< draft-ietf-mpls-bfd-directed-11.txt   draft-ietf-mpls-bfd-directed-12.txt >
MPLS Working Group G. Mirsky MPLS Working Group G. Mirsky
Internet-Draft ZTE Internet-Draft ZTE
Intended status: Standards Track J. Tantsura Intended status: Standards Track J. Tantsura
Expires: October 5, 2019 Nuage Networks Expires: February 22, 2020 Nuage Networks
I. Varlashkin I. Varlashkin
Google Google
M. Chen M. Chen
Huawei Huawei
April 3, 2019 August 21, 2019
Bidirectional Forwarding Detection (BFD) Directed Return Path Bidirectional Forwarding Detection (BFD) Directed Return Path
draft-ietf-mpls-bfd-directed-11 draft-ietf-mpls-bfd-directed-12
Abstract Abstract
Bidirectional Forwarding Detection (BFD) is expected to be able to Bidirectional Forwarding Detection (BFD) is expected to be able to
monitor a wide variety of encapsulations of paths between systems. monitor a wide variety of encapsulations of paths between systems.
When a BFD session monitors an explicitly routed unidirectional path 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 there may be a need to direct egress BFD peer to use a specific path
for the reverse direction of the BFD session. for the reverse direction of the BFD session.
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 5, 2019. This Internet-Draft will expire on February 22, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 3 1.1. Conventions used in this document . . . . . . . . . . . . 3
1.1.1. Requirements Language . . . . . . . . . . . . . . . . 3 1.1.1. Requirements Language . . . . . . . . . . . . . . . . 3
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3 2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
3. Control of the Reverse BFD Path . . . . . . . . . . . . . . . 3 3. Control of the Reverse BFD Path . . . . . . . . . . . . . . . 3
3.1. BFD Reverse Path TLV . . . . . . . . . . . . . . . . . . 3 3.1. BFD Reverse Path TLV . . . . . . . . . . . . . . . . . . 3
3.2. Static and RSVP-TE sub-TLVs . . . . . . . . . . . . . . . 5 3.2. Return Codes . . . . . . . . . . . . . . . . . . . . . . 5
3.3. Return Codes . . . . . . . . . . . . . . . . . . . . . . 5
4. Use Case Scenario . . . . . . . . . . . . . . . . . . . . . . 5 4. Use Case Scenario . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5. Operational Considerations . . . . . . . . . . . . . . . . . 5
5.1. BFD Reverse Path TLV . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5.2. Return Code . . . . . . . . . . . . . . . . . . . . . . . 6 6.1. BFD Reverse Path TLV . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6.2. Return Code . . . . . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. Normative References . . . . . . . . . . . . . . . . . . . . 7
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 8 Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction 1. Introduction
[RFC5880], [RFC5881], and [RFC5883] established the BFD protocol for [RFC5880], [RFC5881], and [RFC5883] established the BFD protocol for
IP networks. [RFC5884] and [RFC7726] set rules for using BFD IP networks. [RFC5884] and [RFC7726] set rules for using BFD
asynchronous mode over IP/MPLS LSPs. These standards do not define asynchronous mode over IP/MPLS LSPs. These standards do not define
means to control the path selection at the egress BFD peer to send means to control the path selection at the egress BFD peer to send
BFD control packets towards the ingress BFD system. BFD control packets towards the ingress BFD system.
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
2. Problem Statement 2. Problem Statement
When BFD is used to monitor explicitly routed unidirectional path, When BFD is used to monitor explicitly routed unidirectional path,
e.g., MPLS-TE LSP, BFD control packets in forward direction would be e.g., MPLS-TE LSP, BFD control packets in forward direction would be
in-band using the mechanism defined in [RFC5884] and [RFC5586]. But in-band using the mechanism defined in [RFC5884]. But the reverse
the reverse direction of the BFD session would follow the shortest direction of the BFD session would follow the shortest path route and
path route and that might lead to the problem in detecting failures that might lead to the problem in detecting failures on an explicit
on an explicit unidirectional path as described below: unidirectional path as described below:
o a failure detection by ingress node on the reverse path may not be o detection by an ingress node of a failure on the reverse path may
interpreted as bi-directional failure unambiguously. 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 To address this scenario, the egress BFD peer would be instructed to
use a specific path for BFD control packets. use a specific path for BFD control packets.
