PCE Working Group
Internet Engineering Task Force (IETF) R. Gandhi, Ed.
Internet-Draft
Request for Comments: 9059 Cisco Systems, Inc.
Intended status:
Category: Standards Track C. Barth
Expires: August 25, 2021
ISSN: 2070-1721 Juniper Networks
B. Wen
Comcast
February 21,
June 2021
Path Computation Element Communication Protocol (PCEP) Extensions for
Associated Bidirectional Label Switched Paths (LSPs)
draft-ietf-pce-association-bidir-14
Abstract
This document defines PCEP Path Computation Element Communication Protocol
(PCEP) extensions for grouping two unidirectional MPLS-TE Label
Switched Paths (LSPs), one in each direction in the network, into an Associated Bidirectional
associated bidirectional LSP. These PCEP extensions can be applied
either using a Stateful stateful PCE for both PCE-Initiated PCE-initiated and PCC-
Initiated LSPs, as well as when PCC-initiated
LSPs or using a Stateless stateless PCE. The PCEP procedures defined are
applicable to the LSPs using RSVP-TE for signaling.
Status of This Memo
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https://www.rfc-editor.org/info/rfc9059.
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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 Single-Sided Initiation . . . . . . . . . . . . . . . . . 5
3.1.1. PCE-Initiated Single-sided Single-Sided Bidirectional LSP . . . . 5
3.1.2. PCC-Initiated Single-sided Single-Sided Bidirectional LSP . . . . 6
3.2. Double-sided Double-Sided Initiation . . . . . . . . . . . . . . . . . 7
3.2.1. PCE-Initiated Double-sided Double-Sided Bidirectional LSP . . . . 7
3.2.2. PCC-Initiated Double-sided Double-Sided Bidirectional LSP . . . . 8
3.3. Co-routed Associated Bidirectional LSP . . . . . . . . . 9
3.4. Summary of PCEP Extensions . . . . . . . . . . . . . . . 9
3.5. Operational Considerations . . . . . . . . . . . . . . . 10
4. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 11
4.1. ASSOCIATION Object . . . . . . . . . . . . . . . . . . . 11
4.2. Bidirectional LSP Association Group TLV . . . . . . . . . 12
5. PCEP Procedure . . . . . . . . . . . . . . . . . . . . . . . 13
5.1. PCE Initiated PCE-Initiated LSPs . . . . . . . . . . . . . . . . . . . 14
5.2. PCC Initiated PCC-Initiated LSPs . . . . . . . . . . . . . . . . . . . 14
5.3. Stateless PCE . . . . . . . . . . . . . . . . . . . . . . 15
5.4. Bidirectional (B) Flag . . . . . . . . . . . . . . . . . 15
5.5. PLSP-ID Usage . . . . . . . . . . . . . . . . . . . . . . 16
5.6. State Synchronization . . . . . . . . . . . . . . . . . . 16
5.7. Error Handling . . . . . . . . . . . . . . . . . . . . . 16
6. Implementation Status . . . . . . . . . . . . . . . . . . . . 17
6.1. Implementation . . . . . . . . . . . . . . . . . . . . . 18
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8.
7. Manageability Considerations . . . . . . . . . . . . . . . . 18
8.1.
7.1. Control of Function and Policy . . . . . . . . . . . . . 18
8.2.
7.2. Information and Data Models . . . . . . . . . . . . . . . 18
8.3.
7.3. Liveness Detection and Monitoring . . . . . . . . . . . . 19
8.4.
7.4. Verify Correct Operations . . . . . . . . . . . . . . . . 19
8.5.
7.5. Requirements On on Other Protocols . . . . . . . . . . . . . 19
8.6.
7.6. Impact On on Network Operations . . . . . . . . . . . . . . 19
9.
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
9.1.
8.1. Association Types . . . . . . . . . . . . . . . . . . . . 19
9.2.
8.2. Bidirectional LSP Association Group TLV . . . . . . . . . 19
9.2.1.
8.2.1. Flag Field in Bidirectional LSP Association Group TLV 20
9.3.
8.3. PCEP Errors . . . . . . . . . . . . . . . . . . . . . . . 20
10.
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
10.1.
9.1. Normative References . . . . . . . . . . . . . . . . . . 21
10.2.
9.2. Informative References . . . . . . . . . . . . . . . . . 22
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
[RFC5440] describes the Path Computation Element Communication
Protocol (PCEP) as a communication mechanism between a Path
Computation Client (PCC) and a Path Computation Element (PCE), or
between PCE and PCC, that enables computation of Multiprotocol Label
Switching (MPLS) - Traffic Engineering (TE) Label Switched Paths
(LSPs).
[RFC8231] specifies extensions to PCEP to enable stateful control of
MPLS-TE LSPs. It describes two modes of operation - Passive Stateful operation: passive stateful
PCE and Active Stateful active stateful PCE. In [RFC8231], the focus is on Active
Stateful active
stateful PCE where LSPs are provisioned on the PCC and control over
them is delegated to a PCE. Further, [RFC8281] describes the setup,
maintenance
maintenance, and teardown of PCE-Initiated PCE-initiated LSPs for the Stateful stateful PCE
model.
[RFC8697] introduces a generic mechanism to create for creating a grouping of
LSPs. This grouping can then be used to define associations between
sets of LSPs or between a set of LSPs and a set of attributes, and it
is equally applicable to the stateful PCE (active and passive modes)
and the stateless PCE.
The MPLS Transport Profile (MPLS-TP) requirements document [RFC5654]
specifies that "MPLS-TP MUST support unidirectional, co-routed
bidirectional, and associated bidirectional point-to-point transport
paths". [RFC7551] defines RSVP signaling extensions for binding
forward and reverse unidirectional LSPs into an associated
bidirectional LSP. The fast reroute (FRR) procedures for associated
bidirectional LSPs are described in [RFC8537].
