rfc9612.original   rfc9612.txt 
MPLS Working Group G. Mirsky Internet Engineering Task Force (IETF) G. Mirsky
Internet-Draft Ericsson Request for Comments: 9612 Ericsson
Intended status: Experimental J. Tantsura Category: Experimental J. Tantsura
Expires: 14 November 2024 NVIDIA ISSN: 2070-1721 NVIDIA
I. Varlashkin I. Varlashkin
Google Google
M. Chen M. Chen
Huawei Huawei
13 May 2024 July 2024
Bidirectional Forwarding Detection (BFD) Directed Return Path for MPLS Bidirectional Forwarding Detection (BFD) Directed Return Path for MPLS
Label Switched Paths (LSPs) Label Switched Paths (LSPs)
draft-ietf-mpls-bfd-directed-31
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 the egress BFD peer to use a specific there may be a need to direct the egress BFD peer to use a specific
path for the reverse direction of the BFD session. This document path for the reverse direction of the BFD session. This document
describes an extension to the MPLS Label Switched Path (LSP) echo describes an extension to the MPLS Label Switched Path (LSP) echo
request that allows a BFD system to request that the remote BFD peer request that allows a BFD system to request that the remote BFD peer
transmits BFD control packets over the specified LSP. transmit BFD control packets over the specified LSP.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This document is not an Internet Standards Track specification; it is
provisions of BCP 78 and BCP 79. published for examination, experimental implementation, and
evaluation.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months This document defines an Experimental Protocol for the Internet
and may be updated, replaced, or obsoleted by other documents at any community. This document is a product of the Internet Engineering
time. It is inappropriate to use Internet-Drafts as reference Task Force (IETF). It represents the consensus of the IETF
material or to cite them other than as "work in progress." community. It has received public review and has been approved for
publication by the Internet Engineering Steering Group (IESG). Not
all documents approved by the IESG are candidates for any level of
Internet Standard; see Section 2 of RFC 7841.
This Internet-Draft will expire on 14 November 2024. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9612.
Copyright Notice Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction
1.1. Conventions used in this document . . . . . . . . . . . . 3 1.1. Conventions Used in This document
1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 3 1.1.1. Terminology
1.1.2. Requirements Language . . . . . . . . . . . . . . . . 3 1.1.2. Requirements Language
2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3 2. Problem Statement
3. Control of the Reverse BFD Path . . . . . . . . . . . . . . . 4 3. Control of the BFD Reverse Path
3.1. BFD Reverse Path TLV . . . . . . . . . . . . . . . . . . 4 3.1. BFD Reverse Path TLV
3.2. Return Codes . . . . . . . . . . . . . . . . . . . . . . 6 3.2. Return Codes
3.3. Failure Characterization . . . . . . . . . . . . . . . . 6 3.3. Failure Characterization
4. Use Case Scenario . . . . . . . . . . . . . . . . . . . . . . 7 4. Use Case Scenario
5. Operational Considerations . . . . . . . . . . . . . . . . . 7 5. Operational Considerations
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 6. IANA Considerations
6.1. BFD Reverse Path TLV . . . . . . . . . . . . . . . . . . 8 6.1. BFD Reverse Path TLV
6.2. Return Code . . . . . . . . . . . . . . . . . . . . . . . 8 6.2. Return Codes
7. Implementation Status . . . . . . . . . . . . . . . . . . . . 9 7. Security Considerations
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10 8. Normative References
9. Normative References . . . . . . . . . . . . . . . . . . . . 10 Acknowledgments
10. Informative References . . . . . . . . . . . . . . . . . . . 11 Authors' Addresses
Appendix A. Acknowledgments . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction 1. Introduction
[RFC5880], [RFC5881], and [RFC5883] established the Bidirectional [RFC5880], [RFC5881], and [RFC5883] established the Bidirectional
Forwarding Detection (BFD) protocol for IP networks. [RFC5884] and Forwarding Detection (BFD) protocol for IP networks. [RFC5884] and
[RFC7726] set rules for using BFD Asynchronous mode over MPLS Label [RFC7726] set rules for using BFD Asynchronous mode over MPLS Label
Switched Paths (LSPs), while not defining means to control the path Switched Paths (LSPs), while not defining means to control the path
an egress BFD system uses to send BFD control packets towards the that an egress BFD system uses to send BFD control packets towards
ingress BFD system. the ingress BFD system.
