PCE Working Group M. Koldychev
Internet-Draft S. Sivabalan
Intended status: Standards Track Cisco Systems, Inc.
Expires: May 4, 2020 C. Barth
Juniper Networks, Inc.
C. Li
Huawei Technologies
H. Bidgoli
Nokia
November 01, 2019
PCEP extension to support Segment Routing Policy Candidate Paths
draft-barth-pce-segment-routing-policy-cp-04
Abstract
This document introduces a mechanism to specify a Segment Routing
(SR) policy, as a collection of SR candidate paths. An SR policy is
identified by <headend, color, end-point> tuple. An SR policy can
contain one or more candidate paths where each candidate path is
identified in PCEP via an PLSP-ID. This document proposes extension
to PCEP to support association among candidate paths of a given SR
policy. The mechanism proposed in this document is applicable to
both MPLS and IPv6 data planes of SR.
Requirements Language
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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on May 4, 2020.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Group Candidate Paths belonging to the same SR policy . . 5
3.2. Instantiation of SR policy candidate paths . . . . . . . 5
3.3. Avoid computing lower preference candidate paths . . . . 5
3.4. Minimal signaling overhead . . . . . . . . . . . . . . . 5
4. Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Choice of Association Parameters . . . . . . . . . . . . 7
4.3. Multiple Optimization Objectives and Constraints . . . . 8
5. SR Policy Association Group . . . . . . . . . . . . . . . . . 8
5.1. SR Policy Identifiers TLV . . . . . . . . . . . . . . . . 9
5.2. SR Policy Name TLV . . . . . . . . . . . . . . . . . . . 10
5.3. SR Policy Candidate Path Identifiers TLV . . . . . . . . 10
5.4. SR Policy Candidate Path Preference TLV . . . . . . . . . 11
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1. PCC Initiated SR Policy with single candidate-path . . . 12
6.2. PCC Initiated SR Policy with multiple candidate-paths . . 12
6.3. PCE Initiated SR Policy with single candidate-path . . . 13
6.4. PCE Initiated SR Policy with multiple candidate-paths . . 14
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7.1. Association Type . . . . . . . . . . . . . . . . . . . . 14
7.2. PCEP Errors . . . . . . . . . . . . . . . . . . . . . . . 15
7.3. SRPAG TLVs . . . . . . . . . . . . . . . . . . . . . . . 15
8. Security Considerations . . . . . . . . . . . . . . . . . . . 16
9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 16
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
10.1. Normative References . . . . . . . . . . . . . . . . . . 16
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10.2. Informative References . . . . . . . . . . . . . . . . . 17
Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction
Path Computation Element (PCE) Communication Protocol (PCEP)
[RFC5440] enables the communication between a Path Computation Client
(PCC) and a Path Control Element (PCE), or between two PCEs based on
the PCE architecture [RFC4655].
PCEP Extensions for the Stateful PCE Model [RFC8231] describes a set
of extensions to PCEP to enable active control of Multiprotocol Label
Switching Traffic Engineering (MPLS-TE) and Generalized MPLS (GMPLS)
tunnels. [RFC8281] describes the setup and teardown of PCE-initiated
LSPs under the active stateful PCE model, without the need for local
configuration on the PCC, thus allowing for dynamic centralized
control of a network.
PCEP Extensions for Segment Routing [I-D.ietf-pce-segment-routing]
specifies extensions to the Path Computation Element Protocol (PCEP)
that allow a stateful PCE to compute and initiate Traffic Engineering
(TE) paths, as well as a PCC to request a path subject to certain
constraint(s) and optimization criteria in SR networks.
PCEP Extensions for Establishing Relationships Between Sets of LSPs
[I-D.ietf-pce-association-group] introduces a generic mechanism to
create a grouping of LSPs which can then be used to define
associations between a set of LSPs and a set of attributes (such as
configuration parameters or behaviors) and is equally applicable to
stateful PCE (active and passive modes) and stateless PCE.
Segment Routing Policy for Traffic Engineering
[I-D.ietf-spring-segment-routing-policy] details the concepts of SR
Policy and approaches to steering traffic into an SR Policy.
