOTS agents is otherwise quiescent, the DOTS client will probe the DOTS server to ensure it has maintained cryptographic state and vice versa. Such probes can also keep firewalls and/or stateful translators bindings alive. This probing reduces the frequency of establishing a new handshake when a DOTS signal needs to be conveyed to the DOTS server.
DOTS servers MAY trigger their heartbeat requests immediately after receiving heartbeat probes from peer DOTS clients. As a reminder, it is the responsibility of DOTS clients to ensure that on-path translators/firewalls are maintaining a binding so that the same external IP address and/or port number is retained for the DOTS signal channel session.
In case of a massive DDoS attack that saturates the incoming link(s) to the DOTS client, all traffic from the DOTS server to the DOTS client will likely be dropped, although the DOTS server receives heartbeat requests in addition to DOTS messages sent by the DOTS client. In this scenario, DOTS clients MUST behave differently to handle message transmission and DOTS signal channel session liveliness during link saturation:
If the DOTS server receives traffic from the peer DOTS client (e.g., peer DOTS client initiated heartbeats) but maximum 'missing-hb-allowed' threshold is reached, the DOTS server MUST NOT consider the DOTS signal channel session disconnected. The DOTS server MUST keep on using the current DOTS signal channel session so that the DOTS client can send mitigation requests over the current DOTS signal channel session. In this case, the DOTS server can identify the DOTS client is under attack and the inbound link to the DOTS client (domain) is saturated. Furthermore, if the DOTS server does not receive a mitigation request from the DOTS client, it implies the DOTS client has not detected the attack or, if an attack mitigation is in progress, it implies the applied DDoS mitigation actions are not yet effective to handle the DDoS attack volume.
If the DOTS server does not receive any traffic from the peer DOTS client during the time span required to exhaust the maximum 'missing-hb-allowed' threshold, the DOTS server concludes the session is disconnected. The DOTS server can then trigger pre-configured mitigation requests for this DOTS client (if any).
In DOTS over UDP, heartbeat messages MUST be exchanged between the DOTS agents using the “CoAP Ping” mechanism defined in Section 4.2 of [RFC7252].
In DOTS over TCP, heartbeat messages MUST be exchanged between the DOTS agents using the Ping and Pong messages specified in Section 5.4 of [RFC8323]. That is, the DOTS agent sends a Ping message and the peer DOTS agent would respond by sending a single Pong message. The sender of a Ping message has to allow up to 'heartbeat-interval' seconds when waiting for a Pong reply. When a failure is detected by a DOTS client, it proceeds with the session recovery following the same approach as the one used for unreliable transports.
This document defines a YANG [RFC7950] module for DOTS mitigation scope, DOTS signal channel session configuration data, and DOTS redirection signaling.
This YANG module (ietf-dots-signal-channel) defines the DOTS client interaction with the DOTS server as seen by the DOTS client. A DOTS server is allowed to update the non-configurable 'ro' entities in the responses. This YANG module is not intended to be used via NETCONF/RESTCONF for DOTS server management purposes; such module is out of the scope of this document. It serves only to provide a data model and encoding, but not a management data model.
A companion YANG module is defined to include a collection of types defined by IANA: "iana-dots-signal-channel" (Section 5.2).
This document defines the YANG module "ietf-dots-signal-channel" (Section 5.3), which has the following tree structure. A DOTS signal message can be a mitigation, a configuration, or a redirect message.
module: ietf-dots-signal-channel
+--rw dots-signal
+--rw (message-type)?
+--:(mitigation-scope)
| +--rw scope* [cuid mid]
| +--rw cdid? string
| +--rw cuid string
| +--rw mid uint32
| +--rw target-prefix* inet:ip-prefix
| +--rw target-port-range* [lower-port]
| | +--rw lower-port inet:port-number
| | +--rw upper-port? inet:port-number
| +--rw target-protocol* uint8
| +--rw target-fqdn* inet:domain-name
| +--rw target-uri* inet:uri
| +--rw alias-name* string
| +--rw lifetime? int32
| +--rw trigger-mitigation? boolean
| +--ro mitigation-start? uint64
| +--ro status? iana-signal:status
| +--ro conflict-information
| | +--ro conflict-status? iana-signal:conflict-status
| | +--ro conflict-cause? iana-signal:conflict-cause
| | +--ro retry-timer? uint32
| | +--ro conflict-scope
| | +--ro target-prefix* inet:ip-prefix
| | +--ro target-port-range* [lower-port]
| | | +--ro lower-port inet:port-number
| | | +--ro upper-port? inet:port-number
| | +--ro target-protocol* uint8
| | +--ro target-fqdn* inet:domain-name
| | +--ro target-uri* inet:uri
| | +--ro alias-name* string
| | +--ro acl-list* [acl-name]
| | | +--ro acl-name
| | | | -> /ietf-data:dots-data/dots-client/acls/
| | | | acl/name
| | | +--ro acl-type?
