Internet Engineering Task Force (IETF) M. Jethanandani
Request for Comments: 9985 Arrcus
Category: Experimental A. Mishra
ISSN: 2070-1721 Aalyria Technologies
J. Haas
HPE
A. Saxena
Ciena Corporation
M. Bhatia
Google
June 2026
Optimizing Bidirectional Forwarding Detection (BFD) Authentication
Abstract
This document describes an experimental optimization to Bidirectional
Forwarding Detection (BFD) Authentication. This optimization enables
BFD to scale better when there is a desire to use authentication
where applying the same authentication mechanism to every BFD Control
Packet may adversely impact performance. This optimization
partitions BFD Authentication into a more computationally intensive
(MCI) mechanism that is applied to BFD significant changes and a less
computationally intensive (LCI) mechanism that is applied to the
majority of BFD Control Packets.
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/rfc9985.
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
1.1. Requirements Language
2. Terminology
3. BFD Control Packets That Require MCI Authentication
3.1. Protecting BFD Significant Changes with MCI Authentication
4. Using LCI Auth Types
5. Periodic MCI Reauthentication
6. Optimized Authentication Modes
7. Signaling Optimized Authentication
7.1. Transmitting and Receiving Using Optimized Authentication
7.2. Optimized Authentication Operations
8. Optimizing Authentication YANG Data Model
8.1. Data Model Overview
8.2. Tree Diagram
8.3. The YANG Data Model
9. IANA Considerations
9.1. IETF XML Registry
9.2. The YANG Module Names Registry
10. Security Considerations
10.1. Protocol Security Considerations
10.2. YANG Security Considerations
11. References
11.1. Normative References
11.2. Informative References
Appendix A. Examples
A.1. Single-Hop BFD Configuration
Appendix B. Experimental Status
Acknowledgments
Contributors
Authors' Addresses
1. Introduction
BFD [RFC5880] authentication procedures, when enabled, authenticate
each control packet using the same authentication mechanism. Devices
implementing BFD are often resource-constrained and authentication
may adversely impact the performance of BFD, thus discouraging the
deployment of authentication.
When implemented in software, BFD Authentication mechanisms compete
with other necessary work done by the systems implementing the
protocol. When implemented using hardware acceleration, these
mechanisms may scale better situationally, but they still impose a
cost on the implementation. BFD's value is tied to its ability to
scale in terms of numbers of sessions and a Detection Time that
relies on sending its control packets at a high rate. Implementers
and operators are forced to evaluate trade-offs of the benefits of
authentication vs. its impact on BFD performance.
The authentication mechanisms documented in [RFC5880], MD5
Message-Digest Algorithm [RFC1321], and Secure Hash Algorithm (SHA-1)
[RFC3174] are not particularly strong in a cryptographic sense.
However, they may still not appropriately scale situationally in a
given implementation. In the future, there may be a desire to use
stronger authentication mechanisms than those already specified, and
those mechanisms are likely to use even more resources.
The BFD protocol can broadly be described as the set of procedures
that handle its state machine changes to reach the Up state, and once
BFD is in the Up state, it will send those Up packets at the
negotiated high rate. The number of BFD Control Packets needed to
signal state changes (called significant changes) is very small,
while the majority of the Control Packets validate that the session
remains in the Up state.
This document describes an experimental optimization to BFD
Authentication. This optimization partitions BFD Authentication into
a more computationally intensive (MCI) mechanism used to authenticate
significant changes, and a less computationally intensive (LCI)
mechanism applied to the majority of the BFD Control Packets that
don't signal such significant changes.
The details of the motivation for experimental status are given in
Appendix B.
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. Terminology
The following terms used in this document have been defined in BFD
[RFC5880].
* Auth Type
* Detect Multiplier
* Detection Time
The following terms are introduced in this document.
significant change: A state change, demand mode change (to D bit),
or poll sequence change (P or F bit). Changes to BFD Control
Packets that do not require a poll sequence, such as
bfd.DetectMult, are also considered a significant change.
