MPLS Working Group J. Ryoo Internet-Draft T. Cheung Updates: 7271 (if approved) ETRI Intended status: Standards Track H. Van Helvoort Expires: December 5, 2017 Hai Gaoming BV I. Busi G. Wen Huawei Technologies June 3, 2017 Updates to MPLS Transport Profile (MPLS-TP) Linear Protection in Automatic Protection Switching (APS) Mode draft-ietf-mpls-tp-aps-updates-04.txt Abstract This document contains updates to MPLS Transport Profile (MPLS-TP) linear protection in