Carrying SR-Algorithm in Path Computation Element Communication Protocol (PCEP).
draft-ietf-pce-sid-algo-19
| Document | Type | Active Internet-Draft (pce WG) | |
|---|---|---|---|
| Authors | Samuel Sidor , Zoey Rose , Shaofu Peng , Shuping Peng , Andrew Stone | ||
| Last updated | 2025-05-22 (Latest revision 2025-05-20) | ||
| Replaces | draft-tokar-pce-sid-algo | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | Proposed Standard | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Associated WG milestone |
|
||
| Document shepherd | Dhruv Dhody | ||
| Shepherd write-up | Show Last changed 2025-05-22 | ||
| IESG | IESG state | Publication Requested | |
| Action Holder | |||
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | Ketan Talaulikar | ||
| Send notices to | dd@dhruvdhody.com |
draft-ietf-pce-sid-algo-19
PCE Working Group S. Sidor
Internet-Draft Z. Rose
Updates: 8664 9603 (if approved) Cisco Systems, Inc.
Intended status: Standards Track S. Peng
Expires: 21 November 2025 ZTE Corporation
S. Peng
Huawei Technologies
A. Stone
Nokia
20 May 2025
Carrying SR-Algorithm in Path Computation Element Communication Protocol
(PCEP).
draft-ietf-pce-sid-algo-19
Abstract
This document specifies extensions to the Path Computation Element
Communication Protocol (PCEP) to enhance support for Segment Routing
(SR) with a focus on the use of Segment Identifiers (SIDs) and SR-
Algorithms in Traffic Engineering (TE). The SR-Algorithm associated
with a SID defines the path computation algorithm used by Interior
Gateway Protocols (IGPs). This document proposes an approach for
informing PCEP peers about the SR-Algorithm associated with each SID
used, as well as signaling a specific SR-Algorithm as a constraint to
the Path Computation Element (PCE). The mechanisms for specifying an
SR-Algorithm constraint allow for refined path computations that meet
specific operational needs, such as low-latency or high-bandwidth
paths based primarily on operator-defined criteria using Flexible
Algorithms. Additionally, this document updates RFC 8664 and RFC
9603 to allow encoding of SR-Algorithm of specific SID in Explicit
Route Object (ERO) subobjects.
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."
Sidor, et al. Expires 21 November 2025 [Page 1]
Internet-Draft SR-Algorithm in PCEP May 2025
This Internet-Draft will expire on 21 November 2025.
Copyright Notice
Copyright (c) 2025 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
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Object Formats . . . . . . . . . . . . . . . . . . . . . . . 6
4.1. OPEN Object . . . . . . . . . . . . . . . . . . . . . . . 6
4.1.1. SR PCE Capability Sub-TLV . . . . . . . . . . . . . . 6
4.1.2. SRv6 PCE Capability sub-TLV . . . . . . . . . . . . . 6
4.2. SR-ERO Subobject . . . . . . . . . . . . . . . . . . . . 7
4.3. SRv6-ERO Subobject . . . . . . . . . . . . . . . . . . . 8
4.4. SR-Algorithm TLV . . . . . . . . . . . . . . . . . . . . 9
4.5. Extensions to METRIC Object . . . . . . . . . . . . . . . 10
4.5.1. Path Min Delay Metric value . . . . . . . . . . . . . 11
4.5.2. Path Min Delay Metric . . . . . . . . . . . . . . . . 11
4.5.3. P2MP Path Min Delay Metric . . . . . . . . . . . . . 12
4.5.4. Path Bandwidth Metric value . . . . . . . . . . . . . 12
4.5.5. Path Bandwidth Metric . . . . . . . . . . . . . . . . 13
4.5.6. P2MP Path Bandwidth Metric . . . . . . . . . . . . . 13
4.5.7. User Defined Metric . . . . . . . . . . . . . . . . . 13
5. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.1. ERO Subobjects . . . . . . . . . . . . . . . . . . . . . 14
5.1.1. SR-ERO . . . . . . . . . . . . . . . . . . . . . . . 14
5.1.2. SRv6-ERO . . . . . . . . . . . . . . . . . . . . . . 15
5.2. SR-Algorithm Constraint . . . . . . . . . . . . . . . . . 15
5.2.1. Flexible Algorithm Path Computation . . . . . . . . . 17
5.2.2. Path computation with SID Filtering . . . . . . . . . 18
5.2.3. New Metric types . . . . . . . . . . . . . . . . . . 19
6. Manageability Considerations . . . . . . . . . . . . . . . . 19
6.1. Control of Function and Policy . . . . . . . . . . . . . 19
6.2. Information and Data Models . . . . . . . . . . . . . . . 19
Sidor, et al. Expires 21 November 2025 [Page 2]
Internet-Draft SR-Algorithm in PCEP May 2025
6.3. Liveness Detection and Monitoring . . . . . . . . . . . . 19
6.4. Verify Correct Operations . . . . . . . . . . . . . . . . 19
6.5. Requirements on Other Protocols and Functional
Components . . . . . . . . . . . . . . . . . . . . . . . 20
6.6. Impact On Network Operations . . . . . . . . . . . . . . 20
7. Operational Considerations . . . . . . . . . . . . . . . . . 20
8. Implementation Status . . . . . . . . . . . . . . . . . . . . 20
8.1. Cisco . . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.2. Huawei . . . . . . . . . . . . . . . . . . . . . . . . . 21
9. Security Considerations . . . . . . . . . . . . . . . . . . . 21
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
10.1. SR Capability Flag . . . . . . . . . . . . . . . . . . . 22
10.2. SRv6 PCE Capability Flag . . . . . . . . . . . . . . . . 22
10.3. SR-ERO Flag . . . . . . . . . . . . . . . . . . . . . . 22
10.4. SRv6-ERO Flag . . . . . . . . . . . . . . . . . . . . . 23
10.5. PCEP TLV Types . . . . . . . . . . . . . . . . . . . . . 23
10.6. Metric Types . . . . . . . . . . . . . . . . . . . . . . 23
10.7. PCEP-Error Object . . . . . . . . . . . . . . . . . . . 24
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
11.1. Normative References . . . . . . . . . . . . . . . . . . 24
11.2. Informative References . . . . . . . . . . . . . . . . . 26
Appendix A. Acknowledgement . . . . . . . . . . . . . . . . . . 27
Appendix B. Contributors . . . . . . . . . . . . . . . . . . . . 28
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
1. Introduction
[RFC5440] describes the Path Computation Element Communication
Protocol (PCEP) for communication between a Path Computation Client
(PCC) and a Path Computation Element (PCE) or between a pair of PCEs.
