Network Working Group Xuerong Wang Internet-Draft ZTE Corporation Intended status: Informational Jan 13, 2011 Expires: July 17, 2011 Extensions of Backward-Recursive PCE-Based Computation (BRPC) to Support Inter-Autonomous System (AS) Bidirectional LSP Path Computation draft-wang-pce-inter-as-extentions-00.txt Abstract This document provides extensions for the Backward-Recursive PCE- Based Computation (BRPC) to support bidirectional LSP path computation. 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 http://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." This Internet-Draft will expire on July 17, 2011. Copyright Notice Copyright (c) 2011 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 (http://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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Xuerong Wang Expires July 17, 2011 [Page 1] Internet-Draft BRPC Ext. for Inter-AS Bidir. LSP Jan 2011 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Conventions used in this document . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Problem statement . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Inter-AS TE link . . . . . . . . . . . . . . . . . . . . . 4 3.2. Backward Recursive Path Computation . . . . . . . . . . . 5 4. Solutions of Inter-AS bidirectional path computation . . . . . 6 4.1. Extensions of Backward-Recursive PCE-Based Computation (BRPC) . . . . . . . . . . . . . . . . . . . . . . . . . . 7 4.2. Extensions of PCEP . . . . . . . . . . . . . . . . . . . . 8 4.2.1. IVSPT flag . . . . . . . . . . . . . . . . . . . . . . 8 4.2.2. BRPC Procedure Completion Failure . . . . . . . . . . 9 4.2.3. Inter-AS TE links carried in PCEP message . . . . . . 10 4.2.3.1. Inter-AS Virtual Shortest Path Tree object (IVSPT) . . . . . . . . . . . . . . . . . . . . . 10 4.2.3.2. Extend VSPT to include Inter-AS links . . . . . . 14 5. Security Considerations . . . . . . . . . . . . . . . . . . . 16 6. IANA considerations . . . . . . . . . . . . . . . . . . . . . 16 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 8.1. Normative References . . . . . . . . . . . . . . . . . . . 16 8.2. Informative References . . . . . . . . . . . . . . . . . . 17 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 17 Xuerong Wang Expires July 17, 2011 [Page 2] Internet-Draft BRPC Ext. for Inter-AS Bidir. LSP Jan 2011 1. Introduction Requirements for establishing Multiprotocol Label Switching Traffic Engineering (MPLS-TE) Label Switched Paths (LSPs) that cross multiple Autonomous Systems (ASes) are described in [RFC4216]. As described in [RFC4216], a method SHOULD provide the ability to compute a path spanning multiple ASes. So a path computation entity that may be the head-end Label Switching Router (LSR), an AS Border Router (ASBR), or a Path Computation Element [PCE] needs to know the TE information not only of the links within an AS, but also of the links that connect to other ASes. As described in [RFC5392], two new LSAs are defined to advertise inter-AS TE information for OSPFv2 and OSPFv3 separately, and three new sub-TLVs are added to the existing Link TLV to carry the information about the neighboring AS and the remote ASBR. [RFC5316] defines similar extensions for [ISIS]. In order for bidirectional path computation, PCE needs to get bidirectional Inter-AS TE link information. [RFC5392] introduces a "proxy" for the ASBR at the edge of the other AS and generate a bidirectional TE link. This document extends BRPC in order to support the bidirectional path computation within single procedure. Based on the mechanism in this document, we don't need to introduce the 'proxy'. It shows how the Backward-Recursive PCE-Based Computation (BRPC) - procedures for Inter-AS TE Links can be extended in order for deriving the optimum end-to-end bidirectional path. This document does not propose or define any mechanisms to advertise any other extra-AS TE information within IGP. 1.1. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 2. Terminology o ASBR: Autonomous System Border Router. Router used to connect together ASes of the same or different service providers via one or more inter-AS links. o Boundary Node (BN): a boundary node is either an ABR in the context of inter-area Traffic Engineering or an ASBR in the Xuerong Wang Expires July 17, 2011 [Page 3] Internet-Draft BRPC Ext. for Inter-AS Bidir. LSP Jan 2011 context of inter-AS Traffic Engineering. o Entry BN of domain(n): a BN connecting domain(n-1) to domain(n) along a determined sequence of domains. o Exit BN of domain(n): a BN connecting domain(n) to domain(n+1) along a determined sequence of domains. o PCC: Path Computation Client. Any client application requesting a path computation to be performed by a Path Computation Element. o PCE: Path Computation Element. An entity (component, application, or network node) that is capable of computing a network path or route based on a network graph and applying computational constraints. o PCE(i) is a PCE with the scope of domain(i).d o TED: Traffic Engineering Database. o VSPT: Virtual Shortest Path Tree. o IVSPT: Inter-AS Virtual Shortest Path Tree. 3. Problem statement 3.1. Inter-AS TE link As mentioned in [RFC5392] and [RFC5316], Hellos MUST NOT be exchanged over the Inter-AS TE link, and consequently, an IGP adjacency MUST NOT be formed. In the current operation of TE IGP, the LSRs at each end of a TE link emit LSAs describing the link. The databases in the LSRs then have two entries (one locally generated, the other from the peer) that describe the different 'directions' of the link. This enables Constrained Shortest Path First (CSPF) to do a two-way check on the link when performing path computation and eliminate it from consideration unless both directions of the link satisfy the required constraints. In the case we are considering here (i.e., of a TE link to another AS), there is, by definition, no IGP peering and hence no bidirectional TE link information. The information advertised comes from the ASBR's knowledge of the unidirectional TE capabilities of the link, the ASBR's knowledge of Xuerong Wang Expires July 17, 2011 [Page 4] Internet-Draft BRPC Ext. for Inter-AS Bidir. LSP Jan 2011 the unidirectional current status and usage of the link, and configuration at the ASBR of the remote AS number and remote ASBR TE Router ID. For other properties, e.g., bandwidth and metrics, an ASBR is difficult or impossible to get the latest value of these properties about reverse directional of Inter-AS TE links timely. In order for the CSPF route computation entity to include the link as a candidate path, we have to find a way to solve this problem. 3.2. Backward Recursive Path Computation The Backward Recursive Path Computation (BRPC) [RFC5441] procedure involves cooperation and communication between PCEs in order to compute an optimal end-to-end path across multiple domains. In particular, the PCC sends a PCReq to a PCE in its domain. The request is forwarded between PCEs, domain-by-domain, until the PCE responsible for the domain containing the LSP destination is reached. The PCE in the destination domain creates a tree of potential paths to the destination (the Virtual Shortest Path Tree - VSPT) and passes this back to the previous PCE in a PCRep. Each PCE in turn adds to the VSPT and passes it back until the PCE in the source domain uses the VSPT to select an end-to-end path that the PCE sends to the PCC. VSPT(i) defined