When BFD is used to detect defects of the traffic-engineered LSP, the When BFD is used to detect defects of the traffic-engineered LSP, the
path of the BFD control packets transmitted by the egress BFD system path of the BFD control packets transmitted by the egress BFD system
toward the ingress may be disjoint from the monitored LSP in the toward the ingress may be disjoint from the monitored LSP in the
forward direction. The fact that BFD control packets are not forward direction. The fact that BFD control packets are not
guaranteed to follow the same links and nodes in both forward and guaranteed to follow the same links and nodes in both forward and
reverse directions may be one of the factors contributing to reverse directions may be one of the factors contributing to false
producing false positive defect notifications, i.e., false alarms, at positive defect notifications (i.e., false alarms) at the ingress BFD
the ingress BFD peer. Ensuring that both directions of the BFD peer. Ensuring that both directions of the BFD session use co-routed
session use co-routed paths may, in some environments, improve the paths may, in some environments, improve the determinism of the
determinism of the failure detection and localization. failure detection and localization.
This document defines the BFD Reverse Path TLV as an extension to LSP 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 Ping [RFC8029] and proposes that it be used to instruct the egress
egress BFD system to use an explicit path for its BFD control packets BFD system to use an explicit path for its BFD control packets
associated with a particular BFD session. The TLV will be allocated associated with a particular BFD session. IANA has registered this
from the TLV and sub-TLV registry defined in [RFC8029]. As a special TLV in the "TLVs" registry defined by [RFC8029] (see Section 6.1).
case, forward and reverse directions of the BFD session can form a As a special case, forward and reverse directions of the BFD session
bi-directional co-routed associated channel. can form a bidirectional co-routed associated channel.
The LSP ping extension, described in this document, was developed and The LSP ping extension described in this document was developed and
implemented resulting from the operational experiment. The lessons implemented resulting from the operational experiment. The lessons
learned from the operational experiment enabled the use between learned from the operational experiment enabled the use between
systems conforming to this specification. More implementations are systems conforming to this specification. Further implementation is
encouraged to understand better the operational impact of the encouraged to better understand the operational impact of the
mechanism described in the document. mechanism described in the document.
1.1. Conventions used in this document 1.1. Conventions Used in This document
1.1.1. Terminology 1.1.1. Terminology
BFD: Bidirectional Forwarding Detection BFD: Bidirectional Forwarding Detection
FEC: Forwarding Equivalency Class FEC: Forwarding Equivalence Class
LSP: Label Switched Path LSP: Label Switched Path
LSR: Label-Switching router LSR: Label Switching Router
1.1.2. Requirements Language 1.1.2. Requirements Language
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
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 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 an explicitly routed unidirectional path, When BFD is used to monitor an explicitly routed unidirectional path
e.g., MPLS-TE LSP, BFD control packets in the forward direction would (e.g., MPLS-TE LSP), BFD control packets in the forward direction
be in-band using the mechanism defined in [RFC5884]. However, the would be in-band using the mechanism defined in [RFC5884]. However,
reverse direction of the BFD session would follow the shortest path the reverse direction of the BFD session would follow the shortest
route, which could be completely or partially disjoint from the path route, which could be completely or partially disjoint from the
forward path. This creates the potential for the failure of a forward path. This creates the potential for the failure of a
disjoint resource on the reverse path to trigger a BFD failure disjoint resource on the reverse path to trigger a BFD failure
detection, even though the forward path is unaffected. detection, even though the forward path is unaffected.
If the reverse path is congruent with the forward path, the potential If the reverse path is congruent with the forward path, the potential
for such false positives is greatly reduced. For this purpose, this for such false positives is greatly reduced. For this purpose, this
specification provides a means for the egress BFD peer to be specification provides a means for the egress BFD peer to be
instructed to use a specific path for BFD control packets. instructed to use a specific path for BFD control packets.
