draft-ietf-pce-sr-bidir-path-01.txt   draft-ietf-pce-sr-bidir-path-02.txt 
PCE Working Group C. Li PCE Working Group C. Li
Internet-Draft M. Chen Internet-Draft M. Chen
Intended status: Standards Track Huawei Technologies Intended status: Standards Track Huawei Technologies
Expires: August 17, 2020 W. Cheng Expires: September 14, 2020 W. Cheng
China Mobile China Mobile
R. Gandhi R. Gandhi
Cisco Systems, Inc. Cisco Systems, Inc.
Q. Xiong Q. Xiong
ZTE Corporation ZTE Corporation
February 14, 2020 March 13, 2020
PCEP Extensions for Associated Bidirectional Segment Routing (SR) Paths PCEP Extensions for Associated Bidirectional Segment Routing (SR) Paths
draft-ietf-pce-sr-bidir-path-01 draft-ietf-pce-sr-bidir-path-02
Abstract Abstract
The Path Computation Element Communication Protocol (PCEP) provides The Path Computation Element Communication Protocol (PCEP) provides
mechanisms for Path Computation Elements (PCEs) to perform path mechanisms for Path Computation Elements (PCEs) to perform path
computations in response to Path Computation Clients (PCCs) requests. computations in response to Path Computation Clients (PCCs) requests.
Segment routing (SR) leverages the source routing and tunneling Segment routing (SR) leverages the source routing and tunneling
paradigms. The Stateful PCEP extensions allow stateful control of paradigms. The Stateful PCEP extensions allow stateful control of
Segment Routing (SR) Traffic Engineering (TE) Paths. Furthermore, Segment Routing Traffic Engineering (TE) Paths. Furthermore, PCEP
PCEP can be used for computing SR TE paths in the network. can be used for computing SR TE paths in the network.
This document defines PCEP extensions for grouping two unidirectional This document defines PCEP extensions for grouping two unidirectional
SR Paths (one in each direction in the network) into a single SR Paths (one in each direction in the network) into a single
Associated Bidirectional SR Path. The mechanisms defined in this Associated Bidirectional SR Path. The mechanisms defined in this
document can also be applied using a Stateful PCE for both PCE- document can also be applied using a Stateful PCE for both PCE-
Initiated and PCC-Initiated LSPs, as well as when using a Stateless Initiated and PCC-Initiated LSPs, as well as when using a Stateless
PCE. PCE.
Status of This Memo Status of This Memo
skipping to change at page 1, line 49 skipping to change at page 1, line 49
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-
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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 August 17, 2020. This Internet-Draft will expire on September 14, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 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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include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
3. PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . . 4 3. PCEP Extensions . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Double-sided Bidirectional SR Path Association Group . . 5 3.1. Double-sided Bidirectional with Reverse LSP Association
Group . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1.1. Bidirectional LSP Association Group TLV . . . . . . . 5 3.1.1. Bidirectional LSP Association Group TLV . . . . . . . 5
4. PCEP Procedures . . . . . . . . . . . . . . . . . . . . . . . 5 4. PCEP Procedures . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. PCE Initiated Associated Bidirectional SR Paths . . . . . 6 4.1. PCE Initiated Associated Bidirectional SR Paths . . . . . 7
4.2. PCC Initiated Associated Bidirectional SR Paths . . . . . 7 4.2. PCC Initiated Associated Bidirectional SR Paths . . . . . 7
4.3. Stateless PCE . . . . . . . . . . . . . . . . . . . . . . 9 4.3. Stateless PCE . . . . . . . . . . . . . . . . . . . . . . 9
4.4. Bidirectional (B) Flag . . . . . . . . . . . . . . . . . 9 4.4. Bidirectional (B) Flag . . . . . . . . . . . . . . . . . 10
4.5. State Synchronization . . . . . . . . . . . . . . . . . . 9 4.5. State Synchronization . . . . . . . . . . . . . . . . . . 10
4.6. Error Handling . . . . . . . . . . . . . . . . . . . . . 9 4.6. Error Handling . . . . . . . . . . . . . . . . . . . . . 10
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 9 5. Implementation Status . . . . . . . . . . . . . . . . . . . . 10
5.1. Huawei's Commercial Delivery . . . . . . . . . . . . . . 10 5.1. Huawei's Commercial Delivery . . . . . . . . . . . . . . 11
5.2. ZTE's Commercial Delivery . . . . . . . . . . . . . . . . 10 5.2. ZTE's Commercial Delivery . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11 6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. Manageability Considerations . . . . . . . . . . . . . . . . 11 7. Manageability Considerations . . . . . . . . . . . . . . . . 12
7.1. Control of Function and Policy . . . . . . . . . . . . . 11 7.1. Control of Function and Policy . . . . . . . . . . . . . 12
7.2. Information and Data Models . . . . . . . . . . . . . . . 11 7.2. Information and Data Models . . . . . . . . . . . . . . . 12
7.3. Liveness Detection and Monitoring . . . . . . . . . . . . 11 7.3. Liveness Detection and Monitoring . . . . . . . . . . . . 12
