Optimizing BFD
AuthenticationKloud ServicesUSAmjethanandani@gmail.comAalyria Technologiesashesh@aalyria.comCiena Corporation3939 N 1st StreetSan JoseCA95134USAankurpsaxena@gmail.comGoogleDoddanekkundiBangalore560048Indiamnvbhatia@google.comBFDauthenticationThis document describes an optimization to BFD Authentication as
described in Section 6.7 of BFD RFC 5880. This document updates RFC
5880.Authenticating every BFD control packet
with MD5
Message-Digest Algorithm , or Secure Hash Algorithm (SHA-1)
is a computationally intensive process. This makes it
difficult, if not impossible to authenticate every packet - particularly
at faster rates. Also, the recent escalating series of attacks on MD5
and SHA-1 described in Finding Collisions
in the Full SHA-1 and New Collision
Search for SHA-1 raise concerns about their remaining useful
lifetime as outlined in Updated Security
Considerations for the MD5 Message-Digest and the HMAC-MD5 Algorithm
and Security Considerations for the SHA-0
and SHA-1 Message-Digest Algorithm . If replaced by stronger
algorithms, the computational overhead, will make the task of
authenticating every packet even more difficult to achieve.
This document proposes that BFD control packets that signal a
state change, a demand mode change (to D bit), a poll sequence
change (P or F bit change) be categorized as a significant
change. Control packets that do not require a poll sequence,
such as bfd.RequiredMinRxInterval or
bfd.RequiredMinTxInterval, are also considered as a
significant change. In other words, the contents of an Up
packet MUST NOT change aside from the authentication section
without stronger authentication to take advantage of the
method described in this document.
In the Up state, most packets that are transmitted and received have no state change
associated with them. Limiting authentication to packets that affect a
BFD session's state allows more sessions to be supported with this
optimized method of authentication.
Once the session has reached the Up state, the session can
choose the Auth Type to be one of:
No authentication, i.e., Authentication Present (A-bit) is
zero. Having no authentication provides computational
relief to the system. However, a malicious user can
blindly inject traffic that will be accepted by the BFD
session.
NULL Auth Type as
defined in this document. This type prevents blind
injection, but is vulnerable to active attacks, where the
attacker is aware of the sequence number, and potentially
becomes the PITM. However, periodic check with stronger
authentication can thwart that attack as described below.
Meticulous Keyed ISAAC authentication as described in
Secure
BFD Sequence Numbers. This authentication type
prevents the attack when the Up packets do not change,
because only the paired devices know the shared secret,
key, and sequence number to select the ISAAC result.
To detect a Person In the Middle (PITM) attack when the
session is in Up state, implementations have two options. They
can choose to use:
Test periodic strong authentication using a Poll
sequence. To perform a strong authentication, a Poll
sequence SHOULD be initiated by the sender. If a Fin is
not received within the Detect Interval, the session has
been compromised, and should be brought down. The interval
for initiating a Poll sequence can be configured depending
on the capability of the system.
Meticulous Keyed ISAAC as defined in Securing BFD
Sequence Numbers.
Most packets transmitted on a BFD session are BFD Up packets.
Authenticating a small subset of these packets with a Poll
sequence as described above, for example every one minute,
significantly reduces the computational demand for the system
while maintaining security of the session across the
configured interval.
The rest of this document is structured as follows: Section 2 talks
about the changes to authentication mode as described in BFD. Section 3 goes into the details of the new
Authentication Type.The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in BCP 14 when, and only
when, they appear in all capitals, as shown here.
This document uses several placeholder values throughout the
document. Please replace them as follows and remove this
note before publication.
RFC XXXX, where XXXX is the number assigned to this document
at the time of publication.
2024-02-05 with the actual date of the publication of this
document.
The following terms used in this document have been defined in
BFD.Detect MultiplierDetection TimeThe following terms are introduced in this document.TermMeaningsignificant change
State change, a demand mode change (to D bit) or a poll
sequence change (P or F bit). Control packets that do not
require a poll sequence, such as bfd.RequiredMinRxInterval
bfd.RequiredMinTxInterval, or bfd.DetectMult are also
considered as a significant change.
configured interval
Interval at which BFD control packets are retried with a
stronger authentication.
