Internet DRAFT - draft-ietf-bfd-unaffiliated-echo
draft-ietf-bfd-unaffiliated-echo
BFD Working Group W. Cheng
Internet-Draft R. Wang
Updates: 5880 (if approved) China Mobile
Intended status: Standards Track X. Min, Ed.
Expires: 31 March 2024 ZTE Corp.
R. Rahman
Equinix
R. Boddireddy
Juniper Networks
28 September 2023
Unaffiliated BFD Echo
draft-ietf-bfd-unaffiliated-echo-10
Abstract
Bidirectional Forwarding Detection (BFD) is a fault detection
protocol that can quickly determine a communication failure between
two forwarding engines. This document proposes a use of the BFD Echo
where the local system supports BFD but the neighboring system does
not support BFD. BFD Control packet and its processing procedures
can be executed over the BFD Echo port where the neighboring system
only loops packets back to the local system.
This document updates RFC 5880.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
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-
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 31 March 2024.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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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
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions Used in This Document . . . . . . . . . . . . 3
2. Unaffiliated BFD Echo Procedures . . . . . . . . . . . . . . 3
3. Updates to RFC 5880 . . . . . . . . . . . . . . . . . . . . . 6
4. Unaffiliated BFD Echo Applicability . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
To minimize the impact of device/link faults on services and improve
network availability, in the single-hop cases a network device needs
to be able to quickly detect faults in communication with adjacent
devices. Measures can then be taken to promptly rectify the faults
to ensure service continuity.
BFD [RFC5880] is a low-overhead, short-duration method to detect
faults on the communication path between adjacent forwarding engines.
The faults can be on interfaces, data link(s), and even the
forwarding engines. It is a single, unified mechanism to monitor any
media and protocol layers in real time.
BFD defines Asynchronous and Demand modes to satisfy various
deployment scenarios. It also supports an Echo function to reduce
the device requirement for BFD. When the Echo function is activated,
the local system sends BFD Echo packets and the remote system loops
back the received Echo packets through the forwarding path. If
several consecutive BFD Echo packets are not received by the local
system, then the BFD session is declared to be Down.
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When using BFD Echo function, there are two typical scenarios as
below:
* Full BFD protocol capability with affiliated Echo function. This
scenario requires both the local device and the neighboring device
to support the full BFD protocol.
* BFD Echo-Only method without full BFD protocol capability. This
scenario requires only the local device to support sending and
demultiplexing BFD Control packets. In this scenario, the BFD
Control packets are sent over the BFD Echo port, but that the
processing procedures for Asynchronous mode are used with the
modifications described in this document. Note that this method
monitors the connectivity to a system over a specific interface
and does not verify the availability of a specific IP address at
that system.
The former scenario is referred to as affiliated BFD Echo, which is
not changed by this document in any way. The latter scenario is
referred to as Unaffiliated BFD Echo, which is specified in this
document.
Section 5 of [RFC5880] indicates that the payload of an affiliated
BFD Echo packet is a local matter and hence its contents are outside
the scope of that specification. This document, on the other hand,
specifies the contents of the Unaffiliated BFD Echo packet and what
to do with them.
Section 6.2.2 of [BBF-TR-146] describes one use case of the
Unaffiliated BFD Echo. Section 2 of [I-D.wang-bfd-one-arm-use-case]
describes another use case of the Unaffiliated BFD Echo.
This document describes the use of the Unaffiliated BFD Echo over
IPv4 and IPv6 for single IP hop.
1.1. Conventions Used in This Document
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. Unaffiliated BFD Echo Procedures
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Device A Device B
BFD Enabled BFD packets looped
+--------+ Unaffiliated BFD Echo session +--------+
| A |---------------------------------------| B |
| |Interface 1 Interface 1| |
+--------+ +--------+
BFD is supported. BFD is not supported.
Figure 1: Unaffiliated BFD Echo diagram
As shown in Figure 1, device A supports BFD, whereas device B does
not support BFD. Device A would send Unaffiliated BFD Echo packets,
and after receiving the Unaffiliated 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 device A to rapidly detect
a connectivity loss to device B. Note that device B would not
intercept any received Unaffiliated BFD Echo packet or parse any BFD
protocol field within the Unaffiliated BFD Echo packet.
For unaffiliated echo, a Unaffiliated BFD Echo session is created on
device A, and the Unaffiliated BFD Echo session MUST follow the BFD
state machine defined in Section 6.2 of [RFC5880], except that the
received state is not sent but looped back from the remote system.