An SR policy contains one or more candidate paths where one or more
such paths can be computed via PCE. This document specifies PCEP
extensions to signal additional information to map candidate paths to
their SR policies. Each candidate path maps to a unique PLSP-ID in
PCEP. By associating multiple candidate paths together, a PCE
becomes aware of the hierarchical structure of an SR policy. Thus
the PCE can take computation and control decisions about the
candidate paths, with the additional knowledge that these candidate
paths belong to the same SR policy. This is accomplished via the use
of the existing PCEP Association object, by defining a new
association type specifically for associating SR candidate paths into
a single SR policy.
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[Editor's Note- Currently it is assumed that each candidate path has
only one ERO (SID-List) within the scope of this document. A future
update or another document will deal with a way to allow multiple
ERO/SID-Lists for a candidate path within PCEP.]
2. Terminology
The following terminologies are used in this document:
Endpoint: The IPv4 or IPv6 endpoint address of the SR policy in
question, as described in
[I-D.ietf-spring-segment-routing-policy].
Association parameters: As described in
[I-D.ietf-pce-association-group], the combination of the mandatory
fields Association type, Association ID and Association Source in
the ASSOCIATION object uniquely identify the association group.
If the optional TLVs - Global Association Source or Extended
Association ID are included, then they MUST be included in
combination with mandatory fields to uniquely identify the
association group.
Association information: As described in
[I-D.ietf-pce-association-group], the ASSOCIATION object could
also include other optional TLVs based on the association types,
that provides 'information' related to the association type.
PCC: Path Computation Client. Any client application requesting a
path computation to be performed by a Path Computation Element.
PCE: Path Computation Element. An entity (component, application,
or network node) that is capable of computing a network path or
route based on a network graph and applying computational
constraints.
PCEP: Path Computation Element Protocol.
PCEP Tunnel: The entity identified by the PLSP-ID, as per
[I-D.koldychev-pce-operational].
3. Motivation
The new Association Type (SR Policy Association) and the new TLVs for
the ASSOCIATION object, defined in this document, allow a PCEP peer
to exchange additional parameters of SR candidate paths and of their
parent SR policy. For the SR policy, the parameters are: color and
endpoint. For the candidate path, the parameters are: protocol
origin, originator, discriminator and preference.
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[I-D.ietf-spring-segment-routing-policy] describes the concept of SR
Policy and these parameters.
The motivation for signaling these parameters is summarized in the
following subsections.
3.1. Group Candidate Paths belonging to the same SR policy
Since each candidate path of an SR policy appears as a different LSP
(identified via a PLSP-ID) in PCEP, it is useful to group together
all the candidate paths that belong to the same SR policy.
Furthermore, it is useful for the PCE to have knowledge of the SR
candidate path parameters such as color, protocol origin,
discriminator, and preference.
3.2. Instantiation of SR policy candidate paths
A PCE may want to instantiate one or more candidate paths on the PCC,
as specified in [RFC8281]. In this scenario, the PCE needs to signal
to a PCC <headend, color, end-point, originator, discriminator,
preference> tuple using which the PCC can instantiate a candidate
path for the SR policy identified. Current PCEP standards (as of the
time of this writing) do not provide a way to signal color and
preference. Although end-point can be signaled via the PCEP END-
POINTS object, this object may not be suitable because the end-point
to which the path is computed is not required to be the same IPv4/
IPv6 address as the actual endpoint of the SR policy. Thus, a
separate way to specify SR policy's end-point is provided in this
document.
3.3. Avoid computing lower preference candidate paths
When a PCE knows that a given set of candidate paths all belong to
the same SR policy, then path computation MAY be done on only the
highest preference candidate-path(s). Path computation for lower
preference paths is not necessary if one or two higher preference
paths are already computed. Since computing their paths will not
affect traffic steering, it MAY be postponed until the higher
preference paths become invalid, thus saving computation resources on
the PCE.
3.4. Minimal signaling overhead
When an SR policy contains multiple candidate paths computed by a
PCE, such candidate paths can be created, updated and deleted
independently of each other. This is achieved by making each
candidate path correspond to a unique LSP (identified via PLSP-ID).
