BFD in Demand Mode over Point-to-Point MPLS LSP
draft-mirsky-bfd-mpls-demand-10
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| Author | Greg Mirsky | ||
| Last updated | 2021-10-01 | ||
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draft-mirsky-bfd-mpls-demand-10
BFD Working Group G. Mirsky
Internet-Draft Ericsson
Intended status: Standards Track 1 October 2021
Expires: 4 April 2022
BFD in Demand Mode over Point-to-Point MPLS LSP
draft-mirsky-bfd-mpls-demand-10
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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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
3.1. The Applicability of BFD for Multipoint Networks . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 5
6. Normative References . . . . . . . . . . . . . . . . . . . . 5
7. Informative References . . . . . . . . . . . . . . . . . . . 6
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 6
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
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:
* asymmetric, i.e. used in one direction of a BFD session;
* 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. If the BFD session is configured to use the Demand
mode, once the BFD session is in Up state the ingress LER MUST switch
to the Demand mode as defined in Section 6.6 [RFC5880]. The egress
LER also follows procedures defined in Section 6.6 [RFC5880] 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 SHOULD periodically check continuity of a
bidirectional path between the ingress and egress LERs by using the
Poll Sequence, as described in Section 6.6 [RFC5880]. An
implementation that supports using the Poll Sequence as the mechanism
for bidirectional path continuity check MUST be able to control the
interval between consecutive Poll Sequences. The RECOMMENDED default
value is 1 second.
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 the Down value, and the Diagnostic (Diag) field
set to Control Detection Time Expired value. The egress LER
periodically transmits these Control packets to the ingress LER 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.
An implementation that supports this specification MUST provide
control of the interval between consecutive Poll messages signaling
the expiration of the Detection timer. The RECOMMENDED default value
of the interval is 1 second.
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
LER indicates that the monitored LSP has a failure and sending BFD
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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:
* destination IP address MUST be set to the destination IP address
of the LSP Ping Echo request message [RFC8029];
* destination UDP port set to 4784 [RFC5883];
* Final (F) flag in BFD control packet MUST be set;
* 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.
3.1. The Applicability of BFD for Multipoint Networks
[RFC8562] defines the use of BFD in multipoint networks. This
specification analyzes the case of p2p LSP. In that scenario, the
ingress of the LSP acts as the MultipointHead, and the egress - as
MultipointTail. The BFD state machines for MultipointHead,
MultipointClient, and MultipointTail don't use the three-way
handshakes for session establishment and teardown. As a result, the
Init state is absent, and the session transitions to the Up state
once the BFD session is administratively enabled. Hence, a BFD
session over a p2p LSP, using principles of [RFC8562] or [RFC8563],
can be established faster if the MultipointTail has been provisioned
with the value of My Discriminator used by the MultipointHead for
that BFD session. That value can be provided to the MultipointTail
using different mechanisms, e.g., an extension to IGP. Description
of mechanism to provide the value of My Discriminator used by the
MultipointHead for the particular BFD session is outside the scope of
this specification.
Unsolicited notification of the detected failure by the
MultipointTail to the MultipointClient performs as described above
for the case when the ingress BFD system switches the remote peer
into the Demand mode.
4. IANA Considerations
TBD
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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>.
[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>.
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[RFC8562] Katz, D., Ward, D., Pallagatti, S., Ed., and G. Mirsky,
Ed., "Bidirectional Forwarding Detection (BFD) for
Multipoint Networks", RFC 8562, DOI 10.17487/RFC8562,
April 2019, <https://www.rfc-editor.org/info/rfc8562>.
7. Informative References
[RFC8563] Katz, D., Ward, D., Pallagatti, S., Ed., and G. Mirsky,
Ed., "Bidirectional Forwarding Detection (BFD) Multipoint
Active Tails", RFC 8563, DOI 10.17487/RFC8563, April 2019,
<https://www.rfc-editor.org/info/rfc8563>.
Appendix A. Acknowledgements
TBD
Author's Address
Greg Mirsky
Ericsson
Email: gregimirsky@gmail.com
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