This document defines PCEP extensions for grouping two unidirectional
MPLS-TE LSPs into an Associated Bidirectional associated bidirectional LSP for both single-
sided and double-sided initiation cases either when using a Stateful stateful
PCE for both PCE-Initiated PCE-initiated and PCC-Initiated PCC-initiated LSPs as well as or when using a
Stateless
stateless PCE. The procedures defined are applicable to the LSPs
using Resource Reservation Protocol - Traffic Engineering (RSVP-TE)
for signaling [RFC3209]. Specifically, this document defines two new
Association Types, "Single-sided Single-Sided Bidirectional LSP Association" Association and
"Double-sided
Double-Sided Bidirectional LSP Association", Association, as well as
"Bidirectional the
Bidirectional LSP Association Group TLV" TLV, to carry additional
information for the association.
The procedure for associating two unidirectional Segment Routing (SR)
Paths
paths to form an Associated Bidirectional associated bidirectional SR Path path is defined in
[I-D.ietf-pce-sr-bidir-path],
[BIDIR-PATH] and is outside the scope of this document.
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", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.2. Terminology
The reader is assumed to be familiar with the terminology defined in
[RFC5440], [RFC7551], [RFC8231], and [RFC8697].
3. Overview
As shown in Figure 1, forward and reverse unidirectional LSPs can be
grouped to form an associated bidirectional LSP. The node Node A is the
ingress node for LSP1 and egress node for LSP2, whereas node D is the
ingress node for LSP2 and egress node for LSP1. There are two
methods of initiating the bidirectional Bidirectional LSP association, Association, single-sided
and double-sided, as defined in [RFC7551] and described in the
following sections.
LSP1 --> LSP1 --> LSP1 -->
+-----+ +-----+ +-----+ +-----+
| A +-----------+ B +-----------+ C +-----------+ D |
+-----+ +--+--+ +--+--+ +-----+
<-- LSP2 | | <-- LSP2
| |
| |
+--+--+ +--+--+
| E +-----------+ F |
+-----+ +-----+
<-- LSP2
Figure 1: Example of Associated Bidirectional LSP
3.1. Single-sided Single-Sided Initiation
As specified in [RFC7551], in the single-sided case, the
bidirectional tunnel is provisioned only on one endpoint node (PCC)
of the tunnel. Both endpoint nodes act as PCCs. Both forward and
reverse LSPs of this tunnel are initiated with the Association Type
set to "Single-sided "Single-Sided Bidirectional LSP Association" on the
originating endpoint node. The forward and reverse LSPs are
identified in the "Bidirectional Bidirectional LSP Association Group TLV" TLV of their
PCEP ASSOCIATION Objects. objects.
The originating endpoint node signals the properties for the reverse
LSP in the RSVP REVERSE_LSP Object object [RFC7551] of the forward LSP Path
message. The remote endpoint node then creates the corresponding
reverse tunnel and reverse LSP, and it then signals the reverse LSP
in response to the received RSVP-TE Path message. Similarly, the
remote endpoint node deletes the reverse LSP when it receives the
RSVP-TE message to delete the forward LSP [RFC3209].
As specified in [RFC8537], for fast reroute bypass tunnel assignment,
the LSP starting from the originating endpoint node is identified as
the forward LSP of the single-sided initiated bidirectional LSP.
3.1.1. PCE-Initiated Single-sided Single-Sided Bidirectional LSP
+-----+
| PCE |
+-----+
Initiates: | \
Tunnel 1 (F) | \
(LSP1 (F, 0), LSP2 (R, 0)) | \
Association #1 v \
+-----+ +-----+
| A | | D |
+-----+ +-----+
+-----+
| PCE |
+-----+
Reports: ^ ^ Reports:
Tunnel 1 (F) | \ Tunnel 2 (F)
(LSP1 (F, P1), LSP2 (R, P2)) | \ (LSP2 (F, P3))
Association #1 | \ Association #1
+-----+ +-----+
| A | | D |
+-----+ +-----+
Legends: F=Forward
Legend: F = Forward LSP, R=Reverse R = Reverse LSP, (0,P1,P2,P3)=PLSP-IDs (0,P1,P2,P3) = PLSP-IDs
Figure 2: Example of PCE-Initiated Single-sided Single-Sided Bidirectional LSP
Using partial topology from Figure 1, as shown in Figure 2, the
forward tunnel Tunnel 1 and both forward LSP1 and reverse LSP2 are initiated
on the originating endpoint node A by the PCE. The PLSP-IDs PCEP-specific LSP
identifiers (PLSP-IDs) used are P1 and P2 on the originating endpoint
node A and P3 on the remote endpoint node D. The originating
endpoint node A reports tunnels Tunnel 1 and forward LSP1 and reverse LSP2 to
the PCE. The endpoint (PCC) node D reports tunnel Tunnel 2 and LSP2 to the
PCE.
3.1.2. PCC-Initiated Single-sided Single-Sided Bidirectional LSP
+-----+
| PCE |
+-----+
Reports/Delegates: ^ ^ Reports:
Tunnel 1 (F) | \ Tunnel 2 (F)
(LSP1 (F, P1), LSP2 (R, P2)) | \ (LSP2 (F, P3))
Association #2 | \ Association #2
+-----+ +-----+
| A | | D |
+-----+ +-----+
Legends: F=Forward LSP, R=Reverse
Legend: F = Forward LSP, R = Reverse LSP, (P1,P2,P3)=PLSP-IDs (P1,P2,P3) = PLSP-IDs
Figure 3: Example of PCC-Initiated Single-sided Single-Sided Bidirectional LSP
Using partial topology from Figure 1, as shown in Figure 3, the
forward tunnel Tunnel 1 and both forward LSP1 and reverse LSP2 are initiated
on the originating endpoint node A (the originating PCC). The PLSP-
IDs used are P1 and P2 on the originating endpoint node A and P3 on
the remote endpoint node D. The originating endpoint (PCC) node A
may delegate the forward LSP1 and reverse LSP2 to the PCE. The
originating endpoint node A reports tunnels Tunnel 1 and forward LSP1 and
reverse LSP2 to the PCE. The endpoint (PCC) node D reports tunnel Tunnel 2
and LSP2 to the PCE.