7.4. Verify Correct Operations . . . . . . . . . . . . . . . . 11 7.4. Verify Correct Operations . . . . . . . . . . . . . . . . 12
7.5. Requirements On Other Protocols . . . . . . . . . . . . . 12 7.5. Requirements On Other Protocols . . . . . . . . . . . . . 12
7.6. Impact On Network Operations . . . . . . . . . . . . . . 12 7.6. Impact On Network Operations . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8.1. Association Type . . . . . . . . . . . . . . . . . . . . 12 8.1. Association Type . . . . . . . . . . . . . . . . . . . . 13
8.2. PCEP Errors . . . . . . . . . . . . . . . . . . . . . . . 12 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 9.1. Normative References . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . 12 9.2. Informative References . . . . . . . . . . . . . . . . . 14
9.2. Informative References . . . . . . . . . . . . . . . . . 13
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 15 Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 15
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction 1. Introduction
Segment routing (SR) [RFC8402] leverages the source routing and Segment routing (SR) [RFC8402] leverages the source routing and
tunneling paradigms. SR supports steering packets onto an explicit tunneling paradigms. SR supports steering packets onto an explicit
forwarding path at the ingress node. SR is specified for forwarding path at the ingress node. SR is specified for
unidirectional paths. However, some applications require unidirectional paths. However, some applications require
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[RFC8697] introduces a generic mechanism to create a grouping of LSPs [RFC8697] introduces a generic mechanism to create a grouping of LSPs
which can then be used to define associations between a set of LSPs which can then be used to define associations between a set of LSPs
and/or a set of attributes, and is equally applicable to the active and/or a set of attributes, and is equally applicable to the active
and passive modes of a Stateful PCE [RFC8231] or a stateless PCE and passive modes of a Stateful PCE [RFC8231] or a stateless PCE
[RFC5440]. [RFC5440].
[I-D.ietf-pce-association-bidir] defines PCEP extensions for grouping [I-D.ietf-pce-association-bidir] defines PCEP extensions for grouping
two unidirectional RSVP-TE LSPs into an Associated Bidirectional LSP two unidirectional RSVP-TE LSPs into an Associated Bidirectional LSP
when using a Stateful PCE for both PCE-Initiated and PCC-Initiated when using a Stateful PCE for both PCE-Initiated and PCC-Initiated
LSPs as well as when using a Stateless PCE. It specifies the LSPs as well as when using a Stateless PCE. It specifies the
procedure for Double-sided Bidirectional LSP Association, where the procedure for 'Double-sided Bidirectional LSP Association', where the
PCE creates the association and provisions the forward LSPs at their PCE creates the association and provisions the forward LSPs at their
ingress nodes. The RSVP-TE signals the forward LSPs to the egress ingress nodes. The RSVP-TE signals the forward LSPs to the egress
nodes. Thus, both endpoints learn the reverse LSPs forming the nodes. Thus, both endpoints learn the reverse LSPs forming the
bidirectional LSP association. bidirectional LSP association.
This document extends the bidirectional LSP association to SR by This document extends the bidirectional LSP association to SR by
specifying PCEP extensions for grouping two unidirectional SR Paths specifying PCEP extensions for grouping two unidirectional SR Paths
into a bidirectional SR Path. For bidirectional SR, there are use into a bidirectional SR Path. For bidirectional SR, there are use-
cases such as directed BFD [I-D.ietf-mpls-bfd-directed] and SR cases such as directed BFD [I-D.ietf-mpls-bfd-directed] and SR
performance measurement [I-D.gandhi-spring-twamp-srpm] those require Performance Measurement (PM) [I-D.gandhi-spring-twamp-srpm] those
PCC to be aware of the reverse direction SR path. For such use- require PCC to be aware of the reverse direction SR Path. For such
cases, the reverse SR paths are also communicated to the ingress use-cases, the reverse SR Paths are also communicated to the ingress
nodes using the PCEP extensions defined in this document. This nodes using the PCEP extensions defined in this document. This
allows both endpoints to be aware of SR Paths in both directions, allows both endpoints to be aware of the SR Paths in both directions,
including their status and all other path related information. including their status and all other path related information.
Associating an unidirectional SR Path with a reverse direction
unidirectional RSVP-TE LSP to form a bidirectional LSP and vice
versa, are outside the scope of this document.
2. Terminology 2. Terminology
This document makes use of the terms defined in [RFC8408]. The This document makes use of the terms defined in [RFC8408]. The
reader is assumed to be familiar with the terminology defined in reader is assumed to be familiar with the terminology defined in
[RFC5440], [RFC8231], [RFC8281], [RFC8697], and [RFC5440], [RFC8231], [RFC8281], [RFC8697], and
[I-D.ietf-pce-association-bidir]. [I-D.ietf-pce-association-bidir].