Unaffiliated BFD Echo does not use the AdminDown state. BFD Control
packets are transmitted and received as Unaffiliated BFD Echo packets
using destination UDP port 3785, as defined in [RFC5881]. The
procedures for BFD Async sessions are executed for the looped BFD
Control packets as per [RFC5880], including validation and
authentication.
Once a Unaffiliated BFD Echo session is created on device A, it
starts sending Unaffiliated BFD Echo packets. Unaffiliated BFD Echo
packets with zeroed "Your Discriminator" are demultiplexed to the
proper session based on the source IP address or UDP source port,
once the remote system loops back the local discriminator, all
further received packets are demultiplexed based on the "Your
Discriminator" field only, which is conformed to the procedure
specified in Section 6.3 of [RFC5880]. An Unaffiliated BFD Echo
packet follows the same encapsulation rules as for a BFD Echo packet
as specified in Section 4 of [RFC5881]. All Unaffiliated BFD Echo
packets for the session MUST be sent with a Time to Live (TTL) or Hop
Limit value of 255, and received with a TTL or Hop Limit value of
254, otherwise the received packets MUST be dropped [RFC5082].
Within the Unaffiliated BFD Echo packet, the "Desired Min TX
Interval" and "Required Min RX Interval" defined in [RFC5880] SHOULD
be populated with a certain value, which can avoid unset value being
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a potential vector for disclosure of uninitialized memory. A
suggested value is 1 second (1,000,000 microseconds). These values,
however, MUST be ignored on receipt. Furthermore, these values MUST
NOT be used to calculate the Detection Time.
The "Required Min Echo RX Interval" defined in [RFC5880] SHOULD be
populated with a certain value. A suggested value is 0. This value
MUST be ignored on receipt. The transmission interval for
Unaffiliated BFD Echo packets in the Up state MUST be provisioned on
device A. The Unaffiliated BFD Echo feature depends on device B
performing IP forwarding (actually IP redirect) functionality. While
such functionality may normally be expected to be supported on a
router, it may not be enabled on a host by default. The method for
provisioning device B to loop back Unaffiliated BFD Echo packets is
outside the scope of this document.
Similar to what's specified in [RFC5880], the Unaffiliated BFD Echo
session begins with the periodic, slow transmission of Unaffiliated
BFD Echo packets. The slow transmission rate SHOULD be no less than
one second per packet, until the session is Up. After the session is
Up, the provisioned transmission interval is used. When the
Unaffiliated BFD Echo session goes Down, the slow transmission rate
is resumed. The "Detect Mult" defined in [RFC5880] MUST be set to a
value provisioned on device A. When the bfd.SessionState is Up and a
Detect Mult number of Unaffiliated BFD Echo packets have not arrived
at device A as they should, the device A MUST set bfd.SessionState to
Down and 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
BFD Control packet defined in [RFC5880], and the fields within the
Unaffiliated BFD Echo packet are populated as follows:
* My Discriminator MUST be set to the provisioned local
discriminator.
* Your Discriminator MUST be set to 0 initially, and then MUST be
set to the same as My Discriminator looped back.
* Desired Min TX Interval SHOULD be set to a certain value. A
suggested value is 1 second (1,000,000 microseconds).
* Required Min RX Interval SHOULD be set to a certain value. A
suggested value is 1 second (1,000,000 microseconds).
* Required Min Echo RX Interval SHOULD be set to a certain value. A
suggested value is 0.
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* Detect Mult MUST be set to the provisioned maximum allowable
number of consecutively lost Unaffiliated BFD Echo packets.
3. Updates to RFC 5880
The Unaffiliated BFD Echo described in this document reuses the BFD
Echo function as described in [RFC5880] and [RFC5881], but does not
require BFD Asynchronous or Demand mode. When using the Unaffiliated
BFD Echo, only the local system has the BFD protocol enabled; the
remote system just loops back the received BFD Echo packets as
regular data packets.
This document updates [RFC5880] with respect to its descriptions on
the BFD Echo function as follows.
The 4th paragraph of Section 3.2 of [RFC5880] is updated as below:
OLD TEXT
An adjunct to both modes is the Echo function.
NEW TEXT
An adjunct to both modes is the Echo function, which can also be
running independently.
OLD 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
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
below:
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.
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NEW TEXT
When a system is running with Asynchronous or Demand mode, once
the BFD session is Up, it 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
for Asynchronous mode or eliminated completely for Demand mode
when the Echo function is active.
