Network Working Group Z. Cui Internet-Draft R. Winter Intended status: Informational NEC Expires: August 4, 2016 H. Shah Ciena S. Aldrin Huawei Technologies M. Daikoku KDDI February 1, 2016 Use Cases and Requirements for MPLS-TP multi-failure protection draft-ietf-mpls-tp-mfp-use-case-and-requirements-00 Abstract For the Multiprotocol Label Switching Transport Profile (MPLS-TP) linear protection capable of 1+1 and 1:1 protection has already been defined. That linear protection mechanism has not been designed for handling multiple, simultaneously occuring failures, i.e. multiple failures that affect the working and the protection entity during the same time period. In these situations currently defined protection mechanisms would fail. This document introduces use cases and requirements for mechanisms that are capable of protecting against such failures. It does not specify a multi-failure protection mechanism itself. 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 August 4, 2016. Cui, et al. Expires August 4, 2016 [Page 1] Internet-Draft Multi-failure protection requirements February 2016 Copyright Notice Copyright (c) 2016 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. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Document scope . . . . . . . . . . . . . . . . . . . . . 3 1.2. Requirements notation . . . . . . . . . . . . . . . . . . 3 1.3. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 2. General m:n protection scenario . . . . . . . . . . . . . . . 4 3. Use cases . . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. m:1 (m > 1) protection . . . . . . . . . . . . . . . . . 5 3.1.1. Pre-configuration . . . . . . . . . . . . . . . . . . 5 3.1.2. On-demand configuration . . . . . . . . . . . . . . . 6 3.2. m:n (m, n > 1, n >= m > 1) protection . . . . . . . . . . 6 4. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. Normative References . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction Today's packet optical transport networks concentrate large volumes of traffic onto a relatively small number of nodes and links. As a result, the failure of a single network element can potentially interrupt a large amount of traffic. For this reason, ensuring survivability through careful network design and appropriate technical means is important. In MPLS-TP networks, a basic end-to-end linear protection survivability technique is available as specified in [RFC6378], [RFC7271] and [RFC7324]. That protocol however is limited to 1+1 and 1:1 protection and not designed to handle multiple failures that affect both the working and protection entity at the same time. Cui, et al. Expires August 4, 2016 [Page 2] Internet-Draft Multi-failure protection requirements February 2016 There are various scenarios where multi-failure protection is an important requirement for network survivability. E.g for disaster recovery, after catastrophic events such as earthquakes or tsunamis. During the period after such events, network availability is crucial, in particular for high-priority services such as emergency telephone calls. Existing 1+1 or 1:n protection however is limited to cover single failures which has proven as not sufficient during past events. Beyond the natural disaster use case above, multi-failure protection is also beneficial in situations where the network is particularly vulnerable, e.g., when a working entity or protection entity was closed for maintenance or construction work. During this time, the network service becomes vulnerable to single failures since one entity is already down. If a failure occurs during this time, an operator might not be able to meet service level agreements (SLA). Thus, a technical means for multi-failure protection could take pressure off network operations. 1.1. Document scope This document describes use cases and requirements for m:1 and m:n protection in MPLS-TP networks without the use of control plane protocols. Existing solutions based on a control plane such as GMPLS may be able to restore user traffic when multiple failures occur. Some networks however do not use full control plane operation for reasons such as service provider preferences, certain limitations or the requirement for fast service restoration (faster than achievable with control plane mechanisms). These networks are the focus of this document which defines a set of requirements for m:1 and m:n protection not based on control plane support. This document imposes no formal time constraints on detection times. 1.2. Requirements notation 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]. 1.3. Terminology The terminology used in this document is based on the terminology defined in the MPLS-TP Survivability Framework document [RFC6372], which in turn is based on [RFC4427]. In particular, the following protection schemes are defined in [RFC4427] and used as terms in this document: Cui, et al. Expires August 4, 2016 [Page 3] Internet-Draft Multi-failure protection requirements February 2016 o 1+1 protection o 1:n (n >= 1) protection o m:n (m, n > 1, n >= m > 1) protection o Further, the following additional terminology is from [RFC4427] is used: o "broadcast bridge" o "selector bridge" o "working entity" o "protection entity" This document defines a new protection type: o m:1 (m > 1) protection: A set of m protection entities protecting a single working entity 2. General m:n protection scenario The general underlying assumption of this work is that an m:n relationship between protection entity and working entity exists, i.e. there is no artificial limitation on the ratio between protection and working entities. This general scenario is illustrated in Figure 1 which shows a protection domain with n working entities and m protection entities between Node A and Node Z. At Node A, traffic is transported over its respective working entity and may be simultaneously transported over one of its protection entities (in case of a broadcast bridge), or it is transported over its working entity and only in case of failure over one of the protection entities (in case of a selector bridge). At Node Z, the traffic is selected from either its working entity or one of the protection entities. Note that any of the n working entities and m protection entities should follow a disjoint path through the network from Node A to Node Z. Cui, et al. Expires August 4, 2016 [Page 4] Internet-Draft Multi-failure protection requirements February 2016 +------+ +------+ |Node