3. Control of the Reverse BFD Path 3. Control of the Reverse BFD Path
To bootstrap a BFD session over an MPLS LSP, LSP ping, defined in To bootstrap a BFD session over an MPLS LSP, LSP ping, defined in
[RFC8029], MUST be used with BFD Discriminator TLV [RFC5884]. This [RFC8029], MUST be used with BFD Discriminator TLV [RFC5884]. This
document defines a new TLV, BFD Reverse Path TLV, that MUST contain a document defines a new TLV, BFD Reverse Path TLV, that MUST contain a
single sub-TLV that can be used to carry information about the single sub-TLV that can be used to carry information about the
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| BFD Reverse Path TLV Type | Length | | BFD Reverse Path TLV Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reverse Path | | Reverse Path |
~ ~ ~ ~
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: BFD Reverse Path TLV Figure 1: BFD Reverse Path TLV
BFD Reverse Path TLV Type is two octets in length and has a value of 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 5). TBD1 (to be assigned by IANA as requested in Section 6).
Length field is two octets long and defines the length in octets of Length field is two octets long and defines the length in octets of
the Reverse Path field. the Reverse Path field.
Reverse Path field contains a sub-TLV. Any non-multicast Target FEC Reverse Path field contains a sub-TLV. Any non-multicast Target FEC
Stack sub-TLV (already defined, or to be defined in the future) for 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 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 used in this field. Multicast Target FEC Stack sub-TLVs, i.e., p2mp
and mp2mp, SHOULD NOT be included in Reverse Path field. If the and mp2mp, SHOULD NOT be included in Reverse Path field. If the
egress LSR finds multicast Target Stack sub-TLV, it MUST send echo egress LSR finds multicast Target Stack sub-TLV, it MUST send echo
reply with the received Reverse Path TLV, BFD Discriminator TLV and reply with the received Reverse Path TLV, BFD Discriminator TLV and
set the Return Code to "Inappropriate Target FEC Stack sub-TLV set the Return Code to "Inappropriate Target FEC Stack sub-TLV
present" Section 3.3. None, one or more sub-TLVs MAY be included in 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 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 Reverse Path TLV, the egress BFD peer MUST revert to using the local
policy based decision as described in Section 7 [RFC5884], i.e., policy based decision as described in Section 7 [RFC5884], i.e.,
routed over IP network. routed over IP network.
If the egress LSR cannot find the path specified in the Reverse Path 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, 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 Reverse Path TLV and set the Return Code to "Failed to establish the
BFD session. The specified reverse path was not found" Section 3.3. BFD session. The specified reverse path was not found" Section 3.2.
An implementation MAY provide configuration options to define action An implementation MAY provide configuration options to define action
at the egress BFD peer. For example, if the egress LSR cannot find at the egress BFD peer. For example, if the egress LSR cannot find
the path specified in the Reverse Path TLV it MAY establish the BFD the path specified in the Reverse Path TLV it MAY establish the BFD
session over IP network as defined in [RFC5884]. session over IP network as defined in [RFC5884].
3.2. Static and RSVP-TE sub-TLVs 3.2. Return Codes
When an explicit path on an MPLS data plane 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 will be able to verify that the
forward LSP and the reverse LSP are mapped to the same FECs as BFD
session both at the ingress and the egress systems. Selection and
control of he rate of LSP Ping with Return Path TLV follows the
[RFC5884] that states: "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."