More Computationally Intensive (MCI) authentication: The
authentication mechanism applied to BFD Control Packets that are
significant changes.
Less Computationally Intensive (LCI) authentication: The
authentication mechanism applied to BFD Control Packets that are
NOT significant changes.
configured MCI reauthentication interval: Interval at which BFD
Control Packets are retried using MCI authentication.
The authentication mechanisms described in this optimization are
paired as MCI and LCI. While it will be generally the case that the
relationship between these mechanisms will be "stronger" and "less
strong", this document doesn't use the term "strong" to avoid
conflation with either mechanism's relative cryptographic strength.
The relative criteria for each mechanism is the impact on the
implementation.
3. BFD Control Packets That Require MCI Authentication
The intention of these optimized procedures is to permit more
computationally intensive authentication for BFD state changes and
utilize the less computationally intensive authentication mechanisms
to provide protection for the session in the Up state while
performing less work overall. Such procedures are intended to aid
BFD session scaling without compromising BFD session security.
All BFD Control Packets with the state AdminDown, Down, and Init MUST
use MCI authentication.
Once the BFD state machine has reached the Up state, it will continue
to send BFD Control Packets with MCI authentication in the Up state
for a period as discussed in Section 7.2. If optimized
authentication mechanisms are in use, as defined in Section 6, the
session MAY switch to the LCI mode.
The contents of an Up packet must not change aside from the
Authentication Section unless MCI authentication is in use.
3.1. Protecting BFD Significant Changes with MCI Authentication
This document proposes that BFD Control Packets that signal a state
change, a change in demand mode (D bit), or a poll sequence (P or F
bit change) be categorized as a "significant change". Control
packets that do not require a poll sequence, such as bfd.DetectMult,
are also considered a significant change.
Such significant changes are intended to be protected by more
computationally intensive authentication.
4. Using LCI Auth Types
The majority of packets exchanged in a BFD session in the Up state
are not significant changes. This document proposes a new optimized
authentication mode where packets that are not significant changes
may use an LCI authentication mechanism.
Once the session has reached the Up state, the session can use an LCI
Auth Type derived from the format in Section 7. Currently, this
includes:
* Meticulous Keyed ISAAC Authentication as described in [RFC9986].
This authentication type protects the BFD session when BFD Up
packets do not change, because only the paired devices know the
shared secret, key, and sequence number to select the ISAAC
result.
Other mechanisms may be defined in the future.
5. Periodic MCI Reauthentication
When using the LCI authentication mechanism, BFD should periodically
test the session using the MCI authentication mechanism. MCI
authentication is tested using a Poll sequence. To test MCI
authentication, a Poll sequence SHOULD be initiated by the sender
using the MCI authentication mode rather than the LCI mechanism. If
a control packet with the Final (F) bit is not received using MCI
authentication within twice the Detect Interval as would be
calculated by the receiving system, the session has been compromised,
and it MUST be brought down.
The value "twice the Detect interval as would be calculated by the
receiving system" is, roughly, twice the number of packets the local
system would transmit to the receiving system within its own Detect
Interval. This accommodates for possible packet loss from the
sending system during the Poll sequence to the receiving system, plus
time for the receiving system to transmit a control packet with the
Final (F) bit set to the local system.
This "MCI reauthentication interval" for performing such periodic
tests using the MCI authentication mechanism can be configured
depending on the capability of the system.
Most packets transmitted in a BFD session are BFD Up packets. MCI
authenticating a limited subset of these packets with a Poll sequence
as described above, e.g., every one minute, significantly reduces the
computational demand for the system while maintaining security of the
session across the configured MCI reauthentication interval.
6. Optimized Authentication Modes
The cryptographic authentication mechanisms specified in Section 6.7
of BFD [RFC5880] describe enabling and disabling of authentication as
a one-time operation. The following is stated in Section 6.7.1 of
[RFC5880]:
| ... implementations using this method SHOULD only allow the
| authentication state to be changed at most once without some form
| of intervention (so that authentication cannot be turned on and
| off repeatedly simply based on the receipt of BFD Control Packets
| from remote systems).
