BFD Working Group W. Cheng
Internet-Draft R. Wang
Intended status: Informational China Mobile
Expires: January 14, 2021 X. Min
A. Liu
ZTE Corp.
R. Rahman
Cisco Systems
July 13, 2020
Unaffiliated BFD Echo Function
draft-cw-bfd-unaffiliated-echo-01
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 BFD echo
where the local system supports BFD but the neighboring system does
not support BFD.
Status of This Memo
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Internet-Draft Unaffiliated BFD Echo Function July 2020
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Unaffiliated BFD Echo Behavior . . . . . . . . . . . . . . . 3
3. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 4
7.1. Normative References . . . . . . . . . . . . . . . . . . 5
7.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
To minimize the impact of device 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 path between adjacent forwarding engines. The faults
can be interface, data link, and even forwarding engine faults. It
is a single, unified mechanism to monitor any media and protocol
layers in real time.
BFD defines asynchronous mode to satisfy various deployment
scenarios, also supports echo function to reduce the device
requirement for BFD. When the echo function is activated, the local
system sends a BFD echo packet and the remote system loops back the
packet through the forwarding path. If several consecutive echo
packets are not received, the session is declared to be Down.
When using BFD echo function, it is not clear whether the devices
using echo function need to support the full BFD procotol, including
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:
this scenario requires both the local device and the neighboring
device to support BFD protocol.
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2. Only BFD echo function without full BFD procotol capability:
this scenario requires only the local device to support sending
BFD packets.
The two typical scenarios are both reasonable and useful, and the
latter is referred to as unaffiliated BFD echo function in this
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
unaffiliated BFD echo function, and at least one more use case is
known in the field BFD deployment.
2. Unaffiliated BFD Echo Behavior
With the more and more application of BFD detection, there are some
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
BFD protocol immediately loops back the packet by normal IP
forwarding, implementing quick link failure detection. As shown in
Figure 1, device A supports BFD, whereas device B does not support
BFD. To rapidly detect any faults with the IP link between device A
and device B, a BFD echo session can be provisioned and created at
device A, and device A starts sending BFD echo packets, which should
include a BFD echo session demultiplexing field, such as BFD
discriminator defined in [RFC5880]. After receiving the BFD echo
packets sent from device A, device B immediately loops back them,
this allows device A to rapidly detect a connectivity loss to device
B.
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Device A Device B
BFD echo session
BFD Enabled BFD Echo packets loopback
+--------+ +---------+
| A |---------------------------------| B |
| |Inf 1 Inf 1| |
+--------+10.1.1.1/24 10.1.1.2/24+---------+
BFD is supported. BFD is not supported.
Figure 1: Unaffiliated BFD Echo deployment scenario
3. Discussion
Unaffiliated BFD echo function is reasonable and useful. Firstly,
unaffiliated BFD echo can use BFD protocol capability in the local
BFD-supported device, while using IP forwarding capability in the
peer non-BFD-supported device, so unaffiliated BFD echo can support
fast detecting and manage BFD sessions very effectively. Secondly,
it is scalable when using unaffiliated BFD echo to adapt to different
capabilities of devices.
4. Security Considerations
Unicast Reverse Path Forwarding (uRPF), as specified in [RFC3704] and
[RFC8704], is a security feature that prevents the IP address
spoofing attacks which is commonly used in DoS, DDoS. uRPF has two
modes called strict mode and loose mode. uRPF strict mode means that
the router will perform checks for all incoming packets on a certain
interface: whether the router has a matching entry for the source IP
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.
Note that the use of BFD echo function would prevent the use of uRPF
in strict mode.
5. IANA Considerations
This document has no IANA action requested.
6. Acknowledgements
TBD.
7. References
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7.1. Normative References
[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>.
7.2. 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>.
[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
CN
Email: chengweiqiang@chinamobile.com
Ruixue Wang
China Mobile
Beijing
CN
Email: wangruixue@chinamobile.com
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Xiao Min
ZTE Corp.
Nanjing
CN
Email: xiao.min2@zte.com.cn
Aihua Liu
ZTE Corp.
Shenzhen
CN
Email: liu.aihua@zte.com.cn
Reshad Rahman
Cisco Systems
Kanata
CA
Email: rrahman@cisco.com
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