Network Working Group Qilei Wang Internet-Draft Muliu Tao Intended status: Standards Track Xihua Fu Expires: July 1, 2012 ZTE Corporation Ruiquan Jing Xiaoli Huo China Telecom Dec 29, 2011 LDP Extensions for Pseudo Wire (PW) Transfer in an MPLS-TP Network draft-bao-pwe3-pw-transfer-02.txt Abstract As defined in [RFC5654] MPLS-TP transport path includes LSP and PW. And the possibility of transferring the ownership and control of an existing and in-use path between the management plane and the control plane, without actually affecting data plane traffic being carried over it, is a valuable option for carrier. [RFC5493] and [RFC5852] describe the LSP transfer. This memo gives the requirement and LDP extensions for PW transfer in an MPLS-TP network. 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 1, 2012. 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 Qilei Wang, et al. Expires July 1, 2012 [Page 1] Internet-Draft LDP Extension for PW Transfer Dec 2011 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Comparison with Make-before-Break . . . . . . . . . . . . 3 1.2. Conventions used in this document . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Overview of the PW Transfer . . . . . . . . . . . . . . . . . 4 4. Requirements for PW Transfer . . . . . . . . . . . . . . . . . 5 5. LDP Extension for PW Transfer . . . . . . . . . . . . . . . . 6 5.1. LDP Extension . . . . . . . . . . . . . . . . . . . . . . 6 5.1.1. Support PW Transfer Capability with LDP . . . . . . . 6 5.1.2. PW Ownership Transfer TLV . . . . . . . . . . . . . . 6 5.2. Procedures . . . . . . . . . . . . . . . . . . . . . . . . 7 5.2.1. PW Ownership Transfer from MP to CP . . . . . . . . . 7 5.2.1.1. MP2CP PW Transfer Failure . . . . . . . . . . . . 8 5.2.2. PW Ownership Transfer from CP to MP . . . . . . . . . 9 5.2.2.1. CP2MP PW Transfer Failure . . . . . . . . . . . . 9 6. Security Considerations . . . . . . . . . . . . . . . . . . . 9 7. IANA considerations . . . . . . . . . . . . . . . . . . . . . 9 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10 9.1. Normative References . . . . . . . . . . . . . . . . . . . 10 9.2. Informative References . . . . . . . . . . . . . . . . . . 11 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11 Qilei Wang, et al. Expires July 1, 2012 [Page 2] Internet-Draft LDP Extension for PW Transfer Dec 2011 1. Introduction As defined in [RFC5654], MPLS-TP transport path corresponds to an LSP or a PW which is carried in an LSP. And LSP includes unidirectional LSP, co-routed bidirectional LSP and associated bidirectional LSP, while PW includes Single-Segment Pseudowire (SS-PW) and Multi-Segment Pseudowire (MS-PW). For MPLS-TP LSP, it can be created/deleted via GMPLS signaling, see [RFC3945]. However, the creation/deletion of PW can be completed by LDP, and [RFC4447] gives these procedures of SS-PW while [RFC6073] and [DYNAMIC-MS-PW] decribes the ones of MS-PW. Nowdays, some service providers have deployed MPLS-TP network for mobile backhaul. However, most PWs are statically configured by management plane in the first stage. So if control plane is deployed massively, it is desirable for provider to transfer the control of PWs from the management plane (MP) to control plane (CP) in the future. In addition, the control transfer in the opposite direction, i.e. from CP to MP, should be considered as well if operators want to. Both the requirement 55 in [RFC5654] and requirement 47 in [RFC6373] state that an MPLS-TP control plane MUST provide a mechanism for dynamic ownership transfer of the control of MPLS-TP transport paths from the management plane to the control plane and vice versa. Furthermore, section 5.3.3 of [RFC6373] describes the requirement for PW transfer. Since [RFC5493] and [RFC5852] give the requirements and RSVP-TE extensions and procedures for LSP transfer, this memo considers the procedures and LDP extensions for PW transfer. 1.1. Comparison with Make-before-Break The Make-Before-Break (MBB) technology is an alternative method for PW transfer which has three steps. Firstly, a new PW (has the same parameters with the one to be transferred) will be created; then the PW will be switched from old PW to the new one; and after the PW switching completed successfully the old PW will be deleted. From this process, we can find there're many drawbacks with MBB. The creation and swithing steps of MBB will lead to instant interruption which is acceptable if it can be controlled within 50ms. Furthermore, extra resource is need, in the circumstance that the network is almost saturated, there maybe not enough resource for the new PWs, so MBB will be unavailable. Otherwise, MBB will lead to label modification which will make the bundling relationship between PW and LSP modified at the same time. This will triggre many problems, and a new detection mechanism needs to be defined which may Qilei Wang, et al. Expires July 1, 2012 [Page 3] Internet-Draft LDP Extension for PW Transfer Dec 2011 be very complex. In addition, since control plane is used to create the new PW while management plane is responsible for the deletion of the old PW. Thus batch operation can't be used for this process. If there're a large number PWs needed to be transfered, the operator's time will be engaged by this tedious operation which is inefficiency. However, the PW transfer method described in this document will not affect the data plane, the traffic and it's configuration. So it's preference for PW transfer. 