Once enabled, every packet must have the Authentication Present (A)
bit set and the associated Authentication Type appended (Section 4.1
of [RFC5880]). In addition, Section 6.7.1 of [RFC5880] states that
an implementation SHOULD NOT allow the authentication state to be
changed based on the receipt of a BFD Control Packet.
This document proposes that an "optimized" authentication mode that
permits both an MCI authentication mode and an LCI mode be used
within the same BFD session. This pairing of an MCI and an LCI mode
of authentication is carried in new BFD Authentication types
representing a given optimized authentication type pairing.
This document defines which BFD Control Packets require MCI
authentication in Section 3.1. A BFD Control Packet that fails
authentication, or a BFD Control Packet that was supposed to be MCI-
authenticated but was not (e.g., a significant change packet), is
discarded. However, there is no change to the state machine for BFD,
as the decision of a significant change is still decided by how many
valid consecutive packets were received.
In this specification, the contents of an Up packet MUST NOT change
aside from the Authentication Section without MCI authentication.
The full procedure is documented in the following sections.
7. Signaling Optimized Authentication
When the Authentication Present (A) bit is set and the Auth Type
([RFC5880], Section 4.1) is a type supporting Optimized BFD
Authentication, the Auth Type signals a pairing of an MCI
authentication type and an LCI authentication type. This pairing is
advertised in a single Auth Type value in order to permit
implementations to be aware that:
* Optimized BFD procedures will be in use.
* The pairing of the MCI and LCI authentication mechanisms will be
used for that session.
* There is a requirement to carry a Sequence Number.
* The current MCI or LCI mode will be carried as described below.
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 | Opt. Mode |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authentication Specific Data ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Common Optimized BFD Authentication Section
The values of Auth Type and Auth Len are defined in their respective
Optimized BFD Authentication procedural documents.
The values of the Optimized Authentication Mode field are:
1. The MCI authentication type for Optimized BFD Auth Types.
2. The LCI authentication type for Optimized BFD Auth Types.
Authentication Specific Data: When using the more computationally
intensive authentication type, the remainder of the Authentication
Section carries that type's data.
7.1. Transmitting and Receiving Using Optimized Authentication
The procedures for authenticating BFD Control Packets using Optimized
Authentication are similar to the existing procedures covered in
Section 6.7 of [RFC5880]. Optimized Authentication modes have common
procedural requirements for authentication regardless of which more
or less computationally intensive authentication modes are used.
The required value of the Auth Len field for a given Optimized
Authentication mode is defined in the respective specifications for
their respective MCI and LCI modes.
The following common procedures apply to authenticating BFD Control
packets utilizing Optimized Authentication:
* If the received BFD Control Packet does not contain an
Authentication Section ([RFC5880], Section 4.1), or the Auth Type
is not a supported Optimized Authentication Auth Type, then the
received packet MUST be discarded.
* If the received BFD Control Packet contains an optimized
authentication type using these procedures and the Optimized
Authentication Mode field is not 1 or 2, then the received packet
MUST be discarded.
* If bfd.SessionState is AdminDown, Down, or Init and the Optimized
Authentication Mode field is not 1, then the received packet MUST
be discarded.
* If bfd.SessionState is Up and there is a significant change as
defined in Section 3.1, and the Optimized Authentication Mode
field is not 1, then the received packet MUST be discarded.
* If the Auth Len field is not equal to a value appropriate for the
Optimized Authentication Mode field, the packet MUST be discarded.
* If bfd.AuthSeqKnown is 1, examine the Sequence Number field. If
the sequence number lies outside of the inclusive range of
bfd.RcvAuthSeq+1 to bfd.RcvAuthSeq+(3*Detect Mult) when treated as
an unsigned 32-bit circular number space, the received packet MUST
be discarded.
Otherwise (bfd.AuthSeqKnown is 0), bfd.AuthSeqKnown MUST be set to 1,
bfd.RcvAuthSeq MUST be set to the value of the received Sequence
Number field, and the received packet MUST be accepted.
