Bidirectional Forwarding Detection (BFD) Stability
RFC 9978
| Document | Type | RFC - Experimental (June 2026) | |
|---|---|---|---|
| Authors | A. Mishra , M. Jethanandani , A. Saxena , S. Pallagatti , M. Chen | ||
| Last updated | 2026-06-29 | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Additional resources | Mailing list discussion | ||
| IESG | Responsible AD | Ketan Talaulikar | |
| Send notices to | (None) |
RFC 9978
Internet Engineering Task Force (IETF) A. Mishra
Request for Comments: 9978 Aalyria Technologies
Category: Experimental M. Jethanandani
ISSN: 2070-1721 Arrcus, Inc.
A. Saxena
Ciena Corporation
S. Pallagatti
Zscaler
M. Chen
Huawei
June 2026
Bidirectional Forwarding Detection (BFD) Stability
Abstract
This document describes extensions to the Bidirectional Forwarding
Detection (BFD) protocol to measure BFD Stability. Specifically, it
describes a mechanism for the detection of BFD packet loss.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for examination, experimental implementation, and
evaluation.
This document defines an Experimental Protocol for the Internet
community. 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). Not
all documents approved by the IESG are candidates for any level of
Internet Standard; see 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/rfc9978.
Copyright Notice
Copyright (c) 2026 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
2. Terminology
3. Use Cases
4. Functionality
5. NULL Auth Type
6. Theory of Operation
6.1. Loss Measurement
6.2. Out-of-Order Packets
7. Stability YANG Module
7.1. Data Model Overview
7.2. YANG Module
8. IANA Considerations
8.1. Auth Type
8.2. IETF XML Registry
8.3. The "YANG Module Names" Registry
9. Security Considerations
9.1. BFD NULL Auth Type Security Considerations
9.2. YANG Security Considerations
10. References
10.1. Normative References
10.2. Informative References
Appendix A. Experimental Status
Appendix B. Examples
B.1. Single Hop BFD Configuration
B.2. Use of the NULL Auth Type
Acknowledgements
Contributors
Authors' Addresses
1. Introduction
The Bidirectional Forwarding Detection (BFD) [RFC5880] protocol
operates by transmitting and receiving BFD control packets, generally
at a high frequency, over the datapath being monitored. In order to
prevent significant data loss due to a datapath failure, BFD session
Detection Time as defined in [RFC5880] is set to the smallest
feasible value.
A BFD session [RFC5880] will remain in the Up state as long as it
receives at least one BFD packet within the Detection Time interval.
However, additional packet loss within that time interval is not
noted by the BFD state machinery. Noting the other missed packets
provides a valuable indicator of systemic issues or a deteriorating
network that may warrant preventive action.
This document proposes an experimental mechanism to detect packet
loss in a BFD session and describes the datapath fault detection
mechanisms of BFD. Such a mechanism, combined with 'receive-packet-
count' defined in "YANG Data Model for Bidirectional Forwarding
Detection (BFD)" [RFC9314] permits operators to measure the stability
of BFD sessions. The details of the motivation for the Experimental
status of this document can be found in Appendix A. Implementations
may also do additional analysis of the packet loss over a time
interval. Such an analysis is outside the scope of this document.
This document does not propose any BFD extension to measure data
traffic loss or delay on a link or tunnel, and the scope is limited
to BFD packets.
2. Terminology
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 is expected to be familiar with BFD [RFC5880]. In
particular, the term "meticulous" as specified in "Meticulous Keyed
ISAAC for Bidirectional Forwarding Detection (BFD) Optimized
Authentication" [RFC9986] means that the sequence number is
incremented on every new packet that is sent.
3. Use Cases
Bidirectional Forwarding Detection (BFD), as defined in [RFC5880],
cannot detect any BFD packet loss if the loss does not last for the
Detection Time. This document proposes a method to detect dropped
packets on the receiver. For example, if the receiver receives BFD
control packet k at time t, but receives packet k+3 at time t+10 ms,
and never receives packet k+1 and/or k+2, then it has experienced a
packet loss.
