< draft-ietf-mpls-bfd-directed-08.txt   draft-ietf-mpls-bfd-directed-09.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: June 8, 2018 Individual Expires: February 22, 2019 Nuage Networks
I. Varlashkin I. Varlashkin
Google Google
M. Chen M. Chen
Huawei Huawei
December 5, 2017 August 21, 2018
Bidirectional Forwarding Detection (BFD) Directed Return Path Bidirectional Forwarding Detection (BFD) Directed Return Path
draft-ietf-mpls-bfd-directed-08 draft-ietf-mpls-bfd-directed-09
Abstract Abstract
Bidirectional Forwarding Detection (BFD) is expected to be able to Bidirectional Forwarding Detection (BFD) is expected to be able to
monitor 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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provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on June 8, 2018. This Internet-Draft will expire on February 22, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2017 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.
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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. Static and RSVP-TE sub-TLVs . . . . . . . . . . . . . . . 4
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 . . . . . . . . . . . . . . . . . . . 6
7. Normative References . . . . . . . . . . . . . . . . . . . . 6 7. Normative References . . . . . . . . . . . . . . . . . . . . 6
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 of using BFD IP networks. [RFC5884] and [RFC7726] set rules for using BFD
asynchronous mode over IP/MPLS LSPs. These standards implicitly asynchronous mode over IP/MPLS LSPs. These standards do not define
assume that the egress BFD peer will use the shortest path route means to control the path selection at the egress BFD peer to send
regardless of route being used to send BFD control packets towards BFD control packets towards the ingress BFD system.
it.
For the case where a LSP is explicitly routed it is likely that the For the case when BFD is used to detect defects of the traffic
shortest return path to the ingress BFD peer would not follow the engineered LSP the path the BFD control packets transmitted by the
same path as the LSP in the forward direction. The fact that BFD egress BFD system toward the ingress may be disjoint from the LSP in
control packets are not guaranteed to follow the same links and nodes the forward direction. The fact that BFD control packets are not
in both forward and reverse directions is a significant factor in guaranteed to follow the same links and nodes in both forward and
producing false positive defect notifications, i.e. false alarms, if reverse directions contributes to producing false positive defect
used by the ingress BFD peer to deduce the state of the forward notifications, i.e., false alarms, at the ingress BFD peer.
direction.
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
skipping to change at page 3, line 19 skipping to change at page 3, line 17
1.1.1. Requirements Language 1.1.1. 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 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 unidirectional explicitly routed 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 a unidirectional explicit 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 cannot be
interpreted as bi-directional failure unambiguously and thus interpreted as bi-directional failure unambiguously and thus
trigger, for example, protection switchover of the forward trigger, for example, protection switchover of the forward
direction without possibility of being a false positive. 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
LSP ping, defined in [RFC8029], uses BFD Discriminator TLV [RFC5884] To bootstrap a BFD session over an MPLS LSP, LSP ping, defined in
to bootstrap a BFD session over an MPLS LSP. This document defines a [RFC8029], MUST be used with BFD Discriminator TLV [RFC5884]. This
new TLV, BFD Reverse Path TLV, that MUST contain a single sub-TLV document defines a new TLV, BFD Reverse Path TLV, that MUST contain a
that can be used to carry information about the reverse path for the single sub-TLV that can be used to carry information about the
BFD session that is specified by value in BFD Discriminator TLV. reverse path for the BFD session that is specified by the value in
BFD 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 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 as 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 2 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 5).
Length field is 2 octets long and defines the length in octets of the Length field is two octets long and defines the length in octets of
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 into 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 3.3. None, one or more sub-TLVs MAY be included in
the BFD Reverse Path TLV. If none sub-TLVs found in the BFD Reverse the BFD Reverse Path TLV. If no sub-TLVs are found in the BFD
Path TLV, the egress BFD peer MUST revert to using the local policy Reverse Path TLV, the egress BFD peer MUST revert to using the local
based decision as described in Section 7 [RFC5884], i.e., routed over policy based decision as described in Section 7 [RFC5884], i.e.,
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 The egress BFD peer MAY establish the BFD session over IP network as
defined in [RFC5884]. 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 respective sub-TLVs defined in [RFC7110] MAY be used or RSVP-TE LSP, corresponding sub-TLVs, defined in [RFC7110], MAY be
to identify the explicit reverse path for the BFD session. 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 3.2 [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.
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
skipping to change at page 5, line 34 skipping to change at page 5, line 34
available at the egress BFD peer, an Echo Reply with the return available at the egress BFD peer, an Echo Reply with the return
code set to "Failed to establish the BFD session. The specified code set to "Failed to establish the BFD session. The specified
reverse path was not found" MUST be sent back to the ingress BFD reverse path was not found" MUST be sent back to the ingress BFD
peer Section 3.1. peer Section 3.1.
4. Use Case Scenario 4. Use Case Scenario
In the network presented in Figure 2 node A monitors two tunnels to 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 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 monitor the first tunnel, node A MUST include a BFD Discriminator TLV
with Discriminator value (e.g. foobar-1) and MAY include a BFD 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 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 BFD session to monitor the second tunnel, node A MUST include a BFD
Discriminator TLV with a different Discriminator value (e.g. foobar- Discriminator TLV with a different Discriminator value (e.g., foobar-
2) [RFC7726] and MAY include a BFD Reverse Path TLV that references 2) [RFC7726] and MAY include a BFD Reverse Path TLV that references
H-G-F-E-B-A tunnel. 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 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 list of known Reverse Paths it H-G-D-C-B-A tunnel, then by looking up the list of known Reverse
MAY find and use the existing BFD session. Paths it MAY find and use the existing BFD session.
5. IANA Considerations 5. IANA Considerations
5.1. BFD Reverse Path TLV 5.1. 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.
skipping to change at page 8, line 18 skipping to change at page 8, line 18
comments from Eric Gray and Carlos Pignataro. comments from Eric Gray and Carlos Pignataro.
Authors' Addresses Authors' Addresses
Greg Mirsky Greg Mirsky
ZTE ZTE
Email: gregimirsky@gmail.com Email: gregimirsky@gmail.com
Jeff Tantsura Jeff Tantsura
Individual Nuage Networks
Email: jefftant.ietf@gmail.com Email: jefftant.ietf@gmail.com
Ilya Varlashkin Ilya Varlashkin
Google Google
Email: Ilya@nobulus.com Email: Ilya@nobulus.com
Mach(Guoyi) Chen Mach(Guoyi) Chen
Huawei Huawei
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