For example, if an SR policy has 4 candidate paths, then if the PCE
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wants to update one of those candidate paths, only one set of PCUpd
and PCRpt messages needs to be exchanged.
4. Procedure
4.1. Overview
As per [I-D.ietf-pce-association-group], LSPs are placed into an
association group. As per [I-D.koldychev-pce-operational], LSPs are
contained in PCEP Tunnels and a PCEP Tunnel is contained in an
Association if all of its LSPs are in that Association.
PCEP Tunnels naturally map to SR Candidate Paths and PCEP
Associations naturally map to SR Policies. Definition of these
mappings is the central purpose of this document.
The mapping between PCEP Associations and SR Policies is always one-
to-one. However, the mapping between PCEP Tunnels and SR Candidate
Paths may be either one-to-one, or many-to-one. The mapping is one-
to-one when the SR Candidate Path has only a single constraint and
optimization objective. The mapping is many-to-one when the SR
Candidate Path has multiple constraints and optimization objectives.
For more details on multiple optimization objectives and constraints,
see Section 4.3.
[Editor's Note - Segment-lists within a candidate path are not
represented by different PCEP Tunnels. The subject of encoding
multiple segment lists within a candidate path is left to a future
document and is not specified in this document. It is not a good
idea to have each segment-list correspond to a different Tunnel,
because when the PCC wants to get a path, it must know in advance how
many multipaths (i.e., segment-lists) there will be and create that
many Tunnels. For example, if the PCC supports 32 multipaths, then
it must delegate 32 Tunnels for every candidate path, which may not
be scalable.]
A new Association Type is defined in this document, based on the
generic ASSOCIATION object. Association type = TBD1 "SR Policy
Association Type" for SR Policy Association Group (SRPAG). The SRPAG
Association is only meant to be used for SR LSPs and with PCEP peers
which advertise SR capability.
An Association object of SRPAG group contains TLVs that carry
Association Information. The association information can be
subdivided into three parts: Policy identifiers, Candidate path
identifiers, and Candidate path attributes.
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Policy Identifiers uniquely identify the SR policy to which a given
LSP belongs, within the context of the head-end. Policy Identifiers
MUST be the same for all candidate paths in the same SRPAG. Policy
Identifiers MUST NOT change for a given LSP during its lifetime.
Policy Identifiers MUST be different for different SRPAG
associations. When these rules are not satisfied, the PCE MUST send
a PCErr message with Error Code = 26 "Association Error", Error Type
= TBD6 "Conflicting SRPAG TLV". Policy Identifiers consist of:
o Color of SR policy.
o End-point of SR policy.
o Optionally, the policy name.
Candidate Path Identifiers uniquely identify the SR candidate path
within the context of an SR policy. Candidate path Identifiers MUST
NOT change for a given LSP during its lifetime. Candidate path
Identifiers MUST be different for different LSPs within the same
SRPAG. When these rules are not satisfied, the PCE MUST send a PCErr
message with Error Code = 26 "Association Error", Error Type = TBD6
"Conflicting SRPAG TLV". Candidate path Identifiers consist of:
o Protocol Origin of candidate path.
o Originator of candidate path.
o Discriminator of candidate path.
Candidate Path Attributes MUST NOT be used to identify the candidate
path. Candidate path attributes carry additional information about
the candidate path and MAY change during the lifetime of the LSP.
Candidate path Attributes consist of:
o Preference of candidate path.
As per the processing rules specified in section 5.4 of
[I-D.ietf-pce-association-group], if a PCEP speaker does not support
the SRPAG association type, it MUST return a PCErr message with
Error-Type 26 (Early allocation by IANA) "Association Error" and
Error-Value 1 "Association-type is not supported". Please note that
the corresponding PCEP session is not reset.
4.2. Choice of Association Parameters
The Association Parameters (see Section 2) uniquely identify the
Association. In this section, we describe how these are to be set.
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The Association Source MUST be set to the PCC's address. This
applies for both PCC-initiated and PCE-initiated candidate paths.