3.3. Return Codes
This document defines the following Return Codes for MPLS LSP Echo This document defines the following Return Codes for MPLS LSP Echo
Reply: Reply:
o "Inappropriate Target FEC Stack sub-TLV present", (TBD3). When o "Inappropriate Target FEC Stack sub-TLV present", (TBD3). When
multicast Target FEC Stack sub-TLV found in the received Echo multicast Target FEC Stack sub-TLV found in the received Echo
Request by the egress BFD peer, an Echo Reply with the return code Request by the egress BFD peer, an Echo Reply with the return code
set to "Inappropriate Target FEC Stack sub-TLV present" MUST be set to "Inappropriate Target FEC Stack sub-TLV present" MUST be
sent to the ingress BFD peer Section 3.1. sent to the ingress BFD peer Section 3.1.
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A-------B G-----H A-------B G-----H
| | | |
E---------F E---------F
Figure 2: Use Case for BFD Reverse Path TLV Figure 2: Use Case for BFD Reverse Path TLV
If an operator needs node H to monitor a path to node A, e.g. 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 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. Paths it MAY find and use the existing BFD session.
5. IANA Considerations 5. Operational Considerations
5.1. BFD Reverse Path TLV 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."
If an operator planned network maintenance activity that possibly
affects FEC used in the BFD Reverse Path TLV, 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 failure of the BFD session. 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 The IANA is requested to assign a new value for BFD Reverse Path TLV
from the "Multiprotocol Label Switching Architecture (MPLS) Label from the "Multiprotocol Label Switching Architecture (MPLS) Label
Switched Paths (LSPs) Ping Parameters - TLVs" registry, "TLVs and Switched Paths (LSPs) Ping Parameters - TLVs" registry, "TLVs and
sub-TLVs" sub-registry. sub-TLVs" sub-registry.
+--------+----------------------+---------------+ +--------+----------------------+---------------+
| Value | Description | Reference | | Value | Description | Reference |
+--------+----------------------+---------------+ +--------+----------------------+---------------+
| (TBD1) | BFD Reverse Path TLV | This document | | (TBD1) | BFD Reverse Path TLV | This document |
+--------+----------------------+---------------+ +--------+----------------------+---------------+
Table 1: New BFD Reverse Type TLV Table 1: New BFD Reverse Type TLV
5.2. Return Code 6.2. Return Code
The IANA is requested to assign a new Return Code value from the The IANA is requested to assign a new Return Code value from the
"Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs) "Multi-Protocol Label Switching (MPLS) Label Switched Paths (LSPs)
Ping Parameters" registry, "Return Codes" sub-registry, as follows Ping Parameters" registry, "Return Codes" sub-registry, as follows
using a Standards Action value. using a Standards Action value.
+--------+----------------------------------------------+-----------+ +--------+----------------------------------------------+-----------+
| Value | Description | Reference | | Value | Description | Reference |
+--------+----------------------------------------------+-----------+ +--------+----------------------------------------------+-----------+
| (TBD3) | Inappropriate Target FEC Stack sub-TLV | This | | (TBD3) | Inappropriate Target FEC Stack sub-TLV | This |
| | present. | document | | | present. | document |
| (TBD4) | Failed to establish the BFD session. The | This | | (TBD4) | Failed to establish the BFD session. The | This |
| | specified reverse path was not found. | document | | | specified reverse path was not found. | document |
+--------+----------------------------------------------+-----------+ +--------+----------------------------------------------+-----------+
Table 2: New Return Code Table 2: New Return Code
6. Security Considerations 7. Security Considerations
Security considerations discussed in [RFC5880], [RFC5884], [RFC7726], Security considerations discussed in [RFC5880], [RFC5884], [RFC7726],
and [RFC8029], apply to this document. and [RFC8029], apply to this document.
7. Normative References 8. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
"MPLS Generic Associated Channel", RFC 5586,
DOI 10.17487/RFC5586, June 2009,
<https://www.rfc-editor.org/info/rfc5586>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection [RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010, (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>. <https://www.rfc-editor.org/info/rfc5880>.
[RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection [RFC5881] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881, (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
DOI 10.17487/RFC5881, June 2010, DOI 10.17487/RFC5881, June 2010,
<https://www.rfc-editor.org/info/rfc5881>. <https://www.rfc-editor.org/info/rfc5881>.
[RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection [RFC5883] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
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