PCE Working Group C. Barth
Internet-Draft Juniper Networks
Intended status: Standards Track R. Gandhi
Expires: November 22, 2017 Cisco Systems, Inc.
B. Wen
Comcast
May 21, 2017
PCEP Extensions for
Associated Bidirectional Label Switched Paths (LSPs)
draft-barth-pce-association-bidir-02
Abstract
The Path Computation Element Communication Protocol (PCEP) provides
mechanisms for Path Computation Elements (PCEs) to perform path
computations in response to Path Computation Clients (PCCs) requests.
The Stateful PCE extensions allow stateful control of Multiprotocol
Label Switching (MPLS) Traffic Engineering (TE) Label Switched Paths
(LSPs) using PCEP.
This document defines PCEP extensions for binding two reverse
unidirectional MPLS TE LSPs into an Associated Bidirectional Label
Switched Path (LSP) when using a Stateful PCE for both PCE-Initiated
and PCC-Initiated LSPs as well as when using a Stateless PCE.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Copyright Notice
Copyright (c) 2017 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
2.1. Key Word Definitions . . . . . . . . . . . . . . . . . . . 4
2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Single-sided Initiation . . . . . . . . . . . . . . . . . 5
3.2. Double-sided Initiation . . . . . . . . . . . . . . . . . 5
3.3. Co-routed Associated Bidirectional LSP . . . . . . . . . . 6
4. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 6
4.1. Association Object . . . . . . . . . . . . . . . . . . . . 6
4.2. Bidirectional LSP Association Group TLV . . . . . . . . . 6
5. PCEP Procedure . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. PCE Initiated LSPs . . . . . . . . . . . . . . . . . . . . 8
5.2. PCC Initiated LSPs . . . . . . . . . . . . . . . . . . . . 8
5.3. Stateless PCE . . . . . . . . . . . . . . . . . . . . . . 8
5.4. State Synchronization . . . . . . . . . . . . . . . . . . 8
5.5. Error Handling . . . . . . . . . . . . . . . . . . . . . . 8
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. Manageability Considerations . . . . . . . . . . . . . . . . . 9
7.1. Control of Function and Policy . . . . . . . . . . . . . . 9
7.2. Information and Data Models . . . . . . . . . . . . . . . 9
7.3. Liveness Detection and Monitoring . . . . . . . . . . . . 9
7.4. Verify Correct Operations . . . . . . . . . . . . . . . . 9
7.5. Requirements On Other Protocols . . . . . . . . . . . . . 9
7.6. Impact On Network Operations . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8.1. Association Types . . . . . . . . . . . . . . . . . . . . 10
8.2. Bidirectional LSP Association Group TLV . . . . . . . . . 10
8.2.1. Flag Fields in Bidirectional LSP Association Group
TLV . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.3. PCEP Errors . . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
9.1. Normative References . . . . . . . . . . . . . . . . . . . 12
9.2. Informative References . . . . . . . . . . . . . . . . . . 12
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 14
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction
[RFC5440] describes the Path Computation Element Protocol (PCEP) as a
communication mechanism between a Path Computation Client (PCC) and a
Path Control Element (PCE), or between PCE and PCC, that enables
computation of Multiprotocol Label Switching (MPLS) Traffic
Engineering (TE) Label Switched Paths (LSPs).
[I-D.ietf-pce-stateful-pce] specifies extensions to PCEP to enable
stateful control of MPLS TE LSPs. It describes two modes of
operation - Passive Stateful PCE and Active Stateful PCE. In [I-
D.ietf-pce-stateful-pce], the focus is on Active Stateful PCE where
LSPs are provisioned on the PCC and control over them is delegated to
a PCE. Further, [I-D.ietf-pce-pce-initiated-lsp] describes the
setup, maintenance and teardown of PCE-Initiated LSPs for the
Stateful PCE model.
[I-D.ietf-pce-association] introduces a generic mechanism to create a
grouping of LSPs which can then be used to define associations
between a set of LSPs and/or a set of attributes, for example primary
and secondary LSP associations, and is equally applicable to the
active and passive modes of a Stateful PCE [I-D.ietf-pce-stateful-
pce] or a stateless PCE [RFC5440].
The MPLS Transport Profile (MPLS-TP) requirements document [RFC5654]
specifies that MPLS-TP MUST support associated bidirectional point-
to-point LSPs. [RFC7551] specifies RSVP signaling extensions for
binding two reverse unidirectional LSPs into an associated
bidirectional LSP. The fast reroute (FRR) procedures for associated
bidirectional LSPs are described in [I-D.ietf-teas-assoc-corouted-
bidir-frr].