2.1. Requirements Language 2.1. 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.
3. PCEP Extensions 3. PCEP Extensions
As per [RFC8697], TE LSPs are associated by adding them to a common As per [RFC8697], TE LSPs are associated by adding them to a common
association group by a PCEP peer. [I-D.ietf-pce-association-bidir] association group by a PCEP peer. [I-D.ietf-pce-association-bidir]
uses the the association group object and the procedures as specified uses the association group object and the procedures as specified in
in [RFC8697] to group two unidirectional RSVP-TE LSPs. Similarly, [RFC8697] to group two unidirectional RSVP-TE LSPs. Similarly, two
two SR Paths can also be associated using similar technique. This SR Paths can also be associated using similar technique. This
document extends these association mechanisms for bidirectional SR document extends these association mechanisms for bidirectional SR
Paths. Two unidirectional SR Paths (one in each direction in the Paths. Two unidirectional SR Paths (one in each direction in the
network) can be associated together by using the Bidirectional SR network) can be associated together by using the association group
Path Association Group defined in this document for PCEP messages. defined in this document for PCEP messages.
Note that the association group defined in this document is specific Note that the procedure for using the association group defined in
to the bidirectional SR Paths. The procedure for this association this document is specific to the associated bidirectional SR Paths.
group is different than the RSVP-TE bidirectional association groups The procedure for this association group is different than the
defined in [I-D.ietf-pce-association-bidir]. bidirectional association groups defined in
[I-D.ietf-pce-association-bidir] for associated bidirectional RSVP-TE
LSPs.
[I-D.ietf-pce-sr-path-segment] defines a mechanism for communicating [I-D.ietf-pce-sr-path-segment] defines a mechanism for communicating
Path Segment Identifier (PSID) in PCEP for SR. The PSID is defined Path Segment Identifier (PSID) in PCEP for SR. The PSID is defined
for SR-MPLS in [I-D.ietf-spring-mpls-path-segment]. The PSID can be for SR-MPLS in [I-D.ietf-spring-mpls-path-segment]. The PSID can be
used for identifying an SR Path of an associated bidirectional SR used for identifying an SR Path of an associated bidirectional SR
Path. The PATH-SEGMENT TLV MAY be included for each SR Path in the Path. The PATH-SEGMENT TLV MAY be included for each SR Path in the
LSP object to support required use-cases. The PATH-SEGMENT TLV MUST LSP object to support required use-cases. The PATH-SEGMENT TLV MUST
be handled as defined in [I-D.ietf-pce-sr-path-segment] and is not be handled as defined in [I-D.ietf-pce-sr-path-segment] and is not
modified for associated bidirectional SR Path. modified for associated bidirectional SR Path.
3.1. Double-sided Bidirectional SR Path Association Group 3.1. Double-sided Bidirectional with Reverse LSP Association Group
For associating two unidirectional SR paths, this document defines a For associating two unidirectional SR Paths, this document defines a
new Association Type called 'Double-sided Bidirectional SR Path new Association Type called 'Double-sided Bidirectional with Reverse
Association Group' for Association Group Object (Class-Value 40) as LSP Association Group' for Association Group Object (Class-Value 40)
follows: as follows:
o Association Type (TBD1 to be assigned by IANA) = Double-sided o Association Type (TBD1 to be assigned by IANA) = Double-sided
Bidirectional SR Path Association Group Bidirectional with Reverse LSP Association Group
Similar to RSVP-TE bidirectional LSP associations, this Association Similar to RSVP-TE bidirectional LSP associations, this Association
Type is operator-configured in nature and statically created by the Type is also operator-configured in nature and statically created by
operator on the PCEP peers. The paths belonging to this association the operator on the PCEP peers. 'Operator-configured Association
is conveyed via PCEP messages to the PCEP peer. Operator-configured Range' TLV (Value 29) [RFC8697] MUST NOT be sent for this Association
Association Range TLV [RFC8697] MUST NOT be sent for these Type, and MUST be ignored, so that the entire range of association ID
Association Types, and MUST be ignored, so that the entire range of can be used for it.
association ID can be used for them. The handling of the Association
ID, Association Source, optional Global Association Source and
optional Extended Association ID in this association are set in the
same way as [I-D.ietf-pce-association-bidir].
A member of the 'Double-sided Bidirectional SR Path Association The handling of the Association ID, Association Source, optional
Group' can take the role of a forward or reverse SR Path and follow Global Association Source and optional Extended Association ID in
the similar rules defined in [I-D.ietf-pce-association-bidir] for this association are set in the same way as
LSPs. [I-D.ietf-pce-association-bidir].