The reasoning for this is that if different PCEs could set their own
Association Source, then the candidate paths instantiated by
different PCEs would by definition be in different PCEP Associations,
which contradicts our requirement that the SR Policy is represented
by an Association.
The Association ID MUST be chosen by the PCC when the SR policy is
allocated. In PCRpt messages from the PCC, the Association ID MUST
be set to the unique value that was allocated by the PCC at the time
of policy creation. In PCInit messages from the PCE, the Association
ID MUST be set to the reserved value 0xFFFF, which indicates that the
PCE is asking the PCC to choose an ID value. The PCE MUST NOT send
the Extended Association ID TLV in the PCInit messages.
If the PCC receives a PCInit message with Association Source not
equal to the PCCs address, or with Association ID not equal to
0xFFFF, or with Extended Association ID TLV present, the PCC SHOULD
ignore the given ASSOCIATION object.
4.3. Multiple Optimization Objectives and Constraints
In certain scenarios, it is desired for each SR Candidate Path to
contain multiple sub-candidate paths, each of which has a different
optimization objective and constraints. Traffic is then sent ECMP or
UCMP among these sub-candidate paths.
This is represented in PCEP by a many-to-one mapping between PCEP
Tunnels and SR Candidate Paths. This means that multiple PCEP
Tunnels are allocated for each SR Candidate Path. Each PCEP Tunnel
has its own optimization objective and constraints. When a single SR
Candidate Path contains multiple PCEP Tunnels, each of these PCEP
Tunnels MUST have identical values of Candidate Path Identifiers, as
encoded in SRPOLICY-CPATH-ID TLV, see Section 5.3.
5. SR Policy Association Group
Two ASSOCIATION object types for IPv4 and IPv6 are defined in
[I-D.ietf-pce-association-group]. The ASSOCIATION object includes
"Association type" indicating the type of the association group.
This document adds a new Association type.
Association type = TBD1 "SR Policy Association Type" for SR Policy
Association Group (SRPAG).
The operator configured Association Range SHOULD NOT be set for this
association type and MUST be ignored.
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SRPAG MUST carry additional TLVs to communicate Association
Information. This document specifies four new TLVs to carry
Association Information: SRPOLICY-POL-ID TLV, SRPOLICY-POL-NAME TLV,
SRPOLICY-CPATH-ID TLV, SRPOLICY-CPATH-PREFERENCE TLV. These four
TLVs encode the Policy Identifiers, Policy name, Candidate path
Identifiers and Candidate path Preference, respectively. When any of
the mandatory TLVs are missing from the SRPAG association object, the
PCE MUST send a PCErr message with Error Code = 26 "Association
Error", Error Type = TBD7 "Missing mandatory SRPAG TLV".
A given LSP MUST belong to at most one SRPAG, since a candidate path
cannot belong to multiple SR policies. If a PCEP speaker receives a
PCEP message with more than one SRPAG for an LSP, then the PCEP
speaker MUST send a PCErr message with Error-Type 26 "Association
Error" and Error-Value TBD8 "Multiple SRPAG for one LSP". If the
message is a PCRpt message, then the PCEP speaker MUST close the PCEP
connection. Closing the PCEP connection is necessary because
ignoring PCRpt messages may lead to inconsistent LSP DB state between
the two PCEP peers.
If the PCEP speaker receives the SRPAG association when the SR
capability (as per [I-D.ietf-pce-segment-routing] or
[I-D.negi-pce-segment-routing-ipv6]) was not exchanged, the PCEP
speaker MUST send a PCErr message with Error-Type 26 "Association
Error" and Error-Value TBD9 "Use of SRPAG without SR capability
exchange". If the Path Setup Type (PST) of the LSP in SRPAG is not
set to SR or SRv6, then the PCEP speaker MUST send a PCErr message
with Error-Type 26 "Association Error" and Error-Value TBD10 "non-SR
LSP in SRPAG".
5.1. SR Policy Identifiers TLV
The SRPOLICY-POL-ID TLV is a mandatory TLV for the SRPAG Association.