The cryptographic authentication mechanisms specified in BFD describes enabling and disabling of
authentication as a one time operation. As a security precaution, it
mentions that authentication state be allowed to change at most once.
Once enabled, every packet must have Authentication Bit set and the
associated Authentication Type appended. In addition, it 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 the authentication mode be modified to be
enabled on demand. Instead of authenticating every packet, BFD peers are
configured for which packets need to be authenticated, and authenticate
only those packets. The remaining packets MAY be transmitted and received
without authentication, or use a less expensive authentication.
For example, the two ends can be configured such
that BFD control packets that indicate a significant change should be
authenticated and enable authentication on those packets only. If the
two ends have previously been configured as such, but at least one side
decides not to authenticate a significant change packet, then the BFD
session will fail to come up.
The proposal outlines which BFD control packets are required
to be authenticated. A BFD control packet that fails
authentication is discarded, or a BFD control packet that was
supposed to be 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, authenticated or otherwise.
The following table summarizes when the Auth Type should be
set with a Auth or a OPT authentication type. The table
should be read with the column indicating the BFD state the
receiver is currently in, and the row indicating the BFD state
the receiver might transition to based on the BFD control
packet received. The intersection of the two indicates
whether the received BFD control packet should have the
Auth Type set to either Auth, or OPT. The BFD state
refers to the states in BFD state machine described in Section
6.2 of BFD.
to
Auth : Strongly authenticated BFD control packet
OPT : Any or no authentication, as configured.
n/a : Invalid state transition.
Select : Most packets OPT AUTH. Selective (periodic)
packets authenticated.
+--------+--------+--------+--------+
| | DOWN | INIT | UP |
+--------+--------+--------+--------+
| DOWN | OPT | Auth | Auth |
+--------+--------+--------+--------+
| INIT | Auth | OPT | n/a |
+--------+--------+--------+--------+
| UP | Auth | Auth | Select |
+--------+--------+--------+--------+
]]>
In other words, the contents of an Up packet MUST NOT change
aside from the authentication section without stronger
authentication.
Implementations supporting this feature can send BFD packets
with or without authentication that carries a meticulously
increasing sequence number. This meticulously increasing
sequence number prevents replay attacks, and it supports BFD Stability.
The NULL Authentication type is defined in NULL Authentication
Type. This authentication type does not provide any
authentication of the BFD Control Up packets, but does carry a
meticulously increasing sequence number compatible with this
specification.
Secure BFD
Sequence Numbers defines an authentication mechanism
that does not provide any authentication of the BFD Control
packets, carries a meticulously increasing sequence number,
but provides for a stronger mechanism to prevent active
attacks against these procedures for Up packets without
requiring strong authentication.
This section describes a new Authentication Type as:
where:
Auth Type: The Authentication Type, which in this case is TBD
(NULL, to be assigned by IANA, with a suggested value of 6).
Auth Len: The length of the NULL Auth Type, in bytes; i.e. 8 bytesAuth Key ID: The authentication key ID in use for this packet. Must
be set to zero.Reserved: This byte MUST be set to zero on transmit and ignored on
receive.Sequence Number: The sequence number for this packet. Implementations
will use sequence numbers (bfd.XmitAuthSeq) as defined in BFD.
The YANG 1.1 model defined in
this document augments the "ietf-bfd" module to add
configuration relevant to the management of the feature
defined in this document. In particular, it adds crypto
algorithms that are described in this model, and in Secure BFD
Sequence Numbers. It adds a feature statement to
enable optimized authentication. Finally, it adds a flag to
enable optimized authentication, an interval value that
specifies how often the BFD session should be
re-authenticated once it is in the Up state, and the key chain
that should be used in the Up state.
The tree diagram for the YANG modules defined in this
document use annotations defined in YANG Tree Diagrams..
