rfc9747.original   rfc9747.txt 
BFD Working Group W. Cheng Internet Engineering Task Force (IETF) W. Cheng
Internet-Draft R. Wang Request for Comments: 9747 R. Wang
Updates: 5880 (if approved) China Mobile Updates: 5880 China Mobile
Intended status: Standards Track X. Min, Ed. Category: Standards Track X. Min, Ed.
Expires: 13 June 2025 ZTE Corp. ISSN: 2070-1721 ZTE Corp.
R. Rahman R. Rahman
Equinix Equinix
R. Boddireddy R. Boddireddy
Juniper Networks Juniper Networks
10 December 2024 March 2025
Unaffiliated Bidirectional Forwarding Detection (BFD) Echo Unaffiliated Bidirectional Forwarding Detection (BFD) Echo
draft-ietf-bfd-unaffiliated-echo-14
Abstract Abstract
This document specifies an extension to the Bidirectional Forwarding This document specifies an extension to the Bidirectional Forwarding
Detection (BFD) protocol that enables the use of the BFD Echo Detection (BFD) protocol that enables the use of the BFD Echo
function without the need for an associated BFD control session. function without the need for an associated BFD control session.
This "Unaffiliated BFD Echo" mechanism allows rapid detection of This "Unaffiliated BFD Echo" mechanism allows rapid detection of
forwarding path failures in networks where establishing BFD control forwarding path failures in networks where establishing BFD control
sessions is impractical or undesirable. By decoupling the Echo sessions is impractical or undesirable. By decoupling the Echo
function from the control plane, network devices can utilize BFD's function from the control plane, network devices can utilize BFD's
fast failure detection capabilities in a simplified manner, enhancing fast failure detection capabilities in a simplified manner, enhancing
network resiliency and operational efficiency. network resiliency and operational efficiency.
This document updates RFC 5880 by defining a new Unaffiliated BFD This document updates RFC 5880 by defining a new Unaffiliated BFD
Echo mechanism. Echo mechanism.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on 13 June 2025. 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/rfc9747.
Copyright Notice Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction
1.1. Conventions Used in This Document . . . . . . . . . . . . 4 1.1. Conventions Used in This Document
2. Unaffiliated BFD Echo Procedures . . . . . . . . . . . . . . 4 2. Unaffiliated BFD Echo Procedures
3. Updates to RFC 5880 . . . . . . . . . . . . . . . . . . . . . 7 3. Updates to RFC 5880
4. Operational Considerations . . . . . . . . . . . . . . . . . 10 4. Operational Considerations
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 5. Security Considerations
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 6. IANA Considerations
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11 7. References
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 11 7.1. Normative References
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11 7.2. Informative References
9.1. Normative References . . . . . . . . . . . . . . . . . . 11 Acknowledgements
9.2. Informative References . . . . . . . . . . . . . . . . . 12 Contributors
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 Authors' Addresses
1. Introduction 1. Introduction
To minimize the impact of device and link faults on services and to To minimize the impact of device and link faults on services and to
improve network availability in single-hop scenarios, a network improve network availability in single-hop scenarios, a network
device needs the capability to quickly detect communication faults device needs the capability to quickly detect communication faults
with adjacent devices. Prompt detection allows for timely remedial with adjacent devices. Prompt detection allows for timely remedial
actions to ensure service continuity. actions to ensure service continuity.
BFD [RFC5880] provides a low-overhead, short-interval method for BFD [RFC5880] provides a low-overhead, short-interval method for
detecting faults on the communication path between adjacent detecting faults on the communication path between adjacent
forwarding engines, which may include interfaces, data links, and the forwarding engines, which may include interfaces, data links, and the
forwarding engines themselves. BFD offers a unified mechanism to forwarding engines themselves. BFD offers a unified mechanism to
monitor any media and protocol layers in real time. monitor any media and protocol layers in real time.
BFD defines two primary modes-Asynchronous mode and Demand mode-to BFD defines two primary modes -- Asynchronous mode and Demand mode --
accommodate various deployment scenarios. Additionally, it supports to accommodate various deployment scenarios. Additionally, it
an Echo function that reduces the level of BFD support required in supports an Echo function that reduces the level of BFD support
device implementations, as described in Section 3.2 of [RFC5880]. required in device implementations, as described in Section 3.2 of
[RFC5880]. When the Echo function is activated, the local system
When the Echo function is activated, the local system sends BFD Echo sends BFD Echo packets, and the remote system loops back the received
packets, and the remote system loops back the received Echo packets Echo packets through the forwarding path, as described in Section 5
through the forwarding path, as described in Section 5 of [RFC5880] of [RFC5880] and Section 4 of [RFC5881]. If several consecutive BFD
and Section 4 of [RFC5881]. If several consecutive BFD Echo packets Echo packets are not received by the local system, the BFD session is
are not received by the local system, the BFD session is declared declared Down.