[RFC8664] and [RFC9603] specify PCEP extensions to support Segment
Routing (SR) over MPLS and IPv6 respectively.
This document specifies extensions to PCEP to enhance support for SR
Traffic Engineering (TE). Specifically, it focuses on the use of
Segment Identifiers (SIDs) and SR-Algorithms. An SR-Algorithm
associated with a SID defines the path computation algorithm used by
Interior Gateway Protocols (IGPs). This document introduces
mechanisms for PCEP peers to exchange information about the SR-
Algorithm associated with each SID and to signal specific SR-
Algorithm constraints to the PCE for path computation. Furthermore,
this document updates [RFC8664] and [RFC9603] enabling the encoding
of SR-Algorithms for specific SIDs within ERO subobjects.
The PCEP extensions for the SR-Algorithm based path computation
include:
Sidor, et al. Expires 21 November 2025 [Page 3]
Internet-Draft SR-Algorithm in PCEP May 2025
* Extending the Capability Sub-TLVs carried in the OPEN Object to
indicate support for SR-Algorithm.
* Extending SR-ERO, SRv6-ERO, SR-RRO and SRv6-RRO Subobjects to
include Algorithm field
* A new SR-Algorithm TLV carried in the Label Switched Path
Attributes (LSPA) Object to indicate the SR Algorithm as a
constraint
* Defining several new types for the METRIC Object required to
support SR-Algorithm based path computation
The mechanisms described in this document are equally applicable to
both SR-MPLS and SRv6.
1.1. 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.
2. Terminology
This document uses the following terms defined in [RFC5440]: ERO,
LSPA, PCC, PCE, PCEP, PCEP Peer, and PCEP speaker.
This document uses the following term defined in [RFC3031]: LSP.
This document uses the following term defined in [RFC9479] and
[RFC9492]: ASLA.
This document uses the following terms defined in [RFC8664]: NAI and
SR-DB.
The following terminologies are used in this document:
P2MP: Point-to-Multipoint
FAD: Flexible Algorithm Definition [RFC9350]
Winning FAD: The FAD selected according to the rules described in
Section 5.3 of [RFC9350]
Sidor, et al. Expires 21 November 2025 [Page 4]
Internet-Draft SR-Algorithm in PCEP May 2025
The base PCEP specification [RFC4655] originally defined the use of
the PCE architecture for MPLS and GMPLS networks with LSPs
instantiated using the RSVP-TE signaling protocol. Over time,
support for additional path setup types, such as SRv6, has been
introduced [RFC9603]. The term "LSP" is used extensively in PCEP
specifications and, in the context of this document, refers to a
Candidate Path within an SR Policy, which may be an SRv6 path (still
represented using the LSP Object as specified in [RFC8231]).
3. Motivation
Existing PCEP specifications lack the mechanisms to explicitly signal
and negotiate SR-Algorithm capabilities and constraints. This limits
the ability of PCEs to make informed path computation decisions based
on the specific SR-Algorithms supported and desired within the
network.
This document builds on the concepts introduced in [RFC9350] to
extend the applicability of Flexible Algorithms for SR-TE paths in
PCEP. Flexible Algorithms allow the customization of routing
behavior by defining link attributes specific to SR-Algorithms and
also specifying constraints as part of FADs. The PCE leverages these
FADs to compute paths that adhere to operator-defined criteria, such
as minimizing delay or optimizing bandwidth utilization. In the
context of SR-TE, the PCE must ensure that paths computed using
Flexible Algorithms are congruent with the desired routing policies
and constraints. This involves using the same ordered rules to
select FADs when multiple options are available and considering node
participation in the specified SR-Algorithm during path computation.
The PCE must also optimize paths based on metrics defined within the
FAD, ensuring alignment with the operator's objectives. The
introduction of new metric types, such as Path Min Delay Metric and
Path Bandwidth Metric, further enhances the ability of PCE to compute
paths that meet these criteria.
The PCE and the headend router may independently compute SR-TE paths
with different SR-Algorithms. This information needs to be exchanged
between PCEP peers for purposes such as network monitoring and
troubleshooting. In scenarios involving multiple (redundant) PCEs,
when a headend receives a path from the primary PCE, it needs to be
able to report the complete path information, including the SR-
Algorithm, to a backup PCE. This is essential for high availability
(HA) scenarios, ensuring that the backup PCE can correctly verify
Prefix SIDs.
Sidor, et al. Expires 21 November 2025 [Page 5]
Internet-Draft SR-Algorithm in PCEP May 2025
The introduction of an SR-Algorithm TLV within the LSPA object allows
operators to specify SR-Algorithm constraints directly, thereby
refining path computations to meet specific needs, such as low-
latency paths.
The ability to specify an SR-Algorithm per SID in ERO and RRO is
crucial for multiple reasons for example:
* SID types without algorithm specified - Certain SID types, such as
Binding SIDs (BSIDs) [RFC8402], may not have an SR-algorithm
specified. It may be inaccurate to state that an entire end-to-
end path adheres to a specific algorithm if it includes a BSID
from another policy.
* Topologies with two Interior Gateway Protocol (IGP) domains, each
using the same FAD but with differing algorithm numbers.
4. Object Formats
4.1. OPEN Object
4.1.1. SR PCE Capability Sub-TLV
The SR-PCE-CAPABILITY Sub-TLV is defined in Section 4.1.2 of
[RFC8664] to be included in the PATH-SETUP-TYPE-CAPABILITY TLV.
This document defines the following flag in the SR-PCE-CAPABILITY
Sub-TLV:
* SR-Algorithm Capability (S): If the S-flag is set, a PCEP speaker
indicates support for the Algorithm field in the SR-ERO subobject
described in Section 4.2 and the SR-Algorithm TLV described in
Section 4.4 for LSPs setup using Path Setup Type 1 (Segment
Routing) [RFC8664]. It does not indicate support for these
extensions for other Path Setup Types.
4.1.2. SRv6 PCE Capability sub-TLV
The SRv6-PCE-CAPABILITY sub-TLV is defined in Section 4.1.1 of
[RFC9603] to be included in the PATH-SETUP-TYPE-CAPABILITY TLV.
