| DOTS | T. Reddy |
| Internet-Draft | McAfee |
| Intended status: Standards Track | M. Boucadair |
| Expires: October 28, 2019 | Orange |
| J. Shallow | |
| April 26, 2019 |
Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel Call Home
draft-ietf-dots-signal-call-home-01
This document specifies the DOTS signal channel Call Home service, which enables a DOTS server to initiate a secure connection to a DOTS client, and to receive the attack traffic information from the DOTS client. The DOTS server in turn uses the attack traffic information to identify the compromised devices launching the outgoing DDoS attack and takes appropriate mitigation action(s).
The Call Home service is not specific to the home networks; the solution targets any deployment which requires to block DDoS attack traffic closer to the source(s) of a DDoS attack.
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 October 28, 2019.
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.
The DOTS signal channel protocol [I-D.ietf-dots-signal-channel] is used to carry information about a network resource or a network (or a part thereof) that is under a Distributed Denial of Service (DDoS) attack. Such information is sent by a DOTS client to one or multiple DOTS servers so that appropriate mitigation actions are undertaken on traffic deemed suspicious. Various use cases are discussed in [I-D.ietf-dots-use-cases].
Internet of Things (IoT) devices are becoming more and more prevalent in home networks, and with compute and memory becoming cheaper and cheaper, various types of IoT devices become available in the consumer market at affordable price. But on the downside, the main threat being most of these IoT devices are bought off-the-shelf and most manufacturers haven't considered security in the product design. IoT devices deployed in home networks can be easily compromised, they do not have an easy mechanism to upgrade, and IoT manufactures may cease manufacture and/or discontinue patching vulnerabilities on IoT devices (Sections 5.4 and 5.5 of [I-D.irtf-t2trg-iot-seccons]). However, these vulnerable and compromised devices will continue to be used for a long period of time in the home, and the end-user does not know that IoT devices in his/her home are compromised. The compromised IoT devices are typically used for launching DDoS attacks (Section 3 of [I-D.irtf-t2trg-iot-seccons]) on victims while the owner/administrator of the home network is not aware about such misbehaviors. Similar to other DDoS attacks, the victim in this attack can be an application server, a host, a router, a firewall, or an entire network.
Nowadays, network devices in a home network offer network security (e.g., firewall or Intrusion Protection System (IPS) service on a home router) to protect the devices connected to the home network from both external and internal attacks. Over the years several techniques have been identified to detect DDoS attacks, some of these techniques can be enabled on home network devices but most of them are used in the Internet Service Provider (ISP)'s network. The ISP offering DDoS mitigation service can detect outgoing DDoS attack traffic originating from its subscribers or the ISP may receive filtering rules (e.g., using BGP flowspec [RFC5575]) from a downstream service provider to filter, block, or rate-limit DDoS attack traffic originating from the ISP's subscribers to a downstream target.
Some of the DDoS attacks like spoofed RST or FIN packets, Slowloris, and Transport Layer Security (TLS) re-negotiation are difficult to detect on a home network device without adversely affecting its performance. The reason is typically home devices such as home routers have fast path to boost the throughput. For every new TCP/UDP flow, only the first few packets are punted through the slow path. Hence, it is not possible to detect various DDoS attacks in the slow path, since the attack payload is sent to the target server after the flow is switched to fast path. Deep Packet Inspection (DPI) of all the packets of a flow would be able to detect some of the attacks. However, a full-fledged DPI to detect these type of DDoS attacks is functionally or operationally not possible for all the devices attached to the home network owing to the memory and CPU limitations of the home routers. Further, for certain DDoS attacks the ability to distinguish legitimate traffic from attacker traffic on a per packet basis is complex. This complexity is due to that the packet itself may look "legitimate" and no attack signature can be identified. The anomaly can be identified only after detailed statistical analysis.