| | | -> /ietf-data:dots-data/dots-client/acls/
| | | acl/type
| | +--ro mid? -> ../../../mid
| +--ro bytes-dropped? yang:zero-based-counter64
| +--ro bps-dropped? yang:gauge64
| +--ro pkts-dropped? yang:zero-based-counter64
| +--ro pps-dropped? yang:gauge64
| +--rw attack-status? iana-signal:attack-status
+--:(signal-config)
| +--rw sid uint32
| +--rw mitigating-config
| | +--rw heartbeat-interval
| | | +--ro max-value? uint16
| | | +--ro min-value? uint16
| | | +--rw current-value? uint16
| | +--rw missing-hb-allowed
| | | +--ro max-value? uint16
| | | +--ro min-value? uint16
| | | +--rw current-value? uint16
| | +--rw max-retransmit
| | | +--ro max-value? uint16
| | | +--ro min-value? uint16
| | | +--rw current-value? uint16
| | +--rw ack-timeout
| | | +--ro max-value-decimal? decimal64
| | | +--ro min-value-decimal? decimal64
| | | +--rw current-value-decimal? decimal64
| | +--rw ack-random-factor
| | +--ro max-value-decimal? decimal64
| | +--ro min-value-decimal? decimal64
| | +--rw current-value-decimal? decimal64
| +--rw idle-config
| +--rw heartbeat-interval
| | +--ro max-value? uint16
| | +--ro min-value? uint16
| | +--rw current-value? uint16
| +--rw missing-hb-allowed
| | +--ro max-value? uint16
| | +--ro min-value? uint16
| | +--rw current-value? uint16
| +--rw max-retransmit
| | +--ro max-value? uint16
| | +--ro min-value? uint16
| | +--rw current-value? uint16
| +--rw ack-timeout
| | +--ro max-value-decimal? decimal64
| | +--ro min-value-decimal? decimal64
| | +--rw current-value-decimal? decimal64
| +--rw ack-random-factor
| +--ro max-value-decimal? decimal64
| +--ro min-value-decimal? decimal64
| +--rw current-value-decimal? decimal64
+--:(redirected-signal)
+--ro alt-server string
+--ro alt-server-record* inet:ip-address
<CODE BEGINS> file "iana-dots-signal-channel@2019-01-17.yang"
module iana-dots-signal-channel {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:iana-dots-signal-channel";
prefix iana-signal;
organization
"IANA";
contact
"Internet Assigned Numbers Authority
Postal: ICANN
12025 Waterfront Drive, Suite 300
Los Angeles, CA 90094-2536
United States of America
Tel: +1 310 301 5800
<mailto:iana@iana.org>";
description
"This module contains a collection of YANG data types defined
by IANA and used for DOTS signal channel protocol.
Copyright (c) 2019 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 Simplified 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 2019-01-17 {
description
"Initial revision.";
reference
"RFC XXXX: Distributed Denial-of-Service Open Threat
Signaling (DOTS) Signal Channel Specification";
}
typedef status {
type enumeration {
enum attack-mitigation-in-progress {
value 1;
description
"Attack mitigation setup is in progress (e.g., changing
the network path to re-route the inbound traffic
to DOTS mitigator).";
}
enum attack-successfully-mitigated {
value 2;
description
"Attack is being successfully mitigated (e.g., traffic
is redirected to a DDoS mitigator and attack
traffic is dropped or blackholed).";
}
enum attack-stopped {
value 3;
description
"Attack has stopped and the DOTS client can
withdraw the mitigation request.";
}
enum attack-exceeded-capability {
value 4;
description
"Attack has exceeded the mitigation provider
capability.";
}
enum dots-client-withdrawn-mitigation {
value 5;
description
"DOTS client has withdrawn the mitigation
request and the mitigation is active but
terminating.";
}
enum attack-mitigation-terminated {
value 6;
description
"Attack mitigation is now terminated.";
}
enum attack-mitigation-withdrawn {
value 7;
description
"Attack mitigation is withdrawn.";
}
enum attack-mitigation-signal-loss {
value 8;
description
"Attack mitigation will be triggered
for the mitigation request only when
the DOTS signal channel session is lost.";
}
}
description
"Enumeration for status reported by the DOTS server.";
}
typedef conflict-status {
type enumeration {
enum request-inactive-other-active {
value 1;
description
"DOTS Server has detected conflicting mitigation
requests from different DOTS clients.
This mitigation request is currently inactive
until the conflicts are resolved. Another
mitigation request is active.";
}
enum request-active {
value 2;
description
"DOTS Server has detected conflicting mitigation
requests from different DOTS clients.
This mitigation request is currently active.";
}
enum all-requests-inactive {
value 3;
description
"DOTS Server has detected conflicting mitigation
requests from different DOTS clients. All
conflicting mitigation requests are inactive.";
}
}
description
"Enumeration for conflict status.";
}
typedef conflict-cause {
type enumeration {
enum overlapping-targets {
value 1;
description
"Overlapping targets. conflict-scope provides
more details about the exact conflict.";
}
enum conflict-with-acceptlist {
value 2;
description
"Conflicts with an existing accept-list.
This code is returned when the DDoS mitigation
detects that some of the source addresses/prefixes
listed in the accept-list ACLs are actually
attacking the target.";
}
enum cuid-collision {
value 3;
description
"Conflicts with the cuid used by another
DOTS client.";
}
}
description
"Enumeration for conflict causes.";
}
typedef attack-status {
type enumeration {
enum under-attack {
value 1;
description
"The DOTS client determines that it is still under
attack.";
}
enum attack-successfully-mitigated {
value 2;
description
"The DOTS client determines that the attack is
successfully mitigated.";
}
}
description
"Enumeration for attack status codes.";
}
}
<CODE ENDS>
This module uses the common YANG types defined in [RFC6991] and types defined in [I-D.ietf-dots-data-channel].
<CODE BEGINS> file "ietf-dots-signal-channel@2019-01-17.yang"
module ietf-dots-signal-channel {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-dots-signal-channel";
prefix signal;
import ietf-inet-types {
prefix inet;
reference "Section 4 of RFC 6991";
}
import ietf-yang-types {
prefix yang;
reference "Section 3 of RFC 6991";
}
import ietf-dots-data-channel {
prefix ietf-data;
reference
"RFC YYYY: Distributed Denial-of-Service Open Threat Signaling
(DOTS) Data Channel Specification";
}
import iana-dots-signal-channel {
prefix iana-signal;
}
organization
"IETF DDoS Open Threat Signaling (DOTS) Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/dots/>
WG List: <mailto:dots@ietf.org>
Editor: Konda, Tirumaleswar Reddy
<mailto:TirumaleswarReddy_Konda@McAfee.com>
Editor: Mohamed Boucadair
<mailto:mohamed.boucadair@orange.com>
Author: Prashanth Patil
<mailto:praspati@cisco.com>
Author: Andrew Mortensen
<mailto:amortensen@arbor.net>
Author: Nik Teague
<mailto:nteague@verisign.com>";
description
"This module contains YANG definition for the signaling
messages exchanged between a DOTS client and a DOTS server.
Copyright (c) 2019 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 Simplified 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 2019-01-17 {
description
"Initial revision.";
reference
"RFC XXXX: Distributed Denial-of-Service Open Threat
Signaling (DOTS) Signal Channel Specification";
}
/*
* Groupings
*/
grouping mitigation-scope {
description
"Specifies the scope of the mitigation request.";
list scope {
key "cuid mid";
description
"The scope of the request.";
leaf cdid {
type string;
description
"The cdid should be included by a server-domain
DOTS gateway to propagate the client domain
identification information from the
gateway's client-facing-side to the gateway's
server-facing-side, and from the gateway's
server-facing-side to the DOTS server.