in [RFC5441]: In each domain i: o There is a set of X-en(i) entry BNs noted BN-en(k,i) where BN- en(k,i) is the kth entry BN of domain(i). o There is a set of X-ex(i) exit BNs noted BN-ex(k,i) where BN- ex(k,i) is the kth exit BN of domain(i). VSPT(i): MP2P (multipoint-to-point) tree returned by PCE(i) to PCE(i-1): Root (TE LSP destination) / | \ BN-en(1,i) BN-en(2,i) ... BN-en(j,i). where [X-en(i)] is the number of entry BNs in domain i and j<= [X-en(i)] Figure 1: MP2P VSPT Tree in RFC5441 Xuerong Wang Expires July 17, 2011 [Page 5] Internet-Draft BRPC Ext. for Inter-AS Bidir. LSP Jan 2011 Each link of tree VSPT(i) represents the shortest constrained path between BN-en(j,i) and the TE LSP destination that satisfies the set of required constraints for the TE LSP (bandwidth, affinities, etc.). Note that PCE(i) only considers the entry BNs of domain(i), i.e., only the BNs that provide connectivity from domain(i-1). In other words, the set BN-en(k,i) is only made of those BNs that provide connectivity from domain (i-1) to domain(i). Furthermore, some BNs may be excluded according to policy constraints (either due to local policy or policies signaled in the path computation request). BRPC procedure defined in [RFC5441]: Step 1: First, the PCC needs to determine the PCE capable of serving its path computation request (this can be done with local configuration or via IGP discovery (see [RFC5088] and [RFC5089])). The path computation request is then relayed until reaching a PCE(n) such that the TE LSP destination resides in the domain(n). Step 2: PCE(n) computes VSPT(n), the tree made of the list of shortest constrained paths between every BN-en(j,n) and the TE LSP destination using a suitable path computation algorithm (e.g., CSPF) and returns the computed VSPT(n) to PCE(n-1). Step i: For i=n-1 to 2: PCE(i) computes VSPT(i), the tree made of the shortest constrained paths between each BN-en(j,i) and the TE LSP destination. It does this by considering its own TED and the information in VSPT(i+1). Step n: Finally, PCE(1) computes the end-to-end shortest constrained path In the case of inter-domain LSP computation, PCE(i)(i=n-1 to 2) also requires adding the inter-AS TE links that connect the domain(i) and the domain(i+1). So the BRPC procedure requires the knowledge of the traffic engineering attributes of the bidirectional inter-domain TE links at step i. 4. Solutions of Inter-AS bidirectional path computation When multiple PCEs cooperate each other to compute a bidirectional Inter-AS LSP by using BRPC, PCE(i+1) selects some proper Inter-AS TE links including traffic engineering capabilities, current status and usage whose direction is from AS(i+1) to AS(i). These Inter-AS TE links satisfy the required set of unidirectional TE constraints, So PCE(i+1) sends PCRep message to PCE(i) including the selected unidirectional Inter-AS TE links. The bidirectional Inter-AS TE Xuerong Wang Expires July 17, 2011 [Page 6] Internet-Draft BRPC Ext. for Inter-AS Bidir. LSP Jan 2011 links that satisfy the constraints can then be derived by PCE(i). 4.1. Extensions of Backward-Recursive PCE-Based Computation (BRPC) In order to solve the problem about Inter-AS TE links described in previous section, the extension of BRPC procedure for bidirectional Inter-AS TE LSP is described as follows: o After computing the shortest constrained paths(i.e., VSPT) between every entry BN and the TE LSP destination, PCE(i+1) selects the Inter-AS TE links from AS(i+1) to AS(i) that satisfy the constraints and passes them back to the PCE(i) in a PCRep. o Then, the PCE(i) should choose among the Inter-AS TE links carried in received PCRep message that satisfy the constraints in the reverse direction ,and