Down.
There are two typical scenarios when using the BFD Echo function: There are two typical scenarios when using the BFD Echo function:
* Full BFD protocol capability with adjunct Echo function * Full BFD protocol capability with adjunct Echo function
(Affiliated BFD Echo): This scenario requires both the local (Affiliated BFD Echo): This scenario requires both the local
device and the adjacent device to support the full BFD protocol. device and the adjacent device to support the full BFD protocol.
This operation remains unchanged from [RFC5880]. This operation remains unchanged from [RFC5880].
* BFD Echo-Only method without full BFD protocol capability * BFD Echo-Only method without full BFD protocol capability
(Unaffiliated BFD Echo): This scenario requires only the local (Unaffiliated BFD Echo): This scenario requires only the local
skipping to change at page 3, line 35 skipping to change at line 123
method requires the local device to send packets with one of its method requires the local device to send packets with one of its
own IP addresses as the destination address, upon receipt of which own IP addresses as the destination address, upon receipt of which
the adjacent device loops them back to the local device. Also the adjacent device loops them back to the local device. Also
note that this method monitors the connectivity to a device over a note that this method monitors the connectivity to a device over a
specific interface and does not verify the availability of a specific interface and does not verify the availability of a
specific IP address at that device. specific IP address at that device.
This document specifies the Unaffiliated BFD Echo scenario. This document specifies the Unaffiliated BFD Echo scenario.
Section 5 of [RFC5880] indicates that the payload of an Affiliated Section 5 of [RFC5880] indicates that the payload of an Affiliated
BFD Echo packet is a local matter and, therefore, its contents are BFD Echo packet is a local matter; therefore, its contents are
outside the scope of that specification. This document, however, outside the scope of that specification. This document, however,
specifies the contents of the Unaffiliated BFD Echo packet and the specifies the contents of the Unaffiliated BFD Echo packet and the
procedures for handling them. While this may appear to contravene procedures for handling them. While this may appear to contravene
Section 5 of [RFC5880], the core behavior in that RFC states that the Section 5 of [RFC5880], the core behavior in that RFC states that the
contents of BFD Echo packets are a local matter; this document is contents of BFD Echo packets are a local matter; this document is
defining that "local matter". Regarding the selection of IP defining that "local matter". Regarding the selection of IP
addresses, the rules stated in Section 4 of [RFC5881] are applicable addresses, the rules stated in Section 4 of [RFC5881] are applicable
to the encapsulation of an Unaffiliated BFD Echo packet. to the encapsulation of an Unaffiliated BFD Echo packet.
Section 6.2.2 of [BBF-TR-146] describes a use case for the Section 6.2.2 of [BBF-TR-146] describes a use case for the
Unaffiliated BFD Echo. Unaffiliated BFD Echo.
This document updates [RFC5880] by defining a new method of BFD Echo- This document updates [RFC5880] by defining a new method of BFD Echo-
only operation which only impacts the BFD Echo packets sender without only operation which only impacts the sender of BFD Echo packets
requiring an implementation to support the BFD protocol at the loop- without requiring an implementation to support the BFD protocol at
back device, such that any IP forwarder can loop-back the BFD Echo the loopback device, such that any IP forwarder can loop back the BFD
packets. It specifies the use of the Unaffiliated BFD Echo over IPv4 Echo packets. It specifies the use of the Unaffiliated BFD Echo over
and IPv6 for a single IP hop. The reason why it cannot be used for IPv4 and IPv6 for a single IP hop. The reason why it cannot be used
multihop paths is that the Unaffiliated BFD Echo packets would be for multihop paths is that the Unaffiliated BFD Echo packets would be
looped back by the first hop. A full description of the updates to looped back by the first hop. A full description of the updates to
[RFC5880] is provided in Section 3. [RFC5880] is provided in Section 3.
1.1. Conventions Used in This Document 1.1. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2. Unaffiliated BFD Echo Procedures 2. Unaffiliated BFD Echo Procedures
This section specifies the Unaffiliated BFD Echo procedures. This section specifies the Unaffiliated BFD Echo procedures.
