Internet DRAFT - draft-mirsky-bfd-mpls-demand
draft-mirsky-bfd-mpls-demand
BFD Working Group G. Mirsky
Internet-Draft Ericsson
Intended status: Informational 10 March 2023
Expires: 11 September 2023
BFD in Demand Mode over a Point-to-Point MPLS LSP
draft-mirsky-bfd-mpls-demand-13
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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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 11 September 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . 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. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
7. Normative References . . . . . . . . . . . . . . . . . . . . 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. Acronyms
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.
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
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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 remain 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 default value could be
selected as 1 second.
If the Detection timer at the egress LER expires, the BFD system on
the egress LER sends BFD Control packet to the ingress LER with the
Poll (P) bit set, Status (Sta) field set to the Down (1) value, and
the Diagnostic (Diag) field set to Control Detection Time Expired (1)
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. Thus sending a
BFD control packet with the Final flag set to acknowledge failure
indication over the monitored LSP 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];
* Final (F) flag in BFD control packet is set;
* Demand (D) flag in BFD control packet is cleared.
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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] and [RFC8563] define 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 in
Section 3 for the case after the ingress BFD system switches the
remote peer into the Demand mode.
4. IANA Considerations
This document doesn't require any IANA action. This section can be
removed before the publication of the document.
5. Security Considerations
This document does not introduce new security aspects but inherits
all security considerations from [RFC5880], [RFC5884], [RFC7726],
[RFC8029], [RFC6425], [RFC8562], and [RFC8563]
6. Acknowledgements
The author expresses his genuine appreciation of the extensive
technical comments and the discussion with Jeffrey Haas that helped
to clarify and properly position this document relative to the
existing BFD specifications.
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7. 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>.
[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>.
[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>.
Author's Address
Greg Mirsky
Ericsson
Email: gregimirsky@gmail.com
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