3.2. Double-sided Double-Sided Initiation
As specified in [RFC7551], in the double-sided case, the
bidirectional tunnel is provisioned on 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 "Double-Sided
Bidirectional LSP Association" on both endpoint nodes. The forward
and reverse LSPs are identified in the "Bidirectional Bidirectional LSP Association
Group TLV" TLV of their ASSOCIATION Objects. objects.
As specified in [RFC8537], for fast reroute bypass tunnel assignment,
the LSP with the higher Source Address source address [RFC3209] is identified as the
forward LSP of the double-sided initiated bidirectional LSP.
3.2.1. PCE-Initiated Double-sided Double-Sided Bidirectional LSP
+-----+
| PCE |
+-----+
Initiates: | \ Initiates:
Tunnel 1 (F) | \ Tunnel 2 (F)
(LSP1 (F, 0)) | \ (LSP2 (F, 0))
Association #3 v v Association #3
+-----+ +-----+
| A | | D |
+-----+ +-----+
+-----+
| PCE |
+-----+
Reports: ^ ^ Reports:
Tunnel 1 (F) | \ Tunnel 2 (F)
(LSP1 (F, P4)) | \ (LSP2 (F, P5))
Association #3 | \ Association #3
+-----+ +-----+
| A | | D |
+-----+ +-----+
Legends: F=Forward
Legend: F = Forward LSP, (0,P4,P5)=PLSP-IDs (0,P4,P5) = PLSP-IDs
Figure 4: Example of PCE-Initiated Double-sided Double-Sided Bidirectional LSP
Using partial topology from Figure 1, as shown in Figure 4, the
forward tunnel Tunnel 1 and forward LSP1 are initiated on the endpoint node
A
A, and the reverse tunnel Tunnel 2 and reverse LSP2 are initiated on the
endpoint node D by the PCE. The PLSP-IDs used are P4 on the endpoint
node A and P5 on the endpoint node D. The endpoint node A (PCC)
reports the forward LSP1 LSP1, and endpoint node D reports the forward
LSP2 to the PCE.
3.2.2. PCC-Initiated Double-sided Double-Sided Bidirectional LSP
+-----+
| PCE |
+-----+
Reports/Delegates: ^ ^ Reports/Delegates:
Tunnel 1 (F) | \ Tunnel 2 (F)
(LSP1 (F, P4)) | \ (LSP2 (F, P5))
Association #4 | \ Association #4
+-----+ +-----+
| A | | D |
+-----+ +-----+
Legends: F=Forward
Legend: F = Forward LSP, (P4,P5)=PLSP-IDs (P4,P5) = PLSP-IDs
Figure 5: Example of PCC-Initiated Double-sided Double-Sided Bidirectional LSP
Using partial topology from Figure 1, as shown in Figure 5, the
forward tunnel Tunnel 1 and forward LSP1 are initiated on the endpoint node
A
A, and the reverse tunnel Tunnel 2 and reverse LSP2 are initiated on the
endpoint node D (the PCCs). The PLSP-IDs used are P4 on the endpoint
node A and P5 on the endpoint node D. Both endpoint (PCC) nodes may
delegate the forward LSP1 and LSP2 to the PCE. The endpoint node A
(PCC) reports the forward LSP1 LSP1, and endpoint node D reports the
forward LSP2 to the PCE.
3.3. Co-routed Associated Bidirectional LSP
In both single-sided and double-sided initiation cases, forward and
reverse LSPs can be co-routed as shown in Figure 6, where both
forward and reverse LSPs of a bidirectional LSP follow the same
congruent path in the forward and reverse directions, respectively.
LSP3 --> LSP3 --> LSP3 -->
+-----+ +-----+ +-----+ +-----+
| A +-----------+ B +-----------+ C +-----------+ D |
+-----+ +-----+ +-----+ +-----+
<-- LSP4 <-- LSP4 <-- LSP4
Figure 6: Example of Co-routed Associated Bidirectional LSP
The procedure specified in [RFC8537] for fast reroute bypass tunnel
assignment is also applicable to the Co-routed Associated
Bidirectional co-routed associated
bidirectional LSPs.
3.4. Summary of PCEP Extensions
The PCEP extensions defined in this document cover the following
modes of operations operation under the stateful PCE model:
o
* A PCC initiates the forward and reverse LSP of a Single-sided
Bidirectional single-sided
bidirectional LSP and retains the control of the LSPs. Similarly,
both PCCs initiate the forward LSPs of a Double-sided
Bidirectional double-sided
bidirectional LSP and retain the control of the LSPs. The PCC
computes the path itself or makes a request for path computation
to a PCE. After the path setup, it reports the information and
state of the path to the PCE. This includes the association group
identifying the bidirectional LSP. This is the Passive Stateful passive stateful
mode defined in [RFC8051].
o
* A PCC initiates the forward and reverse LSP of a Single-sided
Bidirectional single-sided
bidirectional LSP and delegates the control of the LSPs to a
Stateful stateful
PCE. Similarly, both PCCs initiate the forward LSPs of a
Double-sided Bidirectional double-
sided bidirectional LSP and delegate the control of the LSPs to a Stateful
stateful PCE. During delegation delegation, the association group
identifying the bidirectional LSP is included. The PCE computes
the path of the LSP and updates the PCC with the information about
the path as long as it controls the LSP. This is the Active
Stateful active
stateful mode defined in [RFC8051].
o
* A PCE initiates the forward and reverse LSP of a Single-sided
Bidirectional single-sided
bidirectional LSP on a PCC and retains the control of the LSP.