compute the shortest constrained paths between every exit BN and the TE LSP destination. Following is the extended BRPC procedure: o Step 1: First, the PCC needs to determine the PCE capable of serving its path computation request (this can be done with local configuration or via IGP discovery (see [RFC5088] and [RFC5089])). The path computation request is then relayed until reaching a PCE(n) such that the TE LSP destination resides in the domain(n). This step is the same as described in [RFC5441]. o Step 2: 2.1. PCE(n) computes the list of shortest constrained paths between every BN-en(j,n) and the TE LSP destination; 2.2. PCE(n) selects the Inter-AS TE links that satisfy the constraints from all of the Inter-AS TE links that provide connectivity from domain (n) to domain(n-1); 2.3. PCE(n) returns PCRep (including result of 2.1 and 2.2) to PCE(n-1). Note that for unidirectional LSP computation, step 2.2 may not be performed. o Step i: For i=n-1 to 2: { Xuerong Wang Expires July 17, 2011 [Page 7] Internet-Draft BRPC Ext. for Inter-AS Bidir. LSP Jan 2011 i.1. With the Inter-AS TE links returned from PCE(i+1), PCE(i) chooses the links that satisfy the constraints in the reverse direction(i.e., the selected Inter-AS TE links satisfy the required constraints in both of the directions.) i.2. PCE(i) computes the shortest constrained paths between each BN-ex(j,i) and the TE LSP destination; i.3. PCE(i) computes the shortest constrained paths between each BN-en(j,i) and the TE LSP destination; i.4. PCE(i) selects the Inter-AS TE links that unidirectionally satisfy the constraints from all of the Inter-AS TE links that provide connectivity from domain (i) to domain(i-1); i.5. PCE(i) returns PCRep (including result of i.3 and i.4) to PCE(i-1). } Note that for unidirectional LSP computation, step i.1, i.2 and i.4 may not be performed. o Step n: n.1. With the Inter-AS TE links returned from PCE(2), PCE(1) chooses the links that satisfy the constraints in the reverse direction (i.e., the selected Inter-AS TE links satisfy the required constraints in both of the directions.); n.2. PCE(1) computes the shortest constrained paths between each BN-ex(j,1) and the TE LSP destination; n.3. Finally, PCE(1) computes the end-to-end shortest constrained path. Note that for unidirectional LSP computation, step n.1.and n.2. may not be performed. Note that uni-direction represents the direction from entry BNs of local domain i to exit BNs of domain i-1, the reverse direction represents the direction from exit BNs of local domain i to entry BNs of domain i+1. 4.2. Extensions of PCEP 4.2.1. IVSPT flag PCEP needs to be introduced a new flag in RP object carried within the PCReq message (defined in [RFC5440]). The PCE(i) set this flag Xuerong Wang Expires July 17, 2011 [Page 8] Internet-Draft BRPC Ext. for Inter-AS Bidir. LSP Jan 2011 in PCReq to indicates that the Inter-AS TE links from AS(i+1) to AS(i) satisfying the constraints must be return. In other words, the PCE(i) requests the computation of an inter-domain TE LSP using the new BRPC procedure defined in this document. The IVSPT Flag set in PCRep to indicates that requested PCE support the new enhanced BRPC procedure, and Inter-AS TE links from AS(i+1) to AS(i) satisfying the constraints have been included in PCRep. The following new flag of the RP object is defined: IVSPT Flag Bit Number Name Flag ------- ------ TBD IVSPT 4.2.2. BRPC Procedure Completion Failure If PCE(i) send IVSPT flag to PCE(i+1) who doesn't recognizes the IVSPT flag of RP object, PCE(i+1) MUST generate PCErr message with an Error-Type=4 (Not supported object), Error-value=4 (Unsupported parameter). The PCE may include the parent object (RP object) up to and including (but no further than) the unknown or unsupported parameter. In this case where the unknown or unsupported parameter is a bit flag (IVSPT flag), the included RP object should contain the whole bit flag field with all bits after the parameter at issue set to zero. The corresponding path computation request is then cancelled by the PCE without further notification. If PCE(i) send IVSPT flag to PCE(i+1) who recognizes IVSPT flag of RP object but does not support the new BRPC procedure extended in this document, it MUST return a PCErr message to the upstream PCE with an Error-Type " Enhanced BRPC procedure unsupported". The PCErr message MUST be relayed to the requesting PCC. PCEP-ERROR objects are used to report a PCEP protocol error and are characterized by an Error-Type that specifies the type of error and an Error-value that provides additional information about the error type. Both the Error-Type and the Error-value are managed by IANA. A new Error-Type is defined that relates to the BRPC procedure. Xuerong Wang Expires July 17, 2011 [Page 9] Internet-Draft BRPC Ext. for Inter-AS Bidir. LSP Jan 2011 Error-Type Meaning -------- ------- TBD Enhanced BRPC procedure unsupported Error-value 1 Enhanced BRPC procedure not supported by one or more PCEs along the domain path 4.2.3. Inter-AS TE links carried in PCEP message For the enhanced bidirectional Inter-AS TE LSP BRPC procedure referenced in this document, PCE(n) should select the unidirectional Inter-AS TE links that satisfy the constraints from all of the Inter-AS TE links that provide connectivity from domain (n) to domain(n-1),and then PCE(n) should return the selected Inter-AS TE links in PCRep message. Two methods of carrying Inter-AS TE links in PCRep are introduced in this document. One is to introduce a new object (Inter-AS Virtual Shortest Path Tree -IVSPT) to carry Inter-AS TE links separately(see 4.2.3.1.). The other is to extend VSPT to include Inter-AS TE links(see 4.2.3.2.). 4.2.3.1. Inter-AS Virtual Shortest Path Tree object (IVSPT) 4.2.3.1.1. Definition of IVSPT(i) Mode of BRPC Operation is introduced in [RFC 5441]: Definition of VSPT(i) In each domain i: o Step 1: There is a set of X-en(i) entry BNs noted BN-en(k,i) where BN-en(k,i) is the kth entry BN of domain(i). o There is a set of X-ex(i) exit BNs noted BN-ex(k,i) where BN- ex(k,i) is the kth exit BN of domain(i). VSPT(i): MP2P (multipoint-to-point) tree returned by PCE(i) to PCE(i-1): Xuerong Wang Expires July 17, 2011 [Page 10] Internet-Draft BRPC Ext. for Inter-AS Bidir. LSP Jan 2011 Root (TE LSP destination) / | \ BN-en(1,i) BN-en(2,i) ... BN-en(j,i). where [X-en(i)] is the number of entry BNs in domain i and j<= [X-en(i)] Figure 2: MP2P VSPT Each link of tree VSPT(i) represents the shortest constrained path between BN-en(j,i) and the TE LSP destination that satisfies the set of required constraints for the TE LSP (bandwidth, affinities, etc.).These are path segments to reach the TE LSP destination from BN-en(j,i). Note that PCE(i) only considers the entry BNs of domain(i), i.e., only the BNs that provide connectivity from domain(i-1). Besides VSPT, this document defines Inter-AS Virtual Shortest Path Tree (IVSPT) used for describing unidirectional Inter-AS paths whose direction is from AS(i) to AS(i-1). Definition of IVSPT(j,i) : IVSPT(j,i): jth MP2P (multipoint-to-point) tree returned by PCE(i) to PCE(i-1) Xuerong Wang Expires July 17, 2011 [Page 11] Internet-Draft BRPC Ext. for Inter-AS Bidir. LSP Jan 2011 IVSPT(1,i): BN-en(1,i) / | \ BN-ex(1,i-1) BN-ex(2,i-1) ... BN-ex(k1,i-1). IVSPT(2,i): BN-en(2,i) / | \ BN-ex(1,i-1) BN-ex(2,i-1) ... BN-ex(k2,i-1). IVSPT(j,i): BN-en(j,i) / | \ BN-ex(1,i-1) BN-ex(2,i-1) ... BN-ex(kj,i-1). where [X-en(i)] is the number of entry BNs in domain i and j<= [X-en(i)], [Y-ex(i-1)] is the number of exit BNs in domain i-1 and k1,k2,...,kj<= [X-ex(i-1)] Figure 3: IVSPT IVSPT(j,i) represents the Inter-AS paths from BN-en(j,i) of domain i to exit BNs of domain i-1 that satisfies the set of required constraints for the TE LSP (bandwidth, affinities, etc.). 