A| working entity #1 |Node Z| | |=============================| | | | .... | | | | working entity #n | | | |=============================| | | | | | | | | | | | protection entity #1 | | | |*****************************| | | | .... | | | | protection entity #m | | | |*****************************| | +------+ +------+ |--------Protection Domain--------| Figure 1: m:n protection domain 3. Use cases 3.1. m:1 (m > 1) protection With MPLS-TP linear protection such as 1+1/1:1 protection, when a single failure is detected on the working entity, the service can be restored using the protection entity. However, during the time the protection is active the traffic is unprotected until the working entity is restored. m:1 protection can increase service availability and reduce operational pressure since multiple protection entities are available. For any m > 1, m - 1 protection entities may fail and the service still would have a protection entity available. There are different ways to provision these alternative protection entities which are outlined in the following sub-sections. 3.1.1. Pre-configuration The relationship between the working entity and the protection entities is part of the system configuration and needs to be configured before the working entity is being used. The same applies to additional protection entities. Unprotected traffic can be transported over the m protection entities as long as these entities do not carry protected traffic. Cui, et al. Expires August 4, 2016 [Page 5] Internet-Draft Multi-failure protection requirements February 2016 3.1.2. On-demand configuration The protection relationship between a working entity and a protection entity is configured while the system is in operation. Additional protection entities are configured by either a control plane protocol or static configuration using a management system directly after failure detection and/or notification of either the working entity or the protection entities. In case a management system is used, there is no need for a standardized solution. 3.2. m:n (m, n > 1, n >= m > 1) protection Because m:1 protecion introduces additional protection entities compared to 1:1 protection, an additional cost has to be paid. In order to reduce the cost of these additional protection entities, in the m:n scenario, m dedicated protection transport entities are sharing protection resources for n working transport entities. The bandwidth of each protection entity should be allocated in such a way that it may be possible to protect any of the n working entities in case at least one of the m protection entities is available. When a working entity is determined to be impaired, its traffic first must be assigned to an available protection transport entity followed by a transition from the working to the assigned protection entity at both Node A and Node Z of the protected domain. It is noted that when more than m working entities are impaired, only m working entities can be protected. 4. Requirements A number of recovery requirements are defined in [RFC5654]. These requirements however are limited to cover single failure case and not multiple, simultaneously occuring failures. This section extends the list of requirements to support multiple failures scenarios. R1. MPLS-TP SHOULD support m:1 (m > 1) protection. 1. An m:1 protection mechanism MUST protect against multiple failures that are detected on both the working entity and one or more protection entities. 2. Pre-configuration of protection entities SHOULD be supported. 3. On-demand protection entity configuration MAY be supported. 4. On-demand protection resource activation MAY be supported. Cui, et al. Expires August 4, 2016 [Page 6] Internet-Draft Multi-failure protection requirements February 2016 5. A priority scheme MUST be provided, since a protection entity has to be chosen out of two or more protection entities. R2. MPLS-TP SHOULD support m:n (m, n > 1, n >= m > 1) protection. 1. An m:n protection mechanism MUST protect against multiple failures that are simultaneously detected on both a working entity and a protection entity or multiple working entities. 2. A priority scheme MUST be provided, since protection resources are shared by multiple working entities dynamically. If a solution is designed based on an existing mechanism such as PSC, then this solution MUST be backward compatible and not break such mechanisms. 5. Security Considerations General security considerations for MPLS-TP are covered in [RFC5921]. The security considerations for the generic associated control channel are described in [RFC5586]. The requirements described in this document are extensions to the requirements presented in [RFC5654] and does not introduce any new security risks. 6. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC4427] Mannie, E. and D. Papadimitriou, "Recovery (Protection and Restoration) Terminology for Generalized Multi-Protocol Label Switching (GMPLS)", RFC 4427, March 2006. [RFC5586] Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic Associated Channel", RFC 5586, June 2009. [RFC5654] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and S. Ueno, "Requirements of an MPLS Transport Profile", RFC 5654, September 2009. [RFC5921] Bocci, M., Bryant, S., Frost, D., Levrau, L., and L. Berger, "A Framework for MPLS in Transport Networks", RFC 5921, July 2010. [RFC6372] Sprecher, N. and A. Farrel, "MPLS Transport Profile (MPLS- TP) Survivability Framework", RFC 6372, September 2011. Cui, et al. Expires August 4, 2016 [Page 7] Internet-Draft Multi-failure protection requirements February 2016 [RFC6378] Weingarten, Y., Bryant, S., Osborne, E., Sprecher, N., and A. Fulignoli, "MPLS Transport Profile (MPLS-TP) Linear Protection", RFC 6378, October 2011. [RFC7271] Ryoo, J., Gray, E., van Helvoort, H., D'Alessandro, A., Cheung, T., and E. Osborne, "MPLS Transport Profile (MPLS- TP) Linear Protection to Match the Operational Expectations of Synchronous Digital Hierarchy, Optical Transport Network, and Ethernet Transport Network Operators", RFC 7271, June 2014. [RFC7324] Osborne, E., "Updates to MPLS Transport Profile Linear Protection", RFC 7324, July 2014. Authors' Addresses Zhenlong Cui NEC Email: c-sai@bx.jp.nec.com Rolf Winter NEC Email: Rolf.Winter@neclab.eu Himanshu Shah Ciena Email: hshah@ciena.com Sam Aldrin Huawei Technologies Email: aldrin.ietf@gmail.com Masahiro Daikoku KDDI Email: ms-daikoku@kddi.com Cui, et al. Expires August 4, 2016 [Page 8]