3. Control of the Reverse BFD Path 3. Control of the BFD Reverse 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 [RFC8029] MUST
[RFC8029], MUST be used with BFD Discriminator TLV [RFC5884]. This be used with the BFD Discriminator TLV [RFC5884]. This document
document defines a new TLV, BFD Reverse Path TLV, that MAY contain defines a new TLV, the BFD Reverse Path TLV, that MAY contain zero or
none, one or more sub-TLVs that can be used to carry information more sub-TLVs that can be used to carry information about the reverse
about the reverse path for the BFD session that is specified by the path for the BFD session that is specified by the value in the BFD
value in BFD Discriminator TLV. Discriminator TLV.
3.1. BFD Reverse Path TLV 3.1. BFD Reverse Path TLV
The BFD Reverse Path TLV is an optional TLV within the LSP ping The BFD Reverse Path TLV is an optional TLV within the LSP ping
[RFC8029]. However, if used, the BFD Discriminator TLV MUST be [RFC8029]. However, if used, the BFD Discriminator TLV MUST be
included in an Echo Request message as well. If the BFD included in an Echo Request message as well. If the BFD
Discriminator TLV is not present when the BFD Reverse Path TLV is Discriminator TLV is not present when the BFD Reverse Path TLV is
included; then it MUST be treated as malformed Echo Request, as included, then it MUST be treated as a malformed Echo Request, as
described in [RFC8029]. described in [RFC8029].
The BFD Reverse Path TLV carries information about the path onto The BFD Reverse Path TLV carries information about the path onto
which the egress BFD peer of the BFD session referenced by the BFD which the egress BFD peer of the BFD session referenced by the BFD
Discriminator TLV MUST transmit BFD control packets. The format of Discriminator TLV MUST transmit BFD control packets. The format of
the BFD Reverse Path TLV is as presented in Figure 1. the BFD Reverse Path TLV is presented in Figure 1.
0 1 2 3 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 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 | | 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:
TBD1 (to be assigned by IANA as requested in Section 6). This two-octet field has a value of 16384 (see Section 6).
Length field is two octets long and defines the length in octets of Length:
the Reverse Path field. This two-octet field defines the length in octets of the Reverse
Path field.
Reverse Path field contains none, one, or more sub-TLVs. Only non- Reverse Path:
multicast Target FEC Stack sub-TLVs (already defined, or to be This field contains zero or more sub-TLVs. Only non-multicast
defined in the future) for TLV Types 1, 16, and 21 of MPLS LSP Ping Target FEC Stack sub-TLVs (already defined or to be defined in the
Parameters registry are permitted to be used in this field. Any future) for TLV Types 1, 16, and 21 in the "Multiprotocol Label
other sub-TLV MUST NOT be used. (This implies that Multicast Target Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters"
FEC Stack sub-TLVs, i.e., p2mp and mp2mp, are not permitted in the registry are permitted to be used in this field. Other sub-TLVs
Reverse Path field.) If the egress Label-Switching Router (LSR) MUST NOT be used. (This implies that multicast Target FEC Stack
finds multicast Target Stack sub-TLV, it MUST send echo reply with sub-TLVs, i.e., p2mp and mp2mp, are not permitted in the Reverse
the received Reverse Path TLV, BFD Discriminator TLV and set the Path field.)
Return Code to "Inappropriate Target FEC Stack sub-TLV present"
(Section 3.2). The BFD Reverse Path TLV includes none, one or more
sub-TLVs. However, the number of sub-TLVs in the Reverse Path field
MUST be limited. The default limit is 128 sub-TLV entries, but an
implementation MAY be able to control that limit. An empty BFD
Reverse Path TLV, i.e., no sub-TLVs present, is used as withdrawal of
any previously set reverse path for the BFD session identified in the
BFD Discriminator 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 of [RFC5884], i.e., routed
over IP network.
