Internet DRAFT - draft-ietf-mpls-bfd-directed
draft-ietf-mpls-bfd-directed
MPLS Working Group G. Mirsky
Internet-Draft Ericsson
Intended status: Experimental J. Tantsura
Expires: 1 September 2024 NVIDIA
I. Varlashkin
Google
M. Chen
Huawei
29 February 2024
Bidirectional Forwarding Detection (BFD) Directed Return Path for MPLS
Label Switched Paths (LSPs)
draft-ietf-mpls-bfd-directed-26
Abstract
Bidirectional Forwarding Detection (BFD) is expected to be able to
monitor a wide variety of encapsulations of paths between systems.
When a BFD session monitors an explicitly routed unidirectional path
there may be a need to direct egress BFD peer to use a specific path
for the reverse direction of the BFD session. This document
describes an extension to the MPLS Label Switched Path (LSP) echo
request that allows a BFD system requests that the remote BFD peer
transmits BFD control packets over the specified LSP.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 1 September 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 3
1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3
1.1.2. Requirements Language . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 4
3. Control of the Reverse BFD Path . . . . . . . . . . . . . . . 4
3.1. BFD Reverse Path TLV . . . . . . . . . . . . . . . . . . 4
3.2. Return Codes . . . . . . . . . . . . . . . . . . . . . . 6
4. Use Case Scenario . . . . . . . . . . . . . . . . . . . . . . 6
5. Operational Considerations . . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6.1. BFD Reverse Path TLV . . . . . . . . . . . . . . . . . . 7
6.2. Return Code . . . . . . . . . . . . . . . . . . . . . . . 8
7. Implementation Status . . . . . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. Normative References . . . . . . . . . . . . . . . . . . . . 9
10. Informative References . . . . . . . . . . . . . . . . . . . 10
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
[RFC5880], [RFC5881], and [RFC5883] established the Bidirectional
Forwarding Detection (BFD) protocol for IP networks. [RFC5884] and
[RFC7726] set rules for using BFD Asynchronous mode over MPLS Label
Switched Paths (LSPs), while not defining means to control the path
an egress BFD system uses to send BFD control packets towards the
ingress BFD system.
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For the case when BFD is used to detect defects of the traffic
engineered LSP the path the BFD control packets transmitted by the
egress BFD system toward the ingress may be disjoint from the LSP in
the forward direction. The fact that BFD control packets are not
guaranteed to follow the same links and nodes in both forward and
reverse directions may be one of the factors contributing to
producing false positive defect notifications, i.e., false alarms, at
the ingress BFD peer. Ensuring that both directions of the BFD
session use co-routed paths may, in some environments, improve the
determinism of the failure detection and localization.
This document defines the BFD Reverse Path TLV as an extension to LSP
Ping [RFC8029] and proposes that it is to be used to instruct the
egress BFD system to use an explicit path for its BFD control packets
associated with a particular BFD session. The TLV will be allocated
from the TLV and sub-TLV registry defined in [RFC8029]. As a special
case, forward and reverse directions of the BFD session can form a
bi-directional co-routed associated channel.
The LSP ping extension, described in this document, was developed and
implemented resulting from the operational experiment. The lessons
learned from the operational experiment enabled the use between
systems conforming to this specification. More implementations are
encouraged to understand better the operational impact of the
mechanism described in the document.
1.1. Conventions used in this document
1.1.1. Terminology
BFD: Bidirectional Forwarding Detection
LSP: Label Switched Path
1.1.2. 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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2. Problem Statement
When BFD is used to monitor explicitly routed unidirectional path,
e.g., MPLS-TE LSP, BFD control packets in forward direction would be
in-band using the mechanism defined in [RFC5884]. But the reverse
direction of the BFD session would follow the shortest path route and
that might lead to the problem in detecting failures on an explicit
unidirectional path, as described below:
* detection by an ingress node of a failure on the reverse path may
not be unambiguously interpreted as the failure of the path in the
forward direction.
To address this scenario, the egress BFD peer would be instructed to
use a specific path for BFD control packets.
3. Control of the Reverse BFD Path
To bootstrap a BFD session over an MPLS LSP, LSP ping, defined in
[RFC8029], MUST be used with BFD Discriminator TLV [RFC5884]. This
document defines a new TLV, BFD Reverse Path TLV, that MAY contain
none, one or more sub-TLVs that can be used to carry information
about the reverse path for the BFD session that is specified by the
value in BFD Discriminator TLV.
3.1. BFD Reverse Path TLV
The BFD Reverse Path TLV is an optional TLV within the LSP ping
[RFC8029]. However, if used, the BFD Discriminator TLV MUST be
included in an Echo Request message as well. If the BFD
Discriminator TLV is not present when the BFD Reverse Path TLV is
included; then it MUST be treated as malformed Echo Request, as
described in [RFC8029].
