]> Cisco Systems, Inc.

2000 Innovation Drive Kanata Ontario K2K 3E8 Canada mkoldych@cisco.com

Ciena Corporation

385 Terry Fox Dr. Kanata Ontario K2K 0L1 Canada ssivabal@ciena.com

Juniper Networks, Inc.

cbarth@juniper.net

Huawei Technologies

Huawei Campus, No. 156 Beiqing Rd. Beijing 100095 China pengshuping@huawei.com

Nokia

hooman.bidgoli@nokia.com

PCE Working Group A Segment Routing (SR) Policy () is a non-empty set of SR Candidate Paths, that all share the same <headend, color, endpoint> tuple. This document extends 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 . The mechanism is applicable to all data planes of SR (MPLS, SRv6, etc.). 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.

Segment Routing Policy for Traffic Engineering details the concepts of SR Policy and approaches to steering traffic into an SR Policy. PCEP Extensions for Segment Routing specifies extensions to the Path Computation Element Protocol (PCEP) that allow a stateful PCE to compute and initiate Traffic Engineering (TE) paths, as well as a PCC to request a path subject to certain constraint(s) and optimization criteria in SR networks. PCEP Extensions for Establishing Relationships Between Sets of LSPs 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 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.

The following terminologies are used in this document: The IPv4 or IPv6 endpoint address of the SR Policy in question, as described in . SR Policy Association. PCEP ASSOCATION that describes the SR 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. As described in , 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. As described in , the ASSOCIATION object could also include other TLVs based on the association types, that provides non-key information.

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 . 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 , 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.

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.

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.

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.

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 .

Two ASSOCIATION object types for IPv4 and IPv6 are defined in . 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.

As per , 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 ) 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. The Association Source MUST be set to the headend value of the SR Policy, as defined in 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:

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". 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.

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".

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.

Type: 56 for "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. SR Policy Name: SR Policy name, as defined in . It SHOULD be a string of printable ASCII characters, without a NULL terminator.

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.

Type: 57 for "SRPOLICY-CPATH-ID" TLV. Length: 28. Protocol Origin: 8-bit value that encodes the protocol origin, as specified in 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 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 Section 2.4. Discriminator: 32-bit value that encodes the Discriminator of the Candidate Path.

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.

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 . It SHOULD be a string of printable ASCII characters, without a NULL terminator.

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.

Type: 59 for "SRPOLICY-CPATH-PREFERENCE" TLV. Length: 4. Preference: Numerical preference of the Candidate Path, as specified in Section 2.7 of . If the TLV is missing, a default Preference value of 100 is used, as specified in Section 2.7 of .

This section describes various mechanisms that are standardized for SR Policies in , but are equally applicable to other tunnel types, such as RSVP-TE tunnels. Hence this section does not make use of the SRPA.

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 . If the TLV is absent from the LSP object, a default Priority value of 128 is used.

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.

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 .

Type: TBD2 for "ENLP" TLV. Length: 4. ENLP (Explicit NULL Label Policy): same values as in Section 2.4.5 of .

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 . 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.

G: Generic - does not fit into any other categories below. P: Path computation failure - no path was computed for the LSP. F: First-hop resolution failure - head-end first hop resolution has failed. V: Verification failure - OAM/PM/BFD path verification has indicated a breakage.

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.

Specified-BSID-only functionality is defined in Section 6.2.3 of . 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. 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.

defines <intended-path> and <actual-path>, consisting of the ERO and RRO objects, respectively. defines SR-ERO and SR-RRO sub-objects for SR-TE LSPs. 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 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.

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 within the "Path Computation Element Protocol (PCEP) Numbers" registry:

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:

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:

IANA is requested to allocate new bit within the "TE-PATH-BINDING TLV Flag field" sub-registry of the PCEP Numbers registry, as follows:

[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 . 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 , "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".

Organization: Cisco Systems Implementation: IOS-XR PCC and PCE. Description: An experimental code-point is currently used. Maturity Level: Proof of concept. Coverage: Full. Contact: mkoldych@cisco.com

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

This document defines one new type for association, which do not add any new security concerns beyond those discussed in , , , and 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) , as per the recommendations and best current practices in , is RECOMMENDED.

Would like to thank Stephane Litkowski, Boris Khasanov, Praveen Kumar and Tom Petch for review and suggestions.

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