< draft-ietf-mpls-bfd-directed-09.txt   draft-ietf-mpls-bfd-directed-10.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: February 22, 2019 Nuage Networks Expires: April 1, 2019 Nuage Networks
I. Varlashkin I. Varlashkin
Google Google
M. Chen M. Chen
Huawei Huawei
August 21, 2018 September 28, 2018
Bidirectional Forwarding Detection (BFD) Directed Return Path Bidirectional Forwarding Detection (BFD) Directed Return Path
draft-ietf-mpls-bfd-directed-09 draft-ietf-mpls-bfd-directed-10
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
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
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 February 22, 2019. This Internet-Draft will expire on April 1, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2018 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 . . . . . . . . . . . . . . . 4 3.2. Static and RSVP-TE sub-TLVs . . . . . . . . . . . . . . . 5
3.3. Return Codes . . . . . . . . . . . . . . . . . . . . . . 5 3.3. Return Codes . . . . . . . . . . . . . . . . . . . . . . 5
4. Use Case Scenario . . . . . . . . . . . . . . . . . . . . . . 5 4. Use Case Scenario . . . . . . . . . . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
5.1. BFD Reverse Path TLV . . . . . . . . . . . . . . . . . . 6 5.1. BFD Reverse Path TLV . . . . . . . . . . . . . . . . . . 6
5.2. Return Code . . . . . . . . . . . . . . . . . . . . . . . 6 5.2. Return Code . . . . . . . . . . . . . . . . . . . . . . . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Normative References . . . . . . . . . . . . . . . . . . . . 6 7. 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.
For the case when BFD is used to detect defects of the traffic For the case when BFD is used to detect defects of the traffic
engineered LSP the path the BFD control packets transmitted by the engineered LSP the path the BFD control packets transmitted by the
egress BFD system toward the ingress may be disjoint from the LSP in egress BFD system toward the ingress may be disjoint from the LSP in
the forward direction. The fact that BFD control packets are not the 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 contributes to producing false positive defect reverse directions may be one of the factors contributing to
notifications, i.e., false alarms, at the ingress BFD peer. 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 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 is to be used to instruct the
egress BFD peer to use an explicit path for its BFD control packets egress BFD peer 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. The TLV will be allocated
from the TLV and sub-TLV registry defined in [RFC8029]. As a special 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 case, forward and reverse directions of the BFD session can form a
bi-directional co-routed associated channel. bi-directional co-routed associated channel.
1.1. Conventions used in this document 1.1. Conventions used in this document
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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] and [RFC5586]. But
the reverse direction of the BFD session would follow the shortest the reverse direction of the BFD session would follow the shortest
path route and that might lead to the problem in detecting failures path route and that might lead to the problem in detecting failures
on an explicit unidirectional path as described below: on an explicit unidirectional path as described below:
o a failure detection by ingress node on the reverse path cannot be o a failure detection by ingress node on the reverse path may not be
interpreted as bi-directional failure unambiguously and thus interpreted as bi-directional failure unambiguously.
trigger, for example, protection switchover of the forward
direction without the possibility of being a false positive.
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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present" Section 3.3. None, one or more sub-TLVs MAY be included in present" Section 3.3. 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 3.3.
The egress BFD peer MAY establish the BFD session over IP network as An implementation MAY provide configuration options to define action
defined in [RFC5884]. 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
session over IP network as defined in [RFC5884].
3.2. Static and RSVP-TE sub-TLVs 3.2. Static and RSVP-TE sub-TLVs
When an explicit path on an MPLS data plane is set either as Static 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 or RSVP-TE LSP, corresponding sub-TLVs, defined in [RFC7110], MAY be
used to identify the explicit reverse path for the BFD session. If 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, any of defined in [RFC7110] sub-TLVs used in BFD Reverse Path TLV,
then the periodic verification of the control plane against the data then the periodic verification of the control plane against the data
plane, as recommended in Section 3.2 [RFC5884], MUST use the Return 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 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 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 forward LSP and the reverse LSP are mapped to the same FECs as BFD
session both at the ingress and the egress systems. 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 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
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