For the specified Auth Type and Optimized Authentication Mode,
perform the appropriate authentication procedures. If authentication
succeeds, the received packet MUST be accepted. Otherwise, the
received packet MUST be discarded.
7.2. Optimized Authentication Operations
As noted in Section 3.1, when using Optimized BFD procedures, MCI
authentication is used in the BFD state machine to bring a BFD
session to the Up state or to make any change of the BFD parameters
as carried in the BFD Control Packet when in the Up state.
Once the BFD session has reached the Up state, the BFD Up state MUST
be signaled to the remote BFD system using the MCI authentication
mode for an interval that is at least the Detection Time before
switching to the LCI authentication mode. This is to permit
mechanisms such as Meticulous Keyed ISAAC for BFD Optimized
Authentication [RFC9986] or other approved, less intensive
authentication mechanisms to be bootstrapped before switching to the
LCI mode.
It is RECOMMENDED that when using optimized authentication that
implementations switch from MCI authentication to LCI authentication
mode after an interval that is at least the Detection Time. In the
circumstances where a BFD session successfully reaches the Up state
with MCI authentication, but there are problems with the LCI
authentication, this will permit the remote system to tear down the
session as quickly as possible.
BFD sessions using optimized authentication that succeed in reaching
the Up state using MCI authentication and fail using LCI
authentication SHOULD bring the issue to the attention of the
operator. Furthermore, implementations MAY wish to throttle session
restarts.
It is further RECOMMENDED that BFD implementations using optimized
authentication defer notifying their client that the session has
reached the Up state until it has transitioned to using the LCI
authentication mode. In the event where LCI authentication is
failing in the protocol, this avoids propagating the failed
transitions to the LCI mode to their clients.
8. Optimizing Authentication YANG Data Model
8.1. Data Model Overview
The YANG 1.1 [RFC7950] data model defined in this document augments
the "ietf-bfd" module to add data nodes relevant to the management of
the feature defined in this document. It adds an interval value that
specifies how often the BFD session should be reauthenticated using
more computationally intensive authentication once it is in the Up
state.
8.2. Tree Diagram
The tree diagram for the YANG modules defined in this document uses
annotations defined in YANG Tree Diagrams [RFC8340].
module: ietf-bfd-opt-auth
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:authentication:
+--rw reauth-interval? uint32
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:authentication:
+--rw reauth-interval? uint32
augment /rt:routing/rt:control-plane-protocols
/rt:control-plane-protocol/bfd:bfd/bfd-lag:lag
/bfd-lag:sessions/bfd-lag:session/bfd-lag:authentication:
+--rw reauth-interval? uint32
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:authentication:
+--rw reauth-interval? uint32
8.3. The YANG Data Model
This YANG module imports modules defined in "A YANG Data Model for
Routing Management (NMDA Version)" [RFC8349] and "YANG Data Model for
Bidirectional Forwarding Detection (BFD)" [RFC9314].
Implementations supporting the optimization procedures defined in
this document enable optimization by using one of the newly defined
key-chain crypto-algorithms in the ietf-bfd-met-keyed-isaac YANG
module in [RFC9986].
<CODE BEGINS> file "ietf-bfd-opt-auth@2026-06-19.yang"
module ietf-bfd-opt-auth {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-opt-auth";
prefix bfd-oa;
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 (BFD).";
}
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).";
}
organization
"IETF Bidirectional Forwarding Detection (BFD) Working Group";
contact
"WG Web: <http://tools.ietf.org/wg/bfd>
WG List: <rtg-bfd@ietf.org>
Authors: Mahesh Jethanandani (mjethanandani@gmail.com)
Ashesh Mishra (ashesh@aalyria.com)
Ankur Saxena (ankurpsaxena@gmail.com)
Manav Bhatia (mnvbhatia@google.com)
Jeffrey Haas (jeffrey.haas@hpe.com).";
description
"This YANG module augments the base BFD YANG module to add
attributes related to the experimental BFD Optimized
Authentication.