The ISP on the other hand can detect some DDoS attacks originating from a home network (e.g., Section 2.6 of [RFC8517]), but the ISP does not have a mechanism to detect which device in the home network is generating the DDoS attack traffic. The primary reason being that devices in an IPv4 home network are typically behind a Network Address Translation (NAT) border. Even in case of a IPv6 home network, although the ISP can identify the infected device in the home network launching the DDoS traffic by tracking its unique IPv6 address, the infected device can easily change its IPv6 address to evade remediation.
Existing approaches are still suffering from misused access network resources by abusing devices; the support of means for blocking such attacks close to the sources are missing. In particular, the DOTS signal protocol does not discuss cooperative DDoS mitigation between the network hosting an attack source and the ISP to the suppress the outbound DDoS attack traffic originating from that network.
This specification addresses the problems discussed in Section 1.1 and presents the DOTS signal channel Call Home extension, which enables the DOTS server to initiate a secure connection to the DOTS client, and the DOTS client then conveys the attack traffic information to the DOTS server.
A DOTS client relies upon a variety of triggers to make use of the Call Home function (e.g., scrubbing the traffic from the attack source, receiving an alert from an attack target, a peer DDoS Mitigation System (DMS), or a transit provider). The definition of these triggers is deployment-specific. It is therefore out of the scope of this document to elaborate on how these triggers are made available to a DOTS client.
In a typical deployment scenario, the DOTS server is enabled on a Customer Premises Equipment (CPE), which is aligned with recent trends to enrich the CPE with advanced security features. Unlike classic DOTS deployments [I-D.ietf-dots-use-cases], such DOTS server maintains a single DOTS signal channel session for each DOTS-capable upstream provisioning domain [I-D.ietf-dots-multihoming].
For instance, the DOTS server in the home network initiates the Call Home in 'idle' time and then subsequently the DOTS client in the ISP environment can initiate a mitigation request whenever the ISP detects there is an attack from a compromised device in the DOTS server domain (i.e., from within the home network).
The DOTS server uses the DDoS attack traffic information to identify the compromised device in its domain that is responsible for launching the DDoS attack, optionally notifies a network administrator, and takes appropriate mitigation action(s). A mitigation action can be to quarantine the compromised device or block its traffic to the attack target(s) until the mitigation request is withdrawn.
Other motivations for introducing the Call Home function are discussed in Section 1.1 of [RFC8071].
This document assumes that DOTS servers are provisioned with a way to know how to reach the upstream DOTS client(s), which could occur by a variety of means (e.g., [I-D.ietf-dots-server-discovery]). The specification of such means are out of scope of this document.
The aforementioned problems may be encountered in other deployments than those discussed in Section 1.1 (e.g., data centers, enterprise networks). The solution specified in this document can be used for those deployments to block DDoS attack traffic closer to the source(s) of the attack. The Call Home reference architecture is shown in Figure 1.
+-------------+
|Attack Target|
+-----+-------+
| /\
| || Target Network
......................|.||....................
| ||
.--------+-||-------.
( || )-.
.' || '
( Internet || )
( || -'
'-( || )
'------+-||---------'
......................|.||.....................
| || Network Provider
| || (DMS)
.--------+-||-------.
( || )-.
.' DOTS || '
( client || )
( || -'
'-( || )
'------+-||---------'
| ||
......................|.||.......................
| || Source Network
.--------+-||-------.
( || )-.
.' DOTS || '
( server || Outbound )
( || DDoS -'
'-( || Attack )
'------+-||---------'
| ||
+-----+-++----+
|Attack Source|
+-------------+
Figure 1: Call Home Reference Architecture
It is out of the scope of this document to identify an exhaustive list of such deployments.
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.
The reader should be familiar with the terms defined in [I-D.ietf-dots-requirements].
The meaning of the symbols in YANG tree diagrams is defined in [RFC8340].