This proposal enables BFD implementations to generate diagnostic
information on the health of each BFD session. This information
could be used to preempt the probability of a failure on a datapath
that BFD was monitoring by allowing time for a corrective action to
be taken.
In a faulty datapath scenario, an operator can use BFD health
information to trigger the delay and loss measurement Operations,
Administration, and Maintenance (OAM) protocol Connectivity Fault
Management (CFM) [Y-1731] or packet loss and delay measurement for
MPLS networks [RFC6374] to further isolate the issue.
4. Functionality
BFD Stability measurement requires that a BFD Meticulous
authentication type be configured.
The "ietf-bfd-stability" YANG data model, defined in this document,
provides the ability to configure the BFD Stability measurement for
BFD sessions by configuring the 'stability' flag. The
'lost-packet-count' leaf permits monitoring of stability issues as
defined in this document for BFD sessions that have the 'stability'
flag enabled.
The configuration of the BFD Stability measurement and monitoring
using other methods than the attached YANG data model is out of scope
of this document.
5. NULL Auth Type
The NULL Auth Type, defined in this document, can be used to provide
a meticulously increasing sequence number [RFC5880] for stability
measurement. It provides none of the protections desired for
authentication and is used only to provide BFD Stability services to
BFD sessions that otherwise have no authentication in use.
If the Authentication Present (A) bit is set in the header as defined
in Section 4 of [RFC5880], and the Authentication Type field contains
6, the Authentication Section has the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Auth Type | Auth Len | Auth Key ID | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: NULL Auth Type
where:
Auth Type (8 bits): The Authentication Type, which in this case is 6
(NULL).
Auth Len (8 bits): The length of the NULL Auth Type in bytes (i.e.,
8 bytes).
Auth Key ID (8 bits): The authentication key ID in use for this
packet. It MUST be set to zero and MUST be ignored on receipt.
Reserved (8 bits): This byte MUST be set to zero on transmit and
MUST be ignored on receipt.
Sequence Number (32 bits): The sequence number for this packet.
This value is incremented for each successive packet transmitted
for a session. Implementations will use sequence numbers
(bfd.XmitAuthSeq) as defined in [RFC5880].
If bfd.AuthSeqKnown is 1, and the received Sequence Number field is
not equal to bfd.RcvAuthSeq + 1 (in a circular number space), then
the loss count is incremented by the difference between the received
sequence number and bfd.RcvAuthSeq, and bfd.RcvAuthSeq is set to the
received sequence number.
Otherwise (bfd.AuthSeqKnown is 0), bfd.AuthSeqKnown MUST be set to 1,
and bfd.RcvAuthSeq MUST be set to the value of the received Sequence
Number field as defined in [RFC5880], Section 6.8.1, and the packet
MUST be accepted.
According to Section 6.7.3 of [RFC5880], a receiver MUST discard a
received packet that lies outside the range of bfd.RcvAuthSeq and
bfd.RcvAuthSeq + (3 * Detect Multi). If it is within that range, but
is missing a packet, it can be used to detect a loss. In case of
NULL authentication where packets containing sequence numbers are
accepted on receipt, an attacker with an unauthenticated sequence
number could move the sequence number forward. Meanwhile, the actual
BFD neighbor that continues to send packets will find them discarded
and the session would drop. To prevent such an attack, the received
sequence number MUST NOT be compared with bfd.RcvAuthSeq for the
purpose of discarding the BFD packets.
6. Theory of Operation
This mechanism allows operators to measure the loss of BFD control
packets. A BFD authentication type carrying a meticulously
increasing sequence number is required to support this loss
measurement. Authentication types that provide for meticulously
increasing sequence numbers include:
* Meticulously Keyed MD5 and SHA1, defined in [RFC5880].
* Meticulously Keyed ISAAC, defined in [RFC9986].
* The NULL authentication mechanism, which does not provide for
authentication but carries a meticulously increasing sequence
number, is defined in this document.