This document specifies PCEP extensions for binding two reverse
unidirectional MPLS-TE LSPs into an Associated Bidirectional LSP for
both single-sided and double-sided initiation cases when using a
Stateful or Stateless PCE. The PCEP extensions cover the following
cases:
o A PCE initiates the forward and/ or reverse LSP of a single-sided
or double-sided bidirectional LSP on a PCC and retains the control
of the LSP. The PCE computes the path of the LSP and updates the
PCC with the information about the path.
o A PCC initiates the forward and/ or reverse LSP of a single-sided
bidirectional LSP and retains the control of the LSP. The PCC
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computes the path of the LSP and updates the PCE with the
information about the path (as long as it controls the LSP).
o A PCC initiates the forward and/ or reverse LSP of a single-sided
bidirectional LSP and delegates the control of the LSP to a
Stateful PCE. The PCE may compute the path of the LSP and update
the PCC with the information about the path (as long as it
controls the LSP).
o A PCC requests co-routed or non co-routed paths for forward and
reverse LSPs of a bidirectional LSP from a Stateless PCE.
2. Conventions Used in This Document
2.1. Key Word Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2.2. Terminology
The reader is assumed to be familiar with the terminology defined in
[RFC5440] and [RFC7551].
3. Overview
As shown in Figure 1, two reverse unidirectional LSPs can be
associated to form an associated bidirectional LSP. There are two
methods of initiating the bidirectional LSP association, single-sided
and double-sided as described in the following sections.
LSP1 --> LSP1 --> LSP1 -->
+-----+ +-----+ +-----+ +-----+
| A +-----------+ B +-----------+ C +-----------+ D |
+-----+ +--+--+ +--+--+ +-----+
<-- LSP2 | | <-- LSP2
| |
| |
+--+--+ +--+--+
| E +-----------+ F |
+-----+ +-----+
<-- LSP2
Figure 1: Example of Associated Bidirectional LSP
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3.1. Single-sided Initiation
As specified in [RFC7551], in the single-sided initiation case, the
bidirectional tunnel is signaled only by one endpoint node (PCC) of
the tunnel. Both forward and reverse LSPs of this tunnel are
initiated with the Association Type set to "Single-sided
Bidirectional LSP Association" on the originating endpoint node. The
forward and reverse LSPs are identified in the Bidirectional LSP
Association Group TLV of their PCEP Association Objects.
The originating endpoint node signals the properties for the revere
LSP in the RSVP REVERSE_LSP Object [RFC7551] of the forward LSP Path
message. The remote endpoint then creates the corresponding reverse
tunnel and signals the reverse LSP in response to the received RSVP
Path message.
The two unidirectional reverse LSPs on the originating endpoint node
are bound together using the PCEP Association Object and on the
remote endpoint node by the RSVP signaled Association Object.
As shown in Figure 1, both the forward LSP LSP1 and the reverse LSP
LSP2 are initiated on the originating endpoint node A, either by the
PCE or the PCC. The creation of reverse LSP2 on the remote endpoint
node D is triggered by the RSVP signaled LSP1.
As specified in [I-D.ietf-teas-assoc-corouted-bidir-frr], for fast-
reroute bypass tunnel assignment, the LSP starting from the
originating node is identified as the forward LSP of the single-sided
initiated bidirectional LSP.
3.2. Double-sided Initiation
As specified in [RFC7551], in the double-sided initiation case, the
bidirectional LSP is signaled by the both endpoint nodes (PCCs) of
the tunnel. The forward and reverse LSPs of this tunnel are
initiated with the Association Type set to "Double-sided
Bidirectional LSP Association" on both endpoint nodes. The forward
and reverse LSPs are identified in the Bidirectional LSP Association
Group TLV of their Association Objects.
The two reverse unidirectional LSPs on both the endpoint nodes are
bound together by using the PCEP Association Object.
As shown in Figure 1, LSP1 is initiated on the endpoint node A and
LSP2 is initiated on the endpoint node D, both by the PCE.
As specified in [I-D.ietf-teas-assoc-corouted-bidir-frr], for fast-
reroute bypass tunnel assignment, the LSP with the higher source
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address is identified as the forward LSP of the double-sided
initiated bidirectional LSP.
3.3. Co-routed Associated Bidirectional LSP
In both single-sided and double-sided initiation cases, forward and
reverse LSPs may be co-routed as shown in Figure 2, where both
forward and reverse LSPs follow the same congruent path.
LSP3 --> LSP3 --> LSP3 -->
+-----+ +-----+ +-----+ +-----+
| A +-----------+ B +-----------+ C +-----------+ D |
+-----+ +-----+ +-----+ +-----+
<-- LSP4 <-- LSP4 <-- LSP4
Figure 2: Example of Co-routed Associated Bidirectional LSP
4. Protocol Extensions
4.1. Association Object
As per [I-D.ietf-pce-association], LSPs are associated by adding them
to a common association group. This document defines two new
Bidirectional LSP Association Groups to be used by the associated
bidirectional LSPs. A member of the Bidirectional LSP Association
Group can take the role of a forward or reverse LSP. The reverse LSP
source address MUST be the destination address of the forward LSP and
the reverse LSP destination address MUST be the source address of the
forward LSP within a bidirectional LSP association group. An LSP can
not be part of more than one Bidirectional LSP Association Group.