The BFD Reverse Path TLV carries information about the path onto
which the egress BFD peer of the BFD session referenced by the BFD
Discriminator TLV MUST transmit BFD control packets. The format of
the BFD Reverse Path TLV is as presented in Figure 1.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFD Reverse Path TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reverse Path |
~ ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: BFD Reverse Path TLV
BFD Reverse Path TLV Type is two octets in length and has a value of
TBD1 (to be assigned by IANA as requested in Section 6).
Length field is two octets long and defines the length in octets of
the Reverse Path field.
Reverse Path field contains none, one or more sub-TLVs. Any non-
multicast Target FEC Stack sub-TLV (already defined, or to be defined
in the future) for TLV Types 1, 16, and 21 of MPLS LSP Ping
Parameters registry MAY be used in this field. Multicast Target FEC
Stack sub-TLVs, i.e., p2mp and mp2mp, MUST NOT be included in Reverse
Path field. If the egress LSR finds multicast Target Stack sub-TLV,
it MUST send echo reply with the received Reverse Path TLV, BFD
Discriminator TLV and set the Return Code to "Inappropriate Target
FEC Stack sub-TLV present" Section 3.2. None, one or more sub-TLVs
MAY be included in the BFD Reverse Path TLV. If no sub-TLVs are
found in the BFD Reverse Path TLV, the egress BFD peer MUST revert to
using the local policy-based decision as described in Section 7
[RFC5884], i.e., routed over IP network.
If the egress LSR cannot find the path specified in the Reverse Path
TLV it MUST send Echo Reply with the received BFD Discriminator TLV,
Reverse Path TLV and set the Return Code to "Failed to establish the
BFD session. The specified reverse path was not found" Section 3.2.
An implementation MAY provide configuration options to define action
at the egress BFD peer. For example, optionally, if the egress LSR
cannot find the path specified in the Reverse Path TLV, it will
establish the BFD session over an IP network, as defined in
[RFC5884].
The BFD Reverse Path TLV MAY be used in the bootstrapping of a BFD
session process described in Section 6 [RFC5884]. A system that
supports this specification MUST support using the BFD Reverse Path
TLV after the BFD session has been established. If a system that
supports this specification receives an LSP Ping with the BFD
Discriminator TLV and no BFD Reverse Path TLV even though the reverse
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path for the specified BFD session has been established according to
the previously received BFD Reverse Path TLV, the egress LSR MUST
transition to transmitting periodic BFD Control messages as defined
in Section 7 [RFC5884].
3.2. Return Codes
This document defines the following Return Codes for MPLS LSP Echo
Reply:
* "Inappropriate Target FEC Stack sub-TLV present" (TBD3). When
multicast Target FEC Stack sub-TLV found in the received Echo
Request, the egress BFD peer sends an Echo Reply with the return
code set to "Inappropriate Target FEC Stack sub-TLV present" to
the ingress BFD peer Section 3.1.
* "Failed to establish the BFD session. The specified reverse path
was not found" (TBD4). When a specified reverse path is
unavailable, the egress BFD peer sends an Echo Reply with the
return code set to "Failed to establish the BFD session. The
specified reverse path was not found" to the ingress BFD peer
Section 3.1.
4. Use Case Scenario
In the network presented in Figure 2 node A monitors two tunnels to
node H: A-B-C-D-G-H and A-B-E-F-G-H. To bootstrap a BFD session to
monitor the first tunnel, node A MUST include a BFD Discriminator TLV
with Discriminator value (e.g., foobar-1) and MAY include a BFD
Reverse Path TLV that references H-G-D-C-B-A tunnel. To bootstrap a
BFD session to monitor the second tunnel, node A MUST include a BFD
Discriminator TLV with a different Discriminator value (e.g., foobar-
2) [RFC7726] and MAY include a BFD Reverse Path TLV that references
H-G-F-E-B-A tunnel.
C---------D
| |
A-------B G-----H
| |
E---------F
Figure 2: Use Case for BFD Reverse Path TLV
If an operator needs node H to monitor a path to node A, e.g.
H-G-D-C-B-A tunnel, then by looking up the list of known Reverse
Paths it MAY find and use the existing BFD session.