A member of the 'Double-sided Bidirectional with Reverse LSP
Association Group' can take the role of a forward or reverse
direction SR Path and follow the similar rules defined in
[I-D.ietf-pce-association-bidir] for LSPs.
o An SR Path (forward or reverse) cannot be part of more than one o An SR Path (forward or reverse) cannot be part of more than one
'Double-sided Bidirectional SR Path Association Group'. 'Double-sided Bidirectional with Reverse LSP Association Group'.
o The endpoints of the SR Paths in this associations cannot be o The endpoints of the SR Paths in 'Double-sided Bidirectional with
different. Reverse LSP Association Group' cannot be different.
3.1.1. Bidirectional LSP Association Group TLV 3.1.1. Bidirectional LSP Association Group TLV
In Bidirectional SR Association Group, for properties such as forward In 'Double-sided Bidirectional with Reverse LSP Association Group',
and reverse direction and co-routed path, it uses the Bidirectional for properties such as forward and reverse direction and co-routed
LSP Association Group TLV defined in path, it uses the Bidirectional LSP Association Group TLV defined in
[I-D.ietf-pce-association-bidir]. All fields and processing rules [I-D.ietf-pce-association-bidir]. All fields and processing rules
are as per [I-D.ietf-pce-association-bidir]. are as per [I-D.ietf-pce-association-bidir].
4. PCEP Procedures 4. PCEP Procedures
For bidirectional SR path, an ingress PCC is aware of the forward For a Bidirectional SR Path, an ingress PCC is aware of the forward
direction SR path beginning from itself to the egress PCC using the direction SR Path beginning from itself to the egress PCC using the
existing PCEP procedures. For the use-cases which require the existing PCEP procedures. For the use-cases which require the
ingress PCC to be aware of the reverse direction SR path, PCE informs ingress PCC to be aware of the reverse direction SR Path, PCE informs
the reverse SR Path to the ingress PCC. To achieve this, a the reverse SR Path to the ingress PCC. To achieve this, a
PCInitiate message for the reverse SR Path is sent to the ingress PCC PCInitiate message for the reverse SR Path is sent to the ingress PCC
and a PCInitiate message for the forward SR Path is sent to the and a PCInitiate message for the forward SR Path is sent to the
egress PCC (with the matching association group). These PCInitiate egress PCC (with the matching association group). These PCInitiate
message MUST NOT trigger initiation of SR Paths on PCCs. message MUST NOT trigger initiation of SR Paths on PCCs.
The SR Path can be identified by an LSP of an SR Policy as described
in [I-D.barth-pce-segment-routing-policy-cp].
For a bidirectional LSP computation when using both direction LSPs on For a bidirectional LSP computation when using both direction LSPs on
a node, the same LSP would need to be identified using 2 different a node, the same LSP would need to be identified using 2 different
PLSP-IDs based on the PCEP session to the ingress or the egress node. PLSP-IDs based on the PCEP session to the ingress or the egress node.
Note that the PLSP-ID space is independent at each PCC, the PLSP-ID Note that the PLSP-ID space is independent at each PCC, the PLSP-ID
allocated by the egress PCC cannot be used for the LSP at the ingress allocated by the egress PCC cannot be used for the LSP at the ingress
PCC (PLSP-ID conflict may occur). As per normal PCInitiate PCC (PLSP-ID conflict may occur). As per normal PCInitiate
operations, PCC assigns the PLSP-IDs for the local LSPs. Hence, when operations, PCC assigns the PLSP-IDs for the local LSPs. Hence, when
the PCE notifies an ingress PCC of the reverse LSP, it does so by the PCE notifies an ingress PCC of the reverse LSP, it does so by
using PCInitiate operations and sets PLSP-ID to zero and sets the R using PCInitiate operations and sets PLSP-ID to zero and sets the R
bit in the Bidirectional LSP Association Group TLV in the association bit in the Bidirectional LSP Association Group TLV in the association
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these LSPs are part of a bidirectional association. When PCE these LSPs are part of a bidirectional association. When PCE
notifies PCC1 of the reverse direction LSP2, it does so by sending a notifies PCC1 of the reverse direction LSP2, it does so by sending a
PCInitiate to PCC1 with PLSP-ID set to zero and R bit set in the PCInitiate to PCC1 with PLSP-ID set to zero and R bit set in the
Bidirectional LSP Association Group TLV. PCC1 upon reception of this Bidirectional LSP Association Group TLV. PCC1 upon reception of this
generates a new PLSP-ID (example PLSP-ID 300) and issues a PCRpt to generates a new PLSP-ID (example PLSP-ID 300) and issues a PCRpt to
PCE. Thus there would two PLSP-ID associated for LSP2 (300 at PCC1 PCE. Thus there would two PLSP-ID associated for LSP2 (300 at PCC1
and 200 at PCC2). and 200 at PCC2).