(D)TLS is used for statements that apply to both Transport Layer Security (TLS) [RFC8446] and Datagram Transport Layer Security (DTLS) [RFC6347]. Specific terms are used for any statement that applies to either protocol alone.
The DOTS signal channel Call Home extension preserves all but one of the DOTS client/server roles in the DOTS protocol stack, as compared to DOTS client-initiated DOTS signal channel protocol [I-D.ietf-dots-signal-channel]. The role reversal that occurs is at the (D)TLS layer; that is, (1) the DOTS server acts as a DTLS client and the DOTS client acts as a DTLS server or (2) the DOTS server acts as a TLS client initiating the underlying TCP connection and the DOTS client acts as a TLS server. The DOTS server initiates (D)TLS handshake to the DOTS client.
For example, a home network element (e.g., home router) co-located with a DOTS server (likely, a client-domain DOTS gateway) is the (D)TLS server. However, when calling home, the DOTS server initially assumes the role of the (D)TLS client, but the network element's role as a DOTS server remains the same. Furthermore, existing certificate chains and mutual authentication mechanisms between the DOTS agents are unaffected by the Call Home function. This Call Home function enables the DOTS server co-located with a network element (possibly behind NATs and firewalls) reachable by only the intended DOTS client and hence the DOTS server cannot be subjected to DDoS attacks.
Figure 2 illustrates a sample Call Home flow exchange:
+--------+ +--------+
| DOTS | | DOTS |
| server | | client |
+---+----+ +----+---+
| |
| 1. (D)TLS connection |
|----------------------------------->|
| 2. Mitigation request |
|<-----------------------------------|
| ... |
Figure 2: DOTS Signal Channel Call Home Sequence Diagram
The DOTS signal channel Call Home procedure is as follows:
This specification extends the mitigation request defined in Section 4.4.1 of [I-D.ietf-dots-signal-channel] to convey the attacker source prefixes and source port numbers. The DOTS client conveys the following new parameters in the CBOR body of the mitigation request:
The 'source-prefix' parameter is a mandatory attribute when the attack traffic information is signaled by a DOTS client in the Call Home scenario. The 'target-uri' or 'target-fqdn' parameters can be included in a mitigation request for diagnostic purposes to notify the DOTS server domain administrator, but SHOULD NOT be used to determine the target IP addresses. Note that 'target-prefix' becomes a mandatory attribute in the mitigation request signaling the attack information because 'target-uri' and 'target-fqdn' are optional attributes and 'alias-name' will not be conveyed in a mitigation request.
In order to help attack source identification by a DOTS server, the DOTS client SHOULD include in its mitigation request additional information such as 'source-port-range' or 'source-icmp-type-range'. The DOTS client may not include such information if 'source-prefix' conveys an IPv6 address/prefix.
If a Carrier Grade NAT (CGN, including NAT64) is located between the DOTS client domain and DOTS server domain, communicating an external IP address in a mitigation request is likely to be discarded by the DOTS server because the external IP address is not visible locally to the DOTS server (see Figure 3). The DOTS server is only aware of the internal IP addresses/prefixes bound to its domain. Thus, the DOTS client MUST NOT include the external IP address and/or port number identifying the suspect attack source, but MUST include the internal IP address and/or port number. To that aim, the DOTS client SHOULD rely on mechanisms, such as [RFC8512] or [RFC8513], to retrieve the internal IP address and port number which are mapped to an external IP address and port number.
N | .-------------------.
E | ( )-.
T | .' '
W | ( )
O | ( DOTS server -'
R | '-( )
K | '-------+-----------'
| |
P | |
R | +---+---+
O | | CGN | External Realm
V |..............|.......|......................
I | | | Internel Realm
D | +---+---+
E | |
R | |
--- |
.---------+---------.
( )-.