If the egress peer LSR cannot find the path specified in the Reverse If the egress LSR finds a multicast Target FEC Stack sub-TLV, it MUST
Path TLV, it MUST send Echo Reply with the received BFD Discriminator send an echo reply with the received BFD Reverse Path TLV, BFD
TLV, Reverse Path TLV, and set the Return Code to "Failed to Discriminator TLV and set the Return Code to 192 ("Inappropriate
establish the BFD session. The specified reverse path was not found" Target FEC Stack sub-TLV present") (see Section 3.2). The BFD
(Section 3.2). If an implementation provides additional Reverse Path TLV includes zero or more sub-TLVs. However, the number
configuration options, these can control actions at the egress BFD of sub-TLVs in the Reverse Path field MUST be limited. The default
peer, including when the path specified in the Reverse Path TLV limit is 128 sub-TLV entries, but an implementation MAY be able to
cannot be found. For example, optionally, if the egress peer LSR control that limit. An empty BFD Reverse Path TLV (i.e., a BFD
cannot find the path specified in the Reverse Path TLV, it MAY Reverse Path TLV with no sub-TLVs) is used to withdraw any previously
establish the BFD session over an IP network, as defined in set reverse path for the BFD session identified in the BFD
[RFC5884]. Note that the return code required by the MUST clause Discriminator TLV. If no sub-TLVs are found in the BFD Reverse Path
does not preclude the session from being established over a different TLV, the egress BFD peer MUST revert to using the local policy-based
path as discussed in the MAY clause. decision as described in Section 7 of [RFC5884], i.e., routed over an
IP network.
The BFD Reverse Path TLV MAY be used in the bootstrapping of a BFD If the egress peer LSR cannot find the path specified in the BFD
session process described in Section 6 of [RFC5884]. A system that Reverse Path TLV, it MUST send an Echo Reply with the received BFD
supports this specification MUST support using the BFD Reverse Path Discriminator TLV, BFD Reverse Path TLV and set the Return Code to
TLV after the BFD session has been established. If a system that 193 ("Failed to establish the BFD session. The specified reverse
supports this specification receives an LSP Ping with the BFD path was not found.") (see Section 3.2). If an implementation
provides additional configuration options, these can control actions
at the egress BFD peer, including when the path specified in the BFD
Reverse Path TLV cannot be found. For example, optionally, if the
egress peer LSR cannot find the path specified in the BFD Reverse
Path TLV, it MAY establish the BFD session over an IP network, as
defined in [RFC5884]. Note that the Return Code required by the
"MUST" clause in this paragraph does not preclude the session from
being established over a different path as discussed in the "MAY"
clause.
The BFD Reverse Path TLV MAY be used in the process of bootstrapping
the BFD session as described in Section 6 of [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 Discriminator TLV and no BFD Reverse Path TLV even though the reverse
path for the specified BFD session has been established according to path for the specified BFD session was established according to the
the previously received BFD Reverse Path TLV, the egress BFD peer previously received BFD Reverse Path TLV, the egress BFD peer MUST
MUST transition to transmitting periodic BFD Control messages as transition to transmitting periodic BFD Control messages as described
defined in Section 7 of [RFC5884]. If a BFD system that received an in Section 7 of [RFC5884]. If a BFD system that received an LSP Ping
LSP Ping with the BFD Reverse Path TLV does not support this with the BFD Reverse Path TLV does not support this specification, it
specification, it will "result in the Return Code of 2 ("One or more will "result in the Return Code of 2 ("One or more of the TLVs was
of the TLVs was not understood") being sent in the echo response" not understood") being sent in the echo response" (Section 3 of
(Section 3 of [RFC8029]). [RFC8029]).
3.2. Return Codes 3.2. Return Codes
This document defines the following Return Codes for MPLS LSP Echo This document defines the following Return Codes for the MPLS LSP
Reply: Echo Reply:
* "Inappropriate Target FEC Stack sub-TLV present" (TBD3). When "Inappropriate Target FEC Stack sub-TLV present" (192):
multicast Target FEC Stack sub-TLV found in the received Echo When a multicast Target FEC Stack sub-TLV is found in the received
Request, the egress BFD peer sends an Echo Reply with the return Echo Request, the egress BFD peer sends an Echo Reply with the
code set to "Inappropriate Target FEC Stack sub-TLV present" to Return Code set to 192 ("Inappropriate Target FEC Stack sub-TLV
the ingress BFD peer Section 3.1. present") to the ingress BFD peer, as described in Section 3.1.
* "Failed to establish the BFD session. The specified reverse path "Failed to establish the BFD session. The specified reverse path
was not found" (TBD4). When a specified reverse path is was not found." (193):
unavailable, the egress BFD peer sends an Echo Reply with the When a specified reverse path is unavailable, the egress BFD peer
return code set to "Failed to establish the BFD session. The sends an Echo Reply with the Return Code set to 193 ("Failed to
specified reverse path was not found" to the ingress BFD peer establish the BFD session. The specified reverse path was not
Section 3.1. found.") to the ingress BFD peer, as described in Section 3.1.
3.3. Failure Characterization 3.3. Failure Characterization
A failure detected by a BFD session that uses the BFD Reverse Path A failure detected by a BFD session that uses the BFD Reverse Path
TLV could be due to a change in the FEC used in the BFD Reverse Path TLV could be due to a change in the FEC used in the BFD Reverse Path
TLV. The ingress BFD peer, upon detection of the network failure, TLV. Upon detection of the network failure, the ingress BFD peer
MUST transmit the LSP Ping Echo request with Return Path TLV to MUST transmit the LSP Ping Echo request with the Return Path TLV to
verify whether the FEC is still valid. If the failure was caused by 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 a change in the FEC used for the reverse direction of the BFD
session, the ingress BFD peer MUST re-direct the reverse path of the session, the ingress BFD peer MUST redirect the reverse path of the
BFD session using another FEC in BFD Reverse Path TLV, and notify an BFD session using another FEC in the BFD Reverse Path TLV and notify
operator. an operator.
4. Use Case Scenario 4. Use Case Scenario
In the network presented in Figure 2, ingress LSR peer A monitors two In the network presented in Figure 2, ingress LSR peer A monitors two
tunnels to the egress LSR peer H: A-B-C-D-G-H and A-B-E-F-G-H. To tunnels to egress LSR peer H: A-B-C-D-G-H and A-B-E-F-G-H. To
bootstrap a BFD session to monitor the first tunnel, the ingress LSR bootstrap a BFD session to monitor the first tunnel, ingress LSR peer
peer A includes a BFD Discriminator TLV with Discriminator value A includes a BFD Discriminator TLV with a Discriminator value (e.g.,
(e.g., foobar-1). Peer A includes a BFD Reverse Path TLV referencing foobar-1). Peer A includes a BFD Reverse Path TLV referencing the
the H-G-D-C-B-A tunnel to control the path from the egress LSR. To H-G-D-C-B-A tunnel to control the path from the egress LSR. To
bootstrap a BFD session to monitor the second tunnel, ingress LSR bootstrap a BFD session to monitor the second tunnel, ingress LSR
peer A, includes a BFD Discriminator TLV with a different peer A includes a BFD Discriminator TLV with a different
Discriminator value (e.g., foobar-2) [RFC7726] and a BFD Reverse Path Discriminator value (e.g., foobar-2) [RFC7726] and a BFD Reverse Path
TLV that references the H-G-F-E-B-A tunnel. TLV that references the H-G-F-E-B-A tunnel.
C---------D C---------D
| | | |
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 egress LSR peer H to monitor a path to the If an operator needs egress LSR peer H to monitor a path to ingress
ingress LSR peer A, e.g., H-G-D-C-B-A tunnel, then by looking up the LSR peer A, e.g., the H-G-D-C-B-A tunnel, then by looking up the list
list of known Reverse Paths, it MAY find and use the existing BFD of known reverse paths, it MAY find and use the existing BFD session.
session.
5. Operational Considerations 5. Operational Considerations
When an explicit path is set either as Static or RSVP-TE LSP, When an explicit path is set as either Static or RSVP-TE LSP,
corresponding sub-TLVs, defined in [RFC7110], MAY be used to identify corresponding sub-TLVs (defined in [RFC7110]) MAY be used to identify
the explicit reverse path for the BFD session. If a particular set the explicit reverse path for the BFD session. If a particular set
of sub-TLVs composes the Return Path TLV [RFC7110] and does not of sub-TLVs composes the Return Path TLV [RFC7110] and does not
increase the length of the Maximum Transmission Unit for the given increase the length of the Maximum Transmission Unit for the given
LSP, that set can be safely used in the BFD Reverse Path TLV. If any LSP, that set can be safely used in the BFD Reverse Path TLV. If any
of defined in [RFC7110] sub-TLVs used in BFD Reverse Path TLV, then of the sub-TLVs defined in [RFC7110] are used in the BFD Reverse Path
the periodic verification of the control plane against the data TLV, then the periodic verification of the control plane against the
plane, as recommended in Section 4 of [RFC5884], MUST use the Return data plane, as recommended in Section 4 of [RFC5884], MUST use the
Path TLV, as per [RFC7110], with that sub-TLV. By using the LSP Ping Return Path TLV, as per [RFC7110], with that sub-TLV. By using the
with Return Path TLV, an operator monitors whether at the egress BFD LSP Ping with the Return Path TLV, an operator monitors whether the
node the reverse LSP is mapped to the same FEC as the BFD session. reverse LSP is mapped to the same FEC as the BFD session at the
Selection and control of the rate of LSP Ping with Return Path TLV egress BFD node. Selection and control of the rate of the LSP Ping
follows the recommendation of [RFC5884]: "The rate of generation of with the Return Path TLV follows the recommendation in [RFC5884]:
these LSP Ping Echo request messages SHOULD be significantly less
than the rate of generation of the BFD Control packets. An | The rate of generation of these LSP Ping Echo request messages
implementation MAY provide configuration options to control the rate | SHOULD be significantly less than the rate of generation of the
of generation of the periodic LSP Ping Echo request messages." | BFD Control packets. An implementation MAY provide configuration
Suppose an operator planned network maintenance activity that | options to control the rate of generation of the periodic LSP Ping
possibly affects FEC used in the BFD Reverse Path TLV. In that case, | Echo request messages.
the operator can avoid the unnecessary disruption by using the LSP
Suppose an operator planned a network maintenance activity that
possibly affects the FEC used in the BFD Reverse Path TLV. In that
case, the operator can avoid unnecessary disruption by using the LSP
Ping with a new FEC in the BFD Reverse Path TLV. But in some Ping with a new FEC in the BFD Reverse Path TLV. But in some
scenarios, proactive measures cannot be taken. Because the frequency scenarios, proactive measures cannot be taken. Because the frequency
of LSP Ping messages will be lower than the defect detection time 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- 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. An path FEC will first be detected as the BFD session's failure. An
operator will be notified as described in Section 3.3. operator will be notified as described in Section 3.3.
6. IANA Considerations 6. IANA Considerations
6.1. BFD Reverse Path TLV 6.1. BFD Reverse Path TLV
The IANA is requested to assign a new value for BFD Reverse Path TLV IANA has assigned the following value for the BFD Reverse Path TLV
from the 16384-31739 range in the "TLVs" registry of "Multiprotocol from the 16384-31739 range in the "TLVs" subregistry within the
Label Switching Architecture (MPLS) Label Switched Paths (LSPs) Ping "Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs)
Parameters" registry. Ping Parameters" registry.
+=======+=======+=============+====================================+
|Type |TLV |Reference | Sub-TLV Registry |
| |Name | | |
+=======+=======+=============+====================================+
| (TBD1)|BFD |This document| Only non-multicast sub-TLV |
| |Reverse| | (already defined or to be defined |
| |Path | | in the future) at |
| |TLV | | [https://www.iana.org/assignments/ |
| | | | mpls-lsp-ping-parameters/mpls-lsp- |
| | | | ping-parameters.xml#sub-tlv- |
| | | | 1-16-21] |
| | | | (https://www.iana.org/assignments/ |
| | | | mpls-lsp-ping-parameters/mpls-lsp- |
| | | | ping-parameters.xml#sub-tlv- |
| | | | 1-16-21) are permitted to be used |
| | | | in this field. Any other sub-TLV |
| | | | MUST NOT be used. |
+-------+-------+-------------+------------------------------------+
Table 1: New BFD Reverse Type TLV
6.2. Return Code
The IANA is requested to assign new Return Code values from the range
192-247 of the "Return Codes" registry of the "Multi-Protocol Label
Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters", as in
Table 2.
+=========+=============================+===============+
| 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.
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 commonly used 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) +=======+=========+===========+====================================+
| Type | TLV | Reference | Sub-TLV Registry |
| | Name | | |
+=======+=========+===========+====================================+
| 16384 | BFD | RFC 9612 | Only non-multicast sub-TLVs |
| | Reverse | | (already defined or to be defined |
| | Path | | in the future) at |
| | | | <https://www.iana.org/assignments/ |
| | | | mpls-lsp-ping-parameters/mpls-lsp- |
| | | | ping-parameters.xml#sub-tlv- |
| | | | 1-16-21> are permitted to be used |
| | | | in this field. Other sub-TLVs |
| | | | MUST NOT be used. |
+-------+---------+-----------+------------------------------------+
- Version compatibility: draft-ietf-mpls-bfd-directed-10. Table 1: New BFD Reverse Path TLV
- Licensing: proprietary. 6.2. Return Codes
- Implementation experience: simple once you support RFC 7110. IANA has assigned the following Return Code values from the 192-247
range in the "Return Codes" subregistry within the "Multiprotocol
Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters"
registry.
- Contact information: Qian Xin qian.xin2@zte.com.cn +=======+===========================================+===========+
| Value | Meaning | Reference |
+=======+===========================================+===========+
| 192 | Inappropriate Target FEC Stack sub-TLV | RFC 9612 |
| | present | |
+-------+-------------------------------------------+-----------+
| 193 | Failed to establish the BFD session. The | RFC 9612 |
| | specified reverse path was not found. | |
+-------+-------------------------------------------+-----------+
- The date when information about this particular implementation was Table 2: New Return Codes
last updated: 12/16/2019
8. Security Considerations 7. Security Considerations
Security considerations discussed in [RFC5880], [RFC5884], [RFC7726], Security considerations discussed in [RFC5880], [RFC5884], [RFC7726],
[RFC8029], and [RFC7110] apply to this document. [RFC8029], and [RFC7110] apply to this document.
BFD Reverse Path TLV may be exploited as an attack vector by The BFD Reverse Path TLV may be exploited as an attack vector by
inflating the number of included sub-TLVs. The number of sub-TLVs inflating the number of included sub-TLVs. The number of sub-TLVs
MUST be limited to mitigate that threat. The default limit for the MUST be limited to mitigate that threat. The default limit for the
number of sub-TLVs is set in Section 3.1 to 128. An implementation number of sub-TLVs is set to 128 (see Section 3.1). An
MAY use a mechanism to control that limit. implementation MAY use a mechanism to control that limit.
9. 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>.
[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>.
skipping to change at page 11, line 31 skipping to change at line 438
[RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N., [RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N.,
Aldrin, S., and M. Chen, "Detecting Multiprotocol Label Aldrin, S., and M. Chen, "Detecting Multiprotocol Label
Switched (MPLS) Data-Plane Failures", RFC 8029, Switched (MPLS) Data-Plane Failures", RFC 8029,
DOI 10.17487/RFC8029, March 2017, DOI 10.17487/RFC8029, March 2017,
<https://www.rfc-editor.org/info/rfc8029>. <https://www.rfc-editor.org/info/rfc8029>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
10. Informative References Acknowledgments
[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 The authors greatly appreciate the thorough reviews and helpful
comments from Eric Gray and Carlos Pignataro. The authors much comments from Eric Gray and Carlos Pignataro. The authors much
appreciate the help of Qian Xin, who provided information about the appreciate the help of Qian Xin, who provided information about the
implementation of this specification. implementation of this specification.
Authors' Addresses Authors' Addresses
Greg Mirsky Greg Mirsky
Ericsson Ericsson
Email: gregimirsky@gmail.com Email: gregimirsky@gmail.com
Jeff Tantsura Jeff Tantsura
NVIDIA NVIDIA
Email: jefftant.ietf@gmail.com Email: jefftant.ietf@gmail.com
Ilya Varlashkin Ilya Varlashkin
Google Google
Email: imv@google.com Email: imv@google.com
Mach(Guoyi) Chen Mach(Guoyi) Chen
Huawei Huawei
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