It may be used by the final DOTS server
for policy enforcement purposes.";
}
leaf cuid {
type string;
description
"A unique identifier that is
generated by a DOTS client to prevent
request collisions. It is expected that the
cuid will remain consistent throughout the
lifetime of the DOTS client.";
}
leaf mid {
type uint32;
description
"Mitigation request identifier.
This identifier must be unique for each mitigation
request bound to the DOTS client.";
}
uses ietf-data:target;
leaf-list alias-name {
type string;
description
"An alias name that points to a resource.";
}
leaf lifetime {
type int32;
units "seconds";
default "3600";
description
"Indicates the lifetime of the mitigation request.
A lifetime of '0' in a mitigation request is an
invalid value.
A lifetime of negative one (-1) indicates indefinite
lifetime for the mitigation request.";
}
leaf trigger-mitigation {
type boolean;
default "true";
description
"If set to 'false', DDoS mitigation will not be
triggered unless the DOTS signal channel
session is lost.";
}
leaf mitigation-start {
type uint64;
config false;
description
"Mitigation start time is represented in seconds
relative to 1970-01-01T00:00:00Z in UTC time.";
}
leaf status {
type iana-signal:status;
config false;
description
"Indicates the status of a mitigation request.
It must be included in responses only.";
}
container conflict-information {
config false;
description
"Indicates that a conflict is detected.
Must only be used for responses.";
leaf conflict-status {
type iana-signal:conflict-status;
description
"Indicates the conflict status.";
}
leaf conflict-cause {
type iana-signal:conflict-cause;
description
"Indicates the cause of the conflict.";
}
leaf retry-timer {
type uint32;
units "seconds";
description
"The DOTS client must not re-send the
same request that has a conflict before the expiry of
this timer.";
}
container conflict-scope {
description
"Provides more information about the conflict scope.";
uses ietf-data:target {
when "../conflict-cause = 'overlapping-targets'";
}
leaf-list alias-name {
when "../../conflict-cause = 'overlapping-targets'";
type string;
description
"Conflicting alias-name.";
}
list acl-list {
when "../../conflict-cause = 'conflict-with-acceptlist'";
key "acl-name";
description
"List of conflicting ACLs as defined in the DOTS data
channel. These ACLs are uniquely defined by
cuid and acl-name.";
leaf acl-name {
type leafref {
path "/ietf-data:dots-data/ietf-data:dots-client/"
+ "ietf-data:acls/ietf-data:acl/ietf-data:name";
}
description
"Reference to the conflicting ACL name bound to
a DOTS client.";
}
leaf acl-type {
type leafref {
path "/ietf-data:dots-data/ietf-data:dots-client/"
+ "ietf-data:acls/ietf-data:acl/ietf-data:type";
}
description
"Reference to the conflicting ACL type bound to
a DOTS client.";
}
}
leaf mid {
when "../../conflict-cause = 'overlapping-targets'";
type leafref {
path "../../../mid";
}
description
"Reference to the conflicting 'mid' bound to
the same DOTS client.";
}
}
}
leaf bytes-dropped {
type yang:zero-based-counter64;
units "bytes";
config false;
description
"The total dropped byte count for the mitigation
request since the attack mitigation is triggered.
The count wraps around when it reaches the maximum value
of counter64 for dropped bytes.";
}
leaf bps-dropped {
type yang:gauge64;
config false;
description
"The average number of dropped bits per second for
the mitigation request since the attack
mitigation is triggered. This should be over
five-minute intervals (that is, measuring bytes
into five-minute buckets and then averaging these
buckets over the time since the mitigation was
triggered).";
}
leaf pkts-dropped {
type yang:zero-based-counter64;
config false;
description
"The total number of dropped packet count for the
mitigation request since the attack mitigation is
triggered. The count wraps around when it reaches
the maximum value of counter64 for dropped packets.";
}
leaf pps-dropped {
type yang:gauge64;
config false;
description
"The average number of dropped packets per second
for the mitigation request since the attack
mitigation is triggered. This should be over
five-minute intervals (that is, measuring packets
into five-minute buckets and then averaging these
buckets over the time since the mitigation was
triggered).";
}
leaf attack-status {
type iana-signal:attack-status;
description
"Indicates the status of an attack as seen by the
DOTS client.";
}
}
}
grouping config-parameters {
description
"Subset of DOTS signal channel session configuration.";
container heartbeat-interval {
description
"DOTS agents regularly send heartbeats to each other
after mutual authentication is successfully
completed in order to keep the DOTS signal channel
open.";
leaf max-value {
type uint16;
units "seconds";
config false;
description
"Maximum acceptable heartbeat-interval value.";
}
leaf min-value {
type uint16;
units "seconds";
config false;
description
"Minimum acceptable heartbeat-interval value.";
}
leaf current-value {
type uint16;
units "seconds";
default "30";
description
"Current heartbeat-interval value.