Only one SRPOLICY-POL-ID TLV can be carried and only the first
occurrence is processed and any others MUST be ignored.
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ End-point ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: The SRPOLICY-POL-ID TLV format
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Type: TBD2 for "SRPOLICY-POL-ID" TLV.
Length: 8 or 20, depending on length of End-point (IPv4 or IPv6)
Color: any unsigned 32-bit number.
End-point: can be either IPv4 or IPv6, depending on whether the
policy endpoint has IPv4 or IPv6 address. This value may be
different from the one contained in the END-POINTS object, or in the
LSP IDENTIFIERS TLV of the LSP object. Endpoint is meant to strictly
correspond to the endpoint of the SR policy, as it is defined in
[I-D.ietf-spring-segment-routing-policy].
5.2. SR Policy Name TLV
The SRPOLICY-POL-NAME TLV is an optional TLV for the SRPAG
Association. At most one SRPOLICY-POL-NAME TLV can be carried and
only the first occurrence is processed and any others MUST be
ignored.
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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Policy Name ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: The SRPOLICY-POL-NAME TLV format
Type: TBD3 for "SRPOLICY-POL-NAME" TLV.
Length: indicates the total length of the TLV in octets and MUST be
greater than 0. The TLV MUST be zero-padded so that the TLV is
4-octet aligned.
Policy Name: Policy name, as defined in
[I-D.ietf-spring-segment-routing-policy]. It SHOULD be a string of
printable ASCII characters, without a NULL terminator.
5.3. SR Policy Candidate Path Identifiers TLV
The SRPOLICY-CPATH-ID TLV is a mandatory TLV for the SRPAG
Association. Only one SRPOLICY-CPATH-ID TLV can be carried and only
the first occurrence is processed and any others MUST be ignored.
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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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Proto. Origin | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator ASN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Originator Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: The SRPOLICY-CPATH-ID TLV format
Type: TBD4 for "SRPOLICY-CPATH-ID" TLV.
Length: 28.
Protocol Origin: 8-bit value that encodes the protocol origin, as
specified in [I-D.ietf-spring-segment-routing-policy] Section 2.3.
Reserved: MUST be set to zero on transmission and ignored on receipt.
Originator ASN: Represented as 4 byte number, part of the originator
identifier, as specified in [I-D.ietf-spring-segment-routing-policy]
Section 2.4.
Originator Address: Represented as 128 bit value where IPv4 address
are encoded in lowest 32 bits, part of the originator identifier, as
specified in [I-D.ietf-spring-segment-routing-policy] Section 2.4.
Discriminator: 32-bit value that encodes the Discriminator of the
candidate path.
5.4. SR Policy Candidate Path Preference TLV
The SRPOLICY-CPATH-PREFERENCE TLV is an optional TLV for the SRPAG
Association. Only one SRPOLICY-CPATH-PREFERENCE TLV can be carried
and only the first occurrence is processed and any others MUST be
ignored.
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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 | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: The SRPOLICY-CPATH-PREFERENCE TLV format
Type: TBD5 for "SRPOLICY-CPATH-PREFERENCE" TLV.
Length: 4.
Preference: Numerical preference of the candidate path, as specified
in [I-D.ietf-spring-segment-routing-policy] Section 2.7.
If the TLV is missing, a default preference of 100 as specified in
[I-D.ietf-spring-segment-routing-policy] is used.
6. Examples
6.1. PCC Initiated SR Policy with single candidate-path
PCReq and PCRep messages are exchanged in the following sequence:
1. PCC sends PCReq message to the PCE, encoding the SRPAG
ASSOCIATION object and TLVs in the PCReq message.
2. PCE returns the path in PCRep message, and echoes back the SRPAG
object that was used in the computation.
PCRpt and PCUpd messages are exchanged in the following sequence:
1. PCC sends PCRpt message to the PCE, including the LSP object and
the SRPAG ASSOCIATION object.
2. PCE computes path, possibly making use of the Association
Information from the SRPAG ASSOCIATION object.
3. PCE updates the SR policy candidate path's ERO using PCUpd
message.