Other authentication types that provide for meticulously increasing
sequence numbers appropriate for this mechanism may be defined in
future specifications.
6.1. Loss Measurement
Loss measurement counts the number of BFD control packets missed at
the receiver during any Detection Time period (see [RFC5880],
Section 6.8.4). The loss is detected by comparing the Sequence
Number field in successive BFD control packets. The sequence number
in each successive control packet generated on a BFD session by the
transmitter is incremented by one. This loss count can then be
exposed using the YANG module defined in the subsequent section. See
discussion on out-of-order packets in Section 6.2 of this document.
The first BFD Authentication Section with a non-zero sequence number,
in a valid BFD control packet, processed by the receiver, is used for
bootstrapping the logic.
6.2. Out-of-Order Packets
Some transmission mechanisms, for example, Link Aggregate Groups
(LAGs) or Equal Cost Multipath (ECMP), can result in out-of-order
packet delivery. In circumstances where BFD packets are not lost,
but are delivered out of order, strict comparison of increasing
sequence numbers may result in classifying the out-of-order packets
as packet loss.
Implementations MAY provide mechanisms wherein all expected packets
received across an expected interval, but delivered out of order, are
not considered lost packets.
7. Stability YANG Module
7.1. Data Model Overview
This YANG module augments the base BFD YANG module to add attributes
such as the 'stability' flag related to the experiment of BFD
Stability. The feature statement 'stability' needs to be enabled to
indicate that BFD Stability is supported by the implementation. In
addition, a loss count per-session or a Label Switched Path (LSP) for
BFD packets that are lost has also been added in this model.
module: ietf-bfd-stability
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:
+--rw stability? boolean {stability}?
augment /rt:routing/rt:control-plane-protocols
/rt:control-plane-protocol/bfd:bfd/bfd-ip-mh:ip-mh
/bfd-ip-mh:session-groups/bfd-ip-mh:session-group:
+--rw stability? boolean {stability}?
augment /rt:routing/rt:control-plane-protocols
/rt:control-plane-protocol/bfd:bfd/bfd-lag:lag
/bfd-lag:sessions/bfd-lag:session:
+--rw stability? boolean {stability}?
augment /rt:routing/rt:control-plane-protocols
/rt:control-plane-protocol/bfd:bfd/bfd-mpls:mpls
/bfd-mpls:session-groups/bfd-mpls:session-group:
+--rw stability? boolean {stability}?
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
/bfd-ip-sh:session-statistics:
+--ro lost-packet-count? yang:counter64 {stability}?
augment /rt:routing/rt:control-plane-protocols
/rt:control-plane-protocol/bfd:bfd/bfd-ip-mh:ip-mh
/bfd-ip-mh:session-groups/bfd-ip-mh:session-group
/bfd-ip-mh:sessions/bfd-ip-mh:session-statistics:
+--ro lost-packet-count? yang:counter64 {stability}?
augment /rt:routing/rt:control-plane-protocols
/rt:control-plane-protocol/bfd:bfd/bfd-lag:lag
/bfd-lag:sessions/bfd-lag:session/bfd-lag:member-links
/bfd-lag:micro-bfd-ipv4/bfd-lag:session-statistics:
+--ro lost-packet-count? yang:counter64 {stability}?
augment /rt:routing/rt:control-plane-protocols
/rt:control-plane-protocol/bfd:bfd/bfd-lag:lag
/bfd-lag:sessions/bfd-lag:session/bfd-lag:member-links
/bfd-lag:micro-bfd-ipv6/bfd-lag:session-statistics:
+--ro lost-packet-count? yang:counter64 {stability}?
augment /rt:routing/rt:control-plane-protocols
/rt:control-plane-protocol/bfd:bfd/bfd-mpls:mpls
/bfd-mpls:session-groups/bfd-mpls:session-group
/bfd-mpls:sessions/bfd-mpls:session-statistics:
+--ro lost-packet-count? yang:counter64 {stability}?
7.2. YANG Module
This YANG module imports modules defined in "Common YANG Data Types"
[RFC9911], "YANG Data Model for Key Chains" [RFC8177], "A YANG Data
Model for Routing Management (NMDA Version)" [RFC8349], and "YANG
Data Model for Bidirectional Forwarding Detection (BFD)" [RFC9314].
<CODE BEGINS> file "ietf-bfd-stability@2026-06-29.yang"
module ietf-bfd-stability {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-stability";
prefix bfd-s;
import ietf-yang-types {
prefix yang;
reference
"RFC 9911: Common YANG Data Types";
}
import ietf-routing {
prefix rt;
reference
"RFC 8349: A YANG Data Model for Routing Management
(NMDA Version)";
}
import ietf-bfd {
prefix bfd;
reference
"RFC 9314: YANG Data Model for Bidirectional
Forwarding Detection.";
}
import ietf-bfd-ip-sh {
prefix bfd-ip-sh;
reference
"RFC 9314: YANG Data Model for Bidirectional
Forwarding Detection (BFD)";
}
import ietf-bfd-ip-mh {
prefix bfd-ip-mh;
reference
"RFC 9314: YANG Data Model for Bidirectional
Forwarding Detection (BFD)";
}
import ietf-bfd-lag {
prefix bfd-lag;
reference
"RFC 9314: YANG Data Model for Bidirectional
Forwarding Detection (BFD)";
}
import ietf-bfd-mpls {
prefix bfd-mpls;
reference
"RFC 9314: YANG Data Model for Bidirectional
Forwarding Detection (BFD)";
}
import ietf-key-chain {
prefix key-chain;
reference
"RFC 8177: YANG Data Model for Key Chains";
}
organization
"IETF BFD Working Group";
contact
"WG Web: <https://datatracker.ietf.org/wg/bfd>
WG List: <rtg-bfd@ietf.org>
Authors: Mahesh Jethanandani (mjethanandani@gmail.com)
Ashesh Mishra (mishra.ashesh@gmail.com)
Ankur Saxena (ankurpsaxena@gmail.com)
Santosh Pallagatti (santosh.pallagati@gmail.com)
Mach(Guoyi) Chen (mach.chen@huawei.com).";
description
"This YANG module augments the base BFD YANG data model to add
experimental attributes related to BFD Stability.
In particular, it adds a per-session count for BFD packets
that are lost.
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 (RFC 2119) (RFC 8174) when, and only when,
they appear in all capitals, as shown here.
Copyright (c) 2026 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
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC 9978; see the
RFC itself for full legal notices.";
revision 2026-06-29 {
description
"Initial version.";
reference
"RFC 9978: Bidirectional Forwarding Detection (BFD) Stability";
}
feature stability {
description
"This feature enables BFD sessions to be monitored for lost
packets.";
}
identity null-auth {
base key-chain:crypto-algorithm;
description
"BFD NULL Auth Type defined in this document.";
reference
"RFC 9978: Bidirectional Forwarding Detection (BFD) Stability";
}
grouping lost-packet-count {
leaf lost-packet-count {
if-feature "stability";
type yang:counter64;
description
"Number of BFD packets that were lost, where loss is
determined by the fact that the sequence number is
not consecutive. This counter should be present only if
stability is configured.";
}
description
"Grouping of statistics related to BFD Stability.";
}
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" {
leaf stability {
if-feature "stability";
type boolean;
must "../bfd-ip-sh:authentication/bfd-ip-sh:meticulous = "
+ "'true'";
default "false";
description
"If set to true, this enables the BFD session to monitor
for stability, i.e., to watch how many packets are getting
dropped.";
}
description
"Augment the 'bfd' container to add attributes related to BFD
Stability for IP Single Hop sessions.";
}
augment "/rt:routing/rt:control-plane-protocols/"
+ "rt:control-plane-protocol/bfd:bfd/bfd-ip-mh:ip-mh/"
+ "bfd-ip-mh:session-groups/bfd-ip-mh:session-group" {
leaf stability {
if-feature "stability";
type boolean;
must "../bfd-ip-mh:authentication/bfd-ip-mh:meticulous = "
+ "'true'";
default "false";
description
"If set to true, this enables the BFD session to monitor
for stability, i.e., to watch how many packets are getting
dropped.";
}
description
"Augment the 'bfd' container to add attributes related to BFD
Stability for Multi Hop sessions.";
}
augment "/rt:routing/rt:control-plane-protocols/"
+ "rt:control-plane-protocol/bfd:bfd/bfd-lag:lag/"
+ "bfd-lag:sessions/bfd-lag:session" {
leaf stability {
if-feature "stability";
type boolean;
must "../bfd-lag:authentication/bfd-lag:meticulous = "
+ "'true'";
default "false";
description
"If set to true, this enables the BFD session to monitor
for stability, i.e., to watch how many packets are getting
dropped.";
}
description
"Augment the 'bfd' container to add attributes related to BFD
Stability for LAG session.";
}
augment "/rt:routing/rt:control-plane-protocols/"
+ "rt:control-plane-protocol/bfd:bfd/bfd-mpls:mpls/"
+ "bfd-mpls:session-groups/bfd-mpls:session-group" {
leaf stability {
if-feature "stability";
type boolean;
must "../bfd-mpls:authentication/bfd-mpls:meticulous = "
+ "'true'";
default "false";
description
"If set to true, this enables the BFD session to monitor
for stability, i.e., to watch how many packets are getting
dropped.";
}
description
"Augment the 'bfd' container to add attributes related to BFD
Stability for MPLS.";
}
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/"
+ "bfd-ip-sh:session-statistics" {
uses lost-packet-count;
description
"Augment the 'bfd' container to add statistics related to BFD
Stability for IP Single Hop sessions.";
}
augment "/rt:routing/rt:control-plane-protocols/"
+ "rt:control-plane-protocol/bfd:bfd/bfd-ip-mh:ip-mh/"
+ "bfd-ip-mh:session-groups/bfd-ip-mh:session-group/"
+ "bfd-ip-mh:sessions/bfd-ip-mh:session-statistics" {
uses lost-packet-count;
description
"Augment the 'bfd' container to add statistics related to BFD
Stability for IP Multi Hop sessions.";
}
augment "/rt:routing/rt:control-plane-protocols/"
+ "rt:control-plane-protocol/bfd:bfd/bfd-lag:lag/"
+ "bfd-lag:sessions/bfd-lag:session/bfd-lag:member-links/"
+ "bfd-lag:micro-bfd-ipv4/bfd-lag:session-statistics" {
uses lost-packet-count;
description
"Augment the 'bfd' container to add statistics related to BFD
Stability for Micro BFD sessions for IPv4.";
}
augment "/rt:routing/rt:control-plane-protocols/"
+ "rt:control-plane-protocol/bfd:bfd/bfd-lag:lag/"
+ "bfd-lag:sessions/bfd-lag:session/bfd-lag:member-links/"
+ "bfd-lag:micro-bfd-ipv6/bfd-lag:session-statistics" {
uses lost-packet-count;
description
"Augment the 'bfd' container to add statistics related to BFD
Stability for Micro BFD sessions for IPv6.";
}
augment "/rt:routing/rt:control-plane-protocols/"
+ "rt:control-plane-protocol/bfd:bfd/bfd-mpls:mpls/"
+ "bfd-mpls:session-groups/bfd-mpls:session-group/"
+ "bfd-mpls:sessions/bfd-mpls:session-statistics" {
uses lost-packet-count;
description
"Augment the 'bfd' container to add statistics related to BFD
Stability for MPLS sessions.";
}
}
<CODE ENDS>
8. IANA Considerations
This document registers a new authentication type in the "BFD
Authentication Types" registry, a new URI in the "ns" registry within
the "IETF XML" registry group [RFC3688], and a YANG module in the
"YANG Module Names" registry.
8.1. Auth Type
IANA has registered the following BFD Auth Type in the "BFD
Authentication Types" registry:
Address: 6
BFD Authentication Type Name: NULL
Reference RFC 9978
8.2. IETF XML Registry
IANA has registered the following URI in the "ns" registry [RFC3688]:
URI: urn:ietf:params:xml:ns:yang:ietf-bfd-stability
Registrant Contact: The IESG
XML: N/A; the requested URI is an XML namespace.
8.3. The "YANG Module Names" Registry
IANA has registered the following YANG module in the "YANG Module
Names" registry [RFC6020]:
Name: ietf-bfd-stability
Namespace: urn:ietf:params:xml:ns:yang:ietf-bfd-stability
Prefix: bfd-s
Reference: RFC 9978
9. Security Considerations
9.1. BFD NULL Auth Type Security Considerations
The use of a BFD authentication mechanism that protects the BFD
packets is RECOMMENDED.
The security considerations of [RFC5880] for unauthenticated BFD all
apply to the new NULL Auth Type. The NULL Auth Type, defined in this
document, provides none of the properties desired for authenticating
BFD packets. It is intended to provide BFD sessions that otherwise
would not use authentication with a sequence number that can be used
for the purpose of detecting packet loss.
The lack of a computed AuthKey/Digest over the BFD packet, but the
presence of a sequence number, makes this authentication type
susceptible to injection attacks. BFD without authentication is
vulnerable to session resets; the NULL Auth Type does not change
this.
When the NULL Auth Type is used for BFD Stability purposes,
maliciously injected packets that do not reset the BFD session can
resemble high packet loss. Sessions such as multi-hop routed paths,
tunnels without authentication, or MPLS Label Switched Paths (LSPs),
therefore, have security guarantees that are identical to situations
where BFD is run without authentication.
9.2. YANG Security Considerations
This section is modeled after the template described in Section 3.7.1
of [RFC9907].
The "ietf-bfd-stability" YANG module defines a data model that is
designed to be accessed via YANG-based management protocols, such as
Network Configuration Protocol (NETCONF) [RFC6241] and RESTCONF
[RFC8040]. These YANG-based management protocols (1) have to use a
secure transport layer (e.g., Secure Shell (SSH) [RFC4252], TLS
[RFC8446], and QUIC [RFC9000]) and (2) have to use mutual
authentication.
The Network Configuration Access Control Model (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.
The YANG module does not define any writable/creatable/deletable data
nodes that can have an adverse impact on a BFD session.
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. Specifically, the following
subtrees and data nodes have particular sensitivities/
vulnerabilities:
The model defines a read-only node to indicate the number of packets
that were lost. Access to this information may allow a malicious
user information on which links are experiencing issues. In
addition, and as stated in Section 6.2, on links such as LAG or ECMP,
there is a possibility of packets being delivered out-of-order. A
strict comparison of increasing sequence numbers may result in
classifying those out-of-order packets as packet loss.
The YANG module does not define any RPC operations.
10. References
10.1. 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>.
[RFC4252] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
Authentication Protocol", RFC 4252, DOI 10.17487/RFC4252,
January 2006, <https://www.rfc-editor.org/info/rfc4252>.
[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>.
[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>.
[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>.
[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>.
[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>.
[RFC9911] Schönwälder, J., Ed., "Common YANG Data Types", RFC 9911,
DOI 10.17487/RFC9911, December 2025,
<https://www.rfc-editor.org/info/rfc9911>.
10.2. Informative References
[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>.
[RFC6374] Frost, D. and S. Bryant, "Packet Loss and Delay
Measurement for MPLS Networks", RFC 6374,
DOI 10.17487/RFC6374, September 2011,
<https://www.rfc-editor.org/info/rfc6374>.
[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>.
[RFC8177] Lindem, A., Ed., Qu, Y., Yeung, D., Chen, I., and J.
Zhang, "YANG Data Model for Key Chains", RFC 8177,
DOI 10.17487/RFC8177, June 2017,
<https://www.rfc-editor.org/info/rfc8177>.
[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>.
[RFC9000] Iyengar, J., Ed. and M. Thomson, Ed., "QUIC: A UDP-Based
Multiplexed and Secure Transport", RFC 9000,
DOI 10.17487/RFC9000, May 2021,
<https://www.rfc-editor.org/info/rfc9000>.
[RFC9907] Bierman, A., Boucadair, M., Ed., and Q. Wu, "Guidelines
for Authors and Reviewers of Documents Containing YANG
Data Models", BCP 216, RFC 9907, DOI 10.17487/RFC9907,
March 2026, <https://www.rfc-editor.org/info/rfc9907>.
[RFC9986] DeKok, A., Jethanandani, M., Agarwal, S., Mishra, A., and
J. Haas, "Meticulous Keyed ISAAC for Bidirectional
Forwarding Detection (BFD) Optimized Authentication",
RFC 9986, DOI 10.17487/RFC9986, June 2026,
<https://www.rfc-editor.org/info/rfc9986>.
[Y-1731] ITU-T, "Operation, administration and maintenance (OAM)
functions and mechanisms for Ethernet-based networks",
ITU-T Recommendation G.8013/Y.1731, June 2023,
<https://www.itu.int/rec/T-REC-G.8013-202306-I/en>.
Appendix A. Experimental Status
This document describes an experiment that will present a candidate
solution to predict whether a given BFD session [RFC5880] will
continue to be stable. The experiment will use the packet lost count
and the 'receive-packet-count' defined in "YANG Data Model for
Bidirectional Forwarding Detection (BFD)" [RFC9314] to determine how
stable the session is. The reason this document is on the
Experimental track is because there are no known implementations or
proof of concept. As a result, the authors are not clear whether a
simple lost count is enough to predict the stability or if there will
be a need to be a more granular count.
This document is classified as Experimental and is not part of the
IETF Standards Track.
Appendix B. Examples
This section tries to show some examples of how the model can be
configured for stability.
B.1. Single Hop BFD Configuration
This example demonstrates how a single hop BFD session can be
configured to enable monitoring of a session for stability.
=============== NOTE: '\' line wrapping per RFC 8792 ===============
<?xml version="1.0" encoding="UTF-8"?>
<key-chains
xmlns="urn:ietf:params:xml:ns:yang:ietf-key-chain"
xmlns:kc="urn:ietf:params:xml:ns:yang:ietf-key-chain">
<key-chain>
<name>bfd-stability-config</name>
<description>"An example for BFD Stability configuration."</de\
scription>
<key>
<key-id>55</key-id>
<lifetime>
<send-lifetime>
<start-date-time>2025-01-01T00:00:00Z</start-date-time>
<end-date-time>2025-02-01T00:00:00Z</end-date-time>
</send-lifetime>
<accept-lifetime>
<start-date-time>2024-12-31T23:59:55Z</start-date-time>
<end-date-time>2025-02-01T00:00:05Z</end-date-time>
</accept-lifetime>
</lifetime>
<crypto-algorithm>kc:sha-1</crypto-algorithm>
</key>
</key-chain>
</key-chains>
<interfaces
xmlns="urn:ietf:params:xml:ns:yang:ietf-interfaces"
xmlns:if-type="urn:ietf:params:xml:ns:yang:iana-if-type">
<interface>
<name>eth0</name>
<type>if-type:ethernetCsmacd</type>
</interface>
</interfaces>
<routing
xmlns="urn:ietf:params:xml:ns:yang:ietf-routing"
xmlns:bfd-types="urn:ietf:params:xml:ns:yang:ietf-bfd-types"
xmlns:stability="urn:ietf:params:xml:ns:yang:ietf-bfd-stability\
">
<control-plane-protocols>
<control-plane-protocol>
<type>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">
<sessions>
<session>
<interface>eth0</interface>
<dest-addr>2001:db8:0:113::101</dest-addr>
<desired-min-tx-interval>10000</desired-min-tx-interv\
al>
<required-min-rx-interval>
10000
</required-min-rx-interval>
<stability:stability>true</stability:stability>
<authentication>
<key-chain>bfd-stability-config</key-chain>
<meticulous>true</meticulous>
</authentication>
</session>
</sessions>
</ip-sh>
</bfd>
</control-plane-protocol>
</control-plane-protocols>
</routing>
B.2. Use of the NULL Auth Type
This example demonstrates how to configure the NULL Auth Type to
enable monitoring of a session for stability.
=============== NOTE: '\' line wrapping per RFC 8792 ===============
<?xml version="1.0" encoding="UTF-8"?>
<key-chains
xmlns="urn:ietf:params:xml:ns:yang:ietf-key-chain"
xmlns:stability="urn:ietf:params:xml:ns:yang:ietf-bfd-stability\
">
<key-chain>
<name>bfd-stability-config</name>
<description>"An example for BFD Stability configuration."</des\
cription>
<key>
<key-id>55</key-id>
<lifetime>
<send-lifetime>
<start-date-time>2025-01-01T00:00:00Z</start-date-time>
<end-date-time>2025-02-01T00:00:00Z</end-date-time>
</send-lifetime>
<accept-lifetime>
<start-date-time>2024-12-31T23:59:55Z</start-date-time>
<end-date-time>2025-02-01T00:00:05Z</end-date-time>
</accept-lifetime>
</lifetime>
<crypto-algorithm>stability:null-auth</crypto-algorithm>
</key>
</key-chain>
</key-chains>
<interfaces
xmlns="urn:ietf:params:xml:ns:yang:ietf-interfaces"
xmlns:if-type="urn:ietf:params:xml:ns:yang:iana-if-type">
<interface>
<name>eth0</name>
<type>if-type:ethernetCsmacd</type>
</interface>
</interfaces>
<routing
xmlns="urn:ietf:params:xml:ns:yang:ietf-routing"
xmlns:bfd-types="urn:ietf:params:xml:ns:yang:ietf-bfd-types"
xmlns:stability="urn:ietf:params:xml:ns:yang:ietf-bfd-stability\
">
<control-plane-protocols>
<control-plane-protocol>
<type>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">
<sessions>
<session>
<interface>eth0</interface>
<dest-addr>2001:db8:0:113::101</dest-addr>
<desired-min-tx-interval>10000</desired-min-tx-interv\
al>
<required-min-rx-interval>
10000
</required-min-rx-interval>
<stability:stability>true</stability:stability>
<authentication>
<key-chain>bfd-stability-config</key-chain>
<meticulous>true</meticulous>
</authentication>
</session>
</sessions>
</ip-sh>
</bfd>
</control-plane-protocol>
</control-plane-protocols>
</routing>
Acknowledgements
The authors would like to thank Nobo Akiya, Dileep Singh, Basil Saji,
Sagar Soni, Albert Fu, Peng Fang, and Mallik Mudigonda for
contributing to this document. Thanks to Christian Huitema for the
SECDIR review and Ebben Aries for the YANG Doctors review.
Thanks to Reshad Rehman for being the shepherd of the document.
Contributors
The authors would like to acknowledge Jeff Haas as a contributor to
this document. His contribution lead to significant improvements of
the document. In addition, Manav Bhatia contributed to this
document.
Authors' Addresses
Ashesh Mishra
Aalyria Technologies
Email: ashesh@aalyria.com
Mahesh Jethanandani
Arrcus, Inc.
United States of America
Email: mjethanandani@gmail.com
Ankur Saxena
Ciena Corporation
3939 North 1st Street
San Jose, CA 95134
United States of America
Email: ankurpsaxena@gmail.com
URI: www.ciena.com
Santosh Pallagatti
Zscaler
Bangalore 560103
Karnataka
India
Email: santosh.pallagatti@gmail.com
Mach(Guoyi) Chen
Huawei
Email: mach.chen@huawei.com