This document defines the following flag in the SRv6-PCE-CAPABILITY
sub-TLV:
Sidor, et al. Expires 21 November 2025 [Page 6]
Internet-Draft SR-Algorithm in PCEP May 2025
* SR-Algorithm Capability (S): If the S-flag is set, a PCEP speaker
indicates support for the Algorithm field in the SRv6-ERO
Subobject described in Section 4.3 and the SR-Algorithm TLV
described in Section 4.4 for LSPs setup using Path Setup Type 3
(SRv6) [RFC9603]. It does not indicate support for these
extensions for other Path Setup Types.
4.2. SR-ERO Subobject
This document updates the SR-ERO subobject format defined in
Section 4.3.1 of [RFC8664] with a new Algorithm field. Further, a
new "A" flag in Flags field is as shown in Figure 1.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type=36 | Length | NT | Flags |A|F|S|C|M|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// NAI (variable, optional) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: SR-ERO Subobject Format
A new bit in the Flags field:
* A-flag (SR-Algorithm Flag): If set to '1' by a PCEP speaker, the
Algorithm field is included in the SR-ERO subobject as shown in
Figure 1 and the length of the subobject is extended by 4 octets.
If this flag is set to 0, then the new Reserved and Algorithm
fields are absent and processing described in Section 5.2.1 of
[RFC8664] applies.
Reserved (24 bits): This field is reserved for future use and MUST be
set to zero when sending and ignored when receiving.
Algorithm (8 bits): SR-Algorithm value from registry "IGP Algorithm
Types" of "Interior Gateway Protocol (IGP) Parameters" IANA registry.
This document updates the SR-ERO subobject validation defined in
Section 5.2.1 of [RFC8664] by extending existing validation to
include the Algorithm field and A bit as follows.
Sidor, et al. Expires 21 November 2025 [Page 7]
Internet-Draft SR-Algorithm in PCEP May 2025
On receiving an SR-ERO, a PCC MUST validate that the Length field, S
bit, F bit, A bit, NT field, and Algorithm are consistent, as
follows.
* If A bit is 1
- If NT=0, the F bit MUST be 1, the S bit MUST be zero, and the
Length MUST be 12.
- If NT=1, the F bit MUST be zero. If the S bit is 1, the Length
MUST be 12; otherwise, the Length MUST be 16.
- If NT=2, the F bit MUST be zero. If the S bit is 1, the Length
MUST be 24; otherwise, the Length MUST be 28.
- If NT=3, the F bit MUST be zero. If the S bit is 1, the Length
MUST be 16; otherwise, the Length MUST be 20.
- If NT=4, the F bit MUST be zero. If the S bit is 1, the Length
MUST be 40; otherwise, the Length MUST be 44.
- If NT=5, the F bit MUST be zero. If the S bit is 1, the Length
MUST be 24; otherwise, the Length MUST be 28.
- If NT=6, the F bit MUST be zero. If the S bit is 1, the Length
MUST be 48; otherwise, the Length MUST be 52.
* If A bit is 0, consistency rules defined in Section 5.2.1 of
[RFC8664] applies.
4.3. SRv6-ERO Subobject
This document updates the SRv6-ERO subobject format defined in
Section 4.3.1 of [RFC9603] with Algorithm field carved out of the
Reserved field. Further, a new "A" flag in defined in the existing
Flags field as shown in Figure 2.
Sidor, et al. Expires 21 November 2025 [Page 8]
Internet-Draft SR-Algorithm in PCEP May 2025
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L| Type=40 | Length | NT | Flags |A|V|T|F|S|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Algorithm | Endpoint Behavior |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| SRv6 SID (optional) |
| (128-bit) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// NAI (variable, optional) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID Structure (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SRv6-ERO Subobject Format
A new bit in the Flags field:
A-flag (SR-Algorithm Flag): If set to '1' by a PCEP speaker, the
Algorithm field is included in SRv6-ERO subobject as specified in
Figure 2. If this flag is set to 0, then the Algorithm field is
absent and processing described in Section 5.2.1 of [RFC9603]
applies.
Reserved (8 bits): reduced from 16 to 8 bits. It MUST be set to zero
while sending and ignored on receipt.
Algorithm (8 bits): SR-Algorithm value from registry "IGP Algorithm
Types" of "Interior Gateway Protocol (IGP) Parameters" IANA registry.
4.4. SR-Algorithm TLV
A new TLV for the LSPA Object is introduced to carry the SR-Algorithm
constraint (Section 5.2). This TLV SHOULD only be used when PST
(Path Setup type) = 1 or 3 for SR-MPLS and SRv6, respectively. Only
the first instance of this TLV MUST be processed, subsequent
instances MUST be ignored.
The format of the SR-Algorithm TLV is as follows:
Sidor, et al. Expires 21 November 2025 [Page 9]
Internet-Draft SR-Algorithm in PCEP May 2025
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=66 | Length=4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | Flags |F|S| Algorithm |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: SR-Algorithm TLV Format
Type (16 bits): 66.
Length (16 bits): 4.
The 32-bit value is formatted as follows.
Reserved (16 bits): MUST be set to zero by the sender and MUST be
ignored by the receiver.
Flags (8 bits): This document defines the following flag bits. The
other bits MUST be set to zero by the sender and MUST be ignored
by the receiver.
* S (Strict): If set, the path computation at the PCE MUST fail
if the specified SR-Algorithm constraint cannot be satisfied.
If unset, the PCE SHOULD try to compute the path with SR-
algorithm constraint specified. If the path computation using
the specified SR-Algorithm constraint fails, the PCE SHOULD try
to compute a path that does not satisfy the constraint.
* F (Flexible Algorithm Path Computation): If set, the PCE MUST
perform path computation according to the Flexible Algorithm
procedures outlined in Section 5.2.1. If unset, the PCE MUST
adhere to the path computation procedures with SID filtering
defined in Section 5.2.2. The flag MUST be ignored if the
Algorithm field is set to a value in the range of 0 to 127.
Algorithm (8 bits): SR-Algorithm to be used during path computation
(see Section 5.2).