This YANG module imports YANG Key
Chain , A YANG Data Model for
Routing Management (NMDA version), and YANG Data Model for Bidirectional Forwading
Detection (BFD).
file "ietf-bfd-opt-auth@2024-02-05.yang"
module ietf-bfd-opt-auth {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-opt-auth";
prefix "bfdoa";
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.";
}
import ietf-bfd-ip-mh {
prefix bfd-ip-mh;
reference
"RFC 9314: YANG Data Model for Bidirectional
Forwarding Detection.";
}
import ietf-bfd-lag {
prefix bfd-lag;
reference
"RFC 9314: YANG Data Model for Bidirectional
Forwarding Detection.";
}
import ietf-bfd-mpls {
prefix bfd-mpls;
reference
"RFC 9314: YANG Data Model for Bidirectional
Forwarding Detection.";
}
import ietf-key-chain {
prefix key-chain;
reference
"RFC 8177: YANG Key Chain.";
}
organization
"IETF BFD Working Group";
contact
"WG Web:
WG List:
Authors: Mahesh Jethanandani (mjethanandani@gmail.com)
Ashesh Mishra (mishra.ashesh@gmail.com)
Ankur Saxena (ankurpsaxena@gmail.com)
Manav Bhatia (mnvbhatia@google.com).";
description
"This YANG module augments the base BFD YANG model to add
attributes related to BFD Optimized Authentication.
Copyright (c) 2024 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 XXXX
(https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself
for full legal notices.
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.";
revision "2024-02-05" {
description
"Initial Version.";
reference
"RFC XXXX: Optimizing BFD Authentication.";
}
feature optimized-auth {
description
"When enabled, this implementation supports optimized
authentication as described in this document.";
}
identity no-auth {
base key-chain:crypto-algorithm;
description
"No authentication will be used.";
}
identity null {
base key-chain:crypto-algorithm;
description
"BFD Null type defined in this draft.";
reference
"RFC XXXX: Optimizing BFD Authentication.";
}
identity meticulous-keyed-isaac {
base key-chain:crypto-algorithm;
description
"BFD ISAAC Keyed Meticulous.";
reference
"I-D.ietf-bfd-secure-sequence-numbers: Securing BFD Sequence
Numbers.";
}
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" {
leaf optimized-auth {
if-feature optimized-auth;
type boolean;
default false;
description
"If set to true, BFD Single Hop Sessions will be
enabled for optimized authentication.";
}
leaf reauth-interval {
when "../optimized-auth = 'true'";
type uint32;
units "microseconds";
default "60000000";
description
"Interval of time after which a strong authentication
should be enabled to prevent a Person-In-The-Middle
attack. Default is 1 minute.
This value SHOULD have jitter applied to it to avoid
self-synchronization during expensive authentication
operations.";
}
leaf up-auth-type {
type key-chain:key-chain-ref;
must "(../optimized-auth = 'true') and " +
"(../bfd-ip-sh:meticulous = 'true')";
description
"The authentication type that should be used once the
connection transitions to Up state. In case
of optimized auth, the choices are Reserved (or no
authentication), NULL Auth, or Meticulous Keyed ISAAC.";
}
description
"Augment the 'bfd' container 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" {
leaf optimized-auth {
if-feature optimized-auth;
type boolean;
default false;
description
"If set to true, BFD Multi Hop Sessions will be
enabled for optimized authentication.";
}
leaf reauth-interval {
when "../optimized-auth = 'true'";
type uint32;
units "microseconds";
default "60000000";
description
"Interval of time after which a strong authentication
should be enabled to prevent a Person-In-The-Middle
attack. Default is 1 minute.
This value SHOULD have jitter applied to it to avoid
self-synchronization during expensive authentication
operations.";
}
leaf up-auth-type {
type key-chain:key-chain-ref;
must "(../optimized-auth = 'true') and " +
"(../bfd-ip-mh:meticulous = 'true')";
description
"The authentication type that should be used once the
connection transitions to Up state. In case
of optimized auth, the choices are Reserved (or no
authentication), NULL Auth, or Meticulous Keyed ISAAC.";
}
description
"Augment the 'bfd' container 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" {
leaf optimized-auth {
if-feature optimized-auth;
type boolean;
default false;
description
"If set to true, BFD LAG Sessions will be
enabled for optimized authentication.";
}
leaf reauth-interval {
when "../optimized-auth = 'true'";
type uint32;
units "microseconds";
default "60000000";
description
"Interval of time after which a strong authentication
should be enabled to prevent a Person-In-The-Middle
attack. Default is 1 minute.
