BFD in Demand Mode over Point-to-Point MPLS LSP
draft-mirsky-bfd-mpls-demand-07
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draft-mirsky-bfd-mpls-demand-07
BFD Working Group G. Mirsky
Internet-Draft ZTE Corp.
Intended status: Standards Track June 22, 2020
Expires: December 24, 2020
BFD in Demand Mode over Point-to-Point MPLS LSP
draft-mirsky-bfd-mpls-demand-07
Abstract
This document describes procedures for using Bidirectional Forwarding
Detection (BFD) in Demand mode to detect data plane failures in
Multiprotocol Label Switching (MPLS) point-to-point Label Switched
Paths.
Status of This Memo
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This Internet-Draft will expire on December 24, 2020.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 2
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 2
3. Use of the BFD Demand Mode . . . . . . . . . . . . . . . . . 3
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. Normative References . . . . . . . . . . . . . . . . . . . . 4
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
[RFC5884] defined use of the Asynchronous method of Bidirectional
Detection (BFD) [RFC5880] to monitor and detect failures in the data
path of a Multiprotocol Label Switching (MPLS) Label Switched Path
(LSP). Use of the Demand mode, also specified in [RFC5880], has not
been defined so far. This document describes procedures for using
the Demand mode of BFD protocol to detect data plane failures in MPLS
point-to-point (p2p) LSPs.
2. Conventions used in this document
2.1. Terminology
MPLS: Multiprotocol Label Switching
LSP: Label Switched Path
LER: Label switching Edge Router
BFD: Bidirectional Forwarding Detection
p2p: Point-to-Point
2.2. Requirements Language
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.
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3. Use of the BFD Demand Mode
[RFC5880] defines that the Demand mode MAY be:
o asymmetric, i.e. used in one direction of a BFD session;
o switched to and from without bringing BFD session to Down state
through using a Poll Sequence.
For the case of BFD over MPLS LSP, ingress Label switching Edge
Router (LER) usually acts as Active BFD peer and egress LER acts as
Passive BFD peer. The Active peer bootstraps the BFD session by
using LSP ping. Once the BFD session is in Up state the ingress LER
that supports this specification MUST switch to the Demand mode by
setting Demand (D) bit in its Control packet and initiating a Poll
Sequence. If the egress LER supports this specification it MUST
respond with the Final (F) bit set in its BFD Control packet sent to
the ingress LER and ceases further transmission of periodic BFD
control packets to the ingress LER.
In this state BFD peers MAY remain as long as the egress LER is in Up
state. The ingress LER MAY check liveness of the egress LER by
setting the Poll flag. The egress LER will respond by transmitting
BFD control packet with the Final flag set. If the ingress LER
doesn't receive BFD packet with the Final flag from its peer after
the predetermined period of time, default wait time recommended 1
second, the ingress MAY transmit another packet with the Poll flag
set. If ingress doesn't receive BFD control packet with the Final
flag set in response to three consecutive packets with Poll flag, it
MAY declare the BFD peer non-responsive and change state of the BFD
session to Down state.
If the Detection timer at the egress LER expires it MUST send BFD
Control packet to the ingress LER with the Poll (P) bit set, Status
(Sta) field set to Down value, and the Diagnostic (Diag) field set to
Control Detection Time Expired value. The egress LER sends these
Control packets to the ingress LER at the rate of one per second
until either it receives the valid for this BFD session control
packet with the Final (F) bit set from the ingress LER or the defect
condition clears and the BFD session state reaches Up state at the
egress LER.
The ingress LER transmits BFD Control packets over the MPLS LSP with
the Demand (D) flag set at negotiated interval per [RFC5880], the
greater of bfd.DesiredMinTxInterval and bfd.RemoteMinRxInterval,
until it receives the valid BFD packet from the egress LER with the
Poll (P) bit and the Diagnostic (Diag) field value Control Detection
Time Expired. Reception of such BFD control packet by the ingress
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LER indicates that the monitored LSP has a failure and sending BFD
control packet with the Final flag set to acknowledge failure
indication is likely to fail. Instead, the ingress LER transmits the
BFD Control packet to the egress LER over the IP network with:
o destination IP address MUST be set to the destination IP address
of the LSP Ping Echo request message [RFC8029];
o destination UDP port set to 4784 [RFC5883];
o Final (F) flag in BFD control packet MUST be set;
o Demand (D) flag in BFD control packet MUST be cleared.
The ingress LER changes the state of the BFD session to Down and
changes rate of BFD Control packets transmission to one packet per
second. The ingress LER in Down mode changes to Asynchronous mode
until the BFD session comes to Up state once again. Then the ingress
LER switches to the Demand mode.
4. IANA Considerations
TBD
5. Security Considerations
This document does not introduce new security aspects but inherits
all security considerations from [RFC5880], [RFC5884], [RFC7726],
[RFC8029], and [RFC6425].
6. 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>.
[RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for Multihop Paths", RFC 5883, DOI 10.17487/RFC5883,
June 2010, <https://www.rfc-editor.org/info/rfc5883>.
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[RFC5884] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow,
"Bidirectional Forwarding Detection (BFD) for MPLS Label
Switched Paths (LSPs)", RFC 5884, DOI 10.17487/RFC5884,
June 2010, <https://www.rfc-editor.org/info/rfc5884>.
[RFC6425] Saxena, S., Ed., Swallow, G., Ali, Z., Farrel, A.,
Yasukawa, S., and T. Nadeau, "Detecting Data-Plane
Failures in Point-to-Multipoint MPLS - Extensions to LSP
Ping", RFC 6425, DOI 10.17487/RFC6425, November 2011,
<https://www.rfc-editor.org/info/rfc6425>.
[RFC7726] Govindan, V., Rajaraman, K., Mirsky, G., Akiya, N., and S.
Aldrin, "Clarifying Procedures for Establishing BFD
Sessions for MPLS Label Switched Paths (LSPs)", RFC 7726,
DOI 10.17487/RFC7726, January 2016,
<https://www.rfc-editor.org/info/rfc7726>.
[RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
Switched (MPLS) Data-Plane Failures", RFC 8029,
DOI 10.17487/RFC8029, March 2017,
<https://www.rfc-editor.org/info/rfc8029>.
[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>.
Appendix A. Acknowledgements
TBD
Author's Address
Greg Mirsky
ZTE Corp.
Email: gregimirsky@gmail.com
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