PCEP extension to support Segment Routing Policy Candidate Paths
draft-ietf-pce-segment-routing-policy-cp-09
The information below is for an old version of the document.
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| Authors | Mike Koldychev , Siva Sivabalan , Colby Barth , Shuping Peng , Hooman Bidgoli | ||
| Last updated | 2023-03-07 | ||
| Replaces | draft-barth-pce-segment-routing-policy-cp | ||
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draft-ietf-pce-segment-routing-policy-cp-09
PCE Working Group M. Koldychev
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track S. Sivabalan
Expires: 8 September 2023 Ciena Corporation
C. Barth
Juniper Networks, Inc.
S. Peng
Huawei Technologies
H. Bidgoli
Nokia
7 March 2023
PCEP extension to support Segment Routing Policy Candidate Paths
draft-ietf-pce-segment-routing-policy-cp-09
Abstract
A Segment Routing (SR) Policy ([RFC9256]) is a non-empty set of SR
Candidate Paths, that all share the same <headend, color, endpoint>
tuple. This document extends [RFC8664] to fully support the SR
Policy construct. SR Policy is modeled in PCEP as an Association of
one or more SR Candidate Paths. PCEP extensions are defined to
signal additional attributes of an SR Policy, which are not covered
by [RFC8664]. The mechanism is applicable to all data planes of SR
(MPLS, SRv6, etc.).
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/.
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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."
This Internet-Draft will expire on 8 September 2023.
Copyright Notice
Copyright (c) 2023 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 carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. SR Policy Identifiers . . . . . . . . . . . . . . . . . . 5
3.2. SR Policy Candidate Path Identifiers . . . . . . . . . . 5
3.3. SR Policy Candidate Path Attributes . . . . . . . . . . . 5
3.4. Multiple Optimization Objectives and Constraints . . . . 6
4. SR Policy Association . . . . . . . . . . . . . . . . . . . . 6
4.1. Association Parameters . . . . . . . . . . . . . . . . . 6
4.2. Association Information . . . . . . . . . . . . . . . . . 8
4.2.1. SR Policy Name TLV . . . . . . . . . . . . . . . . . 8
4.2.2. SR Policy Candidate Path Identifiers TLV . . . . . . 9
4.2.3. SR Policy Candidate Path Name TLV . . . . . . . . . . 10
4.2.4. SR Policy Candidate Path Preference TLV . . . . . . . 10
5. Generic Mechanisms . . . . . . . . . . . . . . . . . . . . . 11
5.1. Computation Priority TLV . . . . . . . . . . . . . . . . 11
5.2. Explicit Null Label Policy (ENLP) TLV . . . . . . . . . . 11
5.3. Invalidation TLV . . . . . . . . . . . . . . . . . . . . 12
5.4. Specified-BSID-only . . . . . . . . . . . . . . . . . . . 13
6. Use of RRO object with SR Policy . . . . . . . . . . . . . . 14
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7.1. Association Type . . . . . . . . . . . . . . . . . . . . 14
7.2. PCEP TLV Type Indicators . . . . . . . . . . . . . . . . 14
7.3. PCEP Errors . . . . . . . . . . . . . . . . . . . . . . . 15
7.4. TE-PATH-BINDING TLV Flag field . . . . . . . . . . . . . 16
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8. Implementation Status . . . . . . . . . . . . . . . . . . . . 16
8.1. Cisco . . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.2. Juniper . . . . . . . . . . . . . . . . . . . . . . . . . 17
9. Security Considerations . . . . . . . . . . . . . . . . . . . 17
10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 17
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
11.1. Normative References . . . . . . . . . . . . . . . . . . 17
11.2. Informative References . . . . . . . . . . . . . . . . . 19
Appendix A. Contributors . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
1. Introduction
Segment Routing Policy for Traffic Engineering [RFC9256] details the
concepts of SR Policy and approaches to steering traffic into an SR
Policy.
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.
This document extends [RFC8664] to fully support the SR Policy
construct. SR Policy is modeled in PCEP as an Association of one or
more SR Candidate Paths. By associating multiple SR Candidate Paths,
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 PCEP Association object with a new association type and
several new TLVs.
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 [RFC9256].
SRPA: SR Policy Association. PCEP ASSOCATION that describes the SR
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Policy. Can refer to the PCEP object or to the group of LSPs that
belong to the Association. This should be clear from the context.
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 TLVs based on the association
types, that provides non-key information.