.' Source Network '
( )
( DOTS client -'
'-( )
'------+------------'
|
+-----+-------+
|Attack Source|
+-------------+
Figure 3: Example of a CGN Between DOTS Domains
If a MAP Border Relay [RFC7597] or lwAFTR [RFC7596] is enabled in the provider's domain to service its customers, the identification of an attack source bound to an IPv4 address/prefix MUST also rely on source port numbers because the same IPv4 address is assigned to multiple customers. The port information is required to unambiguously identify the source of an attack.
The DOTS server MUST check that the 'source-prefix' is within the scope of the DOTS server domain in the Call Home scenario. Note that in such scenario, the DOTS server considers, by default, that any routeable IP prefix enclosed in 'target-prefix' is within the scope of the DOTS client. Invalid mitigation requests are handled as per Section 4.4.1 of [I-D.ietf-dots-signal-channel].
If a translator is enabled on the boundaries of the domain hosting the DOTS server (a CPE with NAT enabled as shown in Figure 4, typically), the DOTS server uses the attack traffic information conveyed in a mitigation request to find the internal source IP address of the compromised device and blocks the traffic from the compromised device traffic to the attack target until the mitigation request is withdrawn. Doing so allows to isolate the suspicious device while avoiding to disturb other services.
.-------------------.
( )-.
.' Network Provider '
( (DMS) )
( DOTS server -'
'-( )
'------+------------'
|
|
--- +--+----+
S | | CPE | External Realm
O |..............|.......|................
U | | NAT | Internel Realm
R | +-------+
C | |
E | .--------+----------.
| ( )-.
N | .' '
E | ( )
T | ( DOTS client -'
W | '-( )
O | '------+------------'
R | |
K | +-----+-------+
| |Attack Source|
+-------------+
Figure 4: Example of a DOTS Client Domain with a NAT Embeded in a CPE
The DOTS server domain administrator consent MAY be required to block the traffic from the compromised device to the attack target. An implementation MAY have a configuration knob to block the traffic from the compromised device to the attack target with or without DOTS server domain administrator consent. If the attack traffic is blocked, the DOTS server informs the DOTS client that the attack is being mitigated.
If the attack traffic information is identified by the DOTS server or the DOTS server domain administrator as legitimate traffic, the mitigation request is rejected, and 4.09 (Conflict) is returned to the DOTS client. The conflict-clause (defined in Section 4.4.1 of [I-D.ietf-dots-signal-channel]) indicates the cause of the conflict. The following new value is defined:
Once the request is validated by the DOTS server, appropriate actions are enforced to block the attack traffic within the source network. The DOTS client is informed about the progress of the attack mitigation following the rules in [I-D.ietf-dots-signal-channel]. For example, if the DOTS server is embedded in a CPE, it can program the packet processor to punt all the traffic from the compromised device to the target to slow path. The CPE inspects the punted slow path traffic to detect and block the outgoing DDoS attack traffic or quarantine the device (e.g., using MAC level filtering) until it is remediated, and notifies the CPE administrator about the compromised device.
module: ietf-dots-call-home
augment /ietf-signal:dots-signal/ietf-signal:message-type
/ietf-signal:mitigation-scope/ietf-signal:scope:
+--rw source-prefix* inet:ip-prefix {source-signaling}?
+--rw source-port-range* [lower-port] {source-signaling}?
| +--rw lower-port inet:port-number
| +--rw upper-port? inet:port-number
+--rw source-icmp-type-range*
| [lower-type] {source-signaling}?
+--rw lower-type uint8
+--rw upper-type? uint8
This document augments the "dots-signal-channel" DOTS signal YANG module defined in [I-D.ietf-dots-signal-channel] for signaling the attack traffic information. This document defines the YANG module "ietf-dots-call-home", which has the following tree structure:
This module uses the common YANG types defined in [RFC6991].
