draft-ietf-bfd-unaffiliated-echo-00.txt   draft-ietf-bfd-unaffiliated-echo-01.txt 
BFD Working Group W. Cheng BFD Working Group W. Cheng
Internet-Draft R. Wang Internet-Draft R. Wang
Updates: 5880 (if approved) China Mobile Updates: 5880 (if approved) China Mobile
Intended status: Standards Track X. Min Intended status: Standards Track X. Min
Expires: March 13, 2021 A. Liu Expires: May 6, 2021 ZTE Corp.
ZTE Corp.
R. Rahman R. Rahman
Cisco Systems Cisco Systems
R. Boddireddy R. Boddireddy
Juniper Networks Juniper Networks
September 9, 2020 November 2, 2020
Unaffiliated BFD Echo Function Unaffiliated BFD Echo Function
draft-ietf-bfd-unaffiliated-echo-00 draft-ietf-bfd-unaffiliated-echo-01
Abstract Abstract
Bidirectional Forwarding Detection (BFD) is a fault detection Bidirectional Forwarding Detection (BFD) is a fault detection
protocol that can quickly determine a communication failure between protocol that can quickly determine a communication failure between
two forwarding engines. This document proposes a use of BFD echo two forwarding engines. This document proposes a use of the BFD Echo
where the local system supports BFD but the neighboring system does function where the local system supports BFD but the neighboring
not support BFD. system does not support BFD.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
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This Internet-Draft will expire on March 13, 2021. This Internet-Draft will expire on May 6, 2021.
Copyright Notice Copyright Notice
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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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Unaffiliated BFD Echo Behavior . . . . . . . . . . . . . . . 3 2. Updates to RFC 5880 . . . . . . . . . . . . . . . . . . . . . 3
3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Unaffiliated BFD Echo Procedures . . . . . . . . . . . . . . 6
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 4. Unaffilicated BFD Echo Applicability . . . . . . . . . . . . 7
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
7.1. Normative References . . . . . . . . . . . . . . . . . . 5 8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 8
7.2. Informative References . . . . . . . . . . . . . . . . . 5 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5 9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
To minimize the impact of device faults on services and improve To minimize the impact of device/link faults on services and improve
network availability, a network device must be able to quickly detect network availability, a network device must be able to quickly detect
faults in communication with adjacent devices. Measures can then be faults in communication with adjacent devices. Measures can then be
taken to promptly rectify the faults to ensure service continuity. taken to promptly rectify the faults to ensure service continuity.
BFD [RFC5880] is a low-overhead, short-duration method to detect BFD [RFC5880] is a low-overhead, short-duration method to detect
faults on the path between adjacent forwarding engines. The faults faults on the communication path between adjacent forwarding engines.
can be interface, data link, and even forwarding engine faults. It The faults can be on interface, data link, and even forwarding
is a single, unified mechanism to monitor any media and protocol engine. It is a single, unified mechanism to monitor any media and
layers in real time. protocol layers in real time.
BFD defines asynchronous mode to satisfy various deployment BFD defines Asynchronous mode to satisfy various deployment
scenarios, also supports echo function to reduce the device scenarios, and also supports Echo function to reduce the device
requirement for BFD. When the echo function is activated, the local requirement for BFD. When the Echo function is activated, the local
system sends a BFD echo packet and the remote system loops back the system sends BFD Echo packets and the remote system loops back the
packet through the forwarding path. If several consecutive echo received Echo packets through the forwarding path. If several
packets are not received, the session is declared to be Down. 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, it is not clear whether the devices When using BFD Echo function, there are two typical scenarios as
using echo function need to support the full BFD procotol, including below:
maintaining the state machine of BFD session as described in
[RFC5880] and [RFC5881]. According to different understanding, there
are two typical scenarios as below:
1. Full BFD procotol capability with affiliated echo function: o Full BFD protocol capability with affiliated Echo function: this
this scenario requires both the local device and the neighboring scenario requires both the local device and the neighboring device
device to support BFD protocol. to support full BFD protocol.
2. Only BFD echo function without full BFD procotol capability: o Only BFD Echo function without full BFD protocol capability:
this scenario requires only the local device to support sending this scenario requires only the local device to support sending
BFD packets. and demultiplexing BFD Control packets.
The two typical scenarios are both reasonable and useful, and the The two typical scenarios are both reasonable and useful, and the
latter is referred to as unaffiliated BFD echo function in this latter is referred to as Unaffiliated BFD Echo function in this
document. document.
Unaffiliated BFD echo function described in this document reuses the
BFD echo function as described in [RFC5880] and [RFC5881], but
independent of BFD asynchronous mode, that means it doesn't need BFD
protocol capability of state machine, but only BFD echo function to a
deployed device supporting BFD detection. When using unaffiliated
BFD echo function, just the local device works on BFD protocol and
the BFD peer doesn't, which only loopback the received BFD echo
packets as usual data packets without enabling BFD protocol.