Device A Device B Device A Device B
+----------------+ +----------------+ +----------------+ +----------------+
| | | | | | | |
| |------------| | | | |------------| | |
skipping to change at page 4, line 38 skipping to change at line 175
| | | Unaffiliated BFD Echo | | | | | Unaffiliated BFD Echo | |
| | -------------------------------| BFD | | | -------------------------------| BFD |
| | | | packets | | | | | packets |
| | <-------------------------------| looped | | | <-------------------------------| looped |
| |------------| | | | |------------| | |
| | | | | | | |
| | | | | | | |
+----------------+ +----------------+ +----------------+ +----------------+
BFD supported BFD not supported BFD supported BFD not supported
Figure 1: Unaffiliated BFD Echo diagram Figure 1: Unaffiliated BFD Echo
As shown in Figure 1, device A supports BFD, whereas device B is a As shown in Figure 1, device A supports BFD, whereas device B is a
regular IP forwarder that does not support BFD. Device A would send regular IP forwarder that does not support BFD. Device A would send
Unaffiliated BFD Echo packets, and after receiving the Unaffiliated Unaffiliated BFD Echo packets, and after receiving the Unaffiliated
BFD Echo packets sent from device A, the one-hop-away BFD peer device BFD Echo packets sent from device A, the one-hop-away BFD peer device
B immediately loops them back by normal IP forwarding, this allows B immediately loops them back by normal IP forwarding. This allows
device A to rapidly detect a connectivity loss to device B. Note device A to rapidly detect a connectivity loss to device B. Note
that device B would not intercept any received Unaffiliated BFD Echo that device B would not intercept any received Unaffiliated BFD Echo
packet or parse any BFD protocol field within the Unaffiliated BFD packet or parse any BFD protocol field within the Unaffiliated BFD
Echo packet. Echo packet.
An Unaffiliated BFD Echo session is not actually a BFD session An Unaffiliated BFD Echo session is not actually a BFD session
because there is no coordination of BFD protocol state between the because there is no coordination of BFD protocol state between the
two link ends: the remote end does not support BFD and so cannot two link ends: the remote end does not support BFD and so cannot
engage in a BFD session. The local end as an initiator may regard engage in a BFD session. From the standpoint of the local end (as an
the Unaffiliated BFD Echo session as a BFD session from its own initiator), the Unaffiliated BFD Echo session may be regarded as a
standpoint. BFD session.
For the Unaffiliated Echo procedure, an Unaffiliated BFD Echo session For the Unaffiliated Echo procedure, an Unaffiliated BFD Echo session
is established on device A. The session MUST adhere to the BFD state is established on device A. The session MUST adhere to the BFD state
machine specified in Section 6.2 of [RFC5880], with the exception machine specified in Section 6.2 of [RFC5880], with the exception
that the received state is not derived from BFD Control packets that the received state is not derived from BFD Control packets
originating from the remote system, but rather from packets that are originating from the remote system, but rather from packets that are
generated by the local system and looped back from the remote system. generated by the local system and looped back from the remote system.
Consequently, the AdminDown state is not utilized in Unaffiliated BFD Consequently, the AdminDown state is not utilized in Unaffiliated BFD
Echo. Echo.
BFD Control packets are transmitted and received as Unaffiliated BFD BFD Control packets are transmitted and received as Unaffiliated BFD
Echo packets, using UDP destination port 3785, as defined in Echo packets, using UDP destination port 3785, as defined in
[RFC5881]. The standard procedures for BFD Asynchronous sessions are [RFC5881]. The standard procedures for BFD Asynchronous sessions are
applied to the looped BFD Control packets, including packet applied to the looped BFD Control packets, including packet
validation and authentication, in accordance with [RFC5880]. validation and authentication, in accordance with [RFC5880].
Once an Unaffiliated BFD Echo session is created on device A, it Once an Unaffiliated BFD Echo session is created on device A, it
starts sending Unaffiliated BFD Echo packets. Unaffiliated BFD Echo starts sending Unaffiliated BFD Echo packets. Unaffiliated BFD Echo
packets with zeroed "Your Discriminator" field are demultiplexed to packets with zeroed "Your Discriminator" field are demultiplexed to
the proper session based on the source IP address or UDP source port, the proper session based on the source IP address or UDP source port.