Similarly, a PCE initiates the forward LSPs of a Double-sided
Bidirectional double-sided
bidirectional LSP on both PCCs and retains the control of the LSPs.
The PCE is responsible for computing the path of the LSP and
updating the PCC with the information about the path as well as
the association group identifying the bidirectional LSP. This is
the PCE-Initiated PCE-initiated mode defined in [RFC8281].
o
* A PCC requests co-routed or non-co-routed paths for forward and
reverse LSPs of a bidirectional LSP LSP, including when using a
Stateless
stateless PCE [RFC5440].
3.5. Operational Considerations
The double-sided case has an advantage when compared to the single-
sided case case, summarized as following:
o follows:
* In the double-sided case, two existing unidirectional LSPs in
reverse directions in the network can be associated to form a
bidirectional LSP without significantly increasing the operational
complexity.
The single-sided case has some advantages when compared to the
double-sided case case, summarized as following:
o follows:
* Some Operations, Administration, and Maintenance (OAM) use-cases use cases
may require an endpoint node to know both forward and reverse
direction
paths for monitoring the bidirectional LSP. For such
use-cases, use cases,
the single-sided case may be preferred.
o
* For Co-routed Associated Bidirectional co-routed associated bidirectional LSPs in PCC initiated PCC-initiated mode,
the single-sided case allows the originating PCC to dynamically
compute co-routed forward and reverse paths. This may not be
possible with the double-sided case where the forward and reverse
direction
paths are computed separately as triggered by two different PCCs.
o
* The Associated Bidirectional associated bidirectional LSPs with in the single-sided case can be
deployed in a network where PCEP is only enabled on the
originating endpoint nodes as remote endpoint nodes create the
reverse tunnels using RSVP-TE Path messages.
4. Protocol Extensions
4.1. ASSOCIATION Object
As per [RFC8697], LSPs are associated by adding them to a common
association group. This document defines two new Association Types,
called "Single-sided "Single-Sided Bidirectional LSP" (TBD1) LSP Association" (4) and "Double-sided "Double-
Sided Bidirectional LSP" (TBD2), LSP Association" (5), using the generic
ASSOCIATION Object
((Object-Class object (Object-Class value 40). A member of the
Bidirectional LSP Association can take the role of a forward or
reverse LSP and follows the following rules:
o
* An LSP (forward or reverse) MUST NOT be part of more than one
Bidirectional LSP Association.
o
* The LSPs in a Bidirectional LSP Association MUST have matching
endpoint nodes in the reverse directions.
o
* The Tunnel same tunnel (as defined in Section 2.1 of [RFC3209]) containing MUST
contain the forward and reverse LSPs of the Single-sided Single-Sided
Bidirectional LSP Association on the originating node MUST be the same, node, albeit both
LSPs have reversed endpoint nodes.
The Bidirectional LSP Association types Types are considered to be both
dynamic and operator-configured operator configured in nature. As per [RFC8697], the
association group could be manually created by the operator on the
PCEP peers, and the LSPs belonging to this association are conveyed
via PCEP messages to the PCEP peer; alternately, the association
group could be created dynamically by the PCEP speaker, and both the
association group information and the LSPs belonging to the
association group are conveyed to the PCEP peer. The Operator- operator-
configured Association Range MUST be set for this association-type Association Type to
mark a range of Association Identifiers that are used for operator-
configured associations to avoid any Association Identifier clash
within the scope of the Association Source (Refer (refer to [RFC8697]).
Specifically, for the PCE Initiated Bidirectional PCE-initiated bidirectional LSPs, these
Associations
associations are dynamically created by the PCE on the PCE peers.
Similarly, for both PCE Initiated the PCE-initiated and PCC Initiated single-sided
case, the PCC-initiated single-
sided cases, these associations are also dynamically created on the
remote endpoint node using the information received from the RSVP
message from the originating node.
The Association ID, Association Source, optional Global Association
Source TLV TLV, and optional Extended Association ID TLV in the
Bidirectional LSP Association Object ASSOCIATION object are initialized using the
procedures defined in [RFC8697] and [RFC7551].
[RFC8697] specifies the mechanism for the capability advertisement of
the Association Types supported by a PCEP speaker by defining an
ASSOC-Type-List TLV to be carried within an OPEN Object. object. This
capability exchange for the Bidirectional LSP Association Types MUST
be done before using the Bidirectional LSP Association. Thus, the
PCEP speaker MUST include the Bidirectional LSP Association Types in
the ASSOC-Type-List TLV and MUST receive the same from the PCEP peer
before using the Bidirectional LSP Association in PCEP messages.
4.2. Bidirectional LSP Association Group TLV
The "Bidirectional Bidirectional LSP Association Group TLV" TLV is an OPTIONAL TLV for
use with the Bidirectional LSP Associations (ASSOCIATION Object object with
Association Type TBD1 4 for Single-sided Single-Sided Bidirectional LSP Association or TBD2
5 for
Double-sided Double-Sided Bidirectional LSP).
o LSP Association).
* The "Bidirectional Bidirectional LSP Association Group TLV" TLV follows the PCEP TLV
format from [RFC5440].
o
* The Type (16 bits) of the TLV is TBD3, to be assigned by IANA.
o 54.
* The Length is 4 Bytes.
o bytes.