'0' means that heartbeat mechanism is deactivated.";
}
}
container missing-hb-allowed {
description
"Maximum number of missing heartbeats allowed.";
leaf max-value {
type uint16;
config false;
description
"Maximum acceptable missing-hb-allowed value.";
}
leaf min-value {
type uint16;
config false;
description
"Minimum acceptable missing-hb-allowed value.";
}
leaf current-value {
type uint16;
default "5";
description
"Current missing-hb-allowed value.";
}
}
container max-retransmit {
description
"Maximum number of retransmissions of a Confirmable
message.";
leaf max-value {
type uint16;
config false;
description
"Maximum acceptable max-retransmit value.";
}
leaf min-value {
type uint16;
config false;
description
"Minimum acceptable max-retransmit value.";
}
leaf current-value {
type uint16;
default "3";
description
"Current max-retransmit value.";
}
}
container ack-timeout {
description
"Initial retransmission timeout value.";
leaf max-value-decimal {
type decimal64 {
fraction-digits 2;
}
units "seconds";
config false;
description
"Maximum ack-timeout value.";
}
leaf min-value-decimal {
type decimal64 {
fraction-digits 2;
}
units "seconds";
config false;
description
"Minimum ack-timeout value.";
}
leaf current-value-decimal {
type decimal64 {
fraction-digits 2;
}
units "seconds";
default "2";
description
"Current ack-timeout value.";
}
}
container ack-random-factor {
description
"Random factor used to influence the timing of
retransmissions.";
leaf max-value-decimal {
type decimal64 {
fraction-digits 2;
}
config false;
description
"Maximum acceptable ack-random-factor value.";
}
leaf min-value-decimal {
type decimal64 {
fraction-digits 2;
}
config false;
description
"Minimum acceptable ack-random-factor value.";
}
leaf current-value-decimal {
type decimal64 {
fraction-digits 2;
}
default "1.5";
description
"Current ack-random-factor value.";
}
}
}
grouping signal-config {
description
"DOTS signal channel session configuration.";
leaf sid {
type uint32;
mandatory true;
description
"An identifier for the DOTS signal channel
session configuration data.";
}
container mitigating-config {
description
"Configuration parameters to use when a mitigation
is active.";
uses config-parameters;
}
container idle-config {
description
"Configuration parameters to use when no mitigation
is active.";
uses config-parameters;
}
}
grouping redirected-signal {
description
"Grouping for the redirected signaling.";
leaf alt-server {
type string;
config false;
mandatory true;
description
"FQDN of an alternate server.";
}
leaf-list alt-server-record {
type inet:ip-address;
config false;
description
"List of records for the alternate server.";
}
}
/*
* Main Container for DOTS Signal Channel
*/
container dots-signal {
description
"Main container for DOTS signal message.
A DOTS signal message can be a mitigation, a configuration,
or a redirected signal message.";
choice message-type {
description
"Can be a mitigation, a configuration, or a redirect
message.";
case mitigation-scope {
description
"Mitigation scope of a mitigation message.";
uses mitigation-scope;
}
case signal-config {
description
"Configuration message.";
uses signal-config;
}
case redirected-signal {
description
"Redirected signaling.";
uses redirected-signal;
}
}
}
}
<CODE ENDS>
All parameters in the payload of the DOTS signal channel MUST be mapped to CBOR types as shown in Table 4 and are assigned an integer key to save space.
The CBOR key values are divided into two types: comprehension-required and comprehension-optional. DOTS agents can safely ignore comprehension-optional values they don't understand, but cannot successfully process a request if it contains comprehension-required values that are not understood. The 4.00 response SHOULD include a diagnostic payload describing the unknown comprehension-required CBOR key values. The initial set of CBOR key values defined in this specification are of type comprehension-required.
+----------------------+-------------+-----+---------------+--------+
| Parameter Name | YANG | CBOR| CBOR Major | JSON |
| | Type | Key | Type & | Type |
| | | | Information | |
+----------------------+-------------+-----+---------------+--------+
| ietf-dots-signal-cha | | | | |
| nnel:mitigation-scope| container | 1 | 5 map | Object |
| scope | list | 2 | 4 array | Array |
| cdid | string | 3 | 3 text string | String |
| cuid | string | 4 | 3 text string | String |
| mid | uint32 | 5 | 0 unsigned | Number |
| target-prefix | leaf-list | 6 | 4 array | Array |
| | inet: | | | |
| | ip-prefix | | 3 text string | String |
| target-port-range | list | 7 | 4 array | Array |
| lower-port | inet: | | | |
| | port-number| 8 | 0 unsigned | Number |
| upper-port | inet: | | | |
| | port-number| 9 | 0 unsigned | Number |
| target-protocol | leaf-list | 10 | 4 array | Array |
| | uint8 | | 0 unsigned | Number |
| target-fqdn | leaf-list | 11 | 4 array | Array |
| | inet: | | | |
| | domain-name| | 3 text string | String |
| target-uri | leaf-list | 12 | 4 array | Array |
| | inet:uri | | 3 text string | String |
| alias-name | leaf-list | 13 | 4 array | Array |
| | string | | 3 text string | String |
| lifetime | int32 | 14 | 0 unsigned | Number |
| | | | 1 negative | Number |
| mitigation-start | uint64 | 15 | 0 unsigned | String |
| status | enumeration | 16 | 0 unsigned | String |
| conflict-information | container | 17 | 5 map | Object |
| conflict-status | enumeration | 18 | 0 unsigned | String |
| conflict-cause | enumeration | 19 | 0 unsigned | String |
| retry-timer | uint32 | 20 | 0 unsigned | Number |
| conflict-scope | container | 21 | 5 map | Object |
| acl-list | list | 22 | 4 array | Array |
| acl-name | leafref | 23 | 3 text string | String |
| acl-type | leafref | 24 | 3 text string | String |
| bytes-dropped | yang:zero- | | | |
| | based- | | | |
| | counter64 | 25 | 0 unsigned | String |
| bps-dropped | yang:gauge64| 26 | 0 unsigned | String |
| pkts-dropped | yang:zero- | | | |
| | based- | | | |
| | counter64 | 27 | 0 unsigned | String |
| pps-dropped | yang:gauge64| 28 | 0 unsigned | String |
| attack-status | enumeration | 29 | 0 unsigned | String |
| ietf-dots-signal- | | | | |
| channel:signal-config| container | 30 | 5 map | Object |
| sid | uint32 | 31 | 0 unsigned | Number |
| mitigating-config | container | 32 | 5 map | Object |
| heartbeat-interval | container | 33 | 5 map | Object |
| max-value | uint16 | 34 | 0 unsigned | Number |
| min-value | uint16 | 35 | 0 unsigned | Number |
| current-value | uint16 | 36 | 0 unsigned | Number |
| missing-hb-allowed | container | 37 | 5 map | Object |
| max-retransmit | container | 38 | 5 map | Object |
| ack-timeout | container | 39 | 5 map | Object |
| ack-random-factor | container | 40 | 5 map | Object |
| max-value-decimal | decimal64 | 41 | 6 tag 4 | |
| | | | [-2, integer]| String |
| min-value-decimal | decimal64 | 42 | 6 tag 4 | |
| | | | [-2, integer]| String |
| current-value-decimal| decimal64 | 43 | 6 tag 4 | |
| | | | [-2, integer]| String |
| idle-config | container | 44 | 5 map | Object |
| trigger-mitigation | boolean | 45 | 7 bits 20 | False |
| | | | 7 bits 21 | True |
| ietf-dots-signal-cha | | | | |
|nnel:redirected-signal| container | 46 | 5 map | Object |
| alt-server | string | 47 | 3 text string | String |
| alt-server-record | leaf-list | 48 | 4 array | Array |
| | inet: | | | |
| | ip-address | | 3 text string | String |
+----------------------+-------------+-----+---------------+--------+
Table 4: CBOR Key Values Used in DOTS Signal Channel Messages & Their
Mappings to JSON and YANG
This section defines the (D)TLS protocol profile of DOTS signal channel over (D)TLS and DOTS data channel over TLS.