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 9985
(https://www.rfc-editor.org/info/rfc9985); see the RFC itself
for full legal notices.";
revision "2026-06-19" {
description
"Initial Version.";
reference
"RFC 9985: Optimizing BFD Authentication.";
}
feature optimized-auth {
description
"Indicates that the implementation supports optimized
authentication.";
reference
"RFC 9985: Optimizing BFD Authentication.";
}
grouping bfd-opt-auth-config {
description
"Grouping for BFD Optimized Authentication Parameters.";
leaf reauth-interval {
type uint32;
units "seconds";
default "60";
description
"Interval of time after which more computationally intensive
authentication should be utilized to prevent an
on-path-attacker attack.
A value of zero means that we do not do periodic
reauthentication using the more computationally intensive
authentication method.
This value SHOULD have jitter applied to it to avoid
self-synchronization during expensive authentication
operations.";
}
}
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:authentication" {
uses bfd-opt-auth-config;
description
"Augment the 'authentication' container for single-hop BFD
module to add attributes related to BFD Optimized
Authentication.";
}
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:authentication" {
uses bfd-opt-auth-config;
description
"Augment the 'authentication' container for multi-hop BFD
module to add attributes related to BFD Optimized
Authentication.";
}
augment "/rt:routing/rt:control-plane-protocols"
+ "/rt:control-plane-protocol/bfd:bfd/bfd-lag:lag"
+ "/bfd-lag:sessions/bfd-lag:session"
+ "/bfd-lag:authentication" {
uses bfd-opt-auth-config;
description
"Augment the 'authentication' container for BFD over LAG
module to add attributes related to BFD Optimized
Authentication.";
}
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:authentication" {
uses bfd-opt-auth-config;
description
"Augment the 'authentication' container for BFD over MPLS
module to add attributes related to BFD Optimized
Authentication.";
}
}
<CODE ENDS>
9. IANA Considerations
IANA has assigned one URI and one YANG module as described in this
section.
9.1. IETF XML Registry
IANA has registered the following URI in the "ns" registry within the
"IETF XML Registry" group [RFC3688]:
URI: urn:ietf:params:xml:ns:yang:ietf-bfd-opt-auth
Registrant Contact: The IESG
XML: N/A; the requested URI is an XML namespace.
9.2. The YANG Module Names Registry
IANA has registered the following YANG module in the "YANG Module
Names" registry [RFC6020] within the "YANG Parameters" registry
group:
Name: ietf-bfd-opt-auth
Maintained by IANA: N
Namespace: urn:ietf:params:xml:ns:yang:ietf-bfd-opt-auth
Prefix: bfd-oa
Reference: RFC 9985
10. Security Considerations
10.1. Protocol Security Considerations
Devices implementing BFD are often resource-constrained, whether in a
single session or a multidimensional set of scaled sessions. Desired
detection intervals for the BFD sessions, and their number, are
common scaling considerations for BFD implementations. Security
mechanisms also impact the performance of implementations, whether in
software or hardware, due to the use of additional computational
resources these mechanisms use.
The optimized procedures in this document provide a different level
of resistance to attack than methods using a single authentication
mechanism:
* The MCI authentication mechanisms used for optimized
authentication are expected to have similar cryptographic strength
acceptable for BFD for authenticating the entire session, as
described in [RFC5880].
* When the BFD state machine is attempting to move from the Down
state to the Up state, the MCI authentication mechanism is
intended to protect vs. attempt to inappropriately start BFD
sessions.
* When the BFD state machine is in the Up state, the MCI
authentication mechanism is intended to protect vs. attempt to
change BFD session parameters or to reset the BFD session.
* When the BFD state machine is in the Up state, the LCI
authentication mechanism is intended to provide resistance to
keeping a BFD session in the Up state inappropriately. Since the
procedures for changing BFD state require utilizing the MCI
mechanism, and the LCI mechanism requires that the contents of the
Control Packet in the Up state remain unchanged, the only thing
that successfully spoofing such packets can do is keep the session
Up.
* The periodic, MCI reauthentication procedure provides protection
against long-term successful spoofing of the LCI authentication
mechanism.