3. Overview
The SR Policy is represented by a PCEP Association, called SR Policy
Association (SRPA). The SR Candidate Paths within a given SR Policy
are the PCEP LSPs within the SRPA. Each SR Policy Candidate Path
contains one or more Segment Lists. The subject of encoding multiple
Segment Lists within an SR Policy Candidate Path is described in
[I-D.ietf-pce-multipath].
This document defines a new Association Type called "SR Policy
Association" (SRPA), of value 6 based on the generic ASSOCIATION
object. As per the processing rules specified in section 6.4 of
[RFC8697], if a PCEP speaker does not support SRPA, it MUST return a
PCErr message with Error-Type = 26 "Association Error", Error-Value =
1 "Association-type is not supported".
A given LSP MUST belong to at most one SRPA, since an SR Policy
Candidate Path cannot belong to multiple SR Policies. If a PCEP
speaker receives a PCEP message requesting to join more than one SRPA
for the same LSP, then the PCEP speaker MUST send a PCErr message
with Error-Type = 26 "Association Error", Error-Value = 7 "Cannot
join the association group".
An SRPA carries three pieces of information: SR Policy Identifiers,
SR Policy Candidate Path Identifiers, and SR Policy Candidate Path
Attributes.
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3.1. SR Policy Identifiers
SR Policy Identifiers uniquely identify the SR Policy within the
context of the headend. SR Policy Identifiers MUST be the same for
all SR Policy Candidate Paths in the same SRPA. SR Policy
Identifiers MUST NOT change for a given SR Policy Candidate Path
during its lifetime. SR Policy Identifiers MUST be different for
different SRPAs. SR Policy Identifiers consist of:
* Headend router where the SR Policy originates.
* Color of SR Policy.
* Endpoint of SR Policy.
3.2. SR Policy Candidate Path Identifiers
SR Policy Candidate Path Identifiers uniquely identify the SR Policy
Candidate Path within the context of an SR Policy. SR Policy
Candidate Path Identifiers MUST NOT change for a given LSP during its
lifetime. SR Policy Candidate Path Identifiers MUST be different for
different Candidate Paths within the same SRPA. When these rules are
not satisfied, the PCE MUST send a PCErr message with Error-Type = 26
"Association Error", Error Value = TBD8 "SR Policy Candidate Path
Identifiers Mismatch". SR Policy Candidate Path Identifiers consist
of:
* Protocol Origin.
* Originator.
* Discriminator.
3.3. SR Policy Candidate Path Attributes
SR Policy Candidate Path Attributes carry non-key information about
the Candidate Path and MAY change during the lifetime of the LSP. SR
Policy Candidate Path Attributes consist of:
* Preference.
* Optionally, the SR Policy Candidate Path name.
* Optionally, the SR Policy name.
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3.4. Multiple Optimization Objectives and Constraints
In certain scenarios, it is desired for each SR Policy 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 Policy Candidate Paths. This means that multiple PCEP
Tunnels are allocated for each SR Policy Candidate Path. Each PCEP
Tunnel has its own optimization objective and constraints. When a
single SR Policy 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 4.2.2.
4. SR Policy Association
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 (6) "SR Policy Association". This Association
Type is dynamic in nature, thus operator-configured Association Range
MUST NOT be set for this Association type and MUST be ignored.
4.1. Association Parameters
As per [RFC9256], an SR Policy is identified through the tuple
<headend, color, endpoint>. the headend is encoded as the Association
Source in the ASSOCIATION object and the color and endpoint are
encoded as part of Extended Association ID TLV.
The Association Parameters (see Section 2) consist of:
* Association Type: set to 6 "SR Policy Association".
* Association Source (IPv4/IPv6): set to the headend IP address.
* Association ID (16-bit): set to "1".
* Extended Association ID TLV: encodes the Color and Endpoint of the
SR Policy.
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The Association Source MUST be set to the headend value of the SR
Policy, as defined in [RFC9256] Section 2.1. If the PCC receives a
PCInit message for a non-existent 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. This value MAY be different
from the one contained in the END-POINTS object, or in the LSP-
IDENTIFIERS TLV of the LSP object. When neither END-POINTS object or
LSP-IDENTIFIERS TLV are present, the PCEP speaker MUST use this
Endpoint value to resolve the intended end-point of the SR Policy.
This value is part of the tuple <color, endpoint> that identifies the
SR Policy on a given headend.
If the PCEP speaker receives an SRPA object whose Association
Parameters do not follow the above specification, then the PCEP
speaker MUST send PCErr message with Error-Type = 26 "Association
Error", Error-Value = TBD7 "SR Policy Identifiers Mismatch".
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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.
4.2. Association Information
The SRPA object contains the following TLVs:
* SRPOLICY-POL-NAME TLV: (optional) encodes SR Policy Name string.