There are known attacks on (D)TLS, such as man-in-the-middle and protocol downgrade attacks. These are general attacks on (D)TLS and, as such, they are not specific to DOTS over (D)TLS; refer to the (D)TLS RFCs for discussion of these security issues. DOTS agents MUST adhere to the (D)TLS implementation recommendations and security considerations of [RFC7525] except with respect to (D)TLS version. Since DOTS signal channel encryption relying upon (D)TLS is virtually a green-field deployment, DOTS agents MUST implement only (D)TLS 1.2 or later.
When a DOTS client is configured with a domain name of the DOTS server, and connects to its configured DOTS server, the server may present it with a PKIX certificate. In order to ensure proper authentication, a DOTS client MUST verify the entire certification path per [RFC5280]. Additionally, the DOTS client MUST use [RFC6125] validation techniques to compare the domain name with the certificate provided. Certification authorities that issue DOTS server certificates SHOULD support the DNS-ID and SRV-ID identifier types. DOTS server SHOULD prefer the use of DNS-ID and SRV-ID over CN-ID identifier types in certificate requests (as described in Section 2.3 of [RFC6125]) and the wildcard character '*' SHOULD NOT be included in the presented identifier. DOTS doesn't use URI-IDs for server identity verification.
A key challenge to deploying DOTS is the provisioning of DOTS clients, including the distribution of keying material to DOTS clients to enable the required mutual authentication of DOTS agents. Enrollment over Secure Transport (EST) [RFC7030] defines a method of certificate enrollment by which domains operating DOTS servers may provide DOTS clients with all the necessary cryptographic keying material, including a private key and a certificate to authenticate themselves. One deployment option is DOTS clients behave as EST clients for certificate enrollment from an EST server provisioned by the mitigation provider. This document does not specify which EST or other mechanism the DOTS client uses to achieve initial enrollment.
The Server Name Indication (SNI) extension [RFC6066] defines a mechanism for a client to tell a (D)TLS server the name of the server it wants to contact. This is a useful extension for hosting environments where multiple virtual servers are reachable over a single IP address. The DOTS client may or may not know if it is interacting with a DOTS server in a virtual server hosting environment, so the DOTS client SHOULD include the DOTS server FQDN in the SNI extension.
Implementations compliant with this profile MUST implement all of the following items:
Implementations compliant with this profile SHOULD implement all of the following items to reduce the delay required to deliver a DOTS signal channel message:
Compared to UDP, DOTS signal channel over TCP requires an additional round-trip time (RTT) of latency to establish a TCP connection. DOTS implementations are encouraged to implement TCP Fast Open [RFC7413] to eliminate that RTT.
TLS 1.3 provides critical latency improvements for connection establishment over TLS 1.2. The DTLS 1.3 protocol [I-D.ietf-tls-dtls13] is based upon the TLS 1.3 protocol and provides equivalent security guarantees. (D)TLS 1.3 provides two basic handshake modes the DOTS signal channel can take advantage of:
DOTS Client DOTS Server
ClientHello
(0-RTT DOTS signal message)
-------->
ServerHello
{EncryptedExtensions}
{Finished}
<-------- [DOTS signal message]
(end_of_early_data)
{Finished} -------->
[DOTS signal message] <-------> [DOTS signal message]
Note that:
() Indicates messages protected 0-RTT keys
{} Indicates messages protected using handshake keys
[] Indicates messages protected using 1-RTT keys
Figure 27: A Simplified TLS 1.3 Handshake with 0-RTT
To avoid DOTS signal message fragmentation and the subsequent decreased probability of message delivery, DOTS agents MUST ensure that the DTLS record fit within a single datagram. As a reminder, DTLS handles fragmentation and reassembly only for handshake messages and not for the application data (Section 4.1.1 of [RFC6347]). If the PMTU cannot be discovered, DOTS agents MUST assume a PMTU of 1280 bytes, as IPv6 requires that every link in the Internet have an MTU of 1280 octets or greater as specified in [RFC8200]. If IPv4 support on legacy or otherwise unusual networks is a consideration and the PMTU is unknown, DOTS implementations MAY assume on a PMTU of 576 bytes for IPv4 datagrams, as every IPv4 host must be capable of receiving a packet whose length is equal to 576 bytes as discussed in [RFC0791] and [RFC1122].
The DOTS client must consider the amount of record expansion expected by the DTLS processing when calculating the size of CoAP message that fits within the path MTU. Path MTU MUST be greater than or equal to [CoAP message size + DTLS 1.2 overhead of 13 octets + authentication overhead of the negotiated DTLS cipher suite + block padding] (Section 4.1.1.1 of [RFC6347]). If the total request size exceeds the path MTU then the DOTS client MUST split the DOTS signal into separate messages; for example, the list of addresses in the 'target-prefix' parameter could be split into multiple lists and each list conveyed in a new PUT request.
Implementation Note: DOTS choice of message size parameters works well with IPv6 and with most of today's IPv4 paths. However, with IPv4, it is harder to safely make sure that there is no IP fragmentation. If the IPv4 path MTU is unknown, implementations may want to limit themselves to more conservative IPv4 datagram sizes such as 576 bytes, as per [RFC0791].
