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+
+Internet Engineering Task Force (IETF) E. Chen
+Request for Comments: 9468 Palo Alto Networks
+Category: Standards Track N. Shen
+ISSN: 2070-1721 Zededa
+ R. Raszuk
+ Arrcus
+ R. Rahman
+ Equinix
+ August 2023
+
+
+ Unsolicited Bidirectional Forwarding Detection (BFD) for Sessionless
+ Applications
+
+Abstract
+
+ For operational simplification of "sessionless" applications using
+ Bidirectional Forwarding Detection (BFD), in this document, we
+ present procedures for "unsolicited BFD" that allow a BFD session to
+ be initiated by only one side and established without explicit per-
+ session configuration or registration by the other side (subject to
+ certain per-interface or global policies).
+
+ We also introduce a new YANG module to configure and manage
+ "unsolicited BFD". The YANG module in this document is based on YANG
+ 1.1, as defined in RFC 7950, and conforms to the Network Management
+ Datastore Architecture (NMDA), as described in RFC 8342. This
+ document augments RFC 9314.
+
+Status of This Memo
+
+ This is an Internet Standards Track document.
+
+ This document is a product of the Internet Engineering Task Force
+ (IETF). It represents the consensus of the IETF community. It has
+ received public review and has been approved for publication by the
+ Internet Engineering Steering Group (IESG). Further information on
+ Internet Standards is available in Section 2 of RFC 7841.
+
+ Information about the current status of this document, any errata,
+ and how to provide feedback on it may be obtained at
+ https://www.rfc-editor.org/info/rfc9468.
+
+Copyright Notice
+
+ Copyright (c) 2023 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 Revised BSD License text as described in Section 4.e of the
+ Trust Legal Provisions and are provided without warranty as described
+ in the Revised BSD License.
+
+Table of Contents
+
+ 1. Introduction
+ 1.1. Requirements Language
+ 2. Procedures for Unsolicited BFD
+ 3. State Variables
+ 4. YANG Data Model
+ 4.1. Unsolicited BFD Hierarchy
+ 4.2. Unsolicited BFD Module
+ 4.3. Data Model Example
+ 5. IANA Considerations
+ 6. Security Considerations
+ 6.1. BFD Protocol Security Considerations
+ 6.2. BFD Protocol Authentication Considerations
+ 6.3. YANG Module Security Considerations
+ 7. References
+ 7.1. Normative References
+ 7.2. Informative References
+ Acknowledgments
+ Authors' Addresses
+
+1. Introduction
+
+ The current implementation and deployment practice for BFD ([RFC5880]
+ and [RFC5881]) usually requires that BFD sessions be explicitly
+ configured or registered on both sides. This requirement is not an
+ issue when an application like BGP [RFC4271] has the concept of a
+ "session" that involves both sides for its establishment. However,
+ this requirement can be operationally challenging when the
+ prerequisite "session" does not naturally exist between two endpoints
+ in an application. Simultaneous configuration and coordination may
+ be required on both sides for BFD to take effect. For example:
+
+ * When BFD is used to keep track of the "liveness" of the next hop
+ of static routes. Although only one side may need the BFD
+ functionality, currently, both sides need to be involved in
+ specific configuration and coordination, and in some cases, static
+ routes are created unnecessarily just for BFD.
+
+ * When BFD is used to keep track of the "liveness" of the third-
+ party next hop of BGP routes received from the Route Server
+ [RFC7947] at an Internet Exchange Point (IXP). As the third-party
+ next hop is different from the peering address of the Route
+ Server, for BFD to work, currently, two routers peering with the
+ Route Server need to have routes and next hops from each other
+ (although indirectly via the Route Server).
+
+ Clearly, it is beneficial and desirable to reduce or eliminate
+ unnecessary configurations and coordination in these "sessionless"
+ applications using BFD.
+
+ In this document, we present procedures for "unsolicited BFD" that
+ allow a BFD session to be initiated by only one side and established
+ without explicit per-session configuration or registration by the
+ other side (subject to certain per-interface or global policies).
+
+ Unsolicited BFD impacts only the initiation of BFD sessions. There
+ is no change to all the other procedures specified in [RFC5880], such
+ as, but not limited to, the Echo function and Demand mode.