* SRPOLICY-CPATH-ID TLV: (mandatory) encodes SR Policy Candidate
Path Identifiers.
* SRPOLICY-CPATH-NAME TLV: (optional) encodes SR Policy Candidate
Path string name.
* SRPOLICY-CPATH-PREFERENCE TLV: (optional) encodes SR Policy
Candidate Path preference value.
Of these new TLVs, SRPOLICY-CPATH-ID TLV is mandatory. When a
mandatory TLV is missing from the SRPA object, the PCE MUST send a
PCErr message with Error-Type = 6 "Mandatory Object Missing", Error-
Value = TBD6 "Missing Mandatory TLV".
4.2.1. SR Policy Name TLV
The SRPOLICY-POL-NAME TLV is an optional TLV for the SRPA object. At
most one SRPOLICY-POL-NAME TLV SHOULD be encoded by the sender 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 Name ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: The SRPOLICY-POL-NAME TLV format
Type: 56 for "SRPOLICY-POL-NAME" TLV.
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Length: indicates the length of the value portion 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 Name: SR Policy name, as defined in [RFC9256]. It SHOULD
be a string of printable ASCII characters, without a NULL terminator.
4.2.2. SR Policy Candidate Path Identifiers TLV
The SRPOLICY-CPATH-ID TLV is a mandatory TLV for the SRPA object.
Only one SRPOLICY-CPATH-ID TLV SHOULD be encoded by the sender 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 | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Originator ASN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Originator Address |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: The SRPOLICY-CPATH-ID TLV format
Type: 57 for "SRPOLICY-CPATH-ID" TLV.
Length: 28.
Protocol Origin: 8-bit value that encodes the protocol origin, as
specified in [RFC9256] Section 2.3. Note that in PCInit messages,
the Protocol Origin is always set to "PCEP".
Originator ASN: Represented as 4 byte number, part of the originator
identifier, as specified in [RFC9256] 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 [RFC9256] Section 2.4.
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Discriminator: 32-bit value that encodes the Discriminator of the
Candidate Path.
4.2.3. SR Policy Candidate Path Name TLV
The SRPOLICY-CPATH-NAME TLV is an optional TLV for the SRPA object.
At most one SRPOLICY-CPATH-NAME TLV SHOULD be encoded by the sender
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: 58 for "SRPOLICY-CPATH-NAME" TLV.
Length: indicates the length of the value portion 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 [RFC9256]. It SHOULD be a string of printable ASCII
characters, without a NULL terminator.
4.2.4. SR Policy Candidate Path Preference TLV
The SRPOLICY-CPATH-PREFERENCE TLV is an optional TLV for the SRPA
object. Only one SRPOLICY-CPATH-PREFERENCE TLV SHOULD be encoded by
the sender 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Preference |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: The SRPOLICY-CPATH-PREFERENCE TLV format
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Type: 59 for "SRPOLICY-CPATH-PREFERENCE" TLV.
Length: 4.
Preference: Numerical preference of the Candidate Path, as specified
in Section 2.7 of [RFC9256].
If the TLV is missing, a default Preference value of 100 is used, as
specified in Section 2.7 of [RFC9256].
5. Generic Mechanisms
This section describes various mechanisms that are standardized for
SR Policies in [RFC9256], but are equally applicable to other tunnel
types, such as RSVP-TE tunnels. Hence this section does not make use
of the SRPA.
5.1. Computation Priority TLV
The COMPUTATION-PRIORITY TLV is an optional TLV for the LSP object.
It is used to signal the numerical computation priority, as specified
in Section 2.12 of [RFC9256]. If the TLV is absent from the LSP
object, a default Priority value of 128 is used.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Priority | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: The COMPUTATION-PRIORITY TLV format
Type: TBD1 for "COMPUTATION-PRIORITY" TLV.
Length: 4.
Priority: Numerical priority with which this LSP is to be recomputed
by the PCE upon topology change.
5.2. Explicit Null Label Policy (ENLP) TLV
The ENLP TLV is an optional TLV for the LSP object. It is used to
implement the "Explicit Null Label Policy", as specified in
Section 2.4.5 of [I-D.ietf-idr-segment-routing-te-policy].
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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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ENLP | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: The Explicit Null Label Policy (ENLP) TLV format
Type: TBD2 for "ENLP" TLV.
Length: 4.
ENLP (Explicit NULL Label Policy): same values as in Section 2.4.5 of
[I-D.ietf-idr-segment-routing-te-policy].