(D)TLS based upon client certificate can be used for mutual authentication between DOTS agents. If, for example, a DOTS gateway is involved, DOTS clients and DOTS gateways must perform mutual authentication; only authorized DOTS clients are allowed to send DOTS signals to a DOTS gateway. The DOTS gateway and the DOTS server must perform mutual authentication; a DOTS server only allows DOTS signal channel messages from an authorized DOTS gateway, thereby creating a two-link chain of transitive authentication between the DOTS client and the DOTS server.
The DOTS server should support certificate-based client authentication. The DOTS client should respond to the DOTS server's TLS CertificateRequest message with the PKIX certificate held by the DOTS client. DOTS client certificate validation must be performed as per [RFC5280] and the DOTS client certificate must conform to the [RFC5280] certificate profile. If a DOTS client does not support TLS client certificate authentication, it must support pre-shared key based or raw public key based client authentication.
+---------------------------------------------+ | example.com domain +---------+ | | | AAA | | | +---------------+ | Server | | | | Application | +------+--+ | | | server +<---------------+ ^ | | | (DOTS client) | | | | | +---------------+ | | | | V V | example.net domain | +-----+----+--+ | +---------------+ | +--------------+ | | | | | | | Guest +<----x---->+ DOTS +<------>+ DOTS | | | (DOTS client)| | gateway | | | server | | +--------------+ | | | | | | +----+--------+ | +---------------+ | ^ | | | | | +----------------+ | | | | DDoS detector | | | | | (DOTS client) +<-------------+ | | +----------------+ | +---------------------------------------------+
Figure 28: Example of Authentication and Authorization of DOTS Agents
In the example depicted in Figure 28, the DOTS gateway and DOTS clients within the 'example.com' domain mutually authenticate. After the DOTS gateway validates the identity of a DOTS client, it communicates with the AAA server in the 'example.com' domain to determine if the DOTS client is authorized to request DDoS mitigation. If the DOTS client is not authorized, a 4.01 (Unauthorized) is returned in the response to the DOTS client. In this example, the DOTS gateway only allows the application server and DDoS attack detector to request DDoS mitigation, but does not permit the user of type 'guest' to request DDoS mitigation.
Also, DOTS gateways and servers located in different domains must perform mutual authentication (e.g., using certificates). A DOTS server will only allow a DOTS gateway with a certificate for a particular domain to request mitigation for that domain. In reference to Figure 28, the DOTS server only allows the DOTS gateway to request mitigation for 'example.com' domain and not for other domains.
IANA is requested to assign the port number TBD to the DOTS signal channel protocol for both UDP and TCP from the "Service Name and Transport Protocol Port Number Registry" available at https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml.
The assignment of port number 4646 is strongly suggested, as 4646 is the ASCII decimal value for ".." (DOTS).
+----------+----------------+---------------------+-----------------+
| URI | Change | Specification | Related |
| suffix | controller | document(s) | information |
+----------+----------------+---------------------+-----------------+
| dots | IETF | [RFCXXXX] | None |
+----------+----------------+---------------------+-----------------+
Table 5: 'dots' well-known URI
This document requests IANA to register the 'dots' well-known URI (Table 5) in the Well-Known URIs registry (https://www.iana.org/assignments/well-known-uris/well-known-uris.xhtml) as defined by [RFC5785]:
This document requests IANA to register the application/dots+cbor media type in the "Media Types" registry [IANA.MediaTypes] in the manner described in [RFC6838], which can be used to indicate that the content is a DOTS signal channel object:
This document requests IANA to register the CoAP Content-Format ID for the "application/dots+cbor" media type in the "CoAP Content-Formats" registry [IANA.CoAP.Content-Formats] (0-255 range):
This section defines the DOTS CBOR tag as another means for applications to declare that a CBOR data structure is a DOTS signal channel object. Its use is optional and is intended for use in cases in which this information would not otherwise be known. DOTS CBOR tag is not required for DOTS signal channel protocol version specified in this document. If present, the DOTS tag MUST prefix a DOTS signal channel object.
This document requests IANA to register the DOTS signal channel CBOR tag in the "CBOR Tags" registry [IANA.CBOR.Tags] using the 24-255 range:
The document requests IANA to create a new registry, entitled "DOTS Signal Channel Registry". The following sections define sub-registries.
The document requests IANA to create a new sub-registry, entitled "DOTS Signal Channel CBOR Key Values".
The structure of this sub-registry is provided in Section 9.6.1.1. Section 9.6.1.2 provides how the registry is initially populated with the values in Table 4.
+----------------------+-------+-------+------------+---------------+
| Parameter Name | CBOR | CBOR | Change | Specification |
| | Key | Major | Controller | Document(s) |
| | Value | Type | | |
+----------------------+-------+-------+------------+---------------+
| ietf-dots-signal-chan| 1 | 5 | IESG | [RFCXXXX] |
| nel:mitigation-scope | | | | |
| scope | 2 | 4 | IESG | [RFCXXXX] |
| cdid | 3 | 3 | IESG | [RFCXXXX] |
| cuid | 4 | 3 | IESG | [RFCXXXX] |
| mid | 5 | 0 | IESG | [RFCXXXX] |
| target-prefix | 6 | 4 | IESG | [RFCXXXX] |
| target-port-range | 7 | 4 | IESG | [RFCXXXX] |
| lower-port | 8 | 0 | IESG | [RFCXXXX] |
| upper-port | 9 | 0 | IESG | [RFCXXXX] |
| target-protocol | 10 | 4 | IESG | [RFCXXXX] |
| target-fqdn | 11 | 4 | IESG | [RFCXXXX] |