This document defines two new Association Types for the Association
Object as follows:
o Association Type (TBD1) = Single-sided Bidirectional LSP
Association Group
o Association Type (TBD2) = Double-sided Bidirectional LSP
Association Group
The Association ID, Association Source, optional Global Association
Source and optional Extended Association ID in the Bidirectional LSP
Association Group Object are populated using the procedures defined
in [RFC7551].
4.2. Bidirectional LSP Association Group TLV
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The Bidirectional LSP Association Group TLV is an optional TLV for
use with the Single-sided and Double-sided Bidirectional LSP
Association Group Object Types.
o The Bidirectional LSP Association Group TLV follows the PCEP TLV
format from [RFC5440].
o The Type (16 bits) of the TLV is TBD3, to be assigned by IANA.
o The Length is 4 Bytes.
o The value comprises of a single field, the Bidirectional LSP
Association Flags (32 bits), where each bit represents a flag
option.
o If the Bidirectional LSP Association Group TLV is missing, it
means the LSP is the forward LSP.
o The Bidirectional LSP Association Group TLV MUST NOT be present
more than once. If it appears more than once, only the first
occurrence is processed and any others MUST be ignored.
The format of the Bidirectional LSP Association Group TLV is shown in
Figure 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = TBD3 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |C|R|F|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Bidirectional LSP Association Group TLV format
Bidirectional LSP Association Flags are defined as following.
F (Forward LSP, 1 bit) - Indicates whether the LSP associated is the
forward LSP of the bidirectional LSP. If this flag is set, the LSP
is a forward LSP.
R (Reverse LSP, 1 bit) - Indicates whether the LSP associated is the
reverse LSP of the bidirectional LSP. If this flag is set, the LSP
is a reverse LSP.
C (Co-routed LSP, 1 bit) - Indicates whether the bidirectional LSP is
co-routed. If this flag is set, the associated bidirectional LSP
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is co-routed. This flag MUST be set for both the forward and
reverse LSPs of a co-routed bidirectional LSP.
The Reserved flags MUST be set to 0 when sent and MUST be ignore when
received.
When an associated bidirectional LSP is delegated to a Stateful PCE,
the C flag is used by the PCE to compute paths of the forward and
reverse LSPs.
5. PCEP Procedure
5.1. PCE Initiated LSPs
As specified in [I-D.ietf-pce-association], Association Groups can be
created by both Stateful PCE and PCC.
A Stateful PCE can create and update the forward and reverse LSPs
independently for both Single-sided and Double-sided bidirectional
LSP association groups.
5.2. PCC Initiated LSPs
A PCC can associate or remove an LSP under its control from the
bidirectional LSP association group. The PCC must report the change
in association to Stateful PCE via PCRpt message.
5.3. Stateless PCE
A PCC can request co-routed or non co-routed forward and reverse
direction paths from a stateless PCE for the bidirectional LSP
association group.
5.4. State Synchronization
During state synchronization, a PCC MUST report all the existing
bidirectional LSP association groups to the Stateful PCE. After the
state synchronization, the PCE MUST remove all stale associations.
5.5. Error Handling
The reverse LSP in the bidirectional LSP association group MUST have
the source address matching the destination address of the forward
LSP and destination address matching the source address of the
forward LSP. If a PCE attempts to add an LSP to a bidirectional LSP
association group not complying to this rule, the PCC for the single-
sided initiation case MUST send PCErr with Error-Type= TBD4
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(Bidirectional LSP Association Error) and Error-Value = 1 (Endpoints
mismatch). Similarly, if a PCC attempts to add an LSP to a
bidirectional LSP association group at PCE not complying to this
rule, the PCE for both single-sided and double-sided initiated
bidirectional LSPs MUST send this PCErr.
6. Security Considerations
This document introduces two new Association Types for the
Association Object, Double-sided Bidirectional LSP Association Group
and Single-sided Associated Bidirectional LSP Group. These types, by
themselves, introduce no additional security concerns beyond those
discussed in [RFC5440], [I-D.ietf-pce-stateful-pce], and [I-D.ietf-
pce-association].
7. Manageability Considerations
7.1. Control of Function and Policy
An operator MUST be allowed to provision the bidirectional LSP
association parameters at PCEP peers.