5.3. Invalidation TLV
The INVALIDATION TLV is an optional TLV for the LSP object. It is
used to control traffic streering into the LSP during the time when
the LSP is operationally down/invalid. In the context of SR Policy,
this TLV facilitates the "Drop upon invalid" behavior, specified in
Section 8.2 of [RFC9256]. Normally, if the LSP is down/invalid then
traffic that is originally destined for that LSP is steered somewhere
else, such as via IGP or via another LSP. The "Drop upon invalid"
behavior specifies that such traffic MUST NOT be re-routed and has to
be dropped at the head-end. While in the "Drop upon invalid" state,
the LSP operational state is "UP", as indicated by the O-flag in the
LSP object. However the ERO object is empty, indicating that traffic
is being dropped.
In addition to the above, this TLV can also be used by the PCC to
report to the PCE various reasons for LSP being invalidated.
Invalidation reasons are represented by a set of flags.
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
| |V|P|F|U|
+-+-+-+-+-+-+-+-+
Figure 8: Invalidation Reasons Flags
* G: Generic - does not fit into any other categories below.
* P: Path computation failure - no path was computed for the LSP.
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* F: First-hop resolution failure - head-end first hop resolution
has failed.
* V: Verification failure - OAM/PM/BFD path verification has
indicated a breakage.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Inval Reason | Drop Upon | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: The INVALIDATION TLV format
Type: TBD3 for "INVALIDATION" TLV.
Length: 4.
Inval Reason: contains "Invalidation Reasons Flags" which encode the
reason(s) why the LSP is currently invalidated. This field can be
set to non-zero values only by the PCC, it MUST be set to 0 by the
PCE and ignored by the PCC.
Drop Upon: contains "Invalidation Reasons Flags" for conditions that
MUST cause the LSP to drop traffic. This field can be set to non-
zero values by both PCC and PCE. When the G-flag is set, this
indicates that the LSP is to go into Drop upon invalid state for any
reason. I.e., when the PCE does not wish to distinguish any reason
for LSP invalidation and just simply wants it to always "Drop upon
invalid" for any reason. Note that when the G-flag is set, the
values of the other flags are irrelevant.
5.4. Specified-BSID-only
Specified-BSID-only functionality is defined in Section 6.2.3 of
[RFC9256]. When specified-BSID-only is enabled for a particular
binding SID, it means that the given binding SID is required to be
allocated and programmed for the LSP to be operationally up. If the
binding SID cannot be allocated or programmed for some reason, then
the LSP must stay down.
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To signal specified-BSID-only, a new bit: S (Specified-BSID-only) is
allocated in the "TE-PATH-BINDING TLV Flag field" of the TE-PATH-
BINDING TLV. When this bit is set for a particular BSID, it means
that the BSID follows the Specified-BSID-only behavior. It is
possible to have a mix of BSIDs for the same LSP: some with S=1 and
some with S=0.
6. Use of RRO object with SR Policy
[RFC8231] defines <intended-path> and <actual-path>, consisting of
the ERO and RRO objects, respectively. [RFC8664] defines SR-ERO and
SR-RRO sub-objects for SR-TE LSPs.
[I-D.ietf-pce-segment-routing-ipv6] further defines SRv6-ERO and
SRv6-RRO sub-objects for SRv6-TE paths.
In RSVP-TE, the RRO is optional and its contents are populated hop-
by-hop along the LSP using the Path and Resv messages. The RRO thus
allows for collection of extra information about the intermediate
hops, such as protection and loose hop expansion. In contrast to
RSVP-TE, the SR Policy Architecture [RFC9256] does not currently make
use of any hop-by-hop signaling. Thus, there is no clear mechanism
by which to populate the RRO in SR Policy.
PCEP speakers SHOULD NOT send the RRO object for an SR Policy. If a
PCEP speaker receives both ERO and RRO for the same SR LSP, it SHOULD
ignore the RRO and interpret only the ERO.
7. IANA Considerations
7.1. Association Type
This document defines a new association type: SR Policy Association.