6.2. PCC Initiated SR Policy with multiple candidate-paths
PCRpt and PCUpd messages are exchanged in the following sequence:
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1. For each candidate path of the SR Policy, the PCC generates a
different PLSP-ID and symbolic-name and sends multiple PCRpt
messages (or one message with multiple LSP objects) to the PCE.
Each LSP object is followed by SRPAG ASSOCIATION object with
identical Color and Endpoint values. The Association Source is
set to the IP address of the PCC and the Association ID is set to
a number that PCC locally chose to represent the SR Policy.
2. PCE takes into account that all the LSPs belong to the same SR
policy. PCE prioritizes computation for the highest preference
LSP and sends PCUpd message(s) back to the PCC.
3. If a new candidate path is added on the PCC by the operator, then
a new PLSP-ID and symbolic name is generated for that candidate
path and a new PCRpt is sent to the PCE.
4. If an existing candidate path is removed from the PCC by the
operator, then that PLSP-ID is deleted from the PCE by sending
PCRpt with the R-flag in the LSP object set.
6.3. PCE Initiated SR Policy with single candidate-path
A candidate-path is created using the following steps:
1. PCE sends PCInitiate message, containing the SRPAG Association
object. The Association Source is set to the IP address of the
PCC and the Association ID is set to 0xFFFF, as described in
Section 4.2.
2. PCC uses the color, endpoint and preference from the SRPAG object
to create a new candidate path. If no SR policy exists to hold
the candidate path, then a new SR policy is created to hold the
new candidate-path. The Originator of the candidate path is set
to be the address of the PCE that is sending the PCInitiate
message.
3. PCC sends a PCRpt message back to the PCE to report the newly
created Candidate Path. The PCRpt message contains the SRPAG
Association object. The Association Source is set to the IP
address of the PCC and the Association ID is set to a number that
PCC locally chose to represent the SR Policy.
A candidate-path is deleted using the following steps:
1. PCE sends PCInitiate message, setting the R-flag in the LSP
object.
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2. PCC uses the PLSP-ID from the LSP object to find the candidate
path and delete it. If this is the last candidate path under the
SR policy, then the containing SR policy is deleted as well.
6.4. PCE Initiated SR Policy with multiple candidate-paths
A candidate-path is created using the following steps:
1. PCE sends a separate PCInitiate message for every candidate path
that it wants to create, or it sends multiple LSP objects within
a single PCInitiate message. The SRPAG Association object is
sent for every LSP in the PCInitiate message. The Association
Source is set to the IP address of the PCC and the Association ID
is set to 0xFFFF, as described in Section 4.2.
2. PCC creates multiple candidate paths under the same SR policy,
identified by Color and Endpoint.
3. PCC sends a PCRpt message back to the PCE to report the newly
created Candidate Path. The PCRpt message contains the SRPAG
Association object. The Association Source is set to the IP
address of the PCC and the Association ID is set to a number that
PCC locally chose to represent the SR Policy.
A candidate path is deleted using the following steps:
1. PCE sends PCInitiate message, setting the R-flag in the LSP
object.
2. PCC uses the PLSP-ID from the LSP object to find the candidate
path and delete it.
