Network Working Group Yuanlin Bao Internet-Draft Xihua Fu Intended status: Informational Gang. Xie Expires: September 1, 2010 ZTE Corporation February 28, 2010 The Requirements for Path Computation Element (PCE) Application for Backup Route draft-bao-pce-backup-route-computation-reqs-00.txt Abstract Backup route is another route for a service which will be used when working path fails. Traditionally, this route is configured by operator manually and can't be updated when LSA changes. This document improves this traditional usage, and PCE (Path Computation Element) is applied for backup route. Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 1, 2010. Copyright Notice Copyright (c) 2010 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 Yuanlin Bao, et al. Expires September 1, 2010 [Page 1] Internet-Draft PCE Application for Backup Route February 2010 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 BSD License. Table of Contents 1. Conventions used in this document . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Application Model . . . . . . . . . . . . . . . . . . . . . . . 3 4. Architecture Analysis and Requirements . . . . . . . . . . . . 4 4.1. Architecture Analysis . . . . . . . . . . . . . . . . . . . 4 4.2. Requirements to PCC and PCE . . . . . . . . . . . . . . . . 5 4.3. Requirements to PCEP . . . . . . . . . . . . . . . . . . . 5 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 7. Normative References . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 6 Yuanlin Bao, et al. Expires September 1, 2010 [Page 2] Internet-Draft PCE Application for Backup Route February 2010 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. Introduction Backup route is a very useful approach to achieve service restoration. Traditionally, except primary route, operator also sets a group of routes (usually with priority), i.e. backup route set, for a service. When the primary route fails, LSR can select a proper restoration route from backup route set. By this way, faster restoration can be achieved. Since backup routes are pre-configured by management plane, it can't be updated when network state changes dynamically. In some cases, e.g. a fiber on the backup route is cut, if operator can't update backup routes in time, the backup routes will become unavailable. Otherwise, generally the backup routes will be verified whether it is available before it is used to signal a connection. This is also due to the problem that backup routes can't be updated timely. And this will introduce another problem that time delay will affect service recovery. This document introduces a PCE-based backup route method, which uses PCE to update backup route at the policy of network management. This method helps provider to offer better service for customer and avoids the unavailablity of backup routes. 3. Application Model Figure 1 is an application model of pce-based backup route computation. A user requests ingress LSR (PCC) for a service with backup route. Then PCC requests PCE to compute a working path and a backup path. PCE returns the results to PCC, and records that a backup route service is requested by the PCC. When PCE receives a LSA change from IGP, it'll check if the backup route computed previously is affected. If the backup route is affected, it will re- compute a new backup route, and send it to the PCC. Yuanlin Bao, et al. Expires September 1, 2010 [Page 3] Internet-Draft PCE Application for Backup Route February 2010 +-------------+ +---------+ | | Change | | Change | PCE |<---------| IGP |<---------- | | of LSA | | of LSA +-------------+ +---------+ ^ | |Path(W+B) |Path |Request/ |Refresh |Response | V V +------+ +-------------+ +-------------+ | | Service | LSR | Signaling | | | USER |--------->| (PCC) |---------->| LSR | | | Request | | | | +------+ +-------------+ +-------------+ Figure 1: Backup Route Application Model 4. Architecture Analysis and Requirements 4.1. Architecture Analysis [RFC4655] introduced 5 PCE models which can be categorized according to whether PCE functionality is integrated into the network element. Under this methodology, two groups of PCE model, i.e. composite PCE and external PCE, is generated. For composite PCE, due to the resource limitation of the card, the power of CPU is relatively weak, so the PCE capability is also limited. However, compared to composite PCE, external PCE has more resources (i.e. memory and CPU power etc), and it even can be presented as a dedicated server. Therefore, external PCE is more powerful than