In other words, the intention of Optimized BFD procedures is to make
it difficult to reset or inappropriately start BFD sessions.
However, protecting against keeping the session Up is seen as a less
interesting attack and can receive less protection.
The recent escalating series of attacks on MD5 and SHA-1 described in
Finding Collisions in the Full SHA-1 [SHA-1-attack1] and New
Collision Search for SHA-1 [SHA-1-attack2] raise concerns about their
remaining useful lifetime as outlined in Updated Security
Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithm
[RFC6151] and Security Considerations for the SHA-0 and SHA-1
Message-Digest Algorithm [RFC6194]. If replaced by stronger
algorithms, the computational overhead will make the task of
authenticating every packet even more difficult to achieve.
The procedures described in this document provide a mechanism that
could enable implementations to leverage stronger security to address
the concerns above when strong authentication is required. However,
this requires operators to evaluate the trade-offs of the less
computationally intensive mechanisms to adequately address their
desired security stance.
Keys generated and distributed out of band for the purposes described
in this specification are generally limited in the security they can
provide. It is essential that these keys are selected well and
protected when stored.
10.2. YANG Security Considerations
This section is modeled after the template described in Section 3.7.1
of [RFC9907].
The "ietf-bfd-opt-auth" YANG module defines a data model that is
designed to be accessed via YANG-based management protocols, such as
the 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.
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). All writable data nodes are likely to be sensitive or
vulnerable in some network environments. Write operations (e.g.,
edit-config) and delete operations to these data nodes without proper
protection or authentication can have a negative effect on network
operations. The following subtrees and data nodes have particular
sensitivities/vulnerabilities:
* 'reauth-interval' specifies the interval in Up state, after which
MCI authentication SHOULD be performed to prevent a Person-in-the-
Middle (PITM) attack. If this interval is set very low, the
utility of these optimization procedures is lessened. If this
interval is set very high, attacks detected by the MCI
authentication mechanisms may happen overly late.
There are no particularly sensitive readable data nodes.
There are no RPC operations defined in this model.
11. References
11.1. 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>.
[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>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/info/rfc7950>.
[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>.
11.2. Informative References
[RFC1321] Rivest, R., "The MD5 Message-Digest Algorithm", RFC 1321,
DOI 10.17487/RFC1321, April 1992,
<https://www.rfc-editor.org/info/rfc1321>.
[RFC2026] Bradner, S., "The Internet Standards Process -- Revision
3", BCP 9, RFC 2026, DOI 10.17487/RFC2026, October 1996,
<https://www.rfc-editor.org/info/rfc2026>.
[RFC3174] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1
(SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001,
<https://www.rfc-editor.org/info/rfc3174>.
[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>.
[RFC6151] Turner, S. and L. Chen, "Updated Security Considerations
for the MD5 Message-Digest and the HMAC-MD5 Algorithms",
RFC 6151, DOI 10.17487/RFC6151, March 2011,
<https://www.rfc-editor.org/info/rfc6151>.
[RFC6194] Polk, T., Chen, L., Turner, S., and P. Hoffman, "Security
Considerations for the SHA-0 and SHA-1 Message-Digest
Algorithms", RFC 6194, DOI 10.17487/RFC6194, March 2011,
<https://www.rfc-editor.org/info/rfc6194>.
[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>.
[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>.
[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>.
[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>.
[RFC8792] Watsen, K., Auerswald, E., Farrel, A., and Q. Wu,
"Handling Long Lines in Content of Internet-Drafts and
RFCs", RFC 8792, DOI 10.17487/RFC8792, June 2020,
<https://www.rfc-editor.org/info/rfc8792>.
[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, June 2026,
<https://www.rfc-editor.org/info/rfc9986>.
[SHA-1-attack1]
Wang, X., Yin, Y., and H. Yu, "Finding Collisions in the
Full SHA-1", Advances in Cryptology - CRYPTO 2005, Lecture
Notes in Computer Science, vol. 3621, pp. 17-36,
DOI 10.1007/11535218_2, 2005,
<https://doi.org/10.1007/11535218_2>.