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5. Operational Considerations
When an explicit path is set either as Static or RSVP-TE LSP,
corresponding sub-TLVs, defined in [RFC7110], MAY be used to identify
the explicit reverse path for the BFD session. If any of defined in
[RFC7110] sub-TLVs used in BFD Reverse Path TLV, then the periodic
verification of the control plane against the data plane, as
recommended in Section 4 [RFC5884], MUST use the Return Path TLV, as
per [RFC7110], with that sub-TLV. By using the LSP Ping with Return
Path TLV, an operator monitors whether at the egress BFD node the
reverse LSP is mapped to the same FEC as the BFD session. Selection
and control of the rate of LSP Ping with Return Path TLV follows the
recommendation of [RFC5884]: "The rate of generation of these LSP
Ping Echo request messages SHOULD be significantly less than the rate
of generation of the BFD Control packets. An implementation MAY
provide configuration options to control the rate of generation of
the periodic LSP Ping Echo request messages."
Suppose an operator planned network maintenance activity that
possibly affects FEC used in the BFD Reverse Path TLV. In that case,
the operator MUST avoid the unnecessary disruption using the LSP Ping
with a new FEC in the BFD Reverse Path TLV. But in some scenarios,
proactive measures cannot be taken. Because the frequency of LSP
Ping messages will be lower than the defect detection time provided
by the BFD session. As a result, a change in the reverse-path FEC
will first be detected as the BFD session's failure. In such a case,
the ingress BFD node SHOULD immediately transmit the LSP Ping Echo
request with Return Path TLV to verify whether the FEC is still
valid. If the failure was caused by the change in the FEC used for
the reverse direction of the BFD session, the ingress BFD node SHOULD
bootstrap a new BFD session using another FEC in BFD Reverse Path
TLV.
6. IANA Considerations
6.1. BFD Reverse Path TLV
The IANA is requested to assign a new value for BFD Reverse Path TLV
from the 16384-31739 range in the "TLVs" registry of "Multiprotocol
Label Switching Architecture (MPLS) Label Switched Paths (LSPs) Ping
Parameters" registry.
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+=========+======================+===============+
| Value | Description | Reference |
+=========+======================+===============+
| (TBD1) | BFD Reverse Path TLV | This document |
+---------+----------------------+---------------+
Table 1: New BFD Reverse Type TLV
6.2. Return Code
The IANA is requested to assign new Return Code values from the
192-247 range of the "Multi-Protocol Label Switching (MPLS) Label
Switched Paths (LSPs) Ping Parameters" registry, "Return Codes" sub-
registry, as follows using a Standards Action value.
+=========+=============================+===============+
| Value | Description | Reference |
+=========+=============================+===============+
| (TBD3) | Inappropriate Target FEC | This document |
| | Stack sub-TLV present. | |
+---------+-----------------------------+---------------+
| (TBD4) | Failed to establish the BFD | This document |
| | session. The specified | |
| | reverse path was not found. | |
+---------+-----------------------------+---------------+
Table 2: New Return Code
7. Implementation Status
Note to RFC Editor: This section MUST be removed before publication
of the document.
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
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According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
- The organization responsible for the implementation: ZTE
Corporation.
- The implementation's name ROSng empowers traditional routers, e.g.,
ZXCTN 6000.
- A brief general description: A Return Path can be specified for a
BFD session over RSVP tunnel or LSP. The same can be specified for a
backup RSVP tunnel/LSP.
The implementation's level of maturity: production.
- Coverage: RSVP LSP (no support for Static LSP)
- Version compatibility: draft-ietf-mpls-bfd-directed-10.
- Licensing: proprietary.
- Implementation experience: simple once you support RFC 7110.
- Contact information: Qian Xin qian.xin2@zte.com.cn
- The date when information about this particular implementation was
last updated: 12/16/2019
8. Security Considerations
Security considerations discussed in [RFC5880], [RFC5884], [RFC7726],
[RFC8029], and [RFC7110] apply to this document.
9. 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>.
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[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>.
[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>.
[RFC7110] Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord,
"Return Path Specified Label Switched Path (LSP) Ping",
RFC 7110, DOI 10.17487/RFC7110, January 2014,
<https://www.rfc-editor.org/info/rfc7110>.
[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>.
10. Informative References
[RFC7942] Sheffer, Y. and A. Farrel, "Improving Awareness of Running
Code: The Implementation Status Section", BCP 205,
RFC 7942, DOI 10.17487/RFC7942, July 2016,
<https://www.rfc-editor.org/info/rfc7942>.
Appendix A. Acknowledgments
The authors greatly appreciate a thorough review and the most helpful
comments from Eric Gray and Carlos Pignataro. The authors much
appreciate the help of Qian Xin, who provided information about the
implementation of this specification.
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Authors' Addresses
Greg Mirsky
Ericsson
Email: gregimirsky@gmail.com
Jeff Tantsura
NVIDIA
Email: jefftant.ietf@gmail.com
Ilya Varlashkin
Google
Email: imv@google.com
Mach(Guoyi) Chen
Huawei
Email: mach.chen@huawei.com
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