Section 6.2.2 of [BBF-TR-146] describes one use case of the Section 6.2.2 of [BBF-TR-146] describes one use case of the
unaffiliated BFD echo function, and at least one more use case is Unaffiliated BFD Echo function, and at least one more use case is
known in the field BFD deployment. known in the field BFD deployment.
2. Unaffiliated BFD Echo Behavior This document describes the use of the Unaffiliated BFD Echo function
over IPv4 and IPv6 for single IP hop.
With the more and more application of BFD detection, there are some 2. Updates to RFC 5880
scenarios the BFD echo function is deployed. And due to the
different capabilities of the devices deploying BFD echo function,
it's required to apply unaffiliated BFD echo to the devices that
couldn't afford the overhead of the full BFD protocol capablity, such
as the servers running virtual machines or some Internet of Things
(IoT) devices. Unaffiliated BFD echo can be used when two devices
are connected and only one of them supports BFD protocol capability.
A BFD echo session can be established at the device that supports
BFD, and the device will send the BFD echo packets with the IP
address destined for itself, whereas the other peer device just
loopback the received BFD echo packets.
After receiving a BFD echo packet, the device that does not support The Unaffiliated BFD Echo function described in this document reuses
BFD protocol immediately loops back the packet by normal IP the BFD Echo function as described in [RFC5880] and [RFC5881], but
forwarding, implementing quick link failure detection. As shown in does not require BFD asynchronous mode. When using the Unaffiliated
Figure 1, device A supports BFD, whereas device B does not support BFD Echo function, only the local system has the BFD protocol
BFD. To rapidly detect any faults with the IP link between device A enabled, the remote system just loops back the received BFD Echo
and device B, a BFD echo session can be provisioned and created at packets as regular data packets.
device A, and device A starts sending BFD echo packets, which should
include a BFD echo session demultiplexing field, such as BFD With that said, this document updates [RFC5880] with respect to its
discriminator defined in [RFC5880]. After receiving the BFD echo descriptions on the BFD Echo function as follows.
packets sent from device A, device B immediately loops back them,
this allows device A to rapidly detect a connectivity loss to device o [RFC5880] states in the 4th paragraph of Section 3.2:
B.
An adjunct to both modes is the Echo function. When the Echo
function is active, a stream of BFD Echo packets is transmitted in
such a way as to have the other system loop them back through its
forwarding path. If a number of packets of the echoed data stream
are not received, the session is declared to be down. The Echo
function may be used with either Asynchronous or 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).
* This paragraph is now updated to:
An adjunct or complement to both modes is the Echo function. When
the Echo function is active, a stream of BFD Echo packets is
transmitted in such a way as to have the other system loop them
back through its forwarding path. If a number of packets of the
echoed data stream are not received, the session is declared to be
down. The Echo function may be used with either Asynchronous or
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). The Echo function may
also be used independently, with neither Asynchronous nor Demand
mode.
o [RFC5880] states in the 3rd and 9th paragraphs of Section 6.1:
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.
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 two paragraphs are now updated to:
When a system is running with Asynchronous 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 when
the Echo function is active.
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.
o [RFC5880] states in the 2nd paragraph of Section 6.4:
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).
* This paragraph is now updated to:
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).
o [RFC5880] states in the 2nd paragraph of Section 6.8:
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.
* This paragraph is now updated to:
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.
o [RFC5880] states in the 7th paragraph of Section 6.8.3:
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.
* This paragraph is now updated to:
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.
o [RFC5880] states in the 1st and 2nd paragraphs of Section 6.8.9:
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.
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, except as follows:
A 25% jitter MAY be applied to the rate of transmission, such
that the actual interval MAY be between 75% and 100% of the
advertised value. A single BFD Echo packet MAY be transmitted
between normally scheduled Echo transmission intervals.
* The two paragraphs are now updated to:
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.
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:
A 25% jitter MAY be applied to the rate of transmission, such
that the actual interval MAY be between 75% and 100% of the
advertised value. A single BFD Echo packet MAY be transmitted
between normally scheduled Echo transmission intervals.
3. Unaffiliated BFD Echo Procedures
As shown in Figure 1, device A supports BFD, whereas device B does
not support BFD. 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 is RECOMMENDED to 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. 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.
Once a BFD Echo session is created at device A, it starts sending BFD
Echo packets, which SHOULD include a BFD Echo session demultiplexing
field, such as BFD Your Discriminator defined in [RFC5880] (BFD My
Discriminator can be set to 0 to avoid confusion), except that device
A can 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.
Considering the BFD peer wouldn't advertise Required Min Echo RX
Interval as defined in [RFC5880], the transmit interval for sending
BFD Echo packets MUST be provisioned at device A, how to make sure
the BFD peer is willing and able to loop back BFD Echo packets sent
with the provisioned transmit interval is outside the scope of this
document. Considering 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 in device A
is equal to the provisioned Detect Mult multiplied by the provisioned
transmit interval.