This value SHOULD have jitter applied to it to avoid
self-synchronization during expensive authentication
operations.";
}
leaf up-auth-type {
type key-chain:key-chain-ref;
must "(../optimized-auth = 'true') and " +
"(../bfd-lag:meticulous = 'true')";
description
"The authentication type that should be used once the
connection transitions to Up state. In case
of optimized auth, the choices are Reserved (or no
authentication), NULL Auth, or Meticulous Keyed ISAAC.";
}
description
"Augment the 'bfd' container 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" {
leaf optimized-auth {
if-feature optimized-auth;
type boolean;
default false;
description
"If set to true, BFD MPLS Sessions will be
enabled for optimized authentication.";
}
leaf reauth-interval {
when "../optimized-auth = 'true'";
type uint32;
units "microseconds";
default "60000000";
description
"Interval of time after which a strong authentication
should be enabled to prevent a Person-In-The-Middle
attack. Default is 1 minute.
This value SHOULD have jitter applied to it to avoid
self-synchronization during expensive authentication
operations.";
}
leaf up-auth-type {
type key-chain:key-chain-ref;
must "(../optimized-auth = 'true') and " +
"(../bfd-mpls:meticulous = 'true')";
description
"The authentication type that should be used once the
connection transitions to Up state. In case
of optimized auth, the choices are Reserved (or no
authentication), NULL Auth, or Meticulous Keyed ISAAC.";
}
description
"Augment the 'bfd' container to add attributes related to BFD
optimized authentication.";
}
}
]]>
This documents requests two new authentication types, one URI,
one YANG model, and an update to an existing IANA YANG model.
This document requests an update to the registry titled "BFD
Authentication Types". IANA is requested to assign two new
BFD AuthType:
NULL Auth Type,
with a suggested value of 6.
Meticulous
Keyed ISAAC Authentication, with a suggested
value of 7.
This document registers one URIs in the "ns" subregistry of
the "IETF XML" registry . Following
the format in , the following
registration is requested:
This document registers one YANG modules in the "YANG Module
Names" registry . Following the
format in , the following
registrations are requested:
This document also requests an update to an existing IANA
YANG module described in Updated BFD IANA
Module
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 or RESTCONF. The lowest NETCONF layer is
the secure transport layer, and the mandatory-to-implement
secure transport is Secure Shell
(SSH). The lowest RESTCONF layer is HTTPS, and the
mandatory-to-implement secure transport is TLS. The NETCONF Access Control Model (NACM)
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. Some of the subtrees and data nodes and their
sensitivity/vulnerability are described here.
'optimized-auth' flag is used to enable optimized
authentication for the session. If this was not intended, or
the other end is not configured with the same flag, the BFD
session will fail to come up.
'reauth-interval' specifies the interval in Up state, after
which a strong authentication SHOULD be performed to prevent
a Person-In-The-Middle (PITM) attack. If this interval is
set very low, or very high, then it will make optimization
worthless.
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.
There are no read-only data nodes defined in this model.
Some of the RPC operations in this YANG module may be
considered sensitive or vulnerable in some network
environments. It is thus important to control access to these
operations.
There are no RPC operations defined in this model.
The approach described in this document enhances the ability
to authenticate a BFD session by taking away the onerous
requirement that every BFD control packet be authenticated. By
authenticating packets that affect the state of the session,
the security of the BFD session is maintained. In this mode,
packets that are a significant change but are not
authenticated, are dropped by the system. Therefore, a
malicious user that tries to inject a non-authenticated
packet; e.g. with a Down state to take a session down will
fail. That combined with the proposal of using sequence number
defined in Secure BFD
Sequence Numbers further enhances the security of BFD
sessions.
Finding Collisions in the Full SHA-1New Collision Search for SHA-1
This section carries the updated IANA BFD Module,
iana-bfd-types.yang module, first defined in YANG Data Model for Bidirectional Forward
Detection (BFD). The updated module carries two new
authentication type enum definitions, 'null' with a suggested
value of 6, and 'meticulous-keyed-isaac' with a suggested
value of 7. This module should replace the version that
currently exists in the IANA registry.
file "iana-bfd-types@2024-02-05.yang"
=============== NOTE: '\' line wrapping per RFC 8792 ===============
module iana-bfd-types {
yang-version 1.1;
namespace "urn:ietf:params:xml:ns:yang:iana-bfd-types";
prefix iana-bfd-types;
organization
"IANA";
contact
"Internet Assigned Numbers Authority
Postal: ICANN
12025 Waterfront Drive, Suite 300
Los Angeles, CA 90094-2536
United States of America
Tel: +1 310 301 5800
";
description
"This module defines YANG data types for IANA-registered
BFD parameters.