4.2.3.1.2. Constrain Route Object(CRO) The CRO is used to encode the Inter-AS paths that satisfies the set of required constraints for the TE LSP. The CRO is carried within a PCRep message to provide the selected Inter-AS links if the path computation was successful. The contents of this object are identical to the contents of the RSVP-TE ERO defined in [RFC3209], [RFC3473], and [RFC3477]. That is, the object is constructed from a series of sub-objects. Any RSVP-TE ERO sub-object already defined or that could be defined in the future for use in the RSVP-TE ERO is acceptable in this object. Xuerong Wang Expires July 17, 2011 [Page 12] Internet-Draft BRPC Ext. for Inter-AS Bidir. LSP Jan 2011 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | // (Sub-objects) // | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Sub-objects: Type Sub-object 1 IPv4 prefix 2 IPv6 prefix 4 Unnumbered Interface ID Figure 4: Format of CRO The format of the PCRep message is updated as follows : ::= where: ::=[] ::= [] [] [] ::=[][] ::= where: ::=[] [] [] [] ::=[] ::=< CRO >[< CRO -list>] Xuerong Wang Expires July 17, 2011 [Page 13] Internet-Draft BRPC Ext. for Inter-AS Bidir. LSP Jan 2011 4.2.3.1.3. IVSPT Encoding The IVSPT is returned within a PCRep message. The encoding consists of a non-ordered list of Constrain Route Objects (CROs) where each CRO represents an Inter-AS link that satisfy the required constraint from domain i to domain i+1. Example: R1------R3----R5-----R7------R9-----R11---- R13 | \ | \ | / | / | \ | \ | ---- | ---------- | \ | \ | / | / R2------R4----R6-----R8------R10----R12 : : <-- AS1 -->:<---- AS2 --->:<------- AS3 ---------> Figure 5: An Example of Inter-AS path computation In the example shown in Figure 5, if we make the assumption that a constrained path exists between each ABR and the destination R13, the VSPT computed by a PCE(3) serving AS 3 consists of the following non- ordered set of EROs: o ERO1: R9(TE Router ID)-R11(Interface IP address)-R13(TE Router ID) o ERO2: R10(TE Router ID)-R13(TE Router ID) If we make the assumption that Inter-AS links R9-->R7 ,R9-->R8 and R10-->R8 satisfy the required constraints, the IVSPT selected by a PCE(3) serving AS 3 consists of the following non-ordered set of CROs: o CRO1: R9(Interface IP address),R7(TE Router ID) o CRO2: R9(Interface IP address),R8(TE Router ID) o CRO3: R10(Interface IP address),R8(TE Router ID) 4.2.3.2. Extend VSPT to include Inter-AS links 4.2.3.2.1. New definition of VSPT(i) In each domain i: o There is a set of X-en(i) entry BNs noted BN-en(k,i) where BN- en(k,i) is the kth entry BN of domain(i). Xuerong Wang Expires July 17, 2011 [Page 14] Internet-Draft BRPC Ext. for Inter-AS Bidir. LSP Jan 2011 o There is a set of X-ex(i) exit BNs noted BN-ex(k,i) where BN- ex(k,i) is the kth exit BN of domain(i). For the bidirectional LSP computation, VSPT(i) may be extended as follows: Root(TE LSP destination) / | | \ / | ... | \ BN-en(1,i)...BN-en(1,i)... BN-en(j,i)...BN-en(j,i) | | | | BN-ex(1,i-1)...BN-ex(k1,i-1) BN-ex(1,i-1)...BN-ex(kj,i-1) where: [X-en(i)] is the number of entry BNs in domain i and j<= [X-en(i)]; [Y-ex(i-1)] is the number of exit BNs in domain i-1, kj is the number of exit BNs in domain i-1 that connect BN-en(j,i)(i.e., the jth entry BN in domain i), and k1,k2,...,kj <= [Y-ex(i-1)] Figure 6: IVSPT IVSPT(i) includes links that represent the shortest constrained path between BN-en(j,i) and the TE LSP destination ，and Inter-AS links that satisfie the set of required constraints for the TE LSP (bandwidth, affinities, etc.) from AS(i) to AS(i+1). These are path segments to reach the TE LSP destination from BN-ex(j,i-1). 