BFD Working Group G. Mirsky
Internet-Draft Ericsson
Intended status: Informational 7 March 2022
Expires: 8 September 2022
BFD in Demand Mode over Point-to-Point MPLS LSP
draft-mirsky-bfd-mpls-demand-11
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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 2
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
3. Use of the BFD Demand Mode . . . . . . . . . . . . . . . . . 2
3.1. The Applicability of BFD for Multipoint Networks . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . 4
6. Normative References . . . . . . . . . . . . . . . . . . . . 4
7. Informative References . . . . . . . . . . . . . . . . . . . 5
Appendix A. Acknowledgements . . . . . . . . . . . . . . . . . . 5
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
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.
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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 switches 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 remains as long as the egress LER is in Up
state. The ingress LER can 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 control the interval
between consecutive Poll Sequences. The Rdefault value could be
selected as 1 second.
If the Detection timer at the egress LER expires, the BFD system on
LER sends 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
provides control of the interval between consecutive Poll messages
signaling the expiration of the Detection timer. The default value
of the interval can be selected as 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
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 is set to the destination IP address of the
LSP Ping Echo request message [RFC8029];
* destination UDP port set to 4784 [RFC5883];
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* Final (F) flag in BFD control packet is set;
* Demand (D) flag in BFD control packet is 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
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
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[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>.
[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
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Author's Address
Greg Mirsky
Ericsson
Email: gregimirsky@gmail.com
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