4.5. Extensions to METRIC Object
The METRIC object is defined in Section 7.8 of [RFC5440]. This
document specifies new types for the METRIC object to enable the
encoding of optimization metric types derived from the FAD during
Flexible Algorithm path computation (see Section 5.2.1). While these
new metric types are defined to support this specific use case, and
their application is not restricted to Flexible Algorithm path
Sidor, et al. Expires 21 November 2025 [Page 10]
Internet-Draft SR-Algorithm in PCEP May 2025
computation and may be utilized in other relevant scenarios.
* T=22: Path Min Delay metric (Section 4.5.2)
* T=23: P2MP Path Min Delay metric (Section 4.5.3)
* T=24: Path Bandwidth Metric (Section 4.5.5)
* T=25: P2MP Path Bandwidth Metric (Section 4.5.6)
* T=128-255: User-defined metric (Section 4.5.7)
The following terminology is used and expanded along the way.
* A network comprises of a set of N links {Li, (i=1...N)}.
* A path P of a point-to-point (P2P) LSP is a list of K links
{Lpi,(i=1...K)}.
* A P2MP tree T comprises a set of M destinations
{Dest_j,(j=1...M)}.
4.5.1. Path Min Delay Metric value
[RFC7471] and [RFC8570] define "Min/Max Unidirectional Link Delay
Sub-TLV" to advertise the link minimum and maximum delay in
microseconds in a 24-bit field.
[RFC5440] defines the METRIC object with a 32-bit metric value
encoded in IEEE floating point format (see [IEEE.754.1985]).
The encoding for the Path Min Delay metric value is quantified in
units of microseconds and encoded in IEEE floating point format.
The conversion from 24-bit integer to 32-bit IEEE floating point
could introduce some loss of precision.
4.5.2. Path Min Delay Metric
The minimum Link Delay metric is defined in [RFC7471] and [RFC8570]
as "Min Unidirectional Link Delay". The Path Min Link Delay metric
represents measured minimum link delay value over a configurable
interval.
The Path Min Delay metric type of the METRIC object in PCEP
represents the sum of the Min Link Delay metric of all links along a
P2P path.
Sidor, et al. Expires 21 November 2025 [Page 11]
Internet-Draft SR-Algorithm in PCEP May 2025
* A Min Link Delay metric of link L is denoted D(L).
* A Path Min Delay metric for the P2P path P = Sum {D(Lpi),
(i=1...K)}.
4.5.3. P2MP Path Min Delay Metric
The P2MP Path Min Delay metric type of the METRIC object in PCEP
encodes the Path Min Delay metric for the destination that observes
the worst delay metric among all destinations of the P2MP tree.
* The P2P Path Min Delay metric of the path to destination Dest_j is
denoted by PMDM(Dest_j).
* The P2MP Path Min Delay metric for the P2MP tree T =
Maximum{PMDM(Dest_j), (j=1...M)}.
4.5.4. Path Bandwidth Metric value
The Section 4 of [I-D.ietf-lsr-flex-algo-bw-con] defines a new metric
type "Bandwidth Metric", which may be advertised in their link metric
advertisements.
When performing Flexible Algorithm path computation as described in
Section 5.2.1, procedures described in sections 4.1 and 5 from
[I-D.ietf-lsr-flex-algo-bw-con] MUST be followed with automatic
metric calculation.
When performing path computation for other algorithms (0-127) and the
Generic Metric sub-TLV with Bandwidth metric type is not advertised
for a link, the PCE implementation MAY apply a local policy to derive
a metric value (similar to the procedures in Sections 4.1.3 and 4.1.4
of [I-D.ietf-lsr-flex-algo-bw-con]) or the link MAY be treated as if
the metric value is unavailable (e.g. by using a default value). If
the Bandwidth metric value is advertised for a link, the PCE MUST use
the advertised value to compute the path metric in accordance with
Section 4.5.5 and Section 4.5.6.
The Path Bandwidth metric value is encoded in IEEE floating point
format.
The conversion from 24-bit integer to 32-bit IEEE floating point
could introduce some loss of precision.
Sidor, et al. Expires 21 November 2025 [Page 12]
Internet-Draft SR-Algorithm in PCEP May 2025
4.5.5. Path Bandwidth Metric
The Path Bandwidth metric type of the METRIC object in PCEP
represents the sum of the Bandwidth Metric of all links along a P2P
path. Note: the link Bandwidth Metric utilized in the formula may be
the original metric advertised on the link, which may have a value
inversely proportional to the link capacity.
* A Bandwidth Metric of link L is denoted B(L).
* A Path Bandwidth metric for the P2P path P = Sum {B(Lpi),
(i=1...K)}.
4.5.6. P2MP Path Bandwidth Metric
The Bandwidth metric type of the METRIC object in PCEP encodes the
Path Bandwidth metric for the destination that observes the worst
bandwidth metric among all destinations of the P2MP tree.
* The P2P Bandwidth metric of the path to destination Dest_j is
denoted by BM(Dest_j).
* The P2MP Path Bandwidth metric for the P2MP tree T =
Maximum{BM(Dest_j), (j=1...M)}.
4.5.7. User Defined Metric
The Section 2 of [I-D.ietf-lsr-flex-algo-bw-con] defined a new metric
type range for "User defined metric", which may be advertised in
their link metric advertisements. These are user defined and can be
assigned by an operator for local use.
User Defined metric values are encoded using the IEEE floating-point
format.
The conversion from 24-bit integer to 32-bit IEEE floating point
could introduce some loss of precision.
The proposed metric type range was chosen to allow mapping with
values assigned in the "IGP Metric-Type Registry". For example, the
User Defined metric type 130 of the METRIC object in PCEP can
represent the sum of the User Defined Metric 130 of all links along a
P2P.
User Defined Metrics are equally applicable to P2P and P2MP paths.
Sidor, et al. Expires 21 November 2025 [Page 13]
Internet-Draft SR-Algorithm in PCEP May 2025
5. Operation
The PCEP extensions defined in Section 4 of this document MUST NOT be
used unless both PCEP speakers have indicated support by setting the
S flag in the Path Setup Type Sub-TLV corresponding to the PST of the
LSP. If this condition is not met, the receiving PCEP speaker MUST
respond with a PCErr message with Error-Type 19 (Invalid Operation)
and Error-Value TBD3 (Attempted use of SR-Algorithm without
advertised capability).