* The value comprises of a single field, the Bidirectional LSP
Association Flag Flags field (32 bits),
where each bit represents a flag option.
o
* If the "Bidirectional Bidirectional LSP Association Group TLV" TLV is missing, it
means the LSP is the forward LSP LSP, and it is not a co-routed LSP.
o
* When "Bidirectional the Bidirectional LSP Association Group TLV" TLV is present, the R
flag MUST be reset for the forward LSP for both co-routed and non non-
co-routed LSPs.
o
* For co-routed LSPs, this TLV MUST be present and the C flag set.
o
* For reverse LSPs, this TLV MUST be present and the R flag set.
o
* The "Bidirectional Bidirectional LSP Association Group TLV" TLV MUST NOT be present
more than once. If it appears more than once, only the first
occurrence is processed processed, and any others MUST be ignored.
The format of the "Bidirectional Bidirectional LSP Association Group TLV" TLV is shown in
Figure 7: 7.
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 54 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |C|R|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Bidirectional LSP Association Group TLV format Format
Flags for "Bidirectional the Bidirectional LSP Association Group TLV" TLV are defined as
following.
follows.
R (Reverse LSP, 1 bit, Bit bit number 31) - 31): Indicates whether the LSP
associated is the reverse LSP of the bidirectional LSP. If this
flag is set, the LSP is a reverse LSP. If this flag is not set,
the LSP is a forward LSP.
C (Co-routed Path, 1 bit, Bit bit number 30) - 30): Indicates whether the
bidirectional LSP is co-routed. This flag MUST be set for both
the forward and reverse LSPs of a co-routed bidirectional LSP.
The C flag is used by the PCE (for both Stateful (both stateful and Stateless) stateless) to
compute bidirectional paths of the forward and reverse LSPs of a co-
routed bidirectional LSP.
The unassigned flags (Bit Number (bit numbers 0-29) MUST be set to 0 when sent
and MUST be ignored when received.
5. PCEP Procedure
The PCEP procedure defined in this document is applicable to the
following three scenarios:
o
* Neither unidirectional LSP exists, and both must be established.
o
* Both unidirectional LSPs exist, but the association must be
established.
o
* One LSP exists, but the reverse associated LSP must be
established.
5.1. PCE Initiated PCE-Initiated LSPs
As specified in [RFC8697], the Bidirectional LSP Associations can be
created and updated by a Stateful stateful PCE.
o
* For Single-sided a Single-Sided Bidirectional LSP Association initiated by the
PCE, it the PCE MUST send a PCInitiate message to the originating
endpoint node with both direction forward and reverse LSPs. For Double-sided a Double-
Sided Bidirectional LSP Association initiated by the PCE, it MUST
send a PCInitiate message to both endpoint nodes with forward direction
LSPs.
o
* Both PCCs MUST report the forward and reverse LSPs in the
Bidirectional LSP Association to the PCE. A PCC reports via a
PCRpt message.
o
* Stateful PCEs MAY create and update the forward and reverse LSPs
independently for the Single-sided Single-Sided Bidirectional LSP Association
on the originating endpoint node.
o
* Stateful PCEs MAY create and update the forward LSP independently
for the Double-sided Double-Sided Bidirectional LSP Association on the endpoint
nodes.
o
* Stateful PCEs establish and remove the association relationship on
a per LSP per-LSP basis.
o
* Stateful PCEs create and update the LSP and the association on
PCCs via PCInitiate and PCUpd messages, respectively, using the
procedures described in [RFC8697].
5.2. PCC Initiated PCC-Initiated LSPs
As specified in [RFC8697], the Bidirectional LSP Associations can also be
created and updated by a PCC.
o
* For Single-sided a Single-Sided Bidirectional LSP Association initiated at a
PCC,
it the PCC MUST send a PCRpt message to the PCE with both direction
forward and reverse LSPs. For Double-sided a Double-Sided Bidirectional LSP
Association initiated at the PCCs, both PCCs MUST send a PCRpt
message to the PCE with forward
direction LSPs.
o
* PCCs on the originating endpoint node MAY create and update the
forward and reverse LSPs independently for the Single-sided Single-Sided
Bidirectional LSP Association.
o
* PCCs on the endpoint nodes MAY create and update the forward LSP
independently for the Double-sided Double-Sided Bidirectional LSP Association.
o
* PCCs establish and remove the association group on a per LSP per-LSP
basis. PCCs MUST report the change in the association group of an
LSP to PCE(s) via a PCRpt message.
o
* PCCs report the forward and reverse LSPs in the Bidirectional LSP
Association independently to PCE(s) via a PCRpt message.
o
* PCCs for the single-sided case MAY delegate the forward and
reverse LSPs independently to a Stateful stateful PCE, where the PCE would
control the LSPs. In this case, the originating (PCC) endpoint
node SHOULD delegate both forward and reverse LSPs of a tunnel
together to a Stateful stateful PCE in order to avoid any race condition.
o
* PCCs for the double-sided case MAY delegate the forward LSPs to a
Stateful
stateful PCE, where the PCE would control the LSPs.
o Stateful
* A stateful PCE updates the LSPs in the Bidirectional LSP
Association via a PCUpd message, using the procedures described in
[RFC8697].
5.3. Stateless PCE
For a stateless PCE, it might be useful to associate a path
computation request to an association group, thus enabling it to
associate a common set of configuration parameters or behaviors with
the request [RFC8697]. A PCC can request co-routed or non-co-routed
forward and reverse direction paths from a stateless PCE for a Bidirectional
LSP Association.
5.4. Bidirectional (B) Flag
As defined in [RFC5440], the Bidirectional (B) flag in the Request
Parameters (RP) Object object is set when the PCC specifies that the path
computation request is for a bidirectional TE LSP with the same TE
requirements in each direction. For an associated bidirectional LSP,
the B-flag B flag is also set when the PCC makes the path computation
request for the same TE requirements for the forward and reverse
direction
LSPs.