+
+ With "unsolicited BFD", there is potential risk for excessive
+ resource usage by BFD from "unexpected" remote systems. To mitigate
+ such risks, several mechanisms are recommended in the Security
+ Considerations section.
+
+ The procedure described in this document could be applied to BFD for
+ multihop paths [RFC5883]. However, because of security risks, this
+ document applies only to BFD for single IP hops [RFC5881].
+
+ Compared to the "Seamless BFD" [RFC7880], this proposal involves only
+ minor procedural enhancements to the widely deployed BFD itself.
+ Thus, we believe that this proposal is inherently simpler in the
+ protocol itself and deployment. As an example, it does not require
+ the exchange of BFD discriminators over an out-of-band channel before
+ BFD session bring-up.
+
+ When BGP ADD-PATH [RFC7911] is deployed at an IXP using a Route
+ Server, multiple BGP paths (when they exist) can be made available to
+ the clients of the Route Server, as described in [RFC7947].
+ Unsolicited BFD can be used by BGP route selection's route
+ resolvability condition (Section 9.1.2.1 of [RFC4271]) to exclude
+ routes where the NEXT_HOP is not reachable using the procedures
+ specified in this document.
+
+1.1. Requirements Language
+
+ 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.
+
+2. Procedures for Unsolicited BFD
+
+ With "unsolicited BFD", one side takes the "Active role" and the
+ other side takes the "Passive role", as described in [RFC5880],
+ Section 6.1.
+
+ Passive unsolicited BFD support MUST be disabled by default and MUST
+ require explicit configuration to be enabled. On the passive side,
+ the following BFD parameters, from [RFC5880], Section 6.8.1, SHOULD
+ be configurable:
+
+ * bfd.DesiredMinTxInterval
+
+ * bfd.RequiredMinRxInterval
+
+ * bfd.DetectMult
+
+ The passive side MAY also choose to use the values of the parameters
+ listed above that the active side uses in its BFD Control packets.
+ However, the bfd.LocalDiscr value MUST be selected by the passive
+ side to allow multiple unsolicited BFD sessions.
+
+ The active side starts sending the BFD Control packets, as specified
+ in [RFC5880]. The passive side does not send BFD Control packets
+ initially; it sends BFD Control packets only after it has received
+ BFD Control packets from the active side.
+
+ When the passive side receives a BFD Control packet from the active
+ side with 0 as "Your Discriminator" and does not find an existing BFD
+ session, the passive side SHOULD create a matching BFD session toward
+ the active side, unless not permitted by local configuration or
+ policy.
+
+ When the passive side receives an incoming BFD Control packet on a
+ numbered interface, the source address of that packet MUST belong to
+ the subnet of the interface on which the BFD packet is received, else
+ the BFD Control packet MUST NOT be processed.
+
+ The passive side MUST then start sending BFD Control packets and
+ perform the necessary procedure for bringing up, maintaining, and
+ tearing down the BFD session. If the BFD session fails to get
+ established within a certain amount of time (which is implementation
+ specific but has to be at least equal to the local failure detection
+ time) or if an established BFD session goes down, the passive side
+ MUST stop sending BFD Control packets and SHOULD delete the BFD
+ session created until BFD Control packets are initiated by the active
+ side again.
+
+ When an unsolicited BFD session goes down, an implementation may
+ retain the session state for a period of time. Retaining this state
+ can be useful for operational purposes.
+
+3. State Variables
+
+ This document defines a new state variable called Role:
+
+ bfd.Role
+
+ This is the role of the local system during BFD session
+ initialization, as per [RFC5880], Section 6.1. Possible values are
+ Active or Passive.
+
+4. YANG Data Model
+
+ This section extends the YANG data model for BFD [RFC9314] to cover
+ unsolicited BFD. The new module imports the YANG modules described
+ in [RFC8349] since the "bfd" container in [RFC9314] is under
+ "control-plane-protocol". The YANG module in this document conforms
+ to the Network Management Datastore Architecture (NMDA) [RFC8342].