The SR-Algorithm used in this document refers to a complete range of
SR-Algorithm values (0-255) if a specific section does not specify
otherwise. Valid SR-Algorithm values are defined in the registry
"IGP Algorithm Types" of "Interior Gateway Protocol (IGP) Parameters"
IANA registry. Refer to Section 3.1.1 of [RFC8402] and [RFC9256] for
the definition of SR-Algorithm in Segment Routing. [RFC8665] and
[RFC8667] are describing the use of the SR-Algorithm in IGP. Note
that some RFCs are referring to SR-Algorithm with different names,
for example "Prefix-SID Algorithm" and "SR Algorithm".
5.1. ERO Subobjects
If a PCC receives the Algorithm field in the ERO subobject within
PCInitiate, PCUpd, or PCRep messages and the path received from those
messages is being included in the ERO of PCRpt message, then the PCC
MUST include the Algorithm field in the encoded subobjects with the
received SR-Algorithm value.
As per [RFC9603] and [RFC8664], the format of the SR-RRO subobject is
the same as that of the SR-ERO subobject, but without the L-Flag,
therefore SR-RRO subobject may also carry the A flag and Algorithm
field.
5.1.1. SR-ERO
A PCEP speaker MAY set the A flag and include the Algorithm field in
an SR-ERO subobject if the S flag has been advertised in SR-PCE-
CAPABILITY Sub-TLV by both PCEP speakers.
If the PCEP peer receives an SR-ERO subobject with the A flag set or
with the SR-Algorithm included, but the S flag was not advertised in
SR-PCE-CAPABILITY Sub-TLV, then it MUST consider the entire ERO as
invalid as described in Section 5.2.1 of [RFC8664].
The Algorithm field in the SR-ERO subobject MUST be included after
the optional SID, NAI, or SID structure and the length of the SR-ERO
subobject MUST be increased by an additional 4 bytes for the Reserved
and Algorithm field.
Sidor, et al. Expires 21 November 2025 [Page 14]
Internet-Draft SR-Algorithm in PCEP May 2025
If the length and the A flag are not consistent as specified in
Section 4.2, PCEP peer MUST consider the entire ERO invalid and MUST
send a PCErr message with Error-Type = 10 ("Reception of an invalid
object") and Error-value = 11 ("Malformed object").
If the SID value is absent (S bit is set to 1), the NAI value is
present (F bit is set to 0) and Algorithm field is set (A bit is set
to 1), the PCC is responsible for choosing the SRv6-SID value based
on values specified in NAI and Algorithm fields. If the PCC cannot
find a SID index in the SR-DB, it MUST send a PCErr message with
Error-Type = 10 ("Reception of an invalid object") and Error-value =
14 ("Unknown SID").
5.1.2. SRv6-ERO
A PCEP speaker MAY set the A flag and include the Algorithm field in
an SRv6-ERO subobject if the S flag has been advertised in SRv6-PCE-
CAPABILITY sub-TLV by both PCEP speakers.
If the PCEP peer receives SRv6-ERO subobject with the A flag set or
with the SR-Algorithm included, but the S flag was not advertised in
SRv6-PCE-CAPABILITY Sub-TLV, then it MUST consider the entire ERO as
invalid as described in Section 5.2.1 of [RFC8664].
The Algorithm field in the SRv6-ERO subobject MUST be included in the
position specified in Section 4.3, the length of the SRv6-ERO
subobject is not impacted by the inclusion of the Algorithm field.
If the SRv6-SID value is absent (S bit is set to 1), the NAI value is
present (F bit is set to 0) and Algorithm field is set (A bit is set
to 1), the PCC is responsible for choosing the SRv6-SID value based
on values specified in NAI and Algorithm fields. If the PCC cannot
find a SID index in the SR-DB, it MUST send a PCErr message with
Error-Type = 10 ("Reception of an invalid object") and Error-value =
14 ("Unknown SID").
5.2. SR-Algorithm Constraint
To signal a specific SR-Algorithm constraint to the PCE, the headend
MUST encode the SR-Algorithm TLV inside the LSPA object.
If PCC received an LSPA object with SR-Algorithm TLV as part of
PCInitiate, PCUpd messages, then it MUST include LSPA object with SR-
Algorithm TLV in PCRpt message as part of intended-attribute-list.
Sidor, et al. Expires 21 November 2025 [Page 15]
Internet-Draft SR-Algorithm in PCEP May 2025
If PCE received an LSPA object with SR-Algorithm TLV in PCRpt or
PCReq, then it MUST include the LSPA object with SR-Algorithm TLV in
PCUpd message, or PCRep message in case of an unsuccessful path
computation based on rules described in Section 7.11 of [RFC5440].
A PCEP peer that did not advertise the S flag in the Path Setup Type
Sub-TLV corresponding to the LSP's PST, it MUST ignore the SR-
Algorithm TLV on receipt.
The PCE MUST NOT use Prefix SIDs of SR-Algorithm other than specified
in SR-Algorithm constraint. It is allowed to use other SID types
(e.g., Adjacency or BSID). Furthermore, the inclusion of a path BSID
from another policy is allowed only if the path associated with such
a policy fully satisfies all the constraints of the current path
computation. This ensures that while leveraging BSIDs from different
policies, requirements of the SR-Algorithm constraints are
maintained.
Specified SR-Algorithm constraint is applied to the end-to-end SR
policy path. Using different SR-Algorithm constraint in each domain
or part of the topology in single path computation is out of the
scope of this document. One possible solution is to determine FAD
mapping using PCE local policy.
If the PCE is unable to find a path with the given SR-Algorithm
constraint or it does not support a combination of specified
constraints, it MUST use empty ERO in PCInitiate for LSP
instantiation or PCUpd message if an update is required or NO-PATH
object in PCRep to indicate that it was not able to find the valid
path.
If the headend is part of multiple IGP domains and the winning FAD
for the specified SR-Algorithm has different constraints in each
domain, the PCE implementation MAY have a local policy with a defined
behavior for selecting a FAD for such path computation, or it may not
support it at all. If such path computation is not supported, PCE
MUST send a PCErr message with Error-Type = 29 (Path computation
failure) and Error-value = TBD4 (Unsupported combination of
constraints).
If the NO-PATH object is included in PCRep, then PCE MAY include SR-
Algorithm TLV to indicate constraint, which cannot be satisfied as
described in section 7.5 of [RFC5440].
SR-Algorithm does not replace the Objective Function defined in
[RFC5541].
Sidor, et al. Expires 21 November 2025 [Page 16]
Internet-Draft SR-Algorithm in PCEP May 2025
5.2.1. Flexible Algorithm Path Computation
This section is applicable only to the Flexible Algorithms range of
SR-Algorithm values.
The PCE must follow the IGP Flexible Algorithm path computation logic
as described in [RFC9350]. This includes using the same ordered
rules to select a FAD if multiple FADs are available, considering the
node participation of the specified SR-Algorithm during path
computation, using ASLA-specific link attributes, and applying other
rules for Flexible Algorithm path computation described in that
document. Path computation must occur on the topology associated
with the specified SR-Algorithm. It is allowed to use SID types
other than Prefix SID (e.g., Adjacency or BSID), but only from nodes
participating in specified SR-Algorithm.
The PCE must optimize the computed path based on the metric type
specified in the FAD. The optimization metric type included in PCEP
messages from the PCC MUST be ignored. The PCE SHOULD use the metric
type from the FAD in messages sent to the PCC. If a corresponding
metric type is not defined in PCEP, PCE SHOULD NOT include any METRIC
object for the optimization metric.
There are corresponding metric types in PCEP for IGP and TE metric
from FAD introduced in [RFC9350], but there were no corresponding
metric types defined for "Min Unidirectional Link Delay" from
[RFC9350] and "Bandwidth Metric", "User Defined Metric" from
[I-D.ietf-lsr-flex-algo-bw-con]. Section 4.5 of this document is
introducing them. Note that the defined "Path Bandwidth Metric" is
accumulative and is different from the Bandwidth Object defined in
[RFC5440].
The PCE MUST use constraints specified in the FAD and also
constraints (except optimization metric type) directly included in
PCEP messages from PCC. The PCE implementation MAY decide to ignore
specific constraints received from PCC based on existing processing
rules for PCEP Objects and TLVs, e.g. P flag described in Section 7.2
of [RFC5440] and processing rules described in [RFC9753]. If the PCE
does not support a specified combination of constraints, it MUST fail
path computation and respond with a PCEP message with PCInitiate or
PCUpd message with empty ERO or PCRep with NO-PATH object. PCC MUST
NOT include constraints from FAD in PCEP message sent to PCE as it
can result in undesired behavior in various cases. PCE SHOULD NOT
include constraints from FAD in PCEP messages sent to PCC.
The combinations of constraints specified in the FAD and constraints
directly included in PCEP messages from PCC may decrease the chance
that Flex-algo specific Prefix SIDs represent optimal path while
Sidor, et al. Expires 21 November 2025 [Page 17]
Internet-Draft SR-Algorithm in PCEP May 2025
satisfying all specified constraints, as a result a longer SID list
may be required for the computed path. Adding more constraints on
top of FAD requires complex path computation and may reduce the
benefit of this scheme.
5.2.2. Path computation with SID Filtering
The SR-Algorithm constraint acts as a filter, restricting which SIDs
may be used as a result of the path computation function. Path
computation is done based on optimization metric type and constraints
specified in the PCEP message received from PCC.
If the specified SR-Algorithm is a Flexible Algorithm, the PCE must
ensure that the IGP path of Flexible Algorithm SIDs is congruent with
computed path.
+----------+ +----------+
| PCC | -- | PCE |
+----------+ +----------+
/ \
10 / \ 20
/ \
+---------+ +---------+
| R2 | | R3 |
+---------+ +---------+
\ /
10 \ / 10
\ /
+----------+
| R4 |
+----------+
Figure 4: Path computation with SID Filtering
In the example shown in Figure 4, values next to links represent the
IGP metric assigned to those links. It is assumed that the FAD for
Flexible Algorithm 128 is advertised with only the metric type IGP
and no constraints from the PCC node. The PCE computes the path for
the SR-TE Policy configured on the PCC with the policy endpoint set
to the prefix of R4 router and the optimization metric set to the IGP
metric. All nodes depicted in the diagram are part of the same IGP
domain.
Sidor, et al. Expires 21 November 2025 [Page 18]
Internet-Draft SR-Algorithm in PCEP May 2025
If all nodes in the diagram participate in Flexible Algorithm 128,
the Flexible Algorithm SID for Algorithm 128 from node R4 can be used
by the PCE. In this case, the computed path (PCC - R2 - R4) is
congruent with the IGP path associated with the SID.
However, if node R2 does not participate in Flexible Algorithm 128
while all other nodes do, the IGP path associated with the of
Flexible Algorithm SID of node R4 will no longer be congruent with
the computed path. In such scenarios, the PCE can use other SID
types (e.g. Adjacency SID) in the computed path to ensure that the
path is congruent with IGP path of SIDs used.
5.2.3. New Metric types
All the rules of processing the METRIC object as explained in
[RFC5440] and [RFC8233] are applicable to new metric types defined in
this document.
6. Manageability Considerations
All manageability requirements and considerations listed in
[RFC5440], [RFC8231], [RFC8281], [RFC8664] and [RFC9603] apply to
PCEP extensions defined in this document. In addition, the
requirements and considerations listed in this section apply.
6.1. Control of Function and Policy
A PCE or PCC implementation SHOULD allow the capability of supporting
PCEP extensions introduced in this document to be enabled or disabled
as part of the global configuration.
6.2. Information and Data Models
An implementation SHOULD allow the operator to view the capability
defined in this document. Sections 4.1 and 4.1.1 of
[I-D.ietf-pce-pcep-yang] should be extended to include the
capabilities introduced in Sections 3.1.1 and 3.1.2 for PCEP peer.
6.3. Liveness Detection and Monitoring
This document does not define any new mechanism that impacts the
liveness detection and monitoring of PCEP.
6.4. Verify Correct Operations
An implementation SHOULD also allow the operator to view FADs, which
MAY be used in Flexible Algorithm path computation defined in
Section 5.2.1.
Sidor, et al. Expires 21 November 2025 [Page 19]
Internet-Draft SR-Algorithm in PCEP May 2025
An implementation SHOULD allow the operator to view nodes
participating in the specified SR-Algorithm.
6.5. Requirements on Other Protocols and Functional Components
This document does not put new requirements but relies on the
necessary IGP extensions.
6.6. Impact On Network Operations
This document inherits considerations from documents describing IGP
Flexible Algorithm - for example [RFC9350] and
[I-D.ietf-lsr-flex-algo-bw-con].
7. Operational Considerations
This document inherits operational considerations from documents
describing IGP Flexible Algorithm - for example [RFC9350] and
[I-D.ietf-lsr-flex-algo-bw-con].
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".
Sidor, et al. Expires 21 November 2025 [Page 20]
Internet-Draft SR-Algorithm in PCEP May 2025
8.1. Cisco
* Organization: Cisco Systems
* Implementation: IOS-XR PCC and PCE.
* Description: SR-MPLS part with experimental codepoints.
* Maturity Level: Production.
* Coverage: Partial.
* Contact: ssidor@cisco.com
8.2. Huawei
* Organization: Huawei
* Implementation: NE Series Routers
* Description: SR Policy with SR Algorithm.
* Maturity Level: Production.
* Coverage: Partial.
* Contact: pengshuping@huawei.com
9. Security Considerations
The security considerations described in [RFC5440], [RFC8231],
[RFC8253], [RFC8281], [RFC8664], [RFC9603] and [RFC9350] in itself.
Note that this specification introduces the possibility of computing
paths by PCE based on Flexible Algorithm related topology attributes
and based on the metric type and constraints from FAD. This creates
additional vulnerabilities, which are already described for the path
computation done by IGP like those described in Security
Considerations section of [RFC9350], but which are also applicable to
path computation done by PCE. Hence, securing the PCEP session using
Transport Layer Security (TLS) [RFC8253] is RECOMMENDED.
10. IANA Considerations
Sidor, et al. Expires 21 November 2025 [Page 21]
Internet-Draft SR-Algorithm in PCEP May 2025
10.1. SR Capability Flag
IANA maintains a registry, named "SR Capability Flag Field", within
the "Path Computation Element Protocol (PCEP) Numbers" registry group
to manage the Flags field of the SR-PCE-CAPABILITY TLV. IANA is
requested to confirm the following early allocation:
+=====+=========================+===============+
| Bit | Description | Reference |
+=====+=========================+===============+
| 5 | SR-Algorithm Capability | This document |
+-----+-------------------------+---------------+
Table 1
10.2. SRv6 PCE Capability Flag
IANA maintains a registry, named "SRv6 PCE Capability Flags", within
the "Path Computation Element Protocol (PCEP) Numbers" registry group
to manage the Flags field of SRv6-PCE-CAPABILITY sub-TLV. IANA is
requested to make the following assignment:
+======+=========================+===============+
| Bit | Description | Reference |
+======+=========================+===============+
| TBD1 | SR-Algorithm Capability | This document |
+------+-------------------------+---------------+
Table 2
10.3. SR-ERO Flag
IANA maintains a registry, named "SR-ERO Flag Field", within the
"Path Computation Element Protocol (PCEP) Numbers" registry group to
manage the Flags field of the SR-ERO Subobject. IANA is requested to
confirm the following early allocation:
+=====+=======================+===============+
| Bit | Description | Reference |
+=====+=======================+===============+
| 7 | SR-Algorithm Flag (A) | This document |
+-----+-----------------------+---------------+
Table 3
Sidor, et al. Expires 21 November 2025 [Page 22]
Internet-Draft SR-Algorithm in PCEP May 2025
10.4. SRv6-ERO Flag
IANA maintains a registry, named "SRv6-ERO Flag Field", within the
"Path Computation Element Protocol (PCEP) Numbers" registry group to
manage the Flags field of the SRv6-ERO subobject. IANA is requested
to make the following assignment:
+======+=======================+===============+
| Bit | Description | Reference |
+======+=======================+===============+
| TBD2 | SR-Algorithm Flag (A) | This document |
+------+-----------------------+---------------+
Table 4
10.5. PCEP TLV Types
IANA maintains a registry, named "PCEP TLV Type Indicators", within
the "Path Computation Element Protocol (PCEP) Numbers" registry
group. IANA is requested to confirm the early allocation of a new
TLV type for the new LSPA TLV specified in this document.
+======+==============+===============+
| Type | Description | Reference |
+======+==============+===============+
| 66 | SR-Algorithm | This document |
+------+--------------+---------------+
Table 5
10.6. Metric Types
IANA maintains a registry for "METRIC Object T Field" within the
"Path Computation Element Protocol (PCEP) Numbers" registry group.
IANA is requested to confirm the early allocated codepoints as
follows:
Sidor, et al. Expires 21 November 2025 [Page 23]
Internet-Draft SR-Algorithm in PCEP May 2025
+=========+============================+===============+
| Type | Description | Reference |
+=========+============================+===============+
| 22 | Path Min Delay Metric | This document |
+---------+----------------------------+---------------+
| 23 | P2MP Path Min Delay Metric | This document |
+---------+----------------------------+---------------+
| 24 | Path Bandwidth Metric | This document |
+---------+----------------------------+---------------+
| 25 | P2MP Path Bandwidth Metric | This document |
+---------+----------------------------+---------------+
| 128-255 | User Defined Metric | This document |
+---------+----------------------------+---------------+
Table 6
10.7. PCEP-Error Object
IANA is requested to allocate new error types and error values within
the "PCEP-ERROR Object Error Types and Values" sub-registry of the
PCEP Numbers registry for the following errors.
+============+=============+====================================+
| Error-Type | Meaning | Error-Value |
+============+=============+====================================+
| 19 | Invalid | TBD3:Attempted use of SR-Algorithm |
| | Operation | without advertised capability |
+------------+-------------+------------------------------------+
| 29 | Path | TBD4:Unsupported combination of |
| | computation | constraints |
| | failure | |
+------------+-------------+------------------------------------+
Table 7
11. References
11.1. Normative References
[I-D.ietf-lsr-flex-algo-bw-con]
Hegde, S., Britto, W., Shetty, R., Decraene, B., Psenak,
P., and T. Li, "IGP Flexible Algorithms: Bandwidth, Delay,
Metrics and Constraints", Work in Progress, Internet-
Draft, draft-ietf-lsr-flex-algo-bw-con-22, 13 February
2025, <https://datatracker.ietf.org/doc/html/draft-ietf-
lsr-flex-algo-bw-con-22>.
Sidor, et al. Expires 21 November 2025 [Page 24]
Internet-Draft SR-Algorithm in PCEP May 2025
[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>.
[RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
Previdi, "OSPF Traffic Engineering (TE) Metric
Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015,
<https://www.rfc-editor.org/info/rfc7471>.
[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>.
[RFC8233] Dhody, D., Wu, Q., Manral, V., Ali, Z., and K. Kumaki,
"Extensions to the Path Computation Element Communication
Protocol (PCEP) to Compute Service-Aware Label Switched
Paths (LSPs)", RFC 8233, DOI 10.17487/RFC8233, September
2017, <https://www.rfc-editor.org/info/rfc8233>.
[RFC8253] Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
"PCEPS: Usage of TLS to Provide a Secure Transport for the
Path Computation Element Communication Protocol (PCEP)",
RFC 8253, DOI 10.17487/RFC8253, October 2017,
<https://www.rfc-editor.org/info/rfc8253>.
[RFC8281] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "Path
Computation Element Communication Protocol (PCEP)
Extensions for PCE-Initiated LSP Setup in a Stateful PCE
Model", RFC 8281, DOI 10.17487/RFC8281, December 2017,
<https://www.rfc-editor.org/info/rfc8281>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
Sidor, et al. Expires 21 November 2025 [Page 25]
Internet-Draft SR-Algorithm in PCEP May 2025
[RFC8570] Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward,
D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE)
Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March
2019, <https://www.rfc-editor.org/info/rfc8570>.
[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>.
[RFC8665] Psenak, P., Ed., Previdi, S., Ed., Filsfils, C., Gredler,
H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
Extensions for Segment Routing", RFC 8665,
DOI 10.17487/RFC8665, December 2019,
<https://www.rfc-editor.org/info/rfc8665>.
[RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C.,
Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
Extensions for Segment Routing", RFC 8667,
DOI 10.17487/RFC8667, December 2019,
<https://www.rfc-editor.org/info/rfc8667>.
[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>.
[RFC9350] Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K.,
and A. Gulko, "IGP Flexible Algorithm", RFC 9350,
DOI 10.17487/RFC9350, February 2023,
<https://www.rfc-editor.org/info/rfc9350>.
[RFC9603] Li, C., Ed., Kaladharan, P., Sivabalan, S., Koldychev, M.,
and Y. Zhu, "Path Computation Element Communication
Protocol (PCEP) Extensions for IPv6 Segment Routing",
RFC 9603, DOI 10.17487/RFC9603, July 2024,
<https://www.rfc-editor.org/info/rfc9603>.
[RFC9753] Li, C., Zheng, H., and S. Litkowski, "Extension for
Stateful PCE to Allow Optional Processing of Path
Computation Element Communication Protocol (PCEP)
Objects", RFC 9753, DOI 10.17487/RFC9753, April 2025,
<https://www.rfc-editor.org/info/rfc9753>.
11.2. Informative References
Sidor, et al. Expires 21 November 2025 [Page 26]
Internet-Draft SR-Algorithm in PCEP May 2025
[I-D.ietf-pce-pcep-yang]
Dhody, D., Beeram, V. P., Hardwick, J., and J. Tantsura,
"A YANG Data Model for Path Computation Element
Communications Protocol (PCEP)", Work in Progress,
Internet-Draft, draft-ietf-pce-pcep-yang-30, 26 January
2025, <https://datatracker.ietf.org/doc/html/draft-ietf-
pce-pcep-yang-30>.
[IEEE.754.1985]
IEEE, "Standard for Binary Floating-Point Arithmetic",
DOI 10.1109/IEEESTD.1985.82928, IEEE Standard 754, October
1985, <https://doi.org/10.1109/IEEESTD.1985.82928>.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<https://www.rfc-editor.org/info/rfc3031>.
[RFC4655] Farrel, A., Vasseur, J.-P., 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>.
[RFC5541] Le Roux, JL., Vasseur, JP., and Y. Lee, "Encoding of
Objective Functions in the Path Computation Element
Communication Protocol (PCEP)", RFC 5541,
DOI 10.17487/RFC5541, June 2009,
<https://www.rfc-editor.org/info/rfc5541>.
[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>.
[RFC9479] Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
J. Drake, "IS-IS Application-Specific Link Attributes",
RFC 9479, DOI 10.17487/RFC9479, October 2023,
<https://www.rfc-editor.org/info/rfc9479>.
[RFC9492] Psenak, P., Ed., Ginsberg, L., Henderickx, W., Tantsura,
J., and J. Drake, "OSPF Application-Specific Link
Attributes", RFC 9492, DOI 10.17487/RFC9492, October 2023,
<https://www.rfc-editor.org/info/rfc9492>.
Appendix A. Acknowledgement
Thanks to Dhruv Dhody for shepherding the document and for his
contributions and suggestions.
Sidor, et al. Expires 21 November 2025 [Page 27]
Internet-Draft SR-Algorithm in PCEP May 2025
Would like to thank Adrian Farrel, Aijun Wang, Boris Khasanov, Jie
Dong, Marina Fizgeer, Nagendra Nainar, Rakesh Gandhi, Russ White,
Shraddha Hegde for review and suggestions.
Appendix B. Contributors
Mike Koldychev
Ciena Corporation
Email: mkoldych@proton.me
Zafar Ali
Cisco Systems, Inc.
Email: zali@cisco.com
Stephane Litkowski
Cisco Systems, Inc.
Email: slitkows.ietf@gmail.com
Siva Sivabalan
Ciena
Email: msiva282@gmail.com
Tarek Saad
Cisco Systems, Inc.
Email: tsaad.net@gmail.com
Mahendra Singh Negi
RtBrick Inc
Email: mahend.ietf@gmail.com
Tom Petch
Email: ietfc@btconnect.com
Authors' Addresses
Samuel Sidor
Cisco Systems, Inc.
Eurovea Central 3.
Pribinova 10
811 09 Bratislava
Slovakia
Email: ssidor@cisco.com
Sidor, et al. Expires 21 November 2025 [Page 28]
Internet-Draft SR-Algorithm in PCEP May 2025
Zoey Rose
Cisco Systems, Inc.
2300 East President George
Richardson, TX 75082
United States of America
Email: atokar@cisco.com
Shaofu Peng
ZTE Corporation
No.50 Software Avenue
Nanjing
Jiangsu, 210012
China
Email: peng.shaofu@zte.com.cn
Shuping Peng
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing
100095
China
Email: pengshuping@huawei.com
Andrew Stone
Nokia
Email: andrew.stone@nokia.com
Sidor, et al. Expires 21 November 2025 [Page 29]