4.2.3.2.2. VSPT Encoding In the example shown in Figure 5, if we make the assumption that a constrained path exists between each ABR and the destination R13(i.e.,R9-R11-R13 and R10-R13), and Inter-AS links R9-->R7 ,R9-->R8 and R10-->R8 satisfy the required constraints, the VSPT computed for the bidirectional LSP by a PCE(3) serving AS 3 consists of the following non-ordered set of EROs: o ERO1: R7(TE Router ID)-R9(Interface IP address)-R11(Interface IP address)-R13(TE Router ID) o ERO2: R8(TE Router ID)-R9(Interface IP address)-R11(Interface IP address)-R13(TE Router ID) o ERO3: R8(TE Router ID)-R10(Interface IP address)-R13(TE Router ID) For the unidirectional LSP computation , VSPT is the same as defined Xuerong Wang Expires July 17, 2011 [Page 15] Internet-Draft BRPC Ext. for Inter-AS Bidir. LSP Jan 2011 in [RFC5441]. 5. Security Considerations TBD. 6. IANA considerations TBD. 7. Acknowledgments TBD. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation Element (PCE)-Based Architecture", RFC 4655, August 2006. [RFC4726] Farrel, A., Vasseur, J., and A. Ayyangar, "A Framework for Inter-Domain Multiprotocol Label Switching Traffic Engineering", RFC 4726, November 2006. [RFC4875] Aggarwal, R., Papadimitriou, D., and S. Yasukawa, "Extensions to Resource Reservation Protocol - Traffic Engineering (RSVP-TE) for Point-to-Multipoint TE Label Switched Paths (LSPs)", RFC 4875, May 2007. [RFC5088] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang, "OSPF Protocol Extensions for Path Computation Element (PCE) Discovery", RFC 5088, January 2008. [RFC5089] Le Roux, JL., Vasseur, JP., Ikejiri, Y., and R. Zhang, "IS-IS Protocol Extensions for Path Computation Element (PCE) Discovery", RFC 5089, January 2008. [RFC5152] Vasseur, JP., Ayyangar, A., and R. Zhang, "A Per-Domain Path Computation Method for Establishing Inter-Domain Traffic Engineering (TE) Label Switched Paths (LSPs)", Xuerong Wang Expires July 17, 2011 [Page 16] Internet-Draft BRPC Ext. for Inter-AS Bidir. LSP Jan 2011 RFC 5152, February 2008. [RFC5316] Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in Support of Inter-Autonomous System (AS) MPLS and GMPLS Traffic Engineering", RFC 5316, December 2008. [RFC5376] Bitar, N., Zhang, R., and K. Kumaki, "Inter-AS Requirements for the Path Computation Element Communication Protocol (PCECP)", RFC 5376, November 2008. [RFC5392] Chen, M., Zhang, R., and X. Duan, "OSPF Extensions in Support of Inter-Autonomous System (AS) MPLS and GMPLS Traffic Engineering", RFC 5392, January 2009. [RFC5394] Bryskin, I., Papadimitriou, D., Berger, L., and J. Ash, "Policy-Enabled Path Computation Framework", RFC 5394, December 2008. [RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, March 2009. [RFC5441] Vasseur, JP., Zhang, R., Bitar, N., and JL. Le Roux, "A Backward-Recursive PCE-Based Computation (BRPC) Procedure to Compute Shortest Constrained Inter-Domain Traffic Engineering Label Switched Paths", RFC 5441, April 2009. 8.2. Informative References [H-PCE] D. King, "The Application of the Path Computation Element Architecture to the Determination of a Sequence of Domains in MPLS & GMPLS", draft-king-pce-hierarchy-fwk-03.txt . Author's Address Xuerong Wang ZTE Corporation 6F, R&D Building 3, ZTE Industrial Park, XiLi LiuXian Road, Nanshan District, Shenzhen 518055 P.R.China Phone: +86 755 26773609 Email: wang.xuerong@zte.com.cn URI: http://www.zte.com.cn/ Xuerong Wang Expires July 17, 2011 [Page 17]