Note that the B-flag B flag defined in a Stateful PCE Request Parameter
(SRP)
Object [I-D.ietf-pce-pcep-stateful-pce-gmpls] object [STATEFUL-PCE-GMPLS] to indicate
'bidirectional co-routed LSP' "bidirectional co-
routed LSP" is used for GMPLS signaled GMPLS-signaled bidirectional LSPs and is not
applicable to the associated bidirectional LSPs.
5.5. PLSP-ID Usage
As defined in [RFC8231], a PCEP-specific LSP Identifier (PLSP-ID) is
created by a PCC to uniquely identify an LSP LSP, and it remains the same
for the lifetime of a PCEP session.
In the case of Single-sided a Single-Sided Bidirectional LSP Association, the
reverse LSP of a bidirectional LSP created on the originating
endpoint node is identified by the PCE using 2 two different PLSP-IDs PLSP-IDs,
based on the PCEP session on the ingress or egress node PCCs for the
LSP. In other words, the LSP will have a PLSP-ID P2 allocated at the
ingress node
PCC PCC, while it will have a PLSP-ID P3 allocated at the
egress node PCC (as shown in Figure Figures 2 and Figure 3). There is no change in
the PLSP-
ID PLSP-ID allocation procedure for the forward LSP of a Single-sided
Bidirectional single-
sided bidirectional LSP created on the originating endpoint node.
In the case of Double-sided a Double-Sided Bidirectional LSP Association, there is
no change in the PLSP-ID allocation procedure for the forward LSPs on
both PCCs.
either PCC.
For an Associated Bidirectional associated bidirectional LSP, the LSP-IDENTIFIERS TLV
[RFC8231] MUST be included in all forward and reverse LSPs.
5.6. State Synchronization
During state synchronization, a PCC MUST report all the existing
Bidirectional LSP Associations to the Stateful PCE stateful PCE, as per [RFC8697].
After the state synchronization, the PCE MUST remove all previous
Bidirectional LSP Associations absent in the report.
5.7. Error Handling
If a PCE speaker receives an LSP with a Bidirectional LSP Association
Type that it does not support, the PCE speaker MUST send PCErr with
Error-Type = 26 (Association Error) and Error-Value Error-value = 1 (Association
Type is not supported).
An LSP (forward or reverse) cannot be part of more than one
Bidirectional LSP Association. If a PCE speaker receives an LSP not
complying to this rule, the PCE speaker MUST send PCErr with Error-
Type = 26 (Association Error) and Error-Value Error-value = TBD4 (Bidirectional
LSP Association - Group Mismatch). 14 (Association group
mismatch).
The LSPs (forward or reverse) in a Single-sided Single-Sided Bidirectional
Association MUST belong to the same TE Tunnel tunnel (as defined in
[RFC3209]). If a PCE speaker attempts to add an LSP in a Single-
sided
Sided Bidirectional LSP Association for a different Tunnel, tunnel, the PCE
speaker MUST send PCErr with Error-Type = 26 (Association Error) and
Error-Value
Error-value = TBD5 (Bidirectional Association - Tunnel Mismatch). 15 (Tunnel mismatch in the association group).
The PCEP Path Setup Type (PST) for RSVP-TE is set to 'Path "Path is set up
using the RSVP-TE signaling protocol' protocol" (Value 0) [RFC8408]. If a PCEP
speaker receives a different PST value for the Bidirectional LSP
Associations defined in this document, the PCE speaker MUST return a
PCErr message with Error-Type = 26 (Association Error) and Error-
Value
value = TBD6 (Bidirectional LSP Association - Path 16 (Path Setup Type Not
Supported). not supported).
A Bidirectional LSP Association cannot have both unidirectional LSPs
identified as Reverse reverse LSPs or both LSPs identified as Forward forward LSPs.
If a PCE speaker receives an LSP not complying to this rule, the PCE
speaker MUST send PCErr with Error-Type = 26 (Association Error) and
Error-Value
Error-value = TBD7 17 (Bidirectional LSP Association - Direction
Mismatch). direction mismatch).
A Bidirectional LSP Association cannot have one unidirectional LSP
identified as co-routed and the other identified as non-co-routed.
If a PCE speaker receives an LSP not complying to this rule, the PCE
speaker MUST send PCErr with Error-Type = 26 (Association Error) and
Error-Value
Error-value = TBD8 18 (Bidirectional LSP Association - Co-routed
Mismatch). co-routed mismatch).
The unidirectional LSPs forming the Bidirectional LSP Association
MUST have matching endpoint nodes in the reverse directions. If a
PCE speaker receives an LSP not complying to this rule, the PCE
speaker MUST send PCErr with Error-Type = 26 (Association Error) and
Error-Value
Error-value = TBD9 (Bidirectional LSP Association - Endpoint
Mismatch). 19 (Endpoint mismatch in the association group).
The processing rules as specified in Section 6.4 of [RFC8697]
continue to apply to the Association Types defined in this document.
7.
6. Security Considerations
The security considerations described in [RFC5440], [RFC8231], and
[RFC8281] apply to the extensions defined in this document as well.
Two new Association Types for the ASSOCIATION Object, Single-sided object, Single-Sided
Bidirectional LSP Association and Double-sided Double-Sided Bidirectional LSP
Association
Association, are introduced in this document. Additional security
considerations related to LSP associations due to a malicious PCEP
speaker is are described in [RFC8697] and apply to these Association
Types. Hence, securing the PCEP session using Transport Layer
Security (TLS) [RFC8253] is RECOMMENDED.
8.
