Extensions to PCEP for Hierarchical Path Computation Elements PCE draft-zhang-pcep-hierarchy-extensions-00 Fatai Zhang Quintin Zhao Oscar Gonzalez de Dios Ramon Casellas Daniel King IETF 79 - Beijing

Objective of the document This document defines the PCEP extensions for the purpose of implementing Hierarchical PCE (H-PCE) procedures described in [PCE-HIERARCHY-FWK]. Specifically, the document describes the following new PCEP extensions and procedures to support H-PCE: – Capability Discovery – Domain Connectivity Collection – Objective Functions – RP Objects – Error Handling – Endpoint localization/reachability [PCE-HIERARCHY-FWK] draft-king-pce-hierarchy-fwk-05draft-king-pce-hierarchy-fwk-05 IETF 79 - Beijing

H-PCE Refresher The parent PCE maintains a topology map. – The nodes are the child domains. – The map contains the inter-domain links. – The TE capabilities of the links are also known. The parent PCE knows the identity and location of the child PCEs responsible for the child domains. – Statically configured or dynamically discovered. Responsible child PCE’s will compute: – Source-to-edge (e.g., Domain 1) – Edge-to-edge (e.g., Domain 2) – Edge-destination (e.g., Domain 3) Domain confidentiality. – A parent PCE is aware of the topology and connections between domains, but is not aware of the contents of the domains. – Child domains are completely confidential. IETF 79 - Beijing

Capability Discovery A PCE (child or parent) domain is a single domain with one or more associated PCE. It is possible for a child PCE to be responsible for multiple domains. The PCE (child or parent) domain may be an IGP area or AS. The child PCE and parent PCE relationship will be configured statically. During the PCEP session establishment procedure, the child PCE needs to verify that the parent PCE is capable of H-PCE computations. No further automated discovery is required, or desired. IETF 79 - Beijing

Domain Connectivity Collection A parent PCE can populate its topology map either from static configuration or from information received from each child PCE. There are two types of domain borders for inter-domain connectivity: – Domain border is a TE link, e.g., the inter-AS TE link which connects two ASs. – Domain border is a node, e.g., the IGP ABR which connects two IGP areas. If a child PCE needs to notify the parent PCE of its inter-domain link connectivity, the relevant information is required to be sent to the parent PCE. IETF 79 - Beijing

Objective Functions Deriving the optimal end-to-end domain path sequence is dependent on the policy applied during domain path computation. An Objective Function (OF) [RFC5541], or set of OFs, may be applied to define the policy being applied to the domain path computation. There are three new objective functions which are defined in [PCE-HIERARCHY-FWK]: – Minimize the number of boundary nodes used. – Limit the number of domains crossed. – Disallow domain re-entry. The child PCE can specify which existing, or new, objective function code(s) to use. [PCE-HIERARCHY-FWK] draft-king-pce-hierarchy-fwk-05draft-king-pce-hierarchy-fwk-05 IETF 79 - Beijing

RP Objects Domain Path Request bit – If a child PCE requests the domain sequence for a multi-domain path computation, it can set the Domain Path Request bit in the RP object carried in a request within a PCReq message. The parent PCE which receives the request will attempt to compute a domain sequence. Destination Domain Query bit – If the parent PCE wishes to get the destination domain ID it will use this bit. – Alternative: “CIDR Prefixes announcement” If the domain path computation succeeds, the parent PCE sends a PCRep message, which carries the domain sequence in the ERO to the child PCE. Domain Connectivity Information notification-type – Once the session between the child PCE and parent PCE is established, the following notification can be used to maintain topology and connectivity information. IETF 79 - Beijing

RP Objects (Continued) Inter-domain Link TLV – Each inter-domain link is identified by a combination of its advertised router ID and the link local IP address or link local unnumbered identifier. Inter-domain Node TLV – The Inter-domain Node TLV carries only the two adjacent domain ID and the router (IGP ABR) ID.  Note: a node may belong to 3 or more domains. Alternative: (D1, N), (D2, N), (D3,N)  N Belongs to D1, D2, D3 Domain-ID TLV – This TLV can be carried in a NOTIFICATION or OPEN object to indicate the domain ID of the PCE who sent the PCNtf/Open message. PCE-ID TLV – This TLV can be carried in a NOTIFICATION or OPEN object to indicate the PCE ID of the PCE who sends the PCNtf/Open message. IETF 79 - Beijing

Error Handling PCEP Error-Type 11 – A parent PCE may not be not be configured to accept H-PCE requests from a specific child PCE. IETF 79 - Beijing

Next Steps This is a 00 draft, we would gladly like feedback. All areas remain open for discussion, but especially: – Do we need adjacencies between child PCEs? – Should the child and parent PCE have persistent PCEP session? – The format of PCEP extensions, including PCE-IDs and Domain-IDs (IPv4 and IPv6). – Endpoint location: polling or announcement? – The construction of a TED at the parent PCE. – Additional error cases and procedures. Anyone else implementing? – We are aware of two early implementations. Awaiting WG recharter to include H-PCE work. IETF 79 - Beijing