OLD TEXT
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.
NEW TEXT
In Asynchronous 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. Demand mode MUST NOT be
active if the session goes Down.
The 2nd paragraph of Section 6.4 of [RFC5880] is updated as below:
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 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:
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.
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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:
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 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. While 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
as below:
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
When a system is using the Echo function with either Asynchronous
or Demand mode, BFD Echo packets MUST NOT be transmitted when
bfd.SessionState is not Up, and 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.
OLD 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...
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NEW TEXT
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...
4. Unaffiliated BFD Echo Applicability
Some devices that would benefit from the use of BFD may be unable to
support the full BFD protocol. Examples of such devices include
servers running virtual machines, or Internet of Things (IoT)
devices.
Unaffiliated BFD Echo can be used when two devices are connected and
only one of them supports the BFD protocol, and the other is capable
of looping Unaffiliated BFD Echo packets.
5. Security Considerations
All Security Considerations from [RFC5880] and [RFC5881] apply.
Unaffiliated BFD Echo requires the remote device to loop Unaffiliated
BFD Echo packets. In order to provide this service, the remote
device cannot make use of Unicast Reverse Path Forwarding (URPF)
[RFC3704] [RFC8704] in strict mode.
As specified in Section 5 of [RFC5880], since BFD Echo packets may be
spoofed, some form of authentication SHOULD be included. Considering
the Unaffiliated BFD Echo packets in this document are also BFD
Control packets, the "Authentication Section" as defined in [RFC5880]
for BFD Control packet is RECOMMENDED to be included within the
Unaffiliated BFD Echo packet.
In order to mitigate the potential reflector attack by the remote
attackers, or infinite loop of the Unaffiliated BFD Echo packets,
it's RECOMMENDED to put two requirements, also known as Generalized
TTL Security Mechanism (GTSM) [RFC5082], on the device looping
Unaffiliated BFD Echo packets, the first one is that a packet SHOULD
NOT be looped unless it has a TTL or Hop Limit value of 255, and the
second one is that a packet being looped MUST NOT reset the TTL or
Hop Limit value to 255, and MUST use a TTL or Hop Limit value of 254.
As stated in Section 2, in order to avoid unset values being a
potential vector for disclosure of uninitialized memory, all fields
of the Unaffiliated BFD Echo packet SHOULD be populated with a
certain value, even if some of the fields are ignored on receipt.
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6. IANA Considerations
This document has no IANA action requested.
7. Acknowledgements
The authors would like to acknowledge Ketan Talaulikar, Greg Mirsky,
Santosh Pallagatti, and Aijun Wang 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 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
9.1. 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>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
DOI 10.17487/RFC5881, June 2010,
<https://www.rfc-editor.org/info/rfc5881>.
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[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>.
9.2. Informative References
[BBF-TR-146]
Broadband Forum, "BBF Technical Report - Subscriber
Sessions Issue 1", 2013, <https://www.broadband-
forum.org/technical/download/TR-146.pdf>.
[I-D.wang-bfd-one-arm-use-case]
Wang, R., Cheng, W., Zhao, Y., and A. Liu, "Using One-Arm
BFD in Cloud Network", Work in Progress, Internet-Draft,
draft-wang-bfd-one-arm-use-case-00, 18 November 2019,
<https://datatracker.ietf.org/doc/html/draft-wang-bfd-one-
arm-use-case-00>.
[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", BCP 84, RFC 3704, DOI 10.17487/RFC3704, March
2004, <https://www.rfc-editor.org/info/rfc3704>.
[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
Pignataro, "The Generalized TTL Security Mechanism
(GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,
<https://www.rfc-editor.org/info/rfc5082>.
[RFC8704] Sriram, K., Montgomery, D., and J. Haas, "Enhanced
Feasible-Path Unicast Reverse Path Forwarding", BCP 84,
RFC 8704, DOI 10.17487/RFC8704, February 2020,
<https://www.rfc-editor.org/info/rfc8704>.
Authors' Addresses
Weiqiang Cheng
China Mobile
Beijing
China
Email: chengweiqiang@chinamobile.com
Ruixue Wang
China Mobile
Beijing
China
Email: wangruixue@chinamobile.com
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Xiao Min (editor)
ZTE Corp.
Nanjing
China
Email: xiao.min2@zte.com.cn
Reshad Rahman
Equinix
Ottawa
Canada
Email: reshad@yahoo.com
Raj Chetan Boddireddy
Juniper Networks
Email: rchetan@juniper.net
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