IANA is requested to make the following codepoint assignment in the
"ASSOCIATION Type Field" subregistry [RFC8697] within the "Path
Computation Element Protocol (PCEP) Numbers" registry:
+-----------+-------------------------------------------+-----------+
| Type | Name | Reference |
+-----------+-------------------------------------------+-----------+
| 6 | SR Policy Association | This.I-D |
+-----------+-------------------------------------------+-----------+
7.2. PCEP TLV Type Indicators
This document defines four 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:
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+-----------+-------------------------------------------+-----------+
| Value | Description | Reference |
+-----------+-------------------------------------------+-----------+
| 56 | SRPOLICY-POL-NAME | This.I-D |
+-----------+-------------------------------------------+-----------+
| 57 | SRPOLICY-CPATH-ID | This.I-D |
+-----------+-------------------------------------------+-----------+
| 58 | SRPOLICY-CPATH-NAME | This.I-D |
+-----------+-------------------------------------------+-----------+
| 59 | SRPOLICY-CPATH-PREFERENCE | This.I-D |
+-----------+-------------------------------------------+-----------+
| TBD1 | COMPUTATION-PRIORITY | This.I-D |
+-----------+-------------------------------------------+-----------+
| TBD2 | EXPLICIT-NULL-LABEL-POLICY | This.I-D |
+-----------+-------------------------------------------+-----------+
| TBD3 | INVALIDATION | This.I-D |
+-----------+-------------------------------------------+-----------+
7.3. PCEP Errors
This document defines one new Error-Value within the "Mandatory
Object Missing" Error-Type and two 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-Type | Meaning | Error-value | Reference |
+------------+------------------+-----------------------+-----------+
| 6 | Mandatory Object | | [RFC5440] |
| | Missing | | |
+------------+------------------+-----------------------+-----------+
| | | TBD6: SR Policy | This.I-D |
| | | Missing Mandatory TLV | |
+------------+------------------+-----------------------+-----------+
| 26 | Association | | [RFC8697] |
| | Error | | |
+------------+------------------+-----------------------+-----------+
| | | TBD7: SR Policy | This.I-D |
| | | Identifers Mismatch | |
+------------+------------------+-----------------------+-----------+
| | | TBD8: SR Policy | This.I-D |
| | | Candidate Path | |
| | | Identifiers Mismatch | |
+------------+------------------+-----------------------+-----------+
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7.4. TE-PATH-BINDING TLV Flag field
IANA is requested to allocate new bit within the "TE-PATH-BINDING TLV
Flag field" sub-registry of the PCEP Numbers registry, as follows:
+------------+------------------------------------------+-----------+
| Bit position | Description | Reference |
+--------------+----------------------------------------+-----------+
| 1 | Specified-BSID-only | This.I-D |
+--------------+----------------------------------------+-----------+
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
* Organization: Cisco Systems
* Implementation: IOS-XR PCC and PCE.
* Description: An experimental code-point is currently used.
* Maturity Level: Proof of concept.
* Coverage: Full.
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* Contact: mkoldych@cisco.com
8.2. Juniper
* Organization: Juniper Networks
* Implementation: Head-end and controller.
* Description: An experimental code-point is currently used.
* Maturity Level: Proof of concept.
* Coverage: Partial.
* Contact: cbarth@juniper.net
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 SRPA 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 SRPA could provide 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, Boris Khasanov, Praveen Kumar
and Tom Petch for review and suggestions.
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>.
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[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>.
[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>.
[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.
[I-D.ietf-idr-segment-routing-te-policy]
Previdi, S., Filsfils, C., Talaulikar, K., Mattes, P.,
Jain, D., and S. Lin, "Advertising Segment Routing
Policies in BGP", Work in Progress, Internet-Draft, draft-
ietf-idr-segment-routing-te-policy-20, 27 July 2022,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
segment-routing-te-policy-20>.
[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>.
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[I-D.ietf-pce-multipath]
Koldychev, M., Sivabalan, S., Saad, T., Beeram, V. P.,
Bidgoli, H., Yadav, B., Peng, S., and G. S. Mishra, "PCEP
Extensions for Signaling Multipath Information", Work in
Progress, Internet-Draft, draft-ietf-pce-multipath-07, 14
November 2022, <https://datatracker.ietf.org/doc/html/
draft-ietf-pce-multipath-07>.
11.2. Informative References
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", 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>.
[I-D.ietf-pce-segment-routing-ipv6]
Li, C., Negi, M. S., Sivabalan, S., Koldychev, M.,
Kaladharan, P., and Y. Zhu, "Path Computation Element
Communication Protocol (PCEP) Extensions for Segment
Routing leveraging the IPv6 dataplane", Work in Progress,
Internet-Draft, draft-ietf-pce-segment-routing-ipv6-16, 6
March 2023, <https://datatracker.ietf.org/doc/html/draft-
ietf-pce-segment-routing-ipv6-16>.
Appendix A. Contributors
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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
Samuel Sidor
Cisco Systems, Inc.
Eurovea Central 3.
Pribinova 10
811 09 Bratislava
Slovakia
Email: ssidor@cisco.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
Colby Barth
Juniper Networks, Inc.
Email: cbarth@juniper.net
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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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