PCE Working Group M. Koldychev
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track S. Sivabalan
Expires: July 26, 2021 Ciena Corporation
C. Barth
Juniper Networks, Inc.
S. Peng
Huawei Technologies
H. Bidgoli
Nokia
January 22, 2021
PCEP extension to support Segment Routing Policy Candidate Paths
draft-ietf-pce-segment-routing-policy-cp-02
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, endpoint> tuple. An SR policy can
contain one or more candidate paths where each candidate path is
identified in PCEP by its uniquely assigned 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
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time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on July 26, 2021.
Copyright Notice
Copyright (c) 2021 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
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 5
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 . . . . . . . . . . . . . . . 6
4. Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Choice of Association Parameters . . . . . . . . . . . . 8
4.3. Multiple Optimization Objectives and Constraints . . . . 9
5. SR Policy Association Group . . . . . . . . . . . . . . . . . 9
5.1. SR Policy Name TLV . . . . . . . . . . . . . . . . . . . 10
5.2. SR Policy Candidate Path Identifiers TLV . . . . . . . . 11
5.3. SR Policy Candidate Path Name TLV . . . . . . . . . . . . 12
5.4. SR Policy Candidate Path Preference TLV . . . . . . . . . 12
6. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 13
6.1. PCC Initiated SR Policy with single candidate-path . . . 13
6.2. PCC Initiated SR Policy with multiple candidate-paths . . 13
6.3. PCE Initiated SR Policy with single candidate-path . . . 14
6.4. PCE Initiated SR Policy with multiple candidate-paths . . 15
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
7.1. Association Type . . . . . . . . . . . . . . . . . . . . 15
7.2. PCEP Errors . . . . . . . . . . . . . . . . . . . . . . . 16
7.3. SRPAG TLVs . . . . . . . . . . . . . . . . . . . . . . . 16
8. Implementation Status . . . . . . . . . . . . . . . . . . . . 17
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8.1. Cisco . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9. Security Considerations . . . . . . . . . . . . . . . . . . . 17
10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 18
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
11.1. Normative References . . . . . . . . . . . . . . . . . . 18
11.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
Path Computation Element (PCE) Communication Protocol (PCEP)
[RFC5440] enables the communication between a Path Computation Client
(PCC) and a Path Computation 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 [RFC8664] 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
[RFC8697] 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
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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.
[Editor's Note- Currently it is assumed that each candidate path has
only one ERO (SID-List) within the scope of this document. 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 [RFC8697], 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 [RFC8697], 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].
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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
associated 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.
[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, endpoint, 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 endpoint can be signaled via the PCEP END-
POINTS object, this object may not be suitable because the endpoint
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 endpoint 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.
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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
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 [RFC8697], 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 another
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.
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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.
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 Endpoint 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.
o Optionally, the candidate path name.
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 [RFC8697], if
a PCEP speaker does not support the SRPAG association type, it MUST
return a PCErr message with Error-Type 26 "Association Error" and
Error-Value 1 "Association-type is not supported". Please note that
the corresponding PCEP session is not reset.
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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.
The Association Source MUST be set to the headend value of the SR
Policy, as defined in [I-D.ietf-spring-segment-routing-policy]. 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.
If the PCC receives a PCInit message for a non-existing SR Policy,
where the Association Source is set not to the headend value but to
some globally unique IP address that the PCC owns, then the PCC
SHOULD accept the PCInit message and create the SR Policy Association
with the Association Source that was sent in the PCInit message.
The 16-bit Association ID field in the ASSOCIATION object MUST be set
to the value of "1". The Extended Association ID TLV MUST be
included and it MUST be in the following format:
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 = 31 | Length = 8 or 20 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Color |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Endpoint ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Extended Association ID TLV format
Type: Extended Association ID TLV, type = 31.
Length: Either 8 or 20, depending on whether IPv4 or IPv6 address is
encoded in the Endpoint.
Color: SR Policy color value.
Endpoint: can be either IPv4 or IPv6, depending on whether the policy
endpoint is IPv4 or IPv6. 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
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endpoint of the SR policy, as it is defined in
[I-D.ietf-spring-segment-routing-policy].
If the PCEP speaker receives an ASSOCIATION object whose ID and
Extended ID do not follow the above specification, then the PCEP
speaker MUST send PCErr message with Error-Type 26 "Association
Error" and Error-Value 7 "Cannot join the association group".
The purpose of choosing the Association Parameters in this way is to
guarantee that there is no possibility of a race condition when
multiple PCEP speakers want to create the same SR Policy at the same
time. By adhering to this format, all PCEP speakers come up with the
same Association Parameters independently of each other. Thus, there
is no chance that different PCEP speakers will come up with different
Association Parameters for the same SR Policy.
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 5.2.
5. SR Policy Association Group
Two ASSOCIATION object types for IPv4 and IPv6 are defined in
[RFC8697]. 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).
This Association type is dynamic in nature and created by the PCC or
PCE for the candidate paths belonging to the same SR policy (as
described in [I-D.ietf-spring-segment-routing-policy]). These
associations are conveyed via PCEP messages to the PCEP peer.