once the remote system loops back the local discriminator, all After the remote system loops back the local discriminator, all
further received packets are demultiplexed based on the "Your further received packets are demultiplexed based on the "Your
Discriminator" field only, which is conformed to the procedure Discriminator" field only, which conforms to the procedure specified
specified in Section 6.3 of [RFC5880]. An Unaffiliated BFD Echo in Section 6.3 of [RFC5880]. An Unaffiliated BFD Echo packet follows
packet follows the same encapsulation rules as for a BFD Echo packet the same encapsulation rules as for a BFD Echo packet as specified in
as specified in Section 4 of [RFC5881]. All Unaffiliated BFD Echo Section 4 of [RFC5881]. All Unaffiliated BFD Echo packets for the
packets for the session MUST be sent with a TTL or Hop Limit value of session MUST be sent with a TTL or Hop Limit value of 255. Received
255. Received packets MUST have a TTL or Hop Limit value of 254 packets MUST have a TTL or Hop Limit value of 254 (similar to
(similar to Appendix A of [RFC5082] to verify against a configured Appendix A of [RFC5082] to verify against a configured number of
number of hops); otherwise, the received packets MUST be dropped. hops); otherwise, the received packets MUST be dropped.
In the context of an Unaffiliated BFD Echo packet, the "Desired Min In the context of an Unaffiliated BFD Echo packet, the "Desired Min
TX Interval" and "Required Min RX Interval" fields, as defined in TX Interval" and "Required Min RX Interval" fields, as defined in
[RFC5880], MUST be populated with a specific value to prevent the [RFC5880], MUST be populated with a specific value to prevent the
potential exposure of uninitialized memory. It is RECOMMENDED that potential exposure of uninitialized memory. It is RECOMMENDED that
these fields be set to a value of 1 second (1,000,000 microseconds). these fields be set to a value of 1 second (1,000,000 microseconds).
However, upon receipt, these values MUST be ignored and MUST NOT be However, upon receipt, these values MUST be ignored and MUST NOT be
used in the calculation of the Detection Time. used in the calculation of the Detection Time.
The "Required Min Echo RX Interval" field, as defined in [RFC5880], The "Required Min Echo RX Interval" field, as defined in [RFC5880],
skipping to change at page 6, line 21 skipping to change at line 252
by default on hosts. The method for provisioning device B to loop by default on hosts. The method for provisioning device B to loop
back Unaffiliated BFD Echo packets is outside the scope of this back Unaffiliated BFD Echo packets is outside the scope of this
document. document.
Similar to what's specified in [RFC5880], the Unaffiliated BFD Echo Similar to what's specified in [RFC5880], the Unaffiliated BFD Echo
session begins with the periodic, slow transmission of Unaffiliated session begins with the periodic, slow transmission of Unaffiliated
BFD Echo packets. The slow transmission rate should be no greater BFD Echo packets. The slow transmission rate should be no greater
than one packet per second, until the session on device A is Up. than one packet per second, until the session on device A is Up.
After the session is Up, the provisioned transmission interval is After the session is Up, the provisioned transmission interval is
used. When the Unaffiliated BFD Echo session on device A goes Down, used. When the Unaffiliated BFD Echo session on device A goes Down,
the slow transmission rate is resumed. The "Detect Mult" defined in the slow transmission rate is resumed. The "Detect Mult" field
[RFC5880] MUST be set to a value provisioned on device A. When the defined in [RFC5880] MUST be set to a value provisioned on device A.
bfd.SessionState is Up and a "Detect Mult" number of Unaffiliated BFD When the bfd.SessionState is Up and a "Detect Mult" number of
Echo packets have not arrived at device A as they should, the device Unaffiliated BFD Echo packets have not arrived at device A as they
A "MUST set bfd.SessionState to Down and bfd.LocalDiag to 2 (Echo should, the device A "MUST set bfd.SessionState to Down and
Function Failed)", as specified in Section 6.8.5 of [RFC5880]. bfd.LocalDiag to 2 (Echo Function Failed)", as specified in
Section 6.8.5 of [RFC5880].
In summary, the Unaffiliated BFD Echo packet reuses the format of the In summary, the Unaffiliated BFD Echo packet reuses the format of the
BFD Control packet defined in [RFC5880], and the fields within the BFD Control packet defined in [RFC5880], and the fields within the
Unaffiliated BFD Echo packet are populated as follows: Unaffiliated BFD Echo packet are populated as follows:
* My Discriminator: MUST be set to the provisioned local * My Discriminator: MUST be set to the provisioned local
discriminator. discriminator.
* Your Discriminator: MUST initially be set to 0, and then MUST be * Your Discriminator: MUST initially be set to 0, and then MUST be
set to the value of "My Discriminator" looped back from the remote set to the value of "My Discriminator" looped back from the remote
skipping to change at page 7, line 20 skipping to change at line 298
Echo operation, only the local system has the BFD protocol enabled, Echo operation, only the local system has the BFD protocol enabled,
while the remote system simply loops back the received BFD Echo while the remote system simply loops back the received BFD Echo
packets as ordinary data packets, without engaging in the BFD packets as ordinary data packets, without engaging in the BFD
protocol. protocol.