+
+4.1. Unsolicited BFD Hierarchy
+
+ Configuration for unsolicited BFD parameters for IP single-hop
+ sessions can be done at 2 levels:
+
+ * globally, i.e., for all interfaces
+
+ * for specific interfaces (this requires support for the
+ "unsolicited-params-per-interface" feature)
+
+ If configuration exists at both levels, per-interface configuration
+ takes precedence over global configuration.
+
+ For operational data, a new "role" leaf node has been added for BFD
+ IP single-hop sessions.
+
+ The tree diagram below uses the graphical representation of data
+ models, as defined in [RFC8340].
+
+
+ module: ietf-bfd-unsolicited
+
+ augment /rt:routing/rt:control-plane-protocols
+ /rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh:
+ +--rw unsolicited?
+ +--rw local-multiplier? multiplier
+ +--rw (interval-config-type)?
+ +--:(tx-rx-intervals)
+ | +--rw desired-min-tx-interval? uint32
+ | +--rw required-min-rx-interval? uint32
+ +--:(single-interval) {single-minimum-interval}?
+ +--rw min-interval? uint32
+ augment /rt:routing/rt:control-plane-protocols
+ /rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh
+ /bfd-ip-sh:interfaces:
+ +--rw unsolicited
+ +--rw enabled? boolean
+ +--rw local-multiplier?
+ bfd-types:multiplier
+ {bfd-unsol:unsolicited-params-per-interface}?
+ +--rw (interval-config-type)?
+ {bfd-unsol:unsolicited-params-per-interface}?
+ +--:(tx-rx-intervals)
+ | +--rw desired-min-tx-interval? uint32
+ | +--rw required-min-rx-interval? uint32
+ +--:(single-interval) {bfd-types:single-minimum-interval}?
+ +--rw min-interval? uint32
+ augment /rt:routing/rt:control-plane-protocols
+ /rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh
+ /bfd-ip-sh:sessions/bfd-ip-sh:session:
+ +--ro role? bfd-unsol:role
+
+4.2. Unsolicited BFD Module
+
+
+ <CODE BEGINS> file "ietf-bfd-unsolicited@2023-08-31.yang"
+ module ietf-bfd-unsolicited {
+
+ yang-version 1.1;
+
+ namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-unsolicited";
+
+ prefix bfd-unsol;
+
+ import ietf-bfd-types {
+ prefix bfd-types;
+ reference
+ "RFC 9314: YANG Data Model for Bidirectional Forwarding
+ Detection (BFD)";
+ }
+
+ import ietf-bfd {
+ prefix bfd;
+ reference
+ "RFC 9314: YANG Data Model for Bidirectional Forwarding
+ Detection (BFD)";
+ }
+
+ import ietf-bfd-ip-sh {
+ prefix bfd-ip-sh;
+ reference
+ "RFC 9314: YANG Data Model for Bidirectional Forwarding
+ Detection (BFD)";
+ }
+
+ import ietf-routing {
+ prefix rt;
+ reference
+ "RFC 8349: A YANG Data Model for Routing Management
+ (NMDA Version)";
+ }
+
+ organization
+ "IETF BFD Working Group";
+
+ contact
+ "WG Web: <https://datatracker.ietf.org/wg/bfd/>
+ WG List: <rtg-bfd@ietf.org>
+
+ Editors: Enke Chen (enchen@paloaltonetworks.com),
+ Naiming Shen (naiming@zededa.com),
+ Robert Raszuk (robert@raszuk.net),
+ Reshad Rahman (reshad@yahoo.com)";
+
+ description
+ "This module contains the YANG definition for unsolicited BFD,
+ as per RFC 9468.
+
+ Copyright (c) 2023 IETF Trust and the persons
+ identified as authors of the code. All rights reserved.
+
+ Redistribution and use in source and binary forms, with or
+ without modification, is permitted pursuant to, and subject
+ to the license terms contained in, the Revised BSD License
+ set forth in Section 4.c of the IETF Trust's Legal Provisions
+ Relating to IETF Documents
+ (http://trustee.ietf.org/license-info).
+
+ This version of this YANG module is part of RFC 9468; see
+ the RFC itself for full legal notices.";
+
+ reference
+ "RFC 9468: Unsolicited Bidirectional Forwarding Detection
+ (BFD) for Sessionless Applications";
+
+ revision 2023-08-31 {
+ description
+ "Initial revision.";
+ reference
+ "RFC 9468: Unsolicited Bidirectional Forwarding Detection (BFD)
+ for Sessionless Applications";
+ }
+
+ /*
+ * Feature definitions
+ */
+ feature unsolicited-params-per-interface {
+ description
+ "This feature indicates that the server supports per-interface
+ parameters for unsolicited sessions.";
+ reference
+ "RFC 9468: Unsolicited Bidirectional Forwarding Detection (BFD)
+ for Sessionless Applications";
+ }
+
+ /*
+ * Type Definitions
+ */
+
+ identity role {
+ description
+ "Base identity from which all roles are derived.
+ Role of local system during BFD session initialization.";
+ }
+
+ identity active {
+ base bfd-unsol:role;
+ description
+ "Active role.";
+ reference
+ "RFC 5880: Bidirectional Forwarding Detection (BFD),
+ Section 6.1";
+ }
+
+ identity passive {
+ base bfd-unsol:role;
+ description
+ "Passive role.";
+ reference
+ "RFC 5880: Bidirectional Forwarding Detection (BFD),
+ Section 6.1";
+ }
+
+ /*
+ * Augments
+ */
+
+ augment "/rt:routing/rt:control-plane-protocols/"
+ + "rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh" {
+ description
+ "Augmentation for unsolicited BFD parameters.";
+ container unsolicited {
+ description
+ "BFD IP single-hop unsolicited top-level container.";
+ uses bfd-types:base-cfg-parms;
+ }
+ }
+
+ augment "/rt:routing/rt:control-plane-protocols/"
+ + "rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh/"
+ + "bfd-ip-sh:interfaces" {
+ description
+ "Augmentation for unsolicited BFD on IP single-hop
+ interface.";
+ container unsolicited {
+ description
+ "BFD IP single-hop interface unsolicited top-level
+ container.";
+ leaf enabled {
+ type boolean;
+ default "false";
+ description
+ "Unsolicited BFD is enabled on this interface.";
+ }
+ /*
+ * The following is the same as bfd-types:base-cfg-parms, but
+ * without default values (for inheritance)
+ */
+ leaf local-multiplier {
+ if-feature "bfd-unsol:unsolicited-params-per-interface";
+ type bfd-types:multiplier;
+ description
+ "Multiplier transmitted by the local system. Defaults to
+ ../../unsolicited/local-multiplier.
+ A multiplier configured under an interface takes
+ precedence over the multiplier configured at the global
+ level.";
+ }
+ choice interval-config-type {
+ if-feature "bfd-unsol:unsolicited-params-per-interface";
+ description
+ "Two interval values or one value used for both transmit
+ and receive. Defaults to
+ ../../unsolicited/interval-config-type. An interval
+ configured under an interface takes precedence over any
+ interval configured at the global level.";
+ case tx-rx-intervals {
+ leaf desired-min-tx-interval {
+ type uint32;
+ units "microseconds";
+ description
+ "Desired minimum transmit interval of control
+ packets.";
+ }
+ leaf required-min-rx-interval {
+ type uint32;
+ units "microseconds";
+ description
+ "Required minimum receive interval of control
+ packets.";
+ }
+ }
+ case single-interval {
+ if-feature "bfd-types:single-minimum-interval";
+ leaf min-interval {
+ type uint32;
+ units "microseconds";
+ description
+ "Desired minimum transmit interval and required
+ minimum receive interval of control packets.";
+ }
+ }
+ }
+ }
+ }
+
+ augment "/rt:routing/rt:control-plane-protocols/"
+ + "rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh/"
+ + "bfd-ip-sh:sessions/bfd-ip-sh:session" {
+ description
+ "Augmentation for unsolicited BFD on IP single-hop session.";
+ leaf role {
+ type identityref {
+ base bfd-unsol:role;
+ }
+ config false;
+ description
+ "Role.";
+ }
+ }
+ }
+ <CODE ENDS>
+
+4.3. Data Model Example
+
+ This section shows an example on how to configure the passive end of
+ unsolicited BFD:
+
+ * We have global BFD IP single-hop unsolicited configuration with a
+ local-multiplier of 2 and min-interval at 50 ms.
+
+ * BFD IP single-hop unsolicited is enabled on interface eth0 with a
+ local-multiplier of 3 and min-interval at 250 ms.
+
+ * BFD IP single-hop unsolicited is enabled on interface eth1. Since
+ there is no parameter configuration for eth1, it inherits from the
+ global configuration.
+
+
+ <?xml version="1.0" encoding="UTF-8"?>
+ <config xmlns="urn:ietf:params:xml:ns:netconf:base:1.0">
+ <interfaces xmlns="urn:ietf:params:xml:ns:yang:ietf-interfaces">
+ <interface>
+ <name>eth0</name>
+ <type
+ xmlns:ianaift="urn:ietf:params:xml:ns:yang:iana-if-type">
+ ianaift:ethernetCsmacd</type>
+ </interface>
+ <interface>
+ <name>eth1</name>
+ <type
+ xmlns:ianaift="urn:ietf:params:xml:ns:yang:iana-if-type">
+ ianaift:ethernetCsmacd</type>
+ </interface>
+ </interfaces>
+ <routing xmlns="urn:ietf:params:xml:ns:yang:ietf-routing">
+ <control-plane-protocols>
+ <control-plane-protocol>
+ <type xmlns:bfd-types=
+ "urn:ietf:params:xml:ns:yang:ietf-bfd-types">
+ bfd-types:bfdv1</type>
+ <name>name:BFD</name>
+ <bfd xmlns="urn:ietf:params:xml:ns:yang:ietf-bfd">
+ <ip-sh xmlns="urn:ietf:params:xml:ns:yang:ietf-bfd-ip-sh">
+ <unsolicited>
+ <local-multiplier>2</local-multiplier>
+ <min-interval>50000</min-interval>
+ </unsolicited>
+ <interfaces>
+ <interface>eth0</interface>
+ <unsolicited>
+ <enabled>true</enabled>
+ <local-multiplier>3</local-multiplier>
+ <min-interval>250000</min-interval>
+ </unsolicited>
+ </interfaces>
+ <interfaces>
+ <interface>eth1</interface>
+ <unsolicited>
+ <enabled>true</enabled>
+ </unsolicited>
+ </interfaces>
+ </ip-sh>
+ </bfd>
+ </control-plane-protocol>
+ </control-plane-protocols>
+ </routing>
+ </config>
+
+5. IANA Considerations
+
+ IANA has registered the following namespace URI in the "ns"
+ subregistry within the "IETF XML Registry" [RFC3688]:
+
+ URI: urn:ietf:params:xml:ns:yang:ietf-bfd-unsolicited
+ Registrant Contact: The IESG.
+ XML: N/A; the requested URI is an XML namespace.
+
+ IANA has registered the following YANG module in the "YANG Module
+ Names" registry [RFC6020]:
+
+ Name: ietf-bfd-unsolicited
+ Maintained by IANA: N
+ Namespace: urn:ietf:params:xml:ns:yang:ietf-bfd-unsolicited
+ Prefix: bfd-unsol
+ Reference: RFC 9468
+
+6. Security Considerations
+
+6.1. BFD Protocol Security Considerations
+
+ The same security considerations and protection measures as those
+ described in [RFC5880] and [RFC5881] apply to this document. In
+ addition, with "unsolicited BFD", there is potential risk for
+ excessive resource usage by BFD from "unexpected" remote systems. To
+ mitigate such risks, implementations of unsolicited BFD MUST:
+
+ * Limit the feature to specific interfaces and to single-hop BFD
+ sessions using the procedures from [RFC5082]. See Section 5 of
+ [RFC5881] for the details of these procedures.
+
+ * Apply policy to process BFD packets only from certain subnets or
+ hosts.
+
+ * Deploy the feature only in an environment that does not offer
+ anonymous participation. Examples include an IXP, where the IXP
+ operator will have a business relationship with all IXP
+ participants, or between a provider and its customers.
+
+6.2. BFD Protocol Authentication Considerations
+
+ Implementations of unsolicited BFD are RECOMMENDED to use BFD
+ authentication; see [RFC5880]. If BFD authentication is used, the
+ strongest BFD authentication mechanism that is supported MUST be
+ used.
+
+ In some environments, such as IXPs, BFD authentication cannot be used
+ because of the lack of coordination for the operation of the two
+ endpoints of the BFD session.
+
+ In other environments, such as when BFD is used to track the next hop
+ of static routes, it is possible to use BFD authentication. This
+ comes with the extra cost of configuring matching key chains between
+ the two endpoints.
+
+6.3. YANG Module Security Considerations
+
+ The YANG module specified in this document defines a schema for data
+ that is designed to be accessed via network management protocols such
+ as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer
+ is the secure transport layer, and the mandatory-to-implement secure
+ transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer
+ is HTTPS, and the mandatory-to-implement secure transport is TLS
+ [RFC8446].
+
+ The Network Configuration Access Control Mode (NACM) [RFC8341]
+ provides the means to restrict access for particular NETCONF or
+ RESTCONF users to a preconfigured subset of all available NETCONF or
+ RESTCONF protocol operations and content.
+
+ There are a number of data nodes defined in this YANG module that are
+ writable/creatable/deletable (i.e., config true, which is the
+ default). These data nodes may be considered sensitive or vulnerable
+ in some network environments. Write operations (e.g., edit-config)
+ to these data nodes without proper protection can have a negative
+ effect on network operations. These are the subtrees and data nodes
+ and their sensitivity/vulnerability:
+
+ /routing/control-plane-protocols/control-plane-protocol/bfd/ip-sh
+ /unsolicited:
+ * Data node "enabled" enables creation of unsolicited BFD IP
+ single-hop sessions globally, i.e., on all interfaces. See
+ Section 6.1.
+
+ * Data nodes "local-multiplier", "desired-min-tx-interval",
+ "required-min-rx-interval", and "min-interval" all impact the
+ parameters of the unsolicited BFD IP single-hop sessions.
+ Write operations to these nodes change the rates of BFD packet
+ generation and detection time of the failures of a BFD session.
+
+ /routing/control-plane-protocols/control-plane-protocol/bfd/ip-sh
+ /interfaces/interface/unsolicited:
+ * Data node "enabled" enables the creation of unsolicited BFD IP
+ single-hop sessions on a specific interface. See Section 6.1.
+
+ * Data nodes "local-multiplier", "desired-min-tx-interval",
+ "required-min-rx-interval", and "min-interval" all impact the
+ parameters of the unsolicited BFD IP single-hop sessions on the
+ interface.
+
+ Some of the readable data nodes in this YANG module may be considered
+ sensitive or vulnerable in some network environments. It is thus
+ important to control read access (e.g., via get, get-config, or
+ notification) to these data nodes. These are the subtrees and data
+ nodes and their sensitivity/vulnerability:
+
+ /routing/control-plane-protocols/control-plane-protocol/bfd/ip-sh
+ /sessions/session/role:
+ Access to this information discloses the role of the local system
+ in the creation of the unsolicited BFD session.
+
+7. References
+
+7.1. Normative References
+
+ [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
+ Requirement Levels", BCP 14, RFC 2119,
+ DOI 10.17487/RFC2119, March 1997,
+ <https://www.rfc-editor.org/info/rfc2119>.
+
+ [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
+ DOI 10.17487/RFC3688, January 2004,
+ <https://www.rfc-editor.org/info/rfc3688>.
+
+ [RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
+ Pignataro, "The Generalized TTL Security Mechanism
+ (GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,
+ <https://www.rfc-editor.org/info/rfc5082>.
+
+ [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
+ (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
+ <https://www.rfc-editor.org/info/rfc5880>.
+
+ [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
+ (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
+ DOI 10.17487/RFC5881, June 2010,
+ <https://www.rfc-editor.org/info/rfc5881>.
+
+ [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for
+ the Network Configuration Protocol (NETCONF)", RFC 6020,
+ DOI 10.17487/RFC6020, October 2010,
+ <https://www.rfc-editor.org/info/rfc6020>.
+
+ [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
+ and A. Bierman, Ed., "Network Configuration Protocol
+ (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
+ <https://www.rfc-editor.org/info/rfc6241>.
+
+ [RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure
+ Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
+ <https://www.rfc-editor.org/info/rfc6242>.
+
+ [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
+ Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
+ <https://www.rfc-editor.org/info/rfc8040>.
+
+ [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
+ 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
+ May 2017, <https://www.rfc-editor.org/info/rfc8174>.
+
+ [RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams",
+ BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018,
+ <https://www.rfc-editor.org/info/rfc8340>.
+
+ [RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration
+ Access Control Model", STD 91, RFC 8341,
+ DOI 10.17487/RFC8341, March 2018,
+ <https://www.rfc-editor.org/info/rfc8341>.
+
+ [RFC8349] Lhotka, L., Lindem, A., and Y. Qu, "A YANG Data Model for
+ Routing Management (NMDA Version)", RFC 8349,
+ DOI 10.17487/RFC8349, March 2018,
+ <https://www.rfc-editor.org/info/rfc8349>.
+
+ [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
+ Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
+ <https://www.rfc-editor.org/info/rfc8446>.
+
+ [RFC9314] Jethanandani, M., Ed., Rahman, R., Ed., Zheng, L., Ed.,
+ Pallagatti, S., and G. Mirsky, "YANG Data Model for
+ Bidirectional Forwarding Detection (BFD)", RFC 9314,
+ DOI 10.17487/RFC9314, September 2022,
+ <https://www.rfc-editor.org/info/rfc9314>.
+
+7.2. Informative References
+
+ [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
+ Border Gateway Protocol 4 (BGP-4)", RFC 4271,
+ DOI 10.17487/RFC4271, January 2006,
+ <https://www.rfc-editor.org/info/rfc4271>.
+
+ [RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
+ (BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883,
+ June 2010, <https://www.rfc-editor.org/info/rfc5883>.
+
+ [RFC7880] Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S.
+ Pallagatti, "Seamless Bidirectional Forwarding Detection
+ (S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016,
+ <https://www.rfc-editor.org/info/rfc7880>.
+
+ [RFC7911] Walton, D., Retana, A., Chen, E., and J. Scudder,
+ "Advertisement of Multiple Paths in BGP", RFC 7911,
+ DOI 10.17487/RFC7911, July 2016,
+ <https://www.rfc-editor.org/info/rfc7911>.
+
+ [RFC7947] Jasinska, E., Hilliard, N., Raszuk, R., and N. Bakker,
+ "Internet Exchange BGP Route Server", RFC 7947,
+ DOI 10.17487/RFC7947, September 2016,
+ <https://www.rfc-editor.org/info/rfc7947>.
+
+ [RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K.,
+ and R. Wilton, "Network Management Datastore Architecture
+ (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018,
+ <https://www.rfc-editor.org/info/rfc8342>.
+
+Acknowledgments
+
+ The authors would like to thank Acee Lindem, Alvaro Retana, Dan
+ Romascanu, Derek Atkins, Greg Mirsky, Gyan Mishra, Henning Rogge,
+ Jeffrey Haas, John Scudder, Lars Eggert, Magnus Westerlund, Mahesh
+ Jethanandani, Murray Kucherawy, Raj Chetan, Robert Wilton, Roman
+ Danyliw, Tom Petch, and Zaheduzzaman Sarker for their reviews and
+ valuable input.
+
+Authors' Addresses
+
+ Enke Chen
+ Palo Alto Networks
+ 3000 Tannery Way
+ Santa Clara, CA 95054
+ United States of America
+ Email: enchen@paloaltonetworks.com
+
+
+ Naiming Shen
+ Zededa
+ 160 W Santa Clara Street
+ San Jose, CA 95113
+ United States of America
+ Email: naiming@zededa.com
+
+
+ Robert Raszuk
+ Arrcus
+ 2077 Gateway Place
+ San Jose, CA 95110
+ United States of America
+ Email: robert@raszuk.net
+
+
+ Reshad Rahman
+ Equinix
+ Canada
+ Email: reshad@yahoo.com