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.
Device A Device B Device A Device B
BFD echo session BFD Echo session
BFD Enabled BFD Echo packets loopback BFD Enabled BFD Echo packets loopback
+--------+ +---------+ +--------+ +---------+
| A |---------------------------------| B | | A |---------------------------------| B |
| |Inf 1 Inf 1| | | |Inf 1 Inf 1| |
+--------+10.1.1.1/24 10.1.1.2/24+---------+ +--------+10.1.1.1/24 10.1.1.2/24+---------+
BFD is supported. BFD is not supported. BFD is supported. BFD is not supported.
Figure 1: Unaffiliated BFD Echo deployment scenario Figure 1: Unaffiliated BFD Echo deployment scenario
3. Discussion 4. Unaffilicated BFD Echo Applicability
Unaffiliated BFD echo function is reasonable and useful. Firstly, With the more and more application of BFD detection, there are some
unaffiliated BFD echo can use BFD protocol capability in the local scenarios the BFD Echo function is deployed. And due to the
BFD-supported device, while using IP forwarding capability in the different capabilities of the devices deploying BFD Echo function,
peer non-BFD-supported device, so unaffiliated BFD echo can support it's required to apply Unaffiliated BFD Echo to the devices that
couldn't afford the overhead of the full BFD protocol capability,
such as the servers running virtual machines or some Internet of
Things (IoT) devices. Unaffiliated BFD Echo can be used when two
devices are connected and only one of them supports BFD protocol
capability.
Unaffiliated BFD Echo function is reasonable and useful. Firstly,
Unaffiliated BFD Echo can use BFD protocol capability at the local
BFD-supported device, while using IP forwarding capability at the
peer BFD-unsupported device, so Unaffiliated BFD Echo can support
fast detecting and manage BFD sessions very effectively. Secondly, fast detecting and manage BFD sessions very effectively. Secondly,
it is scalable when using unaffiliated BFD echo to adapt to different it is scalable when using Unaffiliated BFD Echo to adapt to different
capabilities of devices. capabilities of devices.
4. Security Considerations 5. Security Considerations
Unicast Reverse Path Forwarding (uRPF), as specified in [RFC3704] and Unicast Reverse Path Forwarding (uRPF), as specified in [RFC3704] and
[RFC8704], is a security feature that prevents the IP address [RFC8704], is a security feature that prevents the IP address
spoofing attacks which is commonly used in DoS, DDoS. uRPF has two spoofing attacks which is commonly used in DoS, DDoS. uRPF has two
modes called strict mode and loose mode. uRPF strict mode means that modes called strict mode and loose mode. uRPF strict mode means that
the router will perform checks for all incoming packets on a certain the router will perform checks for all incoming packets on a certain
interface: whether the router has a matching entry for the source IP interface: whether the router has a matching entry for the source IP
in the routing table and whether the router uses the same interface in the routing table and whether the router uses the same interface
to reach this source IP as where the router received this packet on. to reach this source IP as where the router received this packet on.
Note that the use of BFD echo function would prevent the use of uRPF Note that the use of BFD Echo function would prevent the use of uRPF
in strict mode. in strict mode.
5. IANA Considerations 6. IANA Considerations
This document has no IANA action requested. This document has no IANA action requested.
6. Acknowledgements 7. Acknowledgements
TBD. The authors would like to acknowledge Ketan Talaulikar, Greg Mirsky
and Santosh Pallagatti for their careful review and very helpful
comments.
7. References 8. Contributors
7.1. Normative References 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
[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>.
7.2. Informative References 9.2. Informative References
[BBF-TR-146] [BBF-TR-146]
Broadband Forum, "BBF Technical Report - Subscriber Broadband Forum, "BBF Technical Report - Subscriber
Sessions Issue 1", 2013, <https://www.broadband- Sessions Issue 1", 2013, <https://www.broadband-
forum.org/technical/download/TR-146.pdf>. forum.org/technical/download/TR-146.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>.
skipping to change at page 6, line 17 skipping to change at page 10, line 4
CN CN
Email: wangruixue@chinamobile.com Email: wangruixue@chinamobile.com
Xiao Min Xiao Min
ZTE Corp. ZTE Corp.
Nanjing Nanjing
CN CN
Email: xiao.min2@zte.com.cn Email: xiao.min2@zte.com.cn
Aihua Liu
ZTE Corp.
Shenzhen
CN
Email: liu.aihua@zte.com.cn
Reshad Rahman Reshad Rahman
Cisco Systems Cisco Systems
Kanata Kanata
CA CA
Email: rrahman@cisco.com Email: rrahman@cisco.com
Raj Chetan Boddireddy Raj Chetan Boddireddy
Juniper Networks Juniper Networks
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