This document updates [RFC5880] with respect to its descriptions on This document updates [RFC5880] with respect to its descriptions on
the BFD Echo function as follows. the BFD Echo function as follows.
The 4th paragraph of Section 3.2 of [RFC5880] is updated as below: The 4th paragraph of Section 3.2 of [RFC5880] is updated as below:
OLD TEXT OLD TEXT
An adjunct to both modes is the Echo function.
NEW TEXT | An adjunct to both modes is the Echo function.
An adjunct to both modes is the Echo function, which can also be
running independently.
OLD TEXT NEW TEXT
Since the Echo function is handling the task of detection, the
rate of periodic transmission of Control packets may be reduced
(in the case of Asynchronous mode) or eliminated completely (in
the case of Demand mode).
NEW TEXT | An adjunct to both modes is the Echo function, which can also be
Since the Echo function is handling the task of detection, the | running independently.
rate of periodic transmission of Control packets may be reduced
(in the case of Asynchronous mode) or eliminated completely (in OLD TEXT
the case of Demand mode). The Echo function may also be used
independently, with neither Asynchronous nor Demand mode. | Since the Echo function is handling the task of detection, the
| rate of periodic transmission of Control packets may be reduced
| (in the case of Asynchronous mode) or eliminated completely (in
| the case of Demand mode).
NEW TEXT
| Since the Echo function is handling the task of detection, the
| rate of periodic transmission of Control packets may be reduced
| (in the case of Asynchronous mode) or eliminated completely (in
| the case of Demand mode). The Echo function may also be used
| independently, with neither Asynchronous nor Demand mode.
The 3rd and 9th paragraphs of Section 6.1 of [RFC5880] are updated as The 3rd and 9th paragraphs of Section 6.1 of [RFC5880] are updated as
below: below:
OLD TEXT OLD TEXT
Once the BFD session is Up, a system can choose to start the Echo
function if it desires and the other system signals that it will
allow it. The rate of transmission of Control packets is
typically kept low when the Echo function is active.
NEW TEXT | Once the BFD session is Up, a system can choose to start the Echo
When a system is running with Asynchronous or Demand mode, once | function if it desires and the other system signals that it will
the BFD session is Up, it can choose to start the Echo function if | allow it. The rate of transmission of Control packets is
it desires and the other system signals that it will allow it. | typically kept low when the Echo function is active.
The rate of transmission of Control packets is typically kept low NEW TEXT
for Asynchronous mode or eliminated completely for Demand mode
when the Echo function is active.
OLD TEXT | When a system is running with Asynchronous or Demand mode, once
If the session goes Down, the transmission of Echo packets (if | the BFD session is Up, it can choose to start the Echo function if
any) ceases, and the transmission of Control packets goes back to | it desires and the other system signals that it will allow it.
the slow rate. | The rate of transmission of Control packets is typically kept low
| for Asynchronous mode or eliminated completely for Demand mode
| when the Echo function is active.
NEW TEXT OLD TEXT
In Asynchronous mode or Demand mode, if the session goes Down, the
transmission of Echo packets (if any) ceases, and the transmission | If the session goes Down, the transmission of Echo packets (if
of Control packets goes back to the slow rate. | any) ceases, and the transmission of Control packets goes back to
| the slow rate.
NEW TEXT
| In Asynchronous mode or Demand mode, if the session goes Down, the
| transmission of Echo packets (if any) ceases, and the transmission
| of Control packets goes back to the slow rate.
The 2nd paragraph of Section 6.4 of [RFC5880] is updated as below: The 2nd paragraph of Section 6.4 of [RFC5880] is updated as below:
OLD TEXT OLD TEXT
When a system is using the Echo function, it is advantageous to
choose a sedate reception rate for Control packets, since liveness
detection is being handled by the Echo packets. This can be
controlled by manipulating the Required Min RX Interval field (see
section 6.8.3).
NEW TEXT | When a system is using the Echo function, it is advantageous to
When a system is using the Echo function with Asynchronous mode, | choose a sedate reception rate for Control packets, since liveness
it is advantageous to choose a sedate reception rate for Control | detection is being handled by the Echo packets. This can be
packets, since liveness detection is being handled by the Echo | controlled by manipulating the Required Min RX Interval field (see
packets. This can be controlled by manipulating the Required Min | section 6.8.3).