| target-uri | 12 | 4 | IESG | [RFCXXXX] |
| alias-name | 13 | 4 | IESG | [RFCXXXX] |
| lifetime | 14 | 0/1 | IESG | [RFCXXXX] |
| mitigation-start | 15 | 0 | IESG | [RFCXXXX] |
| status | 16 | 0 | IESG | [RFCXXXX] |
| conflict-information | 17 | 5 | IESG | [RFCXXXX] |
| conflict-status | 18 | 0 | IESG | [RFCXXXX] |
| conflict-cause | 19 | 0 | IESG | [RFCXXXX] |
| retry-timer | 20 | 0 | IESG | [RFCXXXX] |
| conflict-scope | 21 | 5 | IESG | [RFCXXXX] |
| acl-list | 22 | 4 | IESG | [RFCXXXX] |
| acl-name | 23 | 3 | IESG | [RFCXXXX] |
| acl-type | 24 | 3 | IESG | [RFCXXXX] |
| bytes-dropped | 25 | 0 | IESG | [RFCXXXX] |
| bps-dropped | 26 | 0 | IESG | [RFCXXXX] |
| pkts-dropped | 27 | 0 | IESG | [RFCXXXX] |
| pps-dropped | 28 | 0 | IESG | [RFCXXXX] |
| attack-status | 29 | 0 | IESG | [RFCXXXX] |
| ietf-dots-signal- | 30 | 5 | IESG | [RFCXXXX] |
| channel:signal-config| | | | |
| sid | 31 | 0 | IESG | [RFCXXXX] |
| mitigating-config | 32 | 5 | IESG | [RFCXXXX] |
| heartbeat-interval | 33 | 5 | IESG | [RFCXXXX] |
| min-value | 34 | 0 | IESG | [RFCXXXX] |
| max-value | 35 | 0 | IESG | [RFCXXXX] |
| current-value | 36 | 0 | IESG | [RFCXXXX] |
| missing-hb-allowed | 37 | 5 | IESG | [RFCXXXX] |
| max-retransmit | 38 | 5 | IESG | [RFCXXXX] |
| ack-timeout | 39 | 5 | IESG | [RFCXXXX] |
| ack-random-factor | 40 | 5 | IESG | [RFCXXXX] |
| min-value-decimal | 41 | 6tag4 | IESG | [RFCXXXX] |
| max-value-decimal | 42 | 6tag4 | IESG | [RFCXXXX] |
| current-value- | 43 | 6tag4 | IESG | [RFCXXXX] |
| decimal | | | | |
| idle-config | 44 | 5 | IESG | [RFCXXXX] |
| trigger-mitigation | 45 | 7 | IESG | [RFCXXXX] |
| ietf-dots-signal-chan| 46 | 5 | IESG | [RFCXXXX] |
| nel:redirected-signal| | | | |
| alt-server | 47 | 3 | IESG | [RFCXXXX] |
| alt-server-record | 48 | 4 | IESG | [RFCXXXX] |
+----------------------+-------+-------+------------+---------------+
Table 6: Initial DOTS Signal Channel CBOR Key Values Registry
The document requests IANA to create a new sub-registry, entitled "DOTS Signal Channel Status Codes". Codes in this registry are used as valid values of 'status' parameter.
The registry is initially populated with the following values:
| Code | Label | Description | Reference |
|---|---|---|---|
| 1 | attack-mitigation-in-progress | Attack mitigation setup is in progress (e.g., changing the network path to redirect the inbound traffic to a DOTS mitigator). | [RFCXXXX] |
| 2 | attack-successfully-mitigated | Attack is being successfully mitigated (e.g., traffic is redirected to a DDoS mitigator and attack traffic is dropped). | [RFCXXXX] |
| 3 | attack-stopped | Attack has stopped and the DOTS client can withdraw the mitigation request. | [RFCXXXX] |
| 4 | attack-exceeded-capability | Attack has exceeded the mitigation provider capability. | [RFCXXXX] |
| 5 | dots-client-withdrawn-mitigation | DOTS client has withdrawn the mitigation request and the mitigation is active but terminating. | [RFCXXXX] |
| 6 | attack-mitigation-terminated | Attack mitigation is now terminated. | [RFCXXXX] |
| 7 | attack-mitigation-withdrawn | Attack mitigation is withdrawn. | [RFCXXXX] |
| 8 | attack-mitigation-signal-loss | Attack mitigation will be triggered for the mitigation request only when the DOTS signal channel session is lost. | [RFCXXXX] |
New codes can be assigned via Standards Action [RFC8126].
The document requests IANA to create a new sub-registry, entitled "DOTS Signal Channel Conflict Status Codes". Codes in this registry are used as valid values of 'conflict-status' parameter.
The registry is initially populated with the following values:
| Code | Label | Description | Reference |
|---|---|---|---|
| 1 | request-inactive-other-active | DOTS server has detected conflicting mitigation requests from different DOTS clients. This mitigation request is currently inactive until the conflicts are resolved. Another mitigation request is active. | [RFCXXXX] |
| 2 | request-active | DOTS server has detected conflicting mitigation requests from different DOTS clients. This mitigation request is currently active. | [RFCXXXX] |
| 3 | all-requests-inactive | DOTS server has detected conflicting mitigation requests from different DOTS clients. All conflicting mitigation requests are inactive. | [RFCXXXX] |
New codes can be assigned via Standards Action [RFC8126].
The document requests IANA to create a new sub-registry, entitled "DOTS Signal Channel Conflict Cause Codes". Codes in this registry are used as valid values of 'conflict-cause' parameter.
The registry is initially populated with the following values:
| Code | Label | Description | Reference |
|---|---|---|---|
| 1 | overlapping-targets | Overlapping targets. | [RFCXXXX] |
| 2 | conflict-with-acceptlist | Conflicts with an existing accept-list. This code is returned when the DDoS mitigation detects source addresses/prefixes in the accept-listed ACLs are attacking the target. | [RFCXXXX] |
| 3 | cuid-collision | CUID Collision. This code is returned when a DOTS client uses a 'cuid' that is already used by another DOTS client. | [RFCXXXX] |
New codes can be assigned via Standards Action [RFC8126].
The document requests IANA to create a new sub-registry, entitled "DOTS Signal Channel Attack Status Codes". Codes in this registry are used as valid values of 'attack-status' parameter.
The registry is initially populated with the following values:
| Code | Label | Description | Reference |
|---|---|---|---|
| 1 | under-attack | The DOTS client determines that it is still under attack. | [RFCXXXX] |
| 2 | attack-successfully-mitigated | The DOTS client determines that the attack is successfully mitigated. | [RFCXXXX] |
New codes can be assigned via Standards Action [RFC8126].
URI: urn:ietf:params:xml:ns:yang:ietf-dots-signal-channel
Registrant Contact: The IESG.
XML: N/A; the requested URI is an XML namespace.
URI: urn:ietf:params:xml:ns:yang:iana-dots-signal-channel
Registrant Contact: IANA.
XML: N/A; the requested URI is an XML namespace.