7. IANA Considerations
7.1. Association Type
This document defines a new association type: SR Policy Association
Group (SRPAG). IANA is requested to make the assignment of a new
value for the sub-registry "ASSOCIATION Type Field" (request to be
created in [I-D.ietf-pce-association-group]), as follows:
+----------------------+-------------------------+------------------+
| Association Type | Association Name | Reference |
| Value | | |
+----------------------+-------------------------+------------------+
| TBD1 | SR Policy Association | This document |
+----------------------+-------------------------+------------------+
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7.2. PCEP Errors
This document defines three new Error-Values within the "Association
Error" Error-Type. IANA is requested to allocate new error values
within the "PCEP-ERROR Object Error Types and Values" sub-registry of
the PCEP Numbers registry, as follows:
+-------+----------+-----------------------------+------------------+
| Error | Error | Meaning | Reference |
| Type | Value | | |
+-------+----------+-----------------------------+------------------+
| 29 | TBD6 | Conflicting SRPAG TLV | This document |
+-------+----------+-----------------------------+------------------+
| 29 | TBD7 | Missing mandatory SRPAG TLV | This document |
+-------+----------+-----------------------------+------------------+
| 29 | TBD8 | Multiple SRPAG for one LSP | This document |
+-------+----------+-----------------------------+------------------+
| 29 | TBD9 | Use of SRPAG without SR | This document |
| | | capability exchange | |
+-------+----------+-----------------------------+------------------+
| 29 | TBD10 | non-SR LSP in SRPAG | This document |
+-------+----------+-----------------------------+------------------+
7.3. SRPAG TLVs
This document defines three new TLVs for carrying additional
information about SR policy and SR candidate paths. IANA is
requested to make the assignment of a new value for the existing
"PCEP TLV Type Indicators" registry as follows:
+------------+-----------------------------------+------------------+
| TLV Type | TLV Name | Reference |
| Value | | |
+------------+-----------------------------------+------------------+
| TBD2 | SRPOLICY-POL-ID | This document |
+------------+-----------------------------------+------------------+
| TBD3 | SRPOLICY-POL-NAME | This document |
+------------+-----------------------------------+------------------+
| TBD4 | SRPOLICY-CPATH-ID | This document |
+------------+-----------------------------------+------------------+
| TBD5 | SRPOLICY-CPATH-PREFERENCE | This document |
+------------+-----------------------------------+------------------+
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8. Security Considerations
This document defines one new type for association, which do not add
any new security concerns beyond those discussed in [RFC5440],
[RFC8231], [I-D.ietf-pce-segment-routing],
[I-D.negi-pce-segment-routing-ipv6] and
[I-D.ietf-pce-association-group] in itself.
The information carried in the SRPAG Association object, as per this
document is related to SR Policy. It often reflects information that
can also be derived from the SR Database, but association provides a
much easier grouping of related LSPs and messages. The SRPAG
association could provides an adversary with the opportunity to
eavesdrop on the relationship between the LSPs. Thus securing the
PCEP session using Transport Layer Security (TLS) [RFC8253], as per
the recommendations and best current practices in [RFC7525], is
RECOMMENDED.
9. Acknowledgement
10. References
10.1. 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>.
[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>.
[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>.
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[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>.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d.,
bogdanov@google.com, b., and P. Mattes, "Segment Routing
Policy Architecture", draft-ietf-spring-segment-routing-
policy-03 (work in progress), May 2019.
[I-D.ietf-pce-association-group]
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)", draft-ietf-pce-association-group-10 (work in
progress), August 2019.
[I-D.ietf-pce-segment-routing]
Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "PCEP Extensions for Segment Routing",
draft-ietf-pce-segment-routing-16 (work in progress),
March 2019.
[I-D.koldychev-pce-operational]
Koldychev, M., Sivabalan, S., Negi, M., Achaval, D., and
H. Kotni, "PCEP Operational Clarification", draft-
koldychev-pce-operational-00 (work in progress), July
2019.
10.2. Informative References
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655,
DOI 10.17487/RFC4655, August 2006,
<https://www.rfc-editor.org/info/rfc4655>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <https://www.rfc-editor.org/info/rfc7525>.
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[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>.
[I-D.negi-pce-segment-routing-ipv6]
Negi, M., Li, C., Sivabalan, S., and P. Kaladharan, "PCEP
Extensions for Segment Routing leveraging the IPv6 data
plane", draft-negi-pce-segment-routing-ipv6-04 (work in
progress), February 2019.
Appendix A. Contributors
Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
Email: dhruv.ietf@gmail.com
Authors' Addresses
Mike Koldychev
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, Ontario K2K 3E8
Canada
Email: mkoldych@cisco.com
Siva Sivabalan
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, Ontario K2K 3E8
Canada
Email: msiva@cisco.com
Colby Barth
Juniper Networks, Inc.
Email: cbarth@juniper.net
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Cheng Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: chengli13@huawei.com
Hooman Bidgoli
Nokia
Email: hooman.bidgoli@nokia.com
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