7. Manageability Considerations
8.1.
7.1. Control of Function and Policy
The mechanisms defined in this document do not imply any control or
policy requirements in addition to those already listed in [RFC5440],
[RFC8231], and [RFC8281].
8.2.
7.2. Information and Data Models
[RFC7420] describes the PCEP MIB, MIB; there are no new MIB Objects objects
defined for LSP associations.
The PCEP YANG module [I-D.ietf-pce-pcep-yang] [PCE-PCEP-YANG] defines a data model for LSP
associations.
8.3.
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], [RFC8231], and [RFC8281].
8.4.
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], [RFC8231], and [RFC8281].
8.5.
7.5. Requirements On on Other Protocols
The mechanisms defined in this document do not add any new
requirements on other protocols.
8.6.
7.6. Impact On on Network Operations
The mechanisms defined in this document do not have any impact on
network operations in addition to those already listed in [RFC5440],
[RFC8231], and [RFC8281].
9.
8. IANA Considerations
9.1.
8.1. Association Types
This document defines two new Association Types, originally described
in Types [RFC8697]. IANA is requested to assign has
assigned the following new values in the "ASSOCIATION Type Field"
subregistry [RFC8697] within the "Path Computation Element Protocol
(PCEP) Numbers" registry:
+======+============================================+===========+
| Type | Name | Reference
---------------------------------------------------------------------
TBD1 Single-sided |
+======+============================================+===========+
| 4 | Single-Sided Bidirectional LSP Association [This document]
TBD2 Double-sided | RFC 9059 |
+------+--------------------------------------------+-----------+
| 5 | Double-Sided Bidirectional LSP Association [This document]
9.2. | RFC 9059 |
+------+--------------------------------------------+-----------+
Table 1: Additions to ASSOCIATION Type Field Subregistry
8.2. Bidirectional LSP Association Group TLV
This document defines a new TLV for carrying additional information
of
about LSPs within a Bidirectional LSP Association. IANA is requested to
add has assigned
the assignment of a new following value in the existing "PCEP TLV Type Indicators" registry as follows: subregistry
within the "Path Computation Element Protocol (PCEP) Numbers"
registry:
+=======+=========================================+===========+
| Value | Meaning | Reference
-------------------------------------------------------------------
TBD3 |
+=======+=========================================+===========+
| 54 | Bidirectional LSP Association Group TLV [This document]
9.2.1. | RFC 9059 |
+-------+-----------------------------------------+-----------+
Table 2: Addition to PCEP TLV Type Indicators Subregistry
8.2.1. Flag Field in Bidirectional LSP Association Group TLV
This document requests that
IANA has created a new sub-registry, subregistry, 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 [RFC8126]. Each bit should be tracked with the
following qualities:
o
* Bit number (count from 0 as the most significant bit)
o
* Description
o
* Reference
The following values are defined in initial contents of this document for the Flag field. registry are as follows:
+======+====================+===========+
| Bit No. | Description | Reference
---------------------------------------------------------
31 R - Reverse LSP [This document] |
+======+====================+===========+
| 0-29 | Unassigned | |
+------+--------------------+-----------+
| 30 | C - Co-routed Path [This document]
0-29 Unassigned
9.3. PCEP Errors
This document defines new Error value for Error Type 26 (Association
Error). IANA is requested to allocate | RFC 9059 |
+------+--------------------+-----------+
| 31 | R - Reverse LSP | RFC 9059 |
+------+--------------------+-----------+
Table 3: New Bidirectional LSP
Association Group TLV Flag Field
Subregistry
8.3. PCEP Errors
This document defines new Error value Error-values for Error-Type 26 (Association
Error). IANA has allocated the following new Error-values within the
"PCEP-ERROR Object Error Types and Values" sub-registry subregistry of the PCEP
Numbers registry, as follows:
Error Type Description "Path
Computation Element Protocol (PCEP) Numbers" registry:
+============+=============+==========================+===========+
| Error-Type | Meaning | Error-value | Reference
--------------------------------------------------------- |
+============+=============+==========================+===========+
| 26 | Association Error
Error value: TBD4 [This document]
Bidirectional LSP | 14: Association - Group Mismatch group | RFC 9059 |
| | Error value: TBD5 [This document]
Bidirectional LSP Association - | mismatch | |
| | +--------------------------+-----------+
| | | 15: Tunnel Mismatch
Error value: TBD6 [This document]
Bidirectional LSP Association - mismatch in | RFC 9059 |
| | | the association group | |
| | +--------------------------+-----------+
| | | 16: Path Setup Type
Not Supported
Error value: TBD7 [This document]
Bidirectional LSP Association - Direction Mismatch
Error value: TBD8 [This document] not | RFC 9059 |
| | | supported | |
| | +--------------------------+-----------+
| | | 17: Bidirectional LSP Association - Co-routed Mismatch
Error value: TBD9 [This document] | RFC 9059 |
| | | direction mismatch | |
| | +--------------------------+-----------+
| | | 18: Bidirectional LSP Association - | RFC 9059 |
| | | co-routed mismatch | |
| | +--------------------------+-----------+
| | | 19: Endpoint Mismatch
10. mismatch in | RFC 9059 |
| | | the association group | |
+------------+-------------+--------------------------+-----------+
Table 4: Additions to PCEP-ERROR Object Error Types and Values
Subregistry
9. References
10.1.
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[RFC5440] Vasseur, JP., Ed. and JL. Le Roux, Ed., "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
DOI 10.17487/RFC5440, March 2009,
<https://www.rfc-editor.org/info/rfc5440>.