7.2. Information and Data Models
A Management Information Base (MIB) module for modeling PCEP is
described in [RFC7420]. However, one may prefer the mechanism for
configuration using YANG data model [I-D.ietf-pce-pcep-yang]. These
SHOULD be enhanced to provide controls and indicators for support of
the associated bidirectional LSP feature. Support for various
configuration parameters as well as counters of messages
sent/received containing the TLVs defined in this document SHOULD be
added.
7.3. Liveness Detection and Monitoring
The mechanisms defined in this document do not imply any new liveness
detection and monitoring requirements in addition to those already
listed in [RFC5440].
7.4. Verify Correct Operations
The mechanisms defined in this document do not imply any new
operation verification requirements in addition to those already
listed in [RFC5440].
7.5. Requirements On Other Protocols
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The mechanisms defined in this document do not add any new
requirements on other protocols.
7.6. Impact On Network Operations
The mechanisms defined in this document do not have any new impact on
network operations.
8. IANA Considerations
8.1. Association Types
This document defines the following Association Types for the
Association Object defined [I-D.ietf-pce-association].
Value Name Reference
---------------------------------------------------------------------
TBD1 Single-sided Bidirectional LSP Association Group [This document]
TBD2 Double-sided Bidirectional LSP Association Group [This document]
8.2. Bidirectional LSP Association Group TLV
This document defines a new TLV for carrying additional LSP
information for the Bidirectional LSP Association Group TLV as
following:
TLV-Type Name Reference
-------------------------------------------------------------------
TBD3 Bidirectional LSP Association Group TLV [This document]
8.2.1. Flag Fields in Bidirectional LSP Association Group TLV
This document requests that a new sub-registry, named "Bidirectional
LSP Association Group TLV Flag Field", is created within the "Path
Computation Element Protocol (PCEP) Numbers" registry to manage the
Flag field in the Bidirectional LSP Association Group TLV.
New values are to be assigned by Standards Action [RFC5226]. Each
bit should be tracked with the following qualities:
o Bit number (counting from bit 0 as the most significant bit)
o Capability description
o Defining RFC
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The following values are defined in this document for the Flag field.
Bit No. Description Reference
---------------------------------------------------------
31 F - Forward LSP [This document]
30 R - Reverse LSP [This document]
29 C - Co-routed LSP [This document]
8.3. PCEP Errors
IANA is requested to allocate new Error-Type and Error-Value within
the " PCEP-ERROR Object Error Types and Values" sub-registry of the
PCEP Numbers registry, as follows:
Error-Type Description Reference
-----------------------------------------------------------------
TBD4 Bidirectional LSP Association Error [This document]
Error-value=1: Endpoints mismatch [This document]
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9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009.
[RFC7551] Zhang, F., Ed., Jing, R., and Gandhi, R., Ed., "RSVP-TE
Extensions for Associated Bidirectional LSPs", RFC 7551,
May 2015.
[I-D.ietf-pce-association] Minei, I., Crabbe, E., Sivabalan, S.,
Ananthakrishnan, H., Zhang, X., and Y. Tanaka, "PCEP
Extensions for Establishing Relationships Between Sets of
LSPs", draft-ietf-pce-association-group (work in
progress).
[I-D.ietf-pce-stateful-pce] Crabbe, E., Minei, I., Medved, J., and
R. Varga, "PCEP Extensions for Stateful PCE", draft-ietf-
pce-stateful-pce (work in progress).
[I-D.ietf-pce-pce-initiated-lsp] Crabbe, E., Minei, I., Sivabalan,
S., and R. Varga, "PCEP Extensions for PCE-initiated LSP
Setup in a Stateful PCE Model", draft-ietf-pce-pce-
initiated-lsp (work in progress).
[I-D.ietf-teas-assoc-corouted-bidir-frr] Gandhi, R., Ed., Shah, H.,
and J. Whittaker, "Fast Reroute Procedures for Associated
Bidirectional Label Switched Paths", draft-ietf-teas-
assoc-corouted-bidir-frr (work-in-progress).
9.2. Informative References
[RFC5654] Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
Sprecher, N., and S. Ueno, "Requirements of an MPLS
Transport Profile", RFC 5654, September 2009.
[RFC7420] Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
Hardwick, "Path Computation Element Communication Protocol
(PCEP) Management Information Base (MIB) Module", RFC
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7420, December 2014.
[I-D.ietf-pce-pcep-yang] Dhody, D., Hardwick, J., Beeram, V., and J.
Tantsura, "A YANG Data Model for Path Computation Element
Communications Protocol (PCEP)", draft-ietf-pce-pcep-yang
(work in progress).
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Acknowledgments
TBA.
Authors' Addresses
Colby Barth
Juniper Networks
Email: cbarth@juniper.net
Rakesh Gandhi
Cisco Systems, Inc.
Email: rgandhi@cisco.com
Bin Wen
Comcast
Email: Bin_Wen@cable.comcast.com
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