4.1. PCE Initiated Associated Bidirectional SR Paths 4.1. PCE Initiated Associated Bidirectional SR Paths
As specified in [RFC8697], Bidirectional SR Path Association Group As specified in [RFC8697], Associated Bidirectional SR Paths can be
can be created by a Stateful PCE as shown in Figure 1. created by a Stateful PCE as shown in Figure 1.
o Stateful PCE can create and update the forward and reverse SR o Stateful PCE can create and update the forward and reverse SR
Paths independently for 'Double-sided Bidirectional SR Path Paths independently for 'Double-sided Bidirectional with Reverse
Association Group'. LSP Association Group'.
o Stateful PCE can establish and remove the association relationship o Stateful PCE can establish and remove the association relationship
on a per SR Path basis. on a per SR Path basis.
o Stateful PCE can create and update the SR Path and the association o Stateful PCE can create and update the SR Path and the association
on a PCC via PCInitiate and PCUpd messages, respectively, using on a PCC via PCInitiate and PCUpd messages, respectively, using
the procedures described in [RFC8697]. the procedures described in [RFC8697].
o The reverse direction SR Path (LSP2(R) at node S, LSP1(R) at node o The reverse direction SR Path (LSP2(R) at node S, LSP1(R) at node
D as shown in Figure 1) SHOULD be informed by the PCE via D as shown in Figure 1) SHOULD be informed by the PCE via
PCInitiate message with the matching association group for the PCInitiate message with the matching association group for the
use-cases which require the PCC to be aware of the reverse use-cases which require the PCC to be aware of the reverse
direction SR path. direction SR Path.
+-----+ +-----+
| PCE | | PCE |
+-----+ +-----+
PCInitiate/PCUpd: / \ PCInitiate/PCUpd: PCInitiate/PCUpd: / \ PCInitiate/PCUpd:
Tunnel 1 (F) / \ Tunnel 2 (F) Tunnel 1 (F) / \ Tunnel 2 (F)
(LSP1 (F), LSP2 (R)) / \ (LSP2 (F), LSP1 (R)) (LSP1 (F), LSP2 (R)) / \ (LSP2 (F), LSP1 (R))
Association #1 / \ Association #1 Association #1 / \ Association #1
/ \ / \
v v v v
+-----+ LSP1 +-----+ +-----+ LSP1 +-----+
| S |------------>| D | | S |------------>| D |
| |<------------| | | |<------------| |
+-----+ LSP2 +-----+ +-----+ LSP2 +-----+
<no signaling> <no signaling>
Figure 1: PCE-Initiated Double-sided Bidirectional SR Path Figure 1: PCE-Initiated Associated Bidirectional SR Path
with Forward and Reverse Direction SR Paths with Forward and Reverse Direction SR Paths
4.2. PCC Initiated Associated Bidirectional SR Paths 4.2. PCC Initiated Associated Bidirectional SR Paths
As specified in [RFC8697], Bidirectional SR Path Association Group As specified in [RFC8697], Associated Bidirectional SR Paths can also
can also be created by a PCC as shown in Figure 2a and 2b. be created by a PCC as shown in Figure 2a and 2b.
o PCC can create and update the forward SR Path and update the o PCC can create and update the forward SR Path and update the
reverse SR Path independently for a 'Double-sided Bidirectional SR reverse SR Path independently for a 'Double-sided Bidirectional
Path Association Group'. with Reverse LSP Association Group'.
o PCC cannot instantiate a reverse SR Path in a bidirectional SR o PCC cannot instantiate a reverse SR Path in a bidirectional SR
Path. Path.
o PCC can establish and remove the association relationship on a per o PCC can establish and remove the association relationship on a per
SR Path basis. SR Path basis.
o PCC MUST report the change in the association group of an SR Path o PCC MUST report the change in the association group of an SR Path
to PCE(s) via PCRpt message. to PCE(s) via PCRpt message.
o PCC can report the forward and reverse SR Paths independently to o PCC can report the forward and reverse SR Paths independently to
PCE(s) via PCRpt message. PCE(s) via PCRpt message.
o PCC can delegate the forward and reverse SR Paths independently to o PCC can delegate the forward and reverse SR Paths independently to
a Stateful PCE, where PCE would control the SR Paths. a Stateful PCE, where PCE would control the SR Paths.
o Stateful PCE can update the SR Paths in the 'Double-sided o Stateful PCE can update the SR Paths in the 'Double-sided
Bidirectional SR Path Association Group' via PCUpd message, using Bidirectional with Reverse LSP Association Group' via PCUpd
the procedures described in [RFC8697]. message, using the procedures described in [RFC8697].
o The reverse direction SR Path (LSP2(R) at node S, LSP1(R) at node o The reverse direction SR Path (LSP2(R) at node S, LSP1(R) at node
D as shown in Figure 2b) SHOULD be informed by the PCE via D as shown in Figure 2b) SHOULD be informed by the PCE via
PCInitiate message with the matching association group for the PCInitiate message with the matching association group for the
use-cases which require the PCC to be aware of the reverse use-cases which require the PCC to be aware of the reverse
direction SR path. direction SR Path.