composite PCE. The application of backup route will increase compuataion burden to PCE. Due to its powerful computation capability, external PCE is more adequate than composite PCE. However, if there is not much application of backup route, composite PCE can also operate well. [RFC4655] also describes stateful PCE and stateless PCE. For statefull PCE, there is a strict synchronization between the PCE and not only the network states (in term of topology and resource information), but also the set of computed paths and reserved resources in use in the network. Since stateful PCE can perceive the network state chang, so it can determine which computed path is affected. Therefore, it is easier to applying backup route on stateful PCE. Yuanlin Bao, et al. Expires September 1, 2010 [Page 4] Internet-Draft PCE Application for Backup Route February 2010 Furthermore, considering the PCE failure, if an implementation has a backup PCE, then the primary and backup PCE MUST keep strict synchronization. And switching to the backup PCE can't affect the correctness of path computation However, the selection of PCE model, stateful PCE or stateless PCE is out of this document. And the synchronization between primary and backup PCE is also out of this document, the operator can make a selection according to the network deployment. 4.2. Requirements to PCC and PCE In order to support the backup route, PCC SHOULD be able to let PCE know that it needs backup route service. Thereby, PCE can start backup service. Otherwise, PCC SHOULD also be able to notify PCE that backup route service is cancelled, so PCE can stop backup route services. As for PCE, it SHOULD record backup route information, and maintain its state. When network state changes, PCE SHOULD compute the affected backup routes and send a new route to PCC. However, PCE MAY also compute backup routes in idle state to obtain the optimized paths. The policy for PCE to compute backup routes SHOULD be able to be configured. 4.3. Requirements to PCEP [RFC4657] gives detailed generic requirements for PCE communication protocol. However, in order to support backup route, specific extensions to PCEP is required. For PCReq, it SHOULD be possible for PCC to request backup route. That is a mechanism is needed to make PCE know that PCC want a backup route service. When PCE receives a PCReq message with a backup route serivce request, it SHOULD perform path computation accroding to the required policy, e.g. node disjoint, link disjoint and SRLG disjoint etc. And in the PCRep message, PCE SHOULD able to specify which one is pre- exsiting route, if PCC requests both primary route and backup route at the same time. If PCE doesn't support backup route it SHOULD give a negative response, and the reason of the computation failure. When network state changes, PCE SHOULD re-compute backup routes according the configured policy. If a better backup route is found, PCE should send it to PCC. When PCC wants to cancel the backup route service, it can send a notify message to PCE. Since current PCNtf message can't achieve this function, some extensions is needed. Yuanlin Bao, et al. Expires September 1, 2010 [Page 5] Internet-Draft PCE Application for Backup Route February 2010 5. Security Considerations This document has no requirement for a change to the security models within associated protocols. 6. Acknowledgements The RFC text was produced using Marshall Rose's xml2rfc tool. 7. 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. [RFC4657] Ash, J. and J. Le Roux, "Path Computation Element (PCE) Communication Protocol Generic Requirements", RFC 4657, September 2006. [RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation Element (PCE) Communication Protocol (PCEP)", RFC 5440, March 2009. Authors' Addresses Yuanlin Bao ZTE Corporation 5F, R&D Building 3, ZTE Industrial Park, XiLi LiuXian Road Nanshan District, Shenzhen 518055 P.R.China Phone: +86 755 26773731 Email: bao.yuanlin@zte.com.cn URI: http://www.zte.com.cn/ Yuanlin Bao, et al. Expires September 1, 2010 [Page 6] Internet-Draft PCE Application for Backup Route February 2010 Xihua Fu ZTE Corporation West District,ZTE Plaza,No.10,Tangyan South Road,Gaoxin District Xi An 710065 P.R.China Phone: +8613798412242 Email: fu.xihua@zte.com.cn URI: http://www.zte.com.cn/ Gang Xie ZTE Corporation ZTE Plaza, No.19, Huayuan Road East, Haidian District Bei Jing 100191 P.R.China Phone: +8613798412242 Email: xie.gang@zte.com.cn URI: http://www.zte.com.cn/ Yuanlin Bao, et al. Expires September 1, 2010 [Page 7]