<CODE BEGINS> file "ietf-dots-call-home@2019-04-25.yang"
module ietf-dots-call-home {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-dots-call-home";
prefix call-home;
import ietf-inet-types {
prefix inet;
reference
"Section 4 of RFC 6991";
}
import ietf-dots-signal-channel {
prefix ietf-signal;
reference
"RFC YYYY: Distributed Denial-of-Service Open Threat
Signaling (DOTS) Signal Channel Specification";
}
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>;
Editor: Jon Shallow
<mailto:ietf-supjps@jpshallow.com>";
description
"This module contains YANG definitions for the signaling
messages exchanged between a DOTS client and a DOTS server
for the Call Home deployment scenario.
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 2019-04-25 {
description
"Initial revision.";
reference
"RFC XXXX: Distributed Denial-of-Service Open Threat
Signaling (DOTS) Signal Channel Call Home";
}
feature source-signaling {
description
"This feature means that source-related information
can be supplied in mitigation requests.";
}
augment "/ietf-signal:dots-signal/ietf-signal:message-type/"
+ "ietf-signal:mitigation-scope/ietf-signal:scope" {
if-feature source-signaling;
description "Attacker source details.";
leaf-list source-prefix {
type inet:ip-prefix;
description
"IPv4 or IPv6 prefix identifying the attacker(s).";
}
list source-port-range {
key "lower-port";
description
"Port range. When only lower-port is
present, it represents a single port number.";
leaf lower-port {
type inet:port-number;
mandatory true;
description
"Lower port number of the port range.";
}
leaf upper-port {
type inet:port-number;
must ". >= ../lower-port" {
error-message
"The upper port number must be greater than
or equal to lower port number.";
}
description
"Upper port number of the port range.";
}
}
list source-icmp-type-range {
key "lower-type";
description
"ICMP type range. When only lower-type is
present, it represents a single ICMP type.";
leaf lower-type {
type uint8;
mandatory true;
description
"Lower ICMP type of the ICMP type range.";
}
leaf upper-type {
type uint8;
must ". >= ../lower-type" {
error-message
"The upper ICMP type must be greater than
or equal to lower ICMP type.";
}
description
"Upper type of the ICMP type range.";
}
}
}
}
<CODE ENDS>
IANA is requested to assign the port number TBD to the DOTS signal channel Call Home 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 4647 is strongly suggested (DOTS signal channel uses port number 4646).
This specification registers the 'source-prefix' and 'source-port-range' parameters in the IANA "DOTS Signal Channel CBOR Mappings" registry established by [I-D.ietf-dots-signal-channel].
The 'source-prefix', 'source-port-range', and ‘source-icmp-type-range' are comprehension-optional parameters.
+-------------------+------------+--------+---------------+--------+ | Parameter Name | YANG | CBOR | CBOR Major | JSON | | | Type | Key | Type & | Type | | | | | Information | | +-------------------+------------+--------+---------------+--------+ | source-prefix | leaf-list | 0x8000 | 4 array | Array | | | inet: | (TBD1) | | | | | ip-prefix | | 3 text string | String | | source-port-range | list | 0x8001 | 4 array | Array | | | | (TBD2) | | | | source-icmp-type- | list | 0x8002 | 4 array | Array | | range | | (TBD3) | | | | lower-type | uint8 | 0x8003 | 0 unsigned | Number | | | | (TBD4) | | | | upper-type | uint8 | 0x8004 | 0 unsigned | Number | | | | (TBD5) | | | +-------------------+------------+--------+---------------+--------+
This document requests IANA to assign a new code from the "DOTS Conflict Cause Codes" registry:
| Code | Label | Description | Reference |
|---|---|---|---|
| 4 | request-rejected | Mitigation request rejected. This code is returned by the DOTS server to indicate the attack traffic has been classified as legitimate traffic. | [RFCXXXX] |
URI: urn:ietf:params:xml:ns:yang:ietf-dots-call-home
Registrant Contact: The IESG.
XML: N/A; the requested URI is an XML namespace.
