BFD Working Group W. Cheng
Internet-Draft R. Wang
Updates: 5880 (if approved) China Mobile
Intended status: Standards Track X. Min, Ed.
Expires: 28 July 2022 ZTE Corp.
R. Rahman
Individual
R. Boddireddy
Juniper Networks
24 January 2022
Unaffiliated BFD Echo
draft-ietf-bfd-unaffiliated-echo-03
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.
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
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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 28 July 2022.
Copyright Notice
Copyright (c) 2022 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions Used in This Document . . . . . . . . . . . . 3
2. Updates to RFC 5880 . . . . . . . . . . . . . . . . . . . . . 3
3. Unaffiliated BFD Echo Procedures . . . . . . . . . . . . . . 6
4. Unaffiliated BFD Echo Applicability . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
To minimize the impact of device/link faults on services and improve
network availability, a network device must 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.
When using BFD Echo function, there are two typical scenarios as
below:
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* 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.
The latter scenario is referred to as Unaffiliated BFD Echo in this
document.
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. 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.
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* 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.
* 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:
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* 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.
* 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
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* 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...
* 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...
3. Unaffiliated BFD Echo Procedures
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Device A Device B
BFD Enabled BFD Echo packets loopback
+--------+ 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 BFD Echo packets, and after
receiving the 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 BFD Echo packet or parse any BFD protocol field within the
BFD Echo packet.
To rapidly detect any IP forwarding faults between device A and
device B, a BFD Echo session MUST be created at device A, and the 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 echoed
from the remote system, and AdminDown state is ruled out because
AdminDown effectively means removal of BFD Echo session. In this
case, although BFD Echo packets are transmitted with destination UDP
port 3785 as defined in [RFC5881], the BFD Echo packets sent by
device A are BFD Control packets too, the looped BFD Echo packets
back from device B would drive BFD state change at device A,
substituting the BFD Control packets sent from the BFD peer. Also
note that when device A receives looped BFD Control packets, the
validation procedures of [RFC5880] are used.
Once a BFD Echo session is created at device A, it starts sending BFD
Echo packets, which MUST include BFD Echo session demultiplexing
fields, such as BFD "Your Discriminator" defined in [RFC5880] (BFD
"My Discriminator" can be set to 0 to avoid confusion), except for
BFD "Your Discriminator", device A can also use IP source address or
UDP source port to demultiplex BFD Echo session, or there is only one
BFD Echo session running at device A. Device A would send BFD Echo
packets with IP destination address destined for itself, such as the
IP address of interface 1 of device A. All BFD Echo packets for the
session MUST be sent with a Time to Live (TTL) or Hop Limit value of
255.
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Within the BFD Echo packet, the "Desired Min TX Interval" and
"Required Min RX Interval" defined in [RFC5880] may be populated with
one second, which however has no real application and would be
ignored by the receiver.
Considering that the BFD peer device B wouldn't advertise "Required
Min Echo RX Interval" as defined in [RFC5880], the transmission
interval for sending BFD Echo packets MUST be provisioned at device
A, how to make sure the BFD peer device B is willing and able to loop
back BFD Echo packets sent with the provisioned transmission interval
is outside the scope of this document. Similar to what's specified
in [RFC5880], the BFD Echo session begins with the periodic, slow
transmission of BFD Echo packets, the slow transmission rate SHOULD
be no less then one second per packet, until the session is Up, after
that the provisioned transmission interval is applied, and reverting
back to the slow rate once the session goes Down. Considering that
the BFD peer wouldn't advertise "Detect Mult" as defined in
[RFC5880], the "Detect Mult" for calculating the Detection Time MUST
be provisioned at device A, the Detection Time at device A is equal
to the provisioned "Detect Mult" multiplied by the provisioned
transmission 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. The 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 BFD Echo packets.
5. Security Considerations
All Security Considerations from [RFC5880] and [RFC5881] apply.
Note that the Unaffiliated BFD Echo prevents the 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 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 BFD Echo packet.
In order to mitigate the potential reflector attack by the remote
attackers, or infinite loop of the BFD Echo packets, it's RECOMMENDED
to put two requirements on the device looping BFD Echo packets, the
first one is that a packet SHOULD NOT be looped unless it has a TTL
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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.
6. IANA Considerations
This document has no IANA action requested.
7. Acknowledgements
The authors would like to acknowledge Ketan Talaulikar, Greg Mirsky
and Santosh Pallagatti for their careful review and very helpful
comments.
The authors would like to acknowledge Jeff Haas for his insightful
review and very helpful comments.
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>.
[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
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[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://www.ietf.org/archive/id/draft-wang-bfd-one-arm-
use-case-00.txt>.
[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>.
[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
Xiao Min (editor)
ZTE Corp.
Nanjing
China
Email: xiao.min2@zte.com.cn
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Reshad Rahman
Individual
Kanata
Canada
Email: reshad@yahoo.com
Raj Chetan Boddireddy
Juniper Networks
Email: rchetan@juniper.net
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