[RFC7551] Zhang, F., Ed., Jing, R., and R. Gandhi, Ed., "RSVP-TE
Extensions for Associated Bidirectional Label Switched
Paths (LSPs)", RFC 7551, DOI 10.17487/RFC7551, May 2015,
<https://www.rfc-editor.org/info/rfc7551>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8231] Crabbe, E., Minei, I., Medved, J., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for Stateful PCE", RFC 8231,
DOI 10.17487/RFC8231, September 2017,
<https://www.rfc-editor.org/info/rfc8231>.
[RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
"PCEPS: Usage of TLS to Provide a Secure Transport for the
Path Computation Element Communication Protocol (PCEP)",
RFC 8253, DOI 10.17487/RFC8253, October 2017,
<https://www.rfc-editor.org/info/rfc8253>.
[RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for PCE-Initiated LSP Setup in a Stateful PCE
Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
<https://www.rfc-editor.org/info/rfc8281>.
[RFC8537] Gandhi, R., Ed., Shah, H., and J. Whittaker, "Updates to
the Fast Reroute Procedures for Co-routed Associated
Bidirectional Label Switched Paths (LSPs)", RFC 8537,
DOI 10.17487/RFC8537, February 2019,
<https://www.rfc-editor.org/info/rfc8537>.
[RFC8697] Minei, I., Crabbe, E., Sivabalan, S., Ananthakrishnan, H.,
Dhody, D., and Y. Tanaka, "Path Computation Element
Communication Protocol (PCEP) Extensions for Establishing
Relationships between Sets of Label Switched Paths
(LSPs)", RFC 8697, DOI 10.17487/RFC8697, January 2020,
<https://www.rfc-editor.org/info/rfc8697>.
10.2.
9.2. Informative References
[I-D.ietf-pce-pcep-stateful-pce-gmpls]
Lee, Y., Zheng, H., Dios, O., Lopez, V.,
[BIDIR-PATH]
Li, C., Chen, M., Cheng, W., Gandhi, R., and Z. Ali, Q. Xiong,
"Path Computation Element (PCE) Communication Protocol (PCEP)
Extensions for Stateful
PCE Usage in GMPLS-controlled Networks", draft-ietf-pce-
pcep-stateful-pce-gmpls-14 (work Associated Bidirectional Segment Routing
(SR) Paths", Work in progress), December
2020.
[I-D.ietf-pce-pcep-yang] Progress, Internet-Draft, draft-ietf-
pce-sr-bidir-path-05, 26 January 2021,
<https://tools.ietf.org/html/draft-ietf-pce-sr-bidir-path-
05>.
[PCE-PCEP-YANG]
Dhody, D., Ed., Hardwick, J., Beeram, V., and J. Tantsura,
"A YANG Data Model for Path Computation Element
Communications Protocol (PCEP)", draft-ietf-pce-pcep-
yang-15 (work Work in progress), October 2020.
[I-D.ietf-pce-sr-bidir-path]
Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong,
"Path Computation Element Communication Protocol (PCEP)
Extensions for Associated Bidirectional Segment Routing
(SR) Paths", draft-ietf-pce-sr-bidir-path-05 (work in
progress), January 2021. Progress,
Internet-Draft, draft-ietf-pce-pcep-yang-16, 22 February
2021,
<https://tools.ietf.org/html/draft-ietf-pce-pcep-yang-16>.
[RFC5654] Niven-Jenkins, B., Ed., Brungard, D., Ed., Betts, M., Ed.,
Sprecher, N., and S. Ueno, "Requirements of an MPLS
Transport Profile", RFC 5654, DOI 10.17487/RFC5654,
September 2009, <https://www.rfc-editor.org/info/rfc5654>.
[RFC7420] Koushik, A., Stephan, E., Zhao, Q., King, D., and J.
Hardwick, "Path Computation Element Communication Protocol
(PCEP) Management Information Base (MIB) Module",
RFC 7420, DOI 10.17487/RFC7420, December 2014,
<https://www.rfc-editor.org/info/rfc7420>.
[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>.
[RFC8051] Zhang, X., Ed. and I. Minei, Ed., "Applicability of a
Stateful Path Computation Element (PCE)", RFC 8051,
DOI 10.17487/RFC8051, January 2017,
<https://www.rfc-editor.org/info/rfc8051>.
[RFC8408] Sivabalan, S., Tantsura, J., Minei, I., Varga, R., and J.
Hardwick, "Conveying Path Setup Type in PCE Communication
Protocol (PCEP) Messages", RFC 8408, DOI 10.17487/RFC8408,
July 2018, <https://www.rfc-editor.org/info/rfc8408>.
[STATEFUL-PCE-GMPLS]
Lee, Y., Ed., Zheng, H., Ed., de Dios, O., Lopez, V., and
Z. Ali, "Path Computation Element (PCE) Protocol
Extensions for Stateful PCE Usage in GMPLS-controlled
Networks", Work in Progress, Internet-Draft, draft-ietf-
pce-pcep-stateful-pce-gmpls-14, 28 December 2020,
<https://tools.ietf.org/html/draft-ietf-pce-pcep-stateful-
pce-gmpls-14>.
Acknowledgments
The authors would like to thank Dhruv Dhody for various discussions
on association groups and inputs to this document. The authors would
also like to thank Mike Taillon, Harish Sitaraman, Al Morton, and
Marina Fizgeer for reviewing this document and providing valuable
comments. The authors would like to thank the following IESG members
for their review comments and suggestions: Barry Leiba, Eric Éric Vyncke,
Benjamin Kaduk, Murray Kucherawy, Martin Duke, and Alvaro Retana.
Authors' Addresses
Rakesh Gandhi (editor)
Cisco Systems, Inc.
Canada
Email: rgandhi@cisco.com
Colby Barth
Juniper Networks
Email: cbarth@juniper.net
Bin Wen
Comcast
Email: Bin_Wen@cable.comcast.com