+-----+ +-----+
| PCE | | PCE |
+-----+ +-----+
Report/Delegate: ^ ^ Report/Delegate: Report/Delegate: ^ ^ Report/Delegate:
Tunnel 1 (F) / \ Tunnel 2 (F) Tunnel 1 (F) / \ Tunnel 2 (F)
(LSP1 (F)) / \ (LSP2 (F)) (LSP1 (F)) / \ (LSP2 (F))
Association #2 / \ Association #2 Association #2 / \ Association #2
/ \ / \
/ \ / \
+-----+ LSP1 +-----+ +-----+ LSP1 +-----+
| S |------------>| D | | S |------------>| D |
| |<------------| | | |<------------| |
+-----+ LSP2 +-----+ +-----+ LSP2 +-----+
<no signaling> <no signaling>
Figure 2a: Step 1: PCC-Initiated Double-sided Bidirectional Figure 2a: Step 1: PCC-Initiated Associated Bidirectional SR
SR Path with Forward Direction SR Paths Path with Forward Direction SR Paths
+-----+ +-----+
| PCE | | PCE |
+-----+ +-----+
PCUpd/PCInitiate: / \ PCUpd/PCInitiate: PCUpd/PCInitiate: / \ PCUpd/PCInitiate:
Tunnel 1 (F) / \ Tunnel 2 (F) Tunnel 1 (F) / \ Tunnel 2 (F)
(LSP1 (F), LSP2 (R)) / \ (LSP2 (F), LSP1 (R)) (LSP1 (F), LSP2 (R)) / \ (LSP2 (F), LSP1 (R))
Association #2 / \ Association #2 Association #2 / \ Association #2
/ \ / \
v v v v
+-----+ LSP1 +-----+ +-----+ LSP1 +-----+
| S |------------>| D | | S |------------>| D |
| |<------------| | | |<------------| |
+-----+ LSP2 +-----+ +-----+ LSP2 +-----+
<no signaling> <no signaling>
Figure 2b: Step 2: PCE-Updated/Initiated Double-sided Bidirectional Figure 2b: Step 2: PCE-Updated/Initiated Associated Bidirectional SR
SR Path with Reverse Direction SR Paths Path with Reverse Direction SR Paths
4.3. Stateless PCE 4.3. Stateless PCE
As defined in [I-D.ietf-pce-association-bidir], for a stateless PCE, As defined in [I-D.ietf-pce-association-bidir], for a stateless PCE,
it might be useful to associate a path computation request to an it might be useful to associate a path computation request to an
association group, thus enabling it to associate a common set of association group, thus enabling it to associate a common set of
configuration parameters or behaviors with the request. A PCC can configuration parameters or behaviors with the request. A PCC can
request co-routed or non-co-routed forward and reverse direction request co-routed or non-co-routed forward and reverse direction
paths from a stateless PCE for a bidirectional SR association group. paths from a stateless PCE for a bidirectional SR association group.
4.4. Bidirectional (B) Flag 4.4. Bidirectional (B) Flag
As defined in [RFC5440], the Bidirectional (B) flag in Request The Bidirectional (B) flag in Request Parameters (RP) object
Parameters (RP) object MUST be set when the PCC specifies that the [RFC5440] and Stateful PCE Request Parameter (SRP) object
path computation request relates to a bidirectional TE LSP. The [I-D.ietf-pce-pcep-stateful-pce-gmpls] follow the procedure defined
B-flag also MUST be set when the PCC specifies that the path in [I-D.ietf-pce-association-bidir].
computation request relates to an associated bidirectional SR Path.
Note that the B-flag defined in Stateful PCE Request Parameter (SRP)
object [I-D.ietf-pce-pcep-stateful-pce-gmpls] is not required for
associated bidirectional SR path as association group is used to
indicate that the path is bidirectional.
4.5. State Synchronization 4.5. State Synchronization
During state synchronization, a PCC MUST report all the existing During state synchronization, a PCC MUST report all the existing
Bidirectional SR Association Groups to the Stateful PCE as per Bidirectional Association Groups to the Stateful PCE as per
[RFC8697]. After the state synchronization, the PCE MUST remove all [RFC8697]. After the state synchronization, the PCE MUST remove all
stale Bidirectional SR Associations. stale Bidirectional Association Groups.
4.6. Error Handling 4.6. Error Handling
The error handling as described in section 5.7 of The error handling as described in section 5.7 of
[I-D.ietf-pce-association-bidir] continue to apply. [I-D.ietf-pce-association-bidir] continue to apply.