RX Interval field (see section 6.8.3). Note that a system
operating in Demand mode would direct the remote system to cease NEW TEXT
the periodic transmission of BFD Control packets, by setting the
Demand (D) bit in its BFD Control packets. | When a system is using the Echo function with Asynchronous mode,
| it is advantageous to choose a sedate reception rate for Control
| packets, since liveness detection is being handled by the Echo
| packets. This can be controlled by manipulating the Required Min
| RX Interval field (see section 6.8.3). Note that a system
| operating in Demand mode would direct the remote system to cease
| the periodic transmission of BFD Control packets, by setting the
| Demand (D) bit in its BFD Control packets.
The 2nd paragraph of Section 6.8 of [RFC5880] is updated as below: The 2nd paragraph of Section 6.8 of [RFC5880] is updated as below:
OLD TEXT OLD TEXT
When a system is said to have "the Echo function active" it means
that the system is sending BFD Echo packets, implying that the
session is Up and the other system has signaled its willingness to
loop back Echo packets.
NEW TEXT | When a system is said to have "the Echo function active" it means
When a system in Asynchronous or Demand mode is said to have "the | that the system is sending BFD Echo packets, implying that the
Echo function active" it means that the system is sending BFD Echo | session is Up and the other system has signaled its willingness to
packets, implying that the session is Up and the other system has | loop back Echo packets.
signaled its willingness to loop back Echo packets.
NEW TEXT
| When a system in Asynchronous or Demand mode is said to have "the
| Echo function active" it means that the system is sending BFD Echo
| packets, implying that the session is Up and the other system has
| signaled its willingness to loop back Echo packets.
The 7th paragraph of Section 6.8.3 of [RFC5880] is updated as below: The 7th paragraph of Section 6.8.3 of [RFC5880] is updated as below:
OLD TEXT OLD TEXT
When the Echo function is active, a system SHOULD set
bfd.RequiredMinRxInterval to a value of not less than one second
(1,000,000 microseconds). This is intended to keep received BFD
Control traffic at a negligible level, since the actual detection
function is being performed using BFD Echo packets.
NEW TEXT | When the Echo function is active, a system SHOULD set
When the Echo function is active with Asynchronous mode, a system | bfd.RequiredMinRxInterval to a value of not less than one second
SHOULD set bfd.RequiredMinRxInterval to a value of not less than | (1,000,000 microseconds). This is intended to keep received BFD
one second (1,000,000 microseconds). This is intended to keep | Control traffic at a negligible level, since the actual detection
received BFD Control traffic at a negligible level, since the | function is being performed using BFD Echo packets.
actual detection function is being performed using BFD Echo
packets. A system operating in Demand mode would not receive BFD NEW TEXT
Control traffic.
| When the Echo function is active with Asynchronous mode, a system
| SHOULD set bfd.RequiredMinRxInterval to a value of not less than
| one second (1,000,000 microseconds). This is intended to keep
| received BFD Control traffic at a negligible level, since the
| actual detection function is being performed using BFD Echo
| packets. A system operating in Demand mode would not receive BFD
| Control traffic.
The 1st and 2nd paragraphs of Section 6.8.9 of [RFC5880] are updated The 1st and 2nd paragraphs of Section 6.8.9 of [RFC5880] are updated
as below: as below:
OLD TEXT OLD TEXT
BFD Echo packets MUST NOT be transmitted when bfd.SessionState is
not Up. BFD Echo packets MUST NOT be transmitted unless the last
BFD Control packet received from the remote system contains a
nonzero value in Required Min Echo RX Interval.
NEW TEXT | BFD Echo packets MUST NOT be transmitted when bfd.SessionState is
When a system is using the Echo function with either Asynchronous | not Up. BFD Echo packets MUST NOT be transmitted unless the last
or Demand mode, BFD Echo packets MUST NOT be transmitted when | BFD Control packet received from the remote system contains a
bfd.SessionState is not Up, and BFD Echo packets MUST NOT be | nonzero value in Required Min Echo RX Interval.
transmitted unless the last BFD Control packet received from the |
remote system contains a nonzero value in Required Min Echo RX | BFD Echo packets MAY be transmitted when bfd.SessionState is Up.
Interval. | The interval between transmitted BFD Echo packets MUST NOT be less
| than the value advertised by the remote system in Required Min
| Echo RX Interval, except as follows: [...]
OLD TEXT NEW TEXT
BFD Echo packets MAY be transmitted when bfd.SessionState is Up.
The interval between transmitted BFD Echo packets MUST NOT be less
than the value advertised by the remote system in Required Min
Echo RX Interval...