This YANG module is maintained by IANA and reflects the
'BFD Diagnostic Codes' and 'BFD Authentication Types'
registries.
Copyright (c) 2021 IETF Trust and the persons identified as
authors of the code. All rights reserved.
Redistribution and use in source and binary forms, with or
without modification, is permitted pursuant to, and subject to
the license terms contained in, the Simplified BSD License set
forth in Section 4.c of the IETF Trust's Legal Provisions
Relating to IETF Documents
(https://trustee.ietf.org/license-info).
This version of this YANG module is part of RFC 9127; see the
RFC itself for full legal notices.";
reference
"RFC 9127: YANG Data Model for Bidirectional Forwarding
Detection (BFD)";
revision 2024-02-05 {
description
"Add NULL and Meticulous ISAAC authentication type.";
reference
"I-D.ietf-bfd-optimized-auth: Optimizing BFD Authentication.";
}
revision 2021-10-21 {
description
"Initial revision.";
reference
"RFC 9127: YANG Data Model for Bidirectional Forwarding
Detection (BFD)";
}
/*
* Type definitions
*/
typedef diagnostic {
type enumeration {
enum none {
value 0;
description
"No Diagnostic.";
}
enum control-expiry {
value 1;
description
"Control Detection Time Expired.";
}
enum echo-failed {
value 2;
description
"Echo Function Failed.";
}
enum neighbor-down {
value 3;
description
"Neighbor Signaled Session Down.";
}
enum forwarding-reset {
value 4;
description
"Forwarding Plane Reset.";
}
enum path-down {
value 5;
description
"Path Down.";
}
enum concatenated-path-down {
value 6;
description
"Concatenated Path Down.";
}
enum admin-down {
value 7;
description
"Administratively Down.";
}
enum reverse-concatenated-path-down {
value 8;
description
"Reverse Concatenated Path Down.";
}
enum mis-connectivity-defect {
value 9;
description
"Mis-connectivity defect.";
reference
"RFC 5880: Bidirectional Forwarding Detection (BFD)
RFC 6428: Proactive Connectivity Verification, Continuity
Check, and Remote Defect Indication for the MPLS Transpo\
rt
Profile";
}
}
description
"BFD diagnostic codes as defined in RFC 5880. Values are
maintained in the 'BFD Diagnostic Codes' IANA registry.
Range is 0 to 31.";
reference
"RFC 5880: Bidirectional Forwarding Detection (BFD)";
}
typedef auth-type {
type enumeration {
enum reserved {
value 0;
description
"Reserved.";
}
enum simple-password {
value 1;
description
"Simple Password.";
}
enum keyed-md5 {
value 2;
description
"Keyed MD5.";
}
enum meticulous-keyed-md5 {
value 3;
description
"Meticulous Keyed MD5.";
}
enum keyed-sha1 {
value 4;
description
"Keyed SHA1.";
}
enum meticulous-keyed-sha1 {
value 5;
description
"Meticulous Keyed SHA1.";
}
enum null {
value 6;
description
"NULL Auth.";
}
enum meticulous-keyed-isaac {
value 7;
description
"Meticulous Keyed ISAAC.";
}
}
description
"BFD authentication type as defined in RFC 5880. Values are
maintained in the 'BFD Authentication Types' IANA registry.
Range is 0 to 255.";
reference
"RFC 5880: Bidirectional Forwarding Detection (BFD)";
}
}
]]>
This section tries to show some examples in how the model can
be configured.
This example demonstrates how a Single Hop BFD session can
be configured for optimized authentication.
bfd-auth-config"An example for BFD Optimized Auth configuration."\
552017-01-01T00:00:00Z2017-02-01T00:00:00Z2016-12-31T23:59:55Z2017-02-01T00:00:05Zopt-auth:meti\
culous-keyed-isaactestvectoreth0if-type:ethernetCsmacdbfd-types:bfdv1name:BFDeth02001:db8:0:113::10110000
10000
truetrue
30000
bfd-auth-config
]]>