[SHA-1-attack2]
Wang, X., Yao, A., and F. Yao, "Cryptanalysis on SHA-1",
2005, <https://csrc.nist.gov/csrc/media/events/first-
cryptographic-hash-workshop/documents/wang_sha1-new-
result.pdf>.
Appendix A. Examples
This section tries to show some examples in how the model can be
configured.
A.1. Single-Hop BFD Configuration
This example demonstrates how a single-hop BFD session can be
configured for optimized authentication. Note that line wrapping is
used per [RFC8792].
=============== 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:opt-auth="urn:ietf:params:xml:ns:yang:ietf-bfd-opt-auth"
xmlns:bfd-mki="urn:ietf:params:xml:ns:yang:ietf-bfd-met-keyed-i\
saac">
<key-chain>
<name>bfd-auth-config</name>
<description>"An example for BFD Optimized Auth configuration."\
</description>
<key>
<key-id>55</key-id>
<lifetime>
<send-lifetime>
<start-date-time>2017-01-01T00:00:00Z</start-date-time>
<end-date-time>2017-02-01T00:00:00Z</end-date-time>
</send-lifetime>
<accept-lifetime>
<start-date-time>2016-12-31T23:59:55Z</start-date-time>
<end-date-time>2017-02-01T00:00:05Z</end-date-time>
</accept-lifetime>
</lifetime>
<crypto-algorithm>bfd-mki:optimized-sha1-meticulous-keyed-isa\
ac</crypto-algorithm>
<key-string>
<keystring>testvector</keystring>
</key-string>
</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:iana-bfd-types="urn:ietf:params:xml:ns:yang:iana-bfd-type\
s"
xmlns:opt-auth="urn:ietf:params:xml:ns:yang:ietf-bfd-opt-auth"
xmlns:bfd-mki="urn:ietf:params:xml:ns:yang:ietf-bfd-met-keyed-i\
saac">
<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>
<authentication>
<key-chain>bfd-auth-config</key-chain>
<opt-auth:reauth-interval>30</opt-auth:reauth-inter\
val>
</authentication>
</session>
</sessions>
</ip-sh>
</bfd>
</control-plane-protocol>
</control-plane-protocols>
</routing>
Appendix B. Experimental Status
This document describes an experiment that presents a candidate
solution to update BFD Authentication that is currently specified in
[RFC5880]. This experiment is intended to provide additional
insights into what happens when the optimized authentication
mechanism defined in this document is used. Here are the reasons why
this document is on the Experimental track:
* In the initial stages of the document, there were significant
participation and reviews from the working group. Since then,
there have been considerable changes to the document, such as the
use of ISAAC, the allowance for ISAAC bootstrapping when a BFD
session comes up, and the use of a single Auth Type to indicate
optimized authentication. These changes did not get significant
review from the working group and therefore do not meet the bar
set in Section 4.1.1 of [RFC2026].
* There are no known implementations at this time.
* The work in this document could become very valuable in the
future, especially if the need for deploying BFD Authentication at
scale becomes a reality.
This document is classified as Experimental and is not part of the
IETF Standards Track. Implementations based on this document should
not be considered as compliant with BFD [RFC5880].
Acknowledgments
The authors would like to thank Qiufang Ma, Stephen Farrell, and Acee
Lindem for providing directorate reviews of this document.
Contributors
The authors of this document would like to acknowledge Reshad Rahman
as a contributor to this document.
Authors' Addresses
Mahesh Jethanandani
Arrcus
United States of America
Email: mjethanandani@gmail.com
Ashesh Mishra
Aalyria Technologies
Email: ashesh@aalyria.com
Jeffrey Haas
HPE
Email: jeffrey.haas@hpe.com
Ankur Saxena
Ciena Corporation
3939 N 1st Street
San Jose, CA 95134
United States of America
Email: ankurpsaxena@gmail.com
Manav Bhatia
Google
Bagmane Capital Park
Bengaluru 560048
Karnataka
India
Email: mnvbhatia@google.com