NEW TEXT | When a system is using the Echo function with either Asynchronous
When a system is using the Echo function with either Asynchronous | or Demand mode, BFD Echo packets MUST NOT be transmitted when
or Demand mode, BFD Echo packets MAY be transmitted when | bfd.SessionState is not Up, and BFD Echo packets MUST NOT be
bfd.SessionState is Up, and the interval between transmitted BFD | transmitted unless the last BFD Control packet received from the
Echo packets MUST NOT be less than the value advertised by the | remote system contains a nonzero value in Required Min Echo RX
remote system in Required Min Echo RX Interval... | Interval.
|
| When a system is using the Echo function with either Asynchronous
| or Demand mode, BFD Echo packets MAY be transmitted when
| bfd.SessionState is Up, and the interval between transmitted BFD
| Echo packets MUST NOT be less than the value advertised by the
| remote system in Required Min Echo RX Interval, except as follows:
| [...]
4. Operational Considerations 4. Operational Considerations
All Operational Considerations from [RFC5880] apply. Since this All operational considerations from [RFC5880] apply. Since this
mechanism leverages existing BFD machinery, particularly periodic mechanism leverages existing BFD machinery, particularly periodic
pacing of traffic based on configuration, there's no real possibility pacing of traffic based on configuration, there's no real possibility
to create congestion. Moreover, creating congestion would be counter to create congestion. Moreover, creating congestion would be
productive to check the bidirectional connectivity. counterproductive to checking the bidirectional connectivity.
Some devices that would benefit from the use of BFD may be unable to Some devices that would benefit from the use of BFD may be unable to
support the full BFD protocol. Examples of such devices include support the full BFD protocol. Examples of such devices include
servers running virtual machines, or Internet of Things (IoT) servers running virtual machines, or Internet of Things (IoT)
devices. By using Unaffiliated BFD Echo, these devices only need to devices. By using Unaffiliated BFD Echo, these devices only need to
support a basic loopback function. support a basic loopback function.
As specified in Section 2 of this document, some configuration is As specified in Section 2 of this document, some configuration is
needed to make the Unaffiliated BFD Echo work, although the needed to make the Unaffiliated BFD Echo work, although the
configuration won't go beyond the scope of [RFC5880]. At a BFD- configuration won't go beyond the scope of [RFC5880]. At a BFD-
enabled local system, the Unaffiliated BFD Echo session can coexist enabled local system, the Unaffiliated BFD Echo session can coexist
with other type of BFD session, in which scenario the remote system with other types of BFD sessions. In that scenario, the remote
for the Unaffiliated BFD Echo session must be different from the system for the Unaffiliated BFD Echo session must be different from
remote system for other type of BFD session, and the local system's the remote system for any other type of BFD session, and the local
discriminators for different BFD sessions must be different, at the system's discriminators for different BFD sessions must be different.
same time it's not necessary for the local system to differentiate At the same time, it's not necessary for the local system to
the Unaffiliated BFD Echo session from other type of BFD session. differentiate the Unaffiliated BFD Echo session from the other types
of BFD sessions.
5. Security Considerations 5. Security Considerations
All Security Considerations from [RFC5880] and [RFC5881] apply. All security considerations from [RFC5880] and [RFC5881] apply.
Unaffiliated BFD Echo requires the remote device to loop Unaffiliated Unaffiliated BFD Echo requires the remote device to loop Unaffiliated
BFD Echo packets. In order to provide this service, the remote BFD Echo packets. In order to provide this service, the remote
device cannot make use of Unicast Strict Reverse Path Forwarding device cannot make use of Unicast Strict Reverse Path Forwarding
(RPF) [RFC3704], otherwise the Unaffiliated BFD Echo packets might (RPF) [RFC3704], otherwise the Unaffiliated BFD Echo packets might
not pass the RPF check at the remote device. not pass the RPF check at the remote device.
As described in Section 5 of [RFC5880], BFD Echo packets may be As described in Section 5 of [RFC5880], BFD Echo packets may be
spoofed. Specifically for Unaffiliated BFD Echo, a DoS attacker may spoofed. Specifically for Unaffiliated BFD Echo, a DoS attacker may
send spoofed Unaffiliated BFD Echo packets to the loop-back device, send spoofed Unaffiliated BFD Echo packets to the loopback device, so
so some form of authentication SHOULD be included. Considering the some form of authentication SHOULD be included. Considering the
Unaffiliated BFD Echo packets in this document are also BFD Control Unaffiliated BFD Echo packets in this document are also BFD Control
packets, the "Authentication Section" as defined in [RFC5880] for BFD packets, the "Authentication Section" as defined in [RFC5880] for a
Control packet is RECOMMENDED to be included within the Unaffiliated BFD Control packet is RECOMMENDED to be included within the
BFD Echo packet. Unaffiliated BFD Echo packet.