The PCEP Path Setup Type (PST) for SR is set to 'TE Path is Setup The PCEP Path Setup Type (PST) for SR is set to 'TE Path is Setup
using Segment Routing' [RFC8408]. If a PCEP speaker receives a using Segment Routing' [RFC8408]. If a PCEP speaker receives a
different PST value for Bidirectional SR Path association group and different PST value for 'Double-sided Bidirectional with Reverse LSP
it does not support; it MUST send a PCErr message with Error-Type = Association Group' and it does not support; it MUST send a PCErr
26 (Association Error) and Error-Value = TBD2 (Bidirectional LSP message with Error-Type = 26 (Association Error) and Error-Value =
Association - Path Setup Type Not Supported). 'Bidirectional LSP Association - Path Setup Type Not Supported'
defined in [I-D.ietf-pce-association-bidir].
5. Implementation Status 5. Implementation Status
[Note to the RFC Editor - remove this section before publication, as [Note to the RFC Editor - remove this section before publication, as
well as remove the reference to [RFC7942]. well as remove the reference to [RFC7942].
This section records the status of known implementations of the This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942]. Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to The description of implementations in this section is intended to
skipping to change at page 11, line 12 skipping to change at page 11, line 43
o Contact: zhan.shuangping@zte.com.cn o Contact: zhan.shuangping@zte.com.cn
6. Security Considerations 6. Security Considerations
The security considerations described in [RFC5440], [RFC8231], The security considerations described in [RFC5440], [RFC8231],
[RFC8281], and [RFC8408] apply to the extensions defined in this [RFC8281], and [RFC8408] apply to the extensions defined in this
document as well. document as well.
A new Association Type for the Association Object, 'Double-sided A new Association Type for the Association Object, 'Double-sided
Associated Bidirectional SR Path Association Group' is introduced in Bidirectional with Reverse LSP Association Group' is introduced in
this document. Additional security considerations related to LSP this document. Additional security considerations related to LSP
associations due to a malicious PCEP speaker is described in associations due to a malicious PCEP speaker is described in
[RFC8697] and apply to this Association Type. Hence, securing the [RFC8697] and apply to this Association Type. Hence, securing the
PCEP session using Transport Layer Security (TLS) [RFC8253] is PCEP session using Transport Layer Security (TLS) [RFC8253] is
recommended. recommended.
7. Manageability Considerations 7. Manageability Considerations
All manageability requirements and considerations listed in All manageability requirements and considerations listed in
[RFC5440], [RFC8231], and [RFC8281] apply to PCEP protocol extensions [RFC5440], [RFC8231], and [RFC8281] apply to PCEP protocol extensions
skipping to change at page 11, line 35 skipping to change at page 12, line 21
7.1. Control of Function and Policy 7.1. Control of Function and Policy
The mechanisms defined in this document do not imply any control or The mechanisms defined in this document do not imply any control or
policy requirements in addition to those already listed in [RFC5440], policy requirements in addition to those already listed in [RFC5440],
[RFC8231], and [RFC8281]. [RFC8231], and [RFC8281].
7.2. Information and Data Models 7.2. Information and Data Models
[RFC7420] describes the PCEP MIB, there are no new MIB Objects [RFC7420] describes the PCEP MIB, there are no new MIB Objects
defined for Bidirectional SR Path associations. The PCEP YANG module defined for 'Double-sided Bidirectional with Reverse LSP Association
[I-D.ietf-pce-pcep-yang] defines data model for Bidirectional SR Path Groups'. The PCEP YANG module [I-D.ietf-pce-pcep-yang] defines data
associations. model for Associated Bidirectional SR Paths.
7.3. Liveness Detection and Monitoring 7.3. Liveness Detection and Monitoring
Mechanisms defined in this document do not imply any new liveness Mechanisms defined in this document do not imply any new liveness
detection and monitoring requirements in addition to those already detection and monitoring requirements in addition to those already
listed in [RFC5440], [RFC8231], and [RFC8281]. listed in [RFC5440], [RFC8231], and [RFC8281].
7.4. Verify Correct Operations 7.4. Verify Correct Operations
Mechanisms defined in this document do not imply any new operation Mechanisms defined in this document do not imply any new operation
skipping to change at page 12, line 16 skipping to change at page 13, line 4
Mechanisms defined in this document do not imply any new requirements Mechanisms defined in this document do not imply any new requirements
on other protocols. on other protocols.
7.6. Impact On Network Operations 7.6. Impact On Network Operations
Mechanisms defined in [RFC5440], [RFC8231], and [RFC8408] also apply Mechanisms defined in [RFC5440], [RFC8231], and [RFC8408] also apply
to PCEP extensions defined in this document. to PCEP extensions defined in this document.