Operator-configured Association Range MUST 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-NAME TLV, SRPOLICY-CPATH-ID
TLV, SRPOLICY-CPATH-NAME TLV, SRPOLICY-CPATH-PREFERENCE TLV. These
five TLVs encode the Policy Identifiers, SR Policy name, Candidate
path identifiers, candidate path name, 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 [RFC8664] or [I-D.ietf-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 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
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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.
5.2. 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.
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.
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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.
5.3. SR Policy Candidate Path Name TLV
The SRPOLICY-CPATH-NAME TLV is an optional TLV for the SRPAG
Association. At most one SRPOLICY-CPATH-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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ SR Policy Candidate Path Name ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: The SRPOLICY-CPATH-NAME TLV format
Type: TBD11 for "SRPOLICY-CPATH-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.
SR Policy Candidate Path Name: SR Policy Candidate Path Name, as
defined in [I-D.ietf-spring-segment-routing-policy]. It SHOULD be a
string of printable ASCII characters, without a NULL terminator.
5.4. 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 5: 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 0, 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 0, 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 [RFC8697]), 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 five 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 five 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 | | |
+------------+-----------------------------------+------------------+
| TBD3 | SRPOLICY-POL-NAME | This document |
+------------+-----------------------------------+------------------+
| TBD4 | SRPOLICY-CPATH-ID | This document |
+------------+-----------------------------------+------------------+
| TBD11 | SRPOLICY-CPATH-NAME | This document |
+------------+-----------------------------------+------------------+
| TBD5 | SRPOLICY-CPATH-PREFERENCE | This document |
+------------+-----------------------------------+------------------+
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8. Implementation Status
[Note to the RFC Editor - remove this section before publication, as
well as remove the reference to RFC 7942.]
This section records the status of known implementations of the
protocol defined by this specification at the time of posting of this
Internet-Draft, and is based on a proposal described in [RFC7942].
The description of implementations in this section is intended to
assist the IETF in its decision processes in progressing drafts to
RFCs. Please note that the listing of any individual implementation
here does not imply endorsement by the IETF. Furthermore, no effort
has been spent to verify the information presented here that was
supplied by IETF contributors. This is not intended as, and must not
be construed to be, a catalog of available implementations or their
features. Readers are advised to note that other implementations may
exist.
According to [RFC7942], "this will allow reviewers and working groups
to assign due consideration to documents that have the benefit of
running code, which may serve as evidence of valuable experimentation
and feedback that have made the implemented protocols more mature.
It is up to the individual working groups to use this information as
they see fit".
8.1. Cisco
o Organization: Cisco Systems
o Implementation: Head-end and controller.
o Description: An experimental code-point is currently used.
o Maturity Level: Proof of concept.
o Coverage: Full.
o Contact: mkoldych@cisco.com
9. Security Considerations
This document defines one new type for association, which do not add
any new security concerns beyond those discussed in [RFC5440],
[RFC8231], [RFC8664], [I-D.ietf-pce-segment-routing-ipv6] and
[RFC8697] in itself.
The information carried in the SRPAG Association object, as per this
document is related to SR Policy. It often reflects information that
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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.
10. Acknowledgement
Would like to thank Stephane Litkowski and Praveen Kumar for review
comments.
11. References
11.1. 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>.
[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>.
[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>.
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[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-09 (work in progress),
November 2020.
[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>.
[RFC8664] Sivabalan, S., Filsfils, C., Tantsura, J., Henderickx, W.,
and J. Hardwick, "Path Computation Element Communication
Protocol (PCEP) Extensions for Segment Routing", RFC 8664,
DOI 10.17487/RFC8664, December 2019,
<https://www.rfc-editor.org/info/rfc8664>.
[I-D.koldychev-pce-operational]
Koldychev, M., Sivabalan, S., Negi, M., Achaval, D., and
H. Kotni, "PCEP Operational Clarification", draft-
koldychev-pce-operational-02 (work in progress), August
2020.
11.2. 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>.
[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>.
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[I-D.ietf-pce-segment-routing-ipv6]
Li, C., Negi, M., Sivabalan, S., Koldychev, M.,
Kaladharan, P., and Y. Zhu, "PCEP Extensions for Segment
Routing leveraging the IPv6 data plane", draft-ietf-pce-
segment-routing-ipv6-08 (work in progress), November 2020.
Appendix A. Contributors
Dhruv Dhody
Huawei Technologies
Divyashree Techno Park, Whitefield
Bangalore, Karnataka 560066
India
Email: dhruv.ietf@gmail.com
Cheng Li
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing, 10095
China
Email: chengli13@huawei.com
Authors' Addresses
Mike Koldychev
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, Ontario K2K 3E8
Canada
Email: mkoldych@cisco.com
Siva Sivabalan
Ciena Corporation
385 Terry Fox Dr.
Kanata, Ontario K2K 0L1
Canada
Email: ssivabal@ciena.com
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Colby Barth
Juniper Networks, Inc.
Email: cbarth@juniper.net
Shuping Peng
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: pengshuping@huawei.com
Hooman Bidgoli
Nokia
Email: hooman.bidgoli@nokia.com
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