As stated in Section 2, in order to avoid unset values being a As stated in Section 2, in order to avoid unset values being a
potential vector for disclosure of uninitialized memory, all fields potential vector for disclosure of uninitialized memory, all fields
of the Unaffiliated BFD Echo packet MUST be populated with a certain of the Unaffiliated BFD Echo packet MUST be populated with a certain
value, even if some of the fields are ignored on receipt. value, even if some of the fields are ignored on receipt.
6. IANA Considerations 6. IANA Considerations
This document has no IANA action requested. This document has no IANA actions.
7. Acknowledgements
The authors would like to acknowledge Ketan Talaulikar, Greg Mirsky,
Santosh Pallagatti, Aijun Wang, Eric Vyncke, Adrian Farrel, Tim
Wicinski, Dhruv Dhody, Stephen Farrell, Gunter Van de Velde, Gyan
Mishra, Brian Trammell, Gorry Fairhurst, Mahesh Jethanandani, John
Scudder, Murray Kucherawy, and Zaheduzzaman Sarker for their careful
review and very helpful comments.
The authors would like to acknowledge Jeff Haas for his guidance,
insightful review, and very helpful comments.
The authors would like to acknowledge Erik Auerswald for his
insightful comments during the discussion of this document.
The authors would like to acknowledge Detao Zhao for the very helpful
discussion.
8. Contributors
Liu Aihua
ZTE
Email: liu.aihua@zte.com.cn
Qian Xin
ZTE
Email: qian.xin2@zte.com.cn
Zhao Yanhua
ZTE
Email: zhao.yanhua3@zte.com.cn
9. References 7. References
9.1. Normative References 7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>. <https://www.rfc-editor.org/info/rfc5880>.
[RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
DOI 10.17487/RFC5881, June 2010, DOI 10.17487/RFC5881, June 2010,
<https://www.rfc-editor.org/info/rfc5881>. <https://www.rfc-editor.org/info/rfc5881>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
9.2. Informative References 7.2. Informative References
[BBF-TR-146] [BBF-TR-146]
Broadband Forum, "BBF Technical Report - Subscriber Broadband Forum, "TR-146: Subscriber Sessions", Broadband
Sessions Issue 1", 2013, <https://www.broadband- Forum Technical Report, TR-146, Issue 1, May 2013,
forum.org/technical/download/TR-146.pdf>. <https://www.broadband-forum.org/pdfs/tr-146-1-0-0.pdf>.
[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed [RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", BCP 84, RFC 3704, DOI 10.17487/RFC3704, March Networks", BCP 84, RFC 3704, DOI 10.17487/RFC3704, March
2004, <https://www.rfc-editor.org/info/rfc3704>. 2004, <https://www.rfc-editor.org/info/rfc3704>.
[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C. [RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
Pignataro, "The Generalized TTL Security Mechanism Pignataro, "The Generalized TTL Security Mechanism
(GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007, (GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,
<https://www.rfc-editor.org/info/rfc5082>. <https://www.rfc-editor.org/info/rfc5082>.
Acknowledgements
The authors would like to acknowledge Ketan Talaulikar, Greg Mirsky,
Santosh Pallagatti, Aijun Wang, Éric Vyncke, Adrian Farrel, Tim
Wicinski, Dhruv Dhody, Stephen Farrell, Gunter Van de Velde, Gyan
Mishra, Brian Trammell, Gorry Fairhurst, Mahesh Jethanandani, John
Scudder, Murray Kucherawy, and Zaheduzzaman Sarker for their careful
reviews and very helpful comments.
The authors would like to acknowledge Jeff Haas for his guidance,
insightful review, and very helpful comments.
The authors would like to acknowledge Erik Auerswald for his
insightful comments during the discussion of this document.
The authors would like to acknowledge Detao Zhao for the very helpful
discussion.
Contributors
Liu Aihua
ZTE
Email: liu.aihua@zte.com.cn
Qian Xin
ZTE
Email: qian.xin2@zte.com.cn
Zhao Yanhua
ZTE
Email: zhao.yanhua3@zte.com.cn
Authors' Addresses Authors' Addresses
Weiqiang Cheng Weiqiang Cheng
China Mobile China Mobile
Beijing Beijing
China China
Email: chengweiqiang@chinamobile.com Email: chengweiqiang@chinamobile.com
Ruixue Wang Ruixue Wang
China Mobile China Mobile
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