8. IANA Considerations 8. IANA Considerations
8.1. Association Type 8.1. Association Type
This document defines a new Association Type for the Association This document defines a new Association Type for the Association
Object (Class Value 40) defined [RFC8697]. IANA is requested to make Object (Class Value 40) defined [RFC8697]. IANA is requested to make
the assignment of a type for the sub-registry "ASSOCIATION Type" as the assignment of a type for the sub-registry "ASSOCIATION Type" as
follows: follows:
Type Name Reference Type Name Reference
------------------------------------------------------------------- -------------------------------------------------------------------
TBD1 Double-sided Bidirectional SR Path This document TBD1 Double-sided Bidirectional with Reverse This document
Association Group LSP Association Group
8.2. PCEP Errors
This document defines new Error value for Error Type 26 (Association
Error). IANA is requested to allocate new Error value within the
"PCEP-ERROR Object Error Types and Values" sub-registry of the PCEP
Numbers registry, as follows:
Error Type Description Reference
-------------------------------------------------------------------
26 Association Error
Error value: TBD2 This document
Bidirectional LSP Association -
Path Setup Type Not Supported
9. References 9. References
9.1. Normative References 9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
skipping to change at page 14, line 34 skipping to change at page 15, line 13
July 2018, <https://www.rfc-editor.org/info/rfc8408>. July 2018, <https://www.rfc-editor.org/info/rfc8408>.
[I-D.ietf-mpls-bfd-directed] [I-D.ietf-mpls-bfd-directed]
Mirsky, G., Tantsura, J., Varlashkin, I., and M. Chen, Mirsky, G., Tantsura, J., Varlashkin, I., and M. Chen,
"Bidirectional Forwarding Detection (BFD) Directed Return "Bidirectional Forwarding Detection (BFD) Directed Return
Path", draft-ietf-mpls-bfd-directed-13 (work in progress), Path", draft-ietf-mpls-bfd-directed-13 (work in progress),
December 2019. December 2019.
[I-D.gandhi-spring-twamp-srpm] [I-D.gandhi-spring-twamp-srpm]
Gandhi, R., Filsfils, C., Voyer, D., Chen, M., and B. Gandhi, R., Filsfils, C., Voyer, D., Chen, M., and B.
Janssens, "Performance Measurement Using TWAMP Light for Janssens, "Performance Measurement Using TWAMP Light and
Segment Routing Networks", draft-gandhi-spring-twamp- STAMP for Segment Routing Networks", draft-gandhi-spring-
srpm-05 (work in progress), December 2019. twamp-srpm-07 (work in progress), March 2020.
[I-D.ietf-spring-mpls-path-segment] [I-D.ietf-spring-mpls-path-segment]
Cheng, W., Li, H., Chen, M., Gandhi, R., and R. Zigler, Cheng, W., Li, H., Chen, M., Gandhi, R., and R. Zigler,
"Path Segment in MPLS Based Segment Routing Network", "Path Segment in MPLS Based Segment Routing Network",
draft-ietf-spring-mpls-path-segment-01 (work in progress), draft-ietf-spring-mpls-path-segment-02 (work in progress),
September 2019. February 2020.
[I-D.ietf-pce-pcep-yang] [I-D.ietf-pce-pcep-yang]
Dhody, D., Hardwick, J., Beeram, V., and J. Tantsura, "A Dhody, D., Hardwick, J., Beeram, V., and J. Tantsura, "A
YANG Data Model for Path Computation Element YANG Data Model for Path Computation Element
Communications Protocol (PCEP)", draft-ietf-pce-pcep- Communications Protocol (PCEP)", draft-ietf-pce-pcep-
yang-13 (work in progress), October 2019. yang-13 (work in progress), October 2019.
[I-D.ietf-pce-pcep-stateful-pce-gmpls] [I-D.ietf-pce-pcep-stateful-pce-gmpls]
Lee, Y., Zheng, H., Dios, O., Lopezalvarez, V., and Z. Lee, Y., Zheng, H., Dios, O., Lopezalvarez, V., and Z.
Ali, "Path Computation Element (PCE) Protocol Extensions Ali, "Path Computation Element (PCE) Protocol Extensions
for Stateful PCE Usage in GMPLS-controlled Networks", for Stateful PCE Usage in GMPLS-controlled Networks",
draft-ietf-pce-pcep-stateful-pce-gmpls-12 (work in draft-ietf-pce-pcep-stateful-pce-gmpls-12 (work in
progress), October 2019. progress), October 2019.
[I-D.barth-pce-segment-routing-policy-cp]
Koldychev, M., Sivabalan, S., Barth, C., Li, C., and H.
Bidgoli, "PCEP extension to support Segment Routing Policy
Candidate Paths", draft-barth-pce-segment-routing-policy-
cp-04 (work in progress), October 2019.
Acknowledgments Acknowledgments
Many thanks to Marina Fizgeer, Adrian Farrel, and Andrew Stone for Many thanks to Marina Fizgeer, Adrian Farrel, and Andrew Stone for
the detailed review of this document and providing many useful the detailed review of this document and providing many useful
comments. comments.
Contributors Contributors
The following people have substantially contributed to this document: The following people have substantially contributed to this document:
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