1.2. 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 Transport Path: A network connection as defined in G.805 [ITU.G805.2000]. In an MPLS-TP environment, a transport path corresponds to an LSP or a PW (see RFC5654). o Single-Segment Pseudowire (SS-PW): A PW setup directly between two T-PE devices. Each PW in one direction of a SS-PW traverses one PSN tunnel that connects the two T-PEs. o Multi-Segment Pseudowire (MS-PW): A static or dynamically configured set of two or more contiguous PW segments that behave and function as a single point-to-point PW. Each end of a MS-PW by definition MUST terminate on a T-PE. o PW Segment: A part of a single-segment or multi-segment PW, which traverses one PSN tunnel in each direction between two PE devices, T-PEs and/or S-PEs. o Resource Ownership: A resource used by an MPLS-TP path is said to be 'owned' by the plane that was used to set up the MPLS-TP path through that part of the network. So, a resource owned by the management/control plane means the resource was used to set up the MPLS-TP path through the management/control plane. See RFC5493 for detailed description. 3. Overview of the PW Transfer The PW transfer includes two reverse procedures. One is the MP to CP (MP2CP) transfer procedure, another is the CP to MP (CP2MP) transfer procedure. Qilei Wang, et al. Expires July 1, 2012 [Page 4] Internet-Draft LDP Extension for PW Transfer Dec 2011 For MP2CP transfer procedure, a PW set up and owned by MP needs to be transferred to CP control. To conduct this transfer, the T-LDP session will be created in CP for PW. After this transfer procedure, the resource ownership is transferred from MP to CP. The CP2MP transfer procedure is the reverse one compared to MP2CP procedure. However, since a LDP session may be shared by multi PWs, the T-LDP session may be retained after one PW transferring from CP to MP, if there're still other PWs remain controlled by CP. So, the CP2MP procedure needs to check whether this signaling session should be retained or not. As an requirement listed in [RFC5493], during both MP2CP and CP2MP transfer procedures, if PW is carrying traffic, its control transfer has to be done without any disruption to the data plane traffic. Furthermore, both MP2CP and CP2MP transfer procedures can be conducted in a batch manner, that is, multiple LSPs or PWs can be transferred all at one time. For example, all PWs on a node can be transferred at one time. However, this transfer manner is out of this document. 4. Requirements for PW Transfer [RFC5493] describes the requirements for the conversion between permanent connection (PC) and switched connection (SC) in a GMPLS network. The terminologies "PC" and "SPC" come from ITU-T standard [G.8081], Because associated bidirectional LSP isn't defined in ITU-T standard. So, both PC and SPC can only be considered as unidirectional LSP and co-routed bidirectional LSP. Therefore, these requirements fully apply to unidirectional LSP and co-routed bidirectional LSP in a MPLS-TP network. Although, some requirements defined in [RFC5493] apply to PW, but other new requirements also need to be explored. This section lists the special requirements for PW transfer. 1) PW attributes MUST not be changed The PW attributes, such as bandwith, PWid , PW type, Control Word, VCCV, Interface Parameter, MUST not be changed during and after the PW transfer. 2) PW transfer MUST be independent of LSP The PW transfer SHOULD not depend on whether the LSP (bearing this PW) is controlled by MP or CP. Since PW transfer procedure Qilei Wang, et al. Expires July 1, 2012 [Page 5] Internet-Draft LDP Extension for PW Transfer Dec 2011 will not impact the data plane path, so PW transfer MUST leave LSP alone. The relationship between PW and LSP MUST NOT be changed. 3) Support partial MS-PW segments transfer Since a MS-PW transit multi domains and these domains may belong to different providers. In this scenario, if some providers have deployed control plane while others not, the PW segments in these domains that control plane are deployed SHOULD be allowed to transfer between MP and CP while other PW segments keep their original states. 5. LDP Extension for PW Transfer 5.1. LDP Extension 5.1.1. Support PW Transfer Capability with LDP A new Capability Parameter TLV is defined, the PW Transfer Capability. Following is the format of the PW Transfer Capability Parameter. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1|0|PW Transfer Capability(TBD)| Length (= 1) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |1| Reserved | +-+-+-+-+-+-+-+-+ Figure 1: PW Transfer Capability The PW Transfer Capability TLV MUST be supported in the LDP Initialization Message([RFC5561]). Advertisement of the PW Transfer Capability indicates support of the procedures for PW transfer between MP and CP detailed in this document. If the peer has not advertised the corresponding capability, then no PW transfer label messages should be sent to the peer. 5.1.2. PW Ownership Transfer TLV To ensure the PW ownership transfer between MP and CP automatically, T-PE/S-PE SHOULD be notified by the PW transfer signaling message. So, the PW path and PW transfer indication MUST be carried in the LDP Label Mapping message. Qilei Wang, et al. Expires July 1, 2012 [Page 6] Internet-Draft LDP Extension for PW Transfer Dec 2011 Since [RFC6073] has defined PW switching point TLV (S-PE TLV) and Sub-TLV to the switching points that the PW traverses, these TLV and Sub-TLV can be used to carry the PW path which is needed to be transferred. ER-TLV which is defined in [draft-ietf-pwe3-mspw-er] can also be used to carry the information of PW path which is needed to be transferred in the scenario of setting up MS-PW using generalized FEC 129 from source PE to destination PE. Therefore, this section only defines a new LDP TLV - Transfer TLV - which can be used to indicate a PW transfer signaling procedure. The PW Ownership Transfer TLV (PW-OH TLV), is defined as follows (TLV type needs to be assigned by IANA): 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |0|0| PW Transfer (0x0105) | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |POT| Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: PW Ownership Transfer TLV POT (2 bits): PW Ownership Transfer. PE MUST carry this TLV in LDP Label Mapping and Notification message defined in [RFC5036] when transferring from MP to CP, or CP to MP. The value of POT is following: 1 - PW ownership transfer from management plane to control plane 2 - PW ownership transfer from control plane to management plane Reserved(30 bits): This field MUST be set to zero on transmission and MUST be ignored on receipt. 5.2. Procedures 5.2.1. PW Ownership Transfer from MP to CP Before transferring from MP to CP, there MUST be a T-LDP session between two T-PE for SS-PW, or T-PE and S-PE for MS-PW. During the LDP initialization stage, the LDP speaker MUST announce it's PW transfer capability according to [RFC5561] by sending the peer a Capability message carrying the PW transfer capability TLV. Qilei Wang, et al. Expires July 1, 2012 [Page 7] Internet-Draft LDP Extension for PW Transfer Dec 2011 To conduct the MP2CP PW transfer, operator sends the MP2CP PW transfer command to the source and destination T-PEs which will inform MP and CP to initiate the MP2CP PW transfer process. When CP gets all the information of the PW to be transferred , the CP of source and destination nodes will build the LDP mapping message based on the procedures described in [RFC 4447], and send the mapping message to its peer T-PE or S-PE. The differences between the normal and the MP2CP PW transfer Label Mapping message are: 1. PW-OH TLV with POT value equals 1 will be encoded into the "Optional Parameters" of the Mapping message for both SS-PW and MS-PW MP2CP transfer. 2. For MS-PW, the PW path will be encoded into S-PE TLVs and Sub- TLVs with local S-PE address according to [RFC6073] or ER-TLV defined in [draft-ietf-pwe3-mspw-er]. When the Label Mapping message is build up, it will be send to source/destination T-PE for SS-PW and to S-PE for MS-PW. For SS-PW, when the source/destination T-PE receives the MP2CP PW transfer Label Mapping message, and also send MP2CP PW transfer Label Mapping message to its peer, it will transfer the PW control from MP to CP. For MS-PW, when the S-PE receives the MP2CP PW transfer Label Mapping message, it will decode the next hop S-PE from local IP address Sub- TLVs in S-PE TLVs then forward this Label Mapping message to the next hop S-PE. Only when S-PE receive the MP2CP PW transfer label mapping message from the reverse direction of PW, it will transfer the PW control from MP to CP. When the source/destination T-PE receives the MP2CP PW transfer Label Mapping message, it will deal with it in the same way as SS-PW described above. When ER-TLV is used in MP2CP transfer label mapping message, the next hop S-PE information can be get from ER-TLV. Transfer label mapping message then is forwarded to the next hop S-PE. Only when S-PEreceive the MP2CP PW transfer label mapping message from the reverse direction, it will transfer the PW control from MP to CP. When T-PE receives the MP2CP PW transfer label mapping message, it will also deal with it in the same way as SS-PW. 5.2.1.1. MP2CP PW Transfer Failure If T-PEs or S-PEs fail to negotiate PW transfer capability, the procedures in [RFC5561] SHOULD be performed. Qilei Wang, et al. Expires July 1, 2012 [Page 8] Internet-Draft LDP Extension for PW Transfer Dec 2011 Since T-LDP runs over TCP, and there is only one hop between T-PEs in SS-PW, if the T-LDP sesseion is created successfully, the PW transfer Label Mapping can be sent and received reliably. For MS-PW, if one of the PW segment fails to transfer from MP to CP, a Notification message SHOULD be sent to source/destionation T-PE to report the failure. Reverse control from CP to MP is needed. And the PW segments successfully transferred SHOULD be remained. 