Name: ietf-dots-signal-channel
Namespace: urn:ietf:params:xml:ns:yang:ietf-dots-signal-channel
Maintained by IANA: N
Prefix: signal
Reference: RFC XXXX
Name: iana-dots-signal-channel
Namespace: urn:ietf:params:xml:ns:yang:iana-dots-signal-channel
Maintained by IANA: Y
Prefix: iana-signal
Reference: RFC XXXX
This document requests IANA to register the following URIs in the "ns" subregistry within the "IETF XML Registry" [RFC3688]: [RFC7950] within the "YANG Parameters" registry.
This document defines the initial version of the IANA-maintained iana-dots-signal-channel YANG module. IANA is requested to add this note:
When a 'status', 'conflict-status', 'conflict-cause', or 'attack-status' value is respectively added to the "DOTS Status Codes", "DOTS Conflict Status Codes", "DOTS Conflict Cause Codes", or "DOTS Attack Status Codes" registry, a new "enum" statement must be added to the iana-dots-signal-channel YANG module. The following "enum" statement, and substatements thereof, should be defined:
When the iana-dots-signal-channel YANG module is updated, a new "revision" statement must be added in front of the existing revision statements.
IANA is requested to add this note to "DOTS Status Codes", "DOTS Conflict Status Codes", "DOTS Conflict Cause Codes", and "DOTS Attack Status Codes" registries:
High-level DOTS security considerations are documented in [RFC8612] and [I-D.ietf-dots-architecture].
Authenticated encryption MUST be used for data confidentiality and message integrity. The interaction between the DOTS agents requires Datagram Transport Layer Security (DTLS) or Transport Layer Security (TLS) with a cipher suite offering confidentiality protection, and the guidance given in [RFC7525] MUST be followed to avoid attacks on (D)TLS. The (D)TLS protocol profile used for the DOTS signal channel is specified in Section 7.
If TCP is used between DOTS agents, an attacker may be able to inject RST packets, bogus application segments, etc., regardless of whether TLS authentication is used. Because the application data is TLS protected, this will not result in the application receiving bogus data, but it will constitute a DoS on the connection. This attack can be countered by using TCP-AO [RFC5925]. Although not widely adopted, if TCP-AO is used, then any bogus packets injected by an attacker will be rejected by the TCP-AO integrity check and therefore will never reach the TLS layer.
An attack vector that can be achieved if the 'cuid' is guessable is a misbehaving DOTS client from within the client's domain which uses the 'cuid' of another DOTS client of the domain to delete or alter active mitigations. For this attack vector to happen, the misbehaving client needs to pass the security validation checks by the DOTS server, and eventually the checks of a client-domain DOTS gateway.
A similar attack can be achieved by a compromised DOTS client which can sniff the TLS 1.2 handshake, use the client certificate to identify the 'cuid' used by another DOTS client. This attack is not possible if algorithms such as version 4 Universally Unique IDentifiers (UUIDs) in Section 4.4 of [RFC4122] are used to generate the 'cuid' because such UUIDs are not a deterministic function of the client certificate. Likewise, this attack is not possible with TLS 1.3 because most of the TLS handshake is encrypted and the client certificate is not visible to eavesdroppers.
A compromised DOTS client can collude with a DDoS attacker to send mitigation request for a target resource, gets the mitigation efficacy from the DOTS server, and conveys the mitigation efficacy to the DDoS attacker to possibly change the DDoS attack strategy. Obviously, signaling an attack by the compromised DOTS client to the DOTS server will trigger attack mitigation. This attack can be prevented by monitoring and auditing DOTS clients to detect misbehavior and to deter misuse, and by only authorizing the DOTS client to request mitigation for specific target resources (e.g., an application server is authorized to request mitigation for its IP addresses but a DDoS mitigator can request mitigation for any target resource in the network). Furthermore, DOTS clients are typically co-located on network security services (e.g., firewall) and a compromised security service potentially can do a lot more damage to the network.
Rate-limiting DOTS requests, including those with new 'cuid' values, from the same DOTS client defends against DoS attacks that would result in varying the 'cuid' to exhaust DOTS server resources. Rate-limit policies SHOULD be enforced on DOTS gateways (if deployed) and DOTS servers.
In order to prevent leaking internal information outside a client-domain, DOTS gateways located in the client-domain SHOULD NOT reveal the identification information that pertains to internal DOTS clients (e.g., source IP address, client's hostname) unless explicitly configured to do so.
DOTS servers MUST verify that requesting DOTS clients are entitled to trigger actions on a given IP prefix. That is, only actions on IP resources that belong to the DOTS client' domain MUST be authorized by a DOTS server. The exact mechanism for the DOTS servers to validate that the target prefixes are within the scope of the DOTS client domain is deployment-specific.
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.
When FQDNs are used as targets, the DOTS server MUST rely upon DNS privacy enabling protocols (e.g., DNS over TLS [RFC7858] or DoH [RFC8484]) to prevent eavesdroppers from possibly identifying the target resources protected by the DDoS mitigation service, and means to ensure the target FQDN resolution is authentic (e.g., DNSSEC [RFC4034]).
CoAP-specific security considerations are discussed in Section 11 of [RFC7252], while CBOR-related security considerations are discussed in Section 8 of [RFC7049].
The following individuals have contributed to this document:
Thanks to Christian Jacquenet, Roland Dobbins, Roman Danyliw, Michael Richardson, Ehud Doron, Kaname Nishizuka, Dave Dolson, Liang Xia, Gilbert Clark, Xialiang Frank, Jim Schaad, Klaus Hartke, Nesredien Suleiman, Stephen Farrell, and Yoshifumi Nishida for the discussion and comments.
The authors would like to give special thanks to Kaname Nishizuka and Jon Shallow for their efforts in implementing the protocol and performing interop testing at IETF Hackathons.
Thanks to the core WG for the recommendations on Hop-Limit and redirect signaling.
Special thanks to Benjamin Kaduk for the detailed AD review.
Thanks to Alexey Melnikov, Adam Roach, Suresh Krishnan, Mirja Kühlewind, and Alissa Cooper for the review.
The document recommends the use of SPKI to generate the 'cuid'. This design choice is motivated by the following reasons: