]> Path Computation Element Communication Protocol (PCEP) Extensions for Segment Routing (SR) Policy Candidate Paths Ciena Corporation
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Ciena Corporation
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Cisco Systems, Inc.
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Juniper Networks, Inc.
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Huawei Technologies
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Nokia
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RTG PCE PCEP SR Policy Candidate Path A Segment Routing (SR) Policy is an ordered list of instructions called "segments" that represent a source-routed policy. Packet flows are steered into an SR Policy on a node where it is instantiated. An SR Policy is made of one or more Candidate Paths. This document specifies the Path Computation Element Communication Protocol (PCEP) extension to signal Candidate Paths of an SR Policy. Additionally, this document updates RFC 8231 to allow delegation and setup of an SR Label Switched Path (LSP) without using the path computation request and reply messages. This document is applicable to both Segment Routing over MPLS (SR-MPLS) and Segment Routing over IPv6 (SRv6).
Introduction "Segment Routing Policy Architecture" details the concepts of Segment Routing (SR) Policy and approaches to steering traffic into an SR Policy. "Path Computation Element Communication Protocol (PCEP) Extensions for Segment Routing" specifies extensions to the PCEP that allow a stateful Path Computation Element (PCE) to compute and initiate Traffic Engineering (TE) paths, as well as a Path Computation Client (PCC) to request a path subject to certain constraints and optimization criteria in an SR domain. Although PCEP extensions introduced in enable the creation of SR-TE paths, these do not constitute SR Policies as defined in . Therefore, they lack support for:
  • Association of SR Policy Candidate Paths signaled via PCEP with Candidate Paths of the same SR Policy signaled via other sources (e.g., local configuration or BGP).
  • Association of an SR Policy with an intent via color, enabling headend-based steering of BGP service routes over SR Policies provisioned via PCEP.
"Path Computation Element Communication Protocol (PCEP) Extensions for Establishing Relationships between Sets of Label Switched Paths (LSPs)" introduces a generic mechanism to create a grouping of LSPs that is called an "Association". An SR Policy is associated with one or more Candidate Paths. A Candidate Path is the unit for signaling an SR Policy to a headend as described in . This document extends to support signaling SR Policy Candidate Paths as LSPs and to signal Candidate Path membership in an SR Policy by means of the Association mechanism. A PCEP Association corresponds to an SR Policy and an LSP corresponds to a Candidate Path. The unit of signaling in PCEP is the LSP, thus, all the information related to an SR Policy is carried at the Candidate Path level. Also, this document updates , making the use of Path Computation Request (PCReq) and Path Computation Reply (PCRep) messages optional for LSPs that are set up using Path Setup Type 1 (for Segment Routing) and Path Setup Type 3 (for SRv6) with the aim of reducing the PCEP message exchanges and simplifying implementation.
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 when, and only when, they appear in all capitals, as shown here.
Terminology This document uses the following terms defined in :
  • Explicit Route Object (ERO)
  • Path Computation Client (PCC)
  • Path Computation Element (PCE)
  • PCEP Peer
  • PCEP speaker
This document uses the following term defined in :
  • Label Switched Path (LSP)
This document uses the following term defined in :
  • Border Gateway Protocol - Link State (BGP-LS)
The following other terms are used in this document:
Endpoint:
The IPv4 or IPv6 endpoint address of an SR Policy, as described in .
Color:
The 32-bit color of an SR Policy, as described in .
Protocol-Origin:
The protocol that was used to create a Candidate Path, as described in .
Originator:
A device that created a Candidate Path, as described in .
Discriminator:
Distinguishes Candidate Paths created by the same device, as described in .
Association parameters:
Refers to the key data that uniquely identifies an Association, as described in .
Association information:
Refers to information related to Association Type, as described in .
SR Policy LSP:
An LSP setup using Path Setup Type 1 (for Segment Routing) or 3 (for SRv6).
SR Policy Association (SRPA):
A new Association Type used to group Candidate Paths belonging to the same SR Policy. Depending on the discussion context, it can refer to the PCEP ASSOCIATION object of an SR Policy type or to a group of LSPs that belong to the association.
The base PCEP specification 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 . 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 ).
Overview The SR Policy is represented by a new type of PCEP Association, called the SR Policy Association (SRPA) (see ). The SR Policy Candidate Paths of a specific SR Policy are the LSPs within the same SRPA. The extensions in this document specify the encoding of a single segment list within an SR Policy Candidate Path. Encoding of multiple segment lists is outside the scope of this document and is specified in . An SRPA carries three pieces of information: SR Policy Identifier, SR Policy Candidate Path Identifier, and SR Policy Candidate Path Attribute(s). This document also specifies some additional information that is not encoded as part of an SRPA: computation priority of the LSP, Explicit NULL Label Policy for the unlabeled IP packets and Drop-Upon-Invalid behavior for traffic steering when the LSP is operationally down (see ).
SR Policy Association (SRPA) Per , LSPs are associated with other LSPs with which they interact by adding them to a common association group. An association group is uniquely identified by the combination of the following fields in the ASSOCIATION object (): Association Type, Association ID, Association Source, and (if present) Global Association Source, or Extended Association ID. These fields are referred to as "association parameters" (). specifies the ASSOCIATION object with two Object-Types for IPv4 and IPv6 that includes the field Association Type. This document defines a new Association Type (6) "SR Policy Association" for an SRPA. specifies the mechanism for the capability advertisement of the Association Types supported by a PCEP speaker by defining an ASSOC-Type-List TLV to be carried within an OPEN object. This capability exchange for the SRPA Type MUST be done before using the SRPA. To that aim, a PCEP speaker MUST include the SRPA Type (6) in the ASSOC-Type-List TLV and MUST receive the same from the PCEP peer before using the SRPA (). An SRPA MUST be assigned for all SR Policy LSPs by the PCEP speaker originating the LSP if the capability was advertised by both PCEP speakers. If the above condition is not satisfied, then the receiving PCEP speaker MUST send a PCErr message with:
  • Error-Type = 6 "Mandatory Object Missing"
  • Error-value = 22 "Missing SR Policy Association"
A given LSP MUST belong to one SRPA at most, 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"
The existing behavior for the use of Binding SID (BSID) with an SR Policy is already documented in . If BSID value allocation failed because of conflict with the BSID used by another policy, then the PCEP peer MUST send a PCErr message with:
  • Error-Type = 32 "Binding label/SID failure"
  • Error-value = 2 "Unable to allocate the specified binding value"
SR Policy Identifier The SR Policy Identifier uniquely identifies an SR Policy within the SR domain. The SR Policy Identifier is assigned by the PCEP peer originating the LSP and MUST be uniform across all the PCEP sessions. Candidate Paths within an SR Policy MUST carry the same SR Policy Identifiers in their SRPAs. Candidate Paths within an SR Policy MUST NOT change their SR Policy Identifiers for the lifetime of the PCEP session. If the above conditions are not satisfied, the receiving PCEP speaker MUST send a PCEP Error (PCErr) message with:
  • Error-Type = 26 "Association Error"
  • Error-value = 20 "SR Policy Identifier Mismatch"
The SR Policy Identifier consists of:
  • Headend router where the SR Policy originates.
  • Color of the SR Policy ().
  • Endpoint of the SR Policy ().
SR Policy Candidate Path Identifier The SR Policy Candidate Path Identifier uniquely identifies the SR Policy Candidate Path within the context of an SR Policy. The SR Policy Candidate Path Identifier is assigned by the PCEP peer originating the LSP. Candidate Paths within an SR Policy MUST NOT change their SR Policy Candidate Path Identifiers for the lifetime of the PCEP session. Two or more Candidate Paths within an SR Policy MUST NOT carry the same SR Policy Candidate Path Identifiers in their SRPAs. If the above conditions are not satisfied, the PCEP speaker MUST send a PCErr message with:
  • Error-Type = 26 "Association Error"
  • Error-value = 21 "SR Policy Candidate Path Identifier Mismatch"
The SR Policy Candidate Path Identifier consists of:
  • Protocol-Origin ()
  • Originator ()
  • Discriminator ()
SR Policy Candidate Path Attributes SR Policy Candidate Path Attributes carry optional, non-key information about a Candidate Path and MAY change during the lifetime of an LSP. SR Policy Candidate Path Attributes consist of:
  • Candidate Path Preference ()
  • Candidate Path name ()
  • SR Policy name ()
Association Parameters Per , an SR Policy is identified through the <Headend, Color, Endpoint> tuple. The association parameters consist of:
Association Type:
Set to 6 "SR Policy Association".
Association Source (IPv4/IPv6):
Set to the headend value of the SR Policy, as defined in .
Association ID (16 bit):
Always set to the numeric value 1.
Extended Association ID TLV:
Mandatory TLV for an SRPA. Encodes the Color and Endpoint of the SR Policy ().
Extended Association ID TLV Format
Type:
31 for the Extended Association ID TLV .
Length:
8 octets if IPv4 address or 20 octets if IPv6 address is encoded in the Endpoint field.
Color:
Unsigned non-zero 32-bit integer value, SR Policy color per .
Endpoint:
Can be either IPv4 (4 octets) or IPv6 address (16 octets). This value MAY be different from the one contained in the destination address field in the END-POINTS object, or in the Tunnel Endpoint Address field in the LSP-IDENTIFIERS TLV ().
If a PCEP speaker receives an SRPA object whose association parameters do not follow the above specification, then the PCEP speaker MUST send a PCErr message with:
  • Error-Type = 26 "Association Error"
  • Error-value = 20 "SR Policy Identifier Mismatch"
The encoding choice of the association parameters in this way is meant to guarantee that there is no possibility of a race condition when multiple PCEP speakers want to associate 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 based on the SR Policy parameters . The last hop of a computed SR Policy Candidate Path MAY differ from the Endpoint contained in the <Headend, Color, Endpoint> tuple. An example use case is to terminate the SR Policy before reaching the Endpoint and have decapsulated traffic be forwarded the rest of the path to the Endpoint node using the Interior Gateway Protocol (IGP) shortest path(s). In this example, the destination of the SR Policy Candidate Paths will be some node before the Endpoint, but the Endpoint value is still used at the headend to steer traffic with that Endpoint IP address into the SR Policy. The destination of the SR Policy Candidate Path is signaled using the END-POINTS object and/or the LSP-IDENTIFIERS TLV, per the usual PCEP procedure. When neither the END-POINTS object nor the LSP-IDENTIFIERS TLV is present, the PCEP speaker MUST extract the destination from the Endpoint field in the SRPA Extended Association ID TLV. SR Policy with Color-Only steering is signaled with the Endpoint value set to unspecified, i.e., 0.0.0.0 for IPv4 or :: for IPv6, per .
Association Information The SRPA object may carry the following TLVs:
SRPOLICY-POL-NAME TLV ():
(optional) encodes the SR Policy Name string.
SRPOLICY-CPATH-ID TLV ():
(mandatory) encodes the SR Policy Candidate Path Identifier.
SRPOLICY-CPATH-NAME TLV ():
(optional) encodes the SR Policy Candidate Path string name.
SRPOLICY-CPATH-PREFERENCE TLV ():
(optional) encodes the SR Policy Candidate Path Preference value.
When a mandatory TLV is missing from an SRPA object, the PCEP speaker MUST send a PCErr message with:
  • Error-Type = 6 "Mandatory Object Missing"
  • Error-value = 21 "Missing SR Policy Mandatory TLV"
Only one TLV instance of each TLV type can be carried in an SRPA object, and only the first occurrence is processed. Any others MUST be silently ignored.
SRPOLICY-POL-NAME TLV The SRPOLICY-POL-NAME TLV () is an optional TLV for the SRPA object. It is RECOMMENDED that the size of the name for the SR Policy is limited to 255 bytes. Implementations MAY choose to truncate long names to 255 bytes to simplify interoperability with other protocols.
SRPOLICY-POL-NAME TLV Format
Type:
56 for the SRPOLICY-POL-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. Padding is not included in the Length field.
SR Policy Name:
SR Policy name, as defined in . It MUST be a string of printable ASCII characters, without a NULL terminator.
SRPOLICY-CPATH-ID TLV The SRPOLICY-CPATH-ID TLV () is a mandatory TLV for the SRPA object.
SRPOLICY-CPATH-ID TLV Format
Type:
57 for the SRPOLICY-CPATH-ID TLV.
Length:
28.
Protocol-Origin:
8-bit unsigned integer value that encodes the Protocol-Origin. The values of this field are specified in the IANA registry "SR Policy Protocol Origin" under the "Segment Routing" registry group, which is introduced in . Note that in the PCInitiate message , the Protocol-Origin is always set to 10 - "PCEP (In PCEP or when BGP-LS Producer is PCE)". The "SR Policy Protocol Origin" IANA registry includes a combination of values intended for use in PCEP and BGP-LS. When the registry contains two variants of values associated with the mechanism or protocol used for provisioning of the Candidate Path, for example 1 - "PCEP" and 10 - "PCEP (In PCEP or when BGP-LS Producer is PCE)", the "(In PCEP or when BGP-LS Producer is PCE)", then variants MUST be used in PCEP.
Reserved:
This field MUST be set to zero on transmission and MUST be ignored on receipt.
Originator Autonomous System Number (ASN):
Represented as a 32-bit unsigned integer value, part of the originator identifier, as specified in . When sending a PCInitiate message , the PCE is the originator of the Candidate Path. If the PCE is configured with an ASN, then it MUST set it; otherwise, the ASN is set to 0.
Originator Address:
Represented as a 128-bit value as specified in . When sending a PCInitiate message, the PCE is acting as the originator and therefore MAY set this to an address that it owns.
Discriminator:
32-bit unsigned integer value that encodes the Discriminator of the Candidate Path, as specified in . This is the field that mainly distinguishes different SR Policy Candidate Paths, coming from the same originator. It is allowed to be any number in the 32-bit range.
SRPOLICY-CPATH-NAME TLV The SRPOLICY-CPATH-NAME TLV () is an optional TLV for the SRPA object. It is RECOMMENDED that the size of the name for the SR Policy is limited to 255 bytes. Implementations MAY choose to truncate long names to 255 bytes to simplify interoperability with other protocols.
SRPOLICY-CPATH-NAME TLV Format
Type:
58 for the 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. Padding is not included in the Length field.
SR Policy Candidate Path Name:
SR Policy Candidate Path Name, as defined in . It MUST be a string of printable ASCII characters, without a NULL terminator.
SRPOLICY-CPATH-PREFERENCE TLV The SRPOLICY-CPATH-PREFERENCE TLV () is an optional TLV for the SRPA object. If the TLV is absent, then the default Preference value is 100, per .
SRPOLICY-CPATH-PREFERENCE TLV Format
Type:
59 for the SRPOLICY-CPATH-PREFERENCE TLV.
Length:
4.
Preference:
32-bit unsigned integer value that encodes the Preference of the Candidate Path as defined in .
SR Policy Signaling Extensions This section introduces mechanisms described for SR Policies in to PCEP. These extensions do not make use of the SRPA for signaling in PCEP; therefore, they cannot rely on the Association capability negotiation in the ASSOC-Type-List TLV. Instead, separate capability negotiation is required. This document specifies four new TLVs to be carried in the OPEN or LSP object. Only one TLV instance of each type can be carried, and only the first occurrence is processed. Any others MUST be ignored.
SRPOLICY-CAPABILITY TLV The SRPOLICY-CAPABILITY TLV () is a TLV for the OPEN object. It is used at session establishment to learn the peer's capabilities with respect to SR Policy. Implementations that support SR Policy MUST include the SRPOLICY-CAPABILITY TLV in the OPEN object if the extension is enabled. In addition, the ASSOC-Type-List TLV containing SRPA Type (6) MUST be present in the OPEN object, as specified in . If a PCEP speaker receives an SRPA but the SRPOLICY-CAPABILITY TLV is not exchanged, then the PCEP speaker MUST send a PCErr message with Error-Type = 10 "Reception of an invalid object" and Error-value = 44 "Missing SRPOLICY-CAPABILITY TLV" and MUST then close the PCEP session.
SRPOLICY-CAPABILITY TLV Format
Type:
71 for the SRPOLICY-CAPABILITY TLV.
Length:
4.
Flags:
32 bits. The following flags are currently defined:
P-flag (Computation Priority):
If set to 1 by a PCEP speaker, the P-flag indicates that the PCEP speaker supports the handling of the COMPUTATION-PRIORITY TLV for the SR Policy (). If this flag is set to 0, then the receiving PCEP speaker MUST NOT send the COMPUTATION-PRIORITY TLV and MUST ignore it on receipt.
E-flag (Explicit NULL Label Policy):
If set to 1 by a PCEP speaker, the E-flag indicates that the PCEP speaker supports the handling of the EXPLICIT-NULL-LABEL-POLICY TLV for the SR Policy (). If this flag is set to 0, then the receiving PCEP speaker MUST NOT send the EXPLICIT-NULL-LABEL-POLICY TLV and MUST ignore it on receipt.
I-flag (Invalidation):
If set to 1 by a PCEP speaker, the I-flag indicates that the PCEP speaker supports the handling of the INVALIDATION TLV for the SR Policy (). If this flag is set to 0, then the receiving PCEP speaker MUST NOT send the INVALIDATION TLV and MUST ignore it on receipt.
L-flag (Stateless Operation):
If set to 1 by a PCEP speaker, the L-flag indicates that the PCEP speaker supports the stateless (PCReq/PCRep) operations for the SR Policy (). If the PCE set this flag to 0, then the PCC MUST NOT send PCReq messages to this PCE for the SR Policy.
Unassigned bits MUST be set to 0 on transmission and MUST be ignored on receipt. More flags can be assigned in the future per ().
LSP Object TLVs This section is introducing three new TLVs to be carried in the LSP object introduced in .
COMPUTATION-PRIORITY TLV The COMPUTATION-PRIORITY TLV () is an optional TLV. It is used to signal the numerical computation priority, as specified in . If the TLV is absent from the LSP object, and the P-flag in the SRPOLICY-CAPABILITY TLV is set to 1, a default Priority value of 128 is used.
COMPUTATION-PRIORITY TLV Format
Type:
68 for the COMPUTATION-PRIORITY TLV.
Length:
4.
Priority:
8-bit unsigned integer value that encodes numerical priority with which this LSP is to be recomputed by the PCE upon topology change. The lowest value is the highest priority.
Reserved:
This field MUST be set to zero on transmission and MUST be ignored on receipt.
EXPLICIT-NULL-LABEL-POLICY TLV To steer an unlabeled IP packet into an SR Policy for the MPLS data plane, it is necessary to push a label stack of one or more labels on that packet. The EXPLICIT-NULL-LABEL-POLICY TLV is an optional TLV for the LSP object used to indicate whether an Explicit NULL label must be pushed on an unlabeled IP packet before any other labels. The contents of this TLV are used by the SR Policy manager as described in . If an EXPLICIT-NULL-LABEL-POLICY TLV is not present, the decision of whether to push an Explicit NULL label on a given packet is a matter of local configuration. Note that Explicit NULL is currently only defined for SR-MPLS and not for SRv6. Therefore, the receiving PCEP speaker MUST ignore the presence of this TLV for SRv6 Policies.
EXPLICIT-NULL-LABEL-POLICY TLV Format
Type:
69 for the EXPLICIT-NULL-LABEL-POLICY TLV.
Length:
4.
ENLP:
Explicit NULL Label Policy. 8-bit unsigned integer value that indicates whether Explicit NULL labels are to be pushed on unlabeled IP packets that are being steered into a given SR Policy. The values of this field are specified in the IANA registry "SR Policy ENLP Values" under the "Segment Routing" registry group, which was introduced in .
Reserved:
This field MUST be set to zero on transmission and MUST be ignored on receipt.
The ENLP unassigned values may be used for future extensions, and implementations MUST ignore the EXPLICIT-NULL-LABEL-POLICY TLV with unrecognized values. The behavior signaled in this TLV MAY be overridden by local configuration by the network operator based on their deployment requirements. describes the behavior on the headend for the handling of the Explicit NULL label.
INVALIDATION TLV The INVALIDATION TLV () is an optional TLV. This TLV is used to control traffic steering into an LSP when the LSP is operationally down/invalid. In the context of SR Policy, this TLV facilitates the Drop-Upon-Invalid behavior, specified in . Normally, if the LSP is down/invalid then it stops attracting traffic; traffic that would have been destined for that LSP is redirected somewhere else, such as via IGP or another LSP. The Drop-Upon-Invalid behavior specifies that the LSP keeps attracting traffic and the traffic has to be dropped at the headend. Such an LSP is said to be "in drop state". While in the drop state, the LSP operational state is "UP", as indicated by the O-flag in the LSP object. However, the ERO object MAY be empty if no valid path has been computed. The INVALIDATION TLV is used in both directions between PCEP peers:
  • PCE -> PCC: The PCE specifies to the PCC whether to enable or disable Drop-Upon-Invalid (Config).
  • PCC -> PCE: The PCC reports the current setting of the Drop-Upon-Invalid (Config) and also whether the LSP is currently in the drop state (Oper).
INVALIDATION TLV Format
Type:
70 for the INVALIDATION TLV.
Length:
4.
Oper:
An 8-bit flag field that encodes the operational state of the LSP. It MUST be set to 0 by the PCE when sending and MUST be ignored by the PCC upon receipt. See for IANA information.
Oper State of Drop-Upon-Invalid Feature
  • D: Dropping - the LSP is actively dropping traffic as a result of Drop-Upon-Invalid behavior being activated.
  • The unassigned bits in the Flag octet MUST be set to zero upon transmission and MUST be ignored upon receipt.
Config:
An 8-bit flag field that encodes the configuration of the LSP. See for IANA information.
Config State of Drop-Upon-Invalid Feature
  • D: Drop enabled - the Candidate Path has Drop-Upon-Invalid feature enabled.
  • The unassigned bits in the Flag octet MUST be set to zero upon transmission and MUST be ignored upon receipt.
Reserved:
This field MUST be set to zero on transmission and MUST be ignored on receipt.
Drop-Upon-Invalid Applies to SR Policy The Drop-Upon-Invalid feature is somewhat special among the other SR Policy features in the way that it is enabled/disabled. This feature is enabled only on the whole SR Policy, not on a particular Candidate Path of that SR Policy, i.e., when any Candidate Path has Drop-Upon-Invalid enabled, it means that the whole SR Policy has the feature enabled. As stated in , an SR Policy is invalid when all its Candidate Paths are invalid. Once all the Candidate Paths of an SR Policy have become invalid, then the SR Policy checks whether any of the Candidate Paths have Drop-Upon-Invalid enabled. If so, the SR Policy enters the drop state and "activates" the highest preference Candidate Path that has the Drop-Upon-Invalid enabled. Note that only one Candidate Path needs to be reported to the PCE with the Dropping (D) flag set.
Updates to RFC 8231 allows delegation of an LSP in operationally down state, but at the same time mandates the use of PCReq before sending PCRpt. This document updates , by making that section of not applicable to SR Policy LSPs. Thus, when a PCC wants to delegate an SR Policy LSP, it MAY proceed directly to sending PCRpt, without first sending PCReq and waiting for PCRep. This has the advantage of reducing the number of PCEP messages and simplifying the implementation. Furthermore, a PCEP speaker is not required to support PCReq/PCRep at all for SR Policies. The PCEP speaker can indicate support for PCReq/PCRep via the L-flag in the SRPOLICY-CAPABILITY TLV (see ). When this flag is cleared, or when the SRPOLICY-CAPABILITY TLV is absent, the given peer MUST NOT be sent PCReq/PCRep messages for SR Policy LSPs. Conversely, when this flag is set, the peer can receive and process PCReq/PCRep messages for SR Policy LSPs. The above applies only to SR Policy LSPs and does not affect other LSP types, such as RSVP-TE LSPs. For other LSP types, continues to apply.
IANA Considerations IANA maintains the "Path Computation Element Protocol (PCEP) Numbers" registry at .
Association Type This document defines a new Association Type: SR Policy Association. IANA has made the following assignment in the "ASSOCIATION Type Field" registry within the "Path Computation Element Protocol (PCEP) Numbers" registry group:
TypeNameReference
6SR Policy AssociationRFC 9862
PCEP TLV Type Indicators This document defines eight new TLVs for carrying additional information about SR Policy and SR Policy Candidate Paths. IANA has made the following assignments in the existing "PCEP TLV Type Indicators" registry:
Value Description Reference
56 SRPOLICY-POL-NAME RFC 9862
57 SRPOLICY-CPATH-ID RFC 9862
58 SRPOLICY-CPATH-NAME RFC 9862
59 SRPOLICY-CPATH-PREFERENCE RFC 9862
68 COMPUTATION-PRIORITY RFC 9862
69 EXPLICIT-NULL-LABEL-POLICY RFC 9862
70 INVALIDATION RFC 9862
71 SRPOLICY-CAPABILITY RFC 9862
PCEP Errors This document defines the following:
  • one new Error-value within the "Mandatory Object Missing" Error-Type,
  • one new Error-value within the "Reception of an invalid object", and
  • two new Error-values within the "Association Error" Error-Type.
IANA has made the following assignments in the "PCEP-ERROR Object Error Types and Values" registry of the "Path Computation Element Protocol (PCEP) Numbers" registry group.
Error-Type Meaning Error-value Reference
6 Mandatory Object Missing
21: Missing SR Policy Mandatory TLV RFC 9862
22: Missing SR Policy Association RFC 9862
10 Reception of an invalid object
44: Missing SRPOLICY-CAPABILITY TLV RFC 9862
26 Association Error
20: SR Policy Identifiers Mismatch RFC 9862
21: SR Policy Candidate Path Identifier Mismatch RFC 9862
TE-PATH-BINDING TLV Flag Field A draft version of this document added a new bit in the "TE-PATH-BINDING TLV Flag Field" registry of the "Path Computation Element Protocol (PCEP) Numbers" registry group, which was early allocated by IANA. IANA has marked the bit position as deprecated.
BitDescriptionReference
1Deprecated (Specified-BSID-only)RFC 9862
SR Policy Invalidation Operational State IANA has created and now maintains a new registry under the "Path Computation Element Protocol (PCEP) Numbers" registry group. The new registry is called "SR Policy Invalidation Operational Flags". New values are to be assigned by "IETF Review" . Each bit will be tracked with the following qualities:
  • Bit (counting from bit 0 as the most significant bit)
  • Description
  • Reference
BitDescriptionReference
0 - 6Unassigned
7D: Dropping - the LSP is actively dropping traffic as a result of Drop-Upon-Invalid behavior being activated.RFC 9862
SR Policy Invalidation Configuration State IANA has created and now maintains a new registry under the "Path Computation Element Protocol (PCEP) Numbers" registry group. The new registry is called "SR Policy Invalidation Configuration Flags". New values are to be assigned by "IETF Review" . Each bit will be tracked with the following qualities:
  • Bit (counting from bit 0 as the most significant bit)
  • Description
  • Reference
BitDescriptionReference
0 - 6Unassigned
7D: Drop enabled - the Candidate Path has Drop-Upon-Invalid feature enabled.RFC 9862
SR Policy Capability TLV Flag Field IANA has created and now maintains a new registry under the "Path Computation Element Protocol (PCEP) Numbers" registry group. The new registry is called "SR Policy Capability TLV Flag Field". New values are to be assigned by "IETF Review" . Each bit will be tracked with the following qualities:
  • Bit (counting from bit 0 as the most significant bit)
  • Description
  • Reference
BitDescriptionReference
0 - 26UnassignedRFC 9862
27Stateless Operation (L-flag)RFC 9862
28UnassignedRFC 9862
29Invalidation (I-flag)RFC 9862
30Explicit NULL Label Policy (E-flag)RFC 9862
31Computation Priority (P-flag)RFC 9862
Security Considerations The information carried in the newly defined SRPA object and TLVs could provide an eavesdropper with additional information about the SR Policy. The security considerations described in , , , , , , and are applicable to this specification. As per , it is RECOMMENDED that these PCEP extensions can only be activated on authenticated and encrypted sessions across PCEs and PCCs belonging to the same administrative authority, using Transport Layer Security (TLS) as per the recommendations and best current practices in .
Manageability Considerations All manageability requirements and considerations listed in , , , , and apply to PCEP protocol extensions defined in this document. In addition, requirements and considerations listed in this section apply.
Control of Function and Policy A PCE or PCC implementation MAY allow the capabilities specified in and the capability for support of an SRPA advertised in the ASSOC-Type-List TLV to be enabled and disabled.
Information and Data Models defines a YANG module with common building blocks for PCEP extensions described in of this document.
Liveness Detection and Monitoring Mechanisms defined in this document do not imply any new liveness detection and monitoring requirements in addition to those already listed in , , and .
Verify Correct Operations Operation verification requirements already listed in , , , , and are applicable to mechanisms defined in this document. An implementation MUST allow the operator to view SR Policy Identifier and SR Policy Candidate Path Identifier advertised in an SRPA object. An implementation SHOULD allow the operator to view the capabilities defined in this document advertised by each PCEP peer. An implementation SHOULD allow the operator to view LSPs associated with a specific SR Policy Identifier.
Requirements on Other Protocols The PCEP extensions defined in this document do not imply any new requirements on other protocols.
Impact on Network Operations The mechanisms defined in , , , and also apply to the PCEP extensions defined in this document.
References Normative References Informative References Advertisement of Segment Routing Policies Using BGP - Link State Individual Cisco Systems Huawei Technologies RtBrick Inc. Nvidia
Acknowledgements We would like to thank , , , , , , , , , , , , , , , , , , , , and for their reviews and suggestions.
Contributors Huawei
India dhruv.ietf@gmail.com
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd. Beijing10095 China chengli13@huawei.com
Cisco Systems, Inc
zali@cisco.com
Cisco Systems, Inc.
2000 Innovation Dr. KanataOntario Canada rmelarco@cisco.com