5.2.2. PW Ownership Transfer from CP to MP Since multiple PWs can share a single T-LDP session, when a PW transferred from CP to MP, the LDP session may be retained for other PWs. So when a PW transfers from CP to MP, a Notification message carring the corresponding PW FEC and PW-OH TLV with the POT value equals 2 SHOULD be send out. All the other S-PEs along the PW received this Notification message, SHOULD send the notification message to next hop S-PE. Only when S-PE receives notification message from reverse direction of PW, it will transfer the PW control from CP to MP and remain the corresponding LDP session. When there is no PW, the session MAY be still remained for the future use. Thus, whether to delete the LDP session depends on the provider's policy. If the provider want to delete the LDP session in which there is no PW, the procedures in [RFC5036] can be conducted. 5.2.2.1. CP2MP PW Transfer Failure Since the PW transfer capability is negotiated before T-LDP session set up, and the T-LDP runs over TCP, CP2MP PW transfer can be performed reliably. For MS-PW, if one PW segment fails to transfer from CP to MP, a Notification message SHOULD be sent to source/destionation T-PE to report the failure. 6. Security Considerations [RFC5036] and [RFC4447] describe the security considerations that apply to the T-LDP specification. The same security framework and considerations apply to the capability mechanism described in this document. 7. IANA considerations TBD. Qilei Wang, et al. Expires July 1, 2012 [Page 9] Internet-Draft LDP Extension for PW Transfer Dec 2011 8. Acknowledgements The authors would like to thank Weilian Jiang, and Kan Hu for their useful comments. 9. References 9.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching (GMPLS) Architecture", RFC 3945, October 2004. [RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to- Edge (PWE3) Architecture", RFC 3985, March 2005. [RFC4447] Martini, L., Rosen, E., El-Aawar, N., Smith, T., and G. Heron, "Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP)", RFC 4447, April 2006. [RFC5036] Andersson, L., Minei, I., and B. Thomas, "LDP Specification", RFC 5036, October 2007. [RFC5493] Caviglia, D., Bramanti, D., Li, D., and D. McDysan, "Requirements for the Conversion between Permanent Connections and Switched Connections in a Generalized Multiprotocol Label Switching (GMPLS) Network", RFC 5493, April 2009. [RFC5561] Thomas, B., Raza, K., Aggarwal, S., Aggarwal, R., and JL. Le Roux, "LDP Capabilities", RFC 5561, July 2009. [RFC5654] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and S. Ueno, "Requirements of an MPLS Transport Profile", RFC 5654, September 2009. [RFC5852] Caviglia, D., Ceccarelli, D., Bramanti, D., Li, D., and S. Bardalai, "RSVP-TE Signaling Extension for LSP Handover from the Management Plane to the Control Plane in a GMPLS- Enabled Transport Network", RFC 5852, April 2010. [RFC6073] Martini, L., Metz, C., Nadeau, T., Bocci, M., and M. Aissaoui, "Segmented Pseudowire", RFC 6073, January 2011. Qilei Wang, et al. Expires July 1, 2012 [Page 10] Internet-Draft LDP Extension for PW Transfer Dec 2011 9.2. Informative References [DYNAMIC-MS-PW] Luca Martini, Matthew Bocci, and Florin Balus, "Dynamic Placement of Multi Segment Pseudo Wires", draft-ietf-pwe3-dynamic-ms-pw-10.txt . [G.8081] International Telecommunications Union, "Terms and definitions for Automatically Switched Optical Networks (ASON)", Recommendation G.8081/Y.1353, June 2004 . [MPLS-TP-CP-FWK] Loa Andersson, Lou Berger, and Luyuan Fang, "MPLS-TP Control Plane Framework", draft-ietf-ccamp-mpls-tp-cp-framework-02.txt . [MPLS-TP-FWK] M. Bocci and S. Bryant etc., "A Framework for MPLS in Transport Networks", draft-ietf-mpls-tp-framework-11.txt . Authors' Addresses Qilei Wang ZTE Corporation Email: wang.qilei@zte.com.cn Muliu Tao ZTE Corporation Phone: +86 755 26773923 Email: tao.muliu@zte.com.cn Xihua Fu ZTE Corporation ZTE Plaza, No.10, Tangyan South Road, Gaoxin District Xi'an 210012 P.R.China Email: fu.xihua@zte.com.cn Qilei Wang, et al. Expires July 1, 2012 [Page 11] Internet-Draft LDP Extension for PW Transfer Dec 2011 Ruiquan Jing China Telecom Email: jingrq@ctbri.com.cn Xiaoli Huo China Telecom Email: huoxl@ctbri.com.cn Qilei Wang, et al. Expires July 1, 2012 [Page 12]