Name: ietf-call-home
Namespace: urn:ietf:params:xml:ns:yang:ietf-dots-call-home
Maintained by IANA: N
Prefix: call-home
Reference: RFC XXXX
This document requests IANA to register the following URI in the "IETF XML Registry" [RFC3688]: [RFC7950].
This document deviates from classic DOTS signal channel usage by having the DOTS server initiate the TLS or DTLS connection. DOTS signal channel related security considerations discussed in Section 10 of [I-D.ietf-dots-signal-channel] MUST be considered. DOTS agents MUST authenticate each other using (D)TLS before a DOTS signal channel session is considered valid.
An attacker may launch a DoS attack on the DOTS client by having it perform computationally expensive operations, before deducing that the attacker doesn't possess a valid key. For instance, in TLS 1.3 [RFC8446], the ServerHello message contains a Key Share value based on an expensive asymmetric key operation for key establishment. Common precautions mitigating DoS attacks are recommended, such as temporarily blacklisting the source address after a set number of unsuccessful authentication attempts.
DOTS servers may not blindly trust mitigation requests from DOTS clients. For example, DOTS servers can use the attack flow information in a mitigation request to enable full-fledged packet inspection function to inspect all the traffic from the compromised to the target or to re-direct the traffic from the compromised device to the target to a DDoS mitigation system to scrub the suspicious traffic. DOTS servers can also seek the consent of DOTS server domain administrator to block the traffic from the compromised device to the target (see Section 3.2.1).
The considerations discussed in [RFC6973] were taken into account to assess whether the DOTS Call Home extension introduces privacy threats.
Concretely, the protocol does not leak any new information that can be used to ease surveillance. In particular, the DOTS server is not required to share information that is local to its network (e.g., internal identifiers of an attack source) with the DOTS client.
The DOTS Call Home extension does not preclude the validation of mitigation requests received from a DOTS client. For example, a security service running on the CPE may require administrator's consent before the CPE acts upon the mitigation request indicated by the DOTS client. How the consent is obtained is out of scope of this document.
Note that a DOTS server can seek for an administrator's consent, validate the request by inspecting the traffic, or proceed with both.
The DOTS Call Home extension is only advisory in nature. Concretely, the DOTS Call Home extension does not impose any action to be enforced within the home network; it is up to the DOTS server (and/or network administrator) to decide whether and which actions are required.
Moreover, the DOTS Call Home extension avoids misattribution by appropriately identifying the network to which a suspect attack source belongs to (e.g., address sharing issues discussed in Section 3.2.1).
Triggers to send a DOTS mitigation request to a DOTS server are deployment-specific. For example, a DOTS client may rely on the output of some DDoS detection systems deployed within the DOTS client domain to detect potential outbound DDoS attacks or on abuse claims received from remote victim networks. Such DDoS detection and mitigation techniques are not meant to track the activity of users, but to protect the Internet and avoid altering the IP reputation of the DOTS client domain.
The following individuals have contributed to this document:
Joshi Harsha McAfee, Inc. Embassy Golf Link Business Park Bangalore, Karnataka 560071 India Email: harsha_joshi@mcafee.com
Thanks to Wei Pei, Xia Liang, Roman Danyliw, Dan Wing, Töma Gavrichenkov, Daniel Migault, and Valery Smyslov for the comments.
| [I-D.ietf-dots-signal-channel] | K, R., Boucadair, M., Patil, P., Mortensen, A. and N. Teague, "Distributed Denial-of-Service Open Threat Signaling (DOTS) Signal Channel Specification", Internet-Draft draft-ietf-dots-signal-channel-31, March 2019. |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [RFC3688] | Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004. |
| [RFC6347] | Rescorla, E. and N. Modadugu, "Datagram Transport Layer Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347, January 2012. |
| [RFC6991] | Schoenwaelder, J., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, July 2013. |
| [RFC7950] | Bjorklund, M., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016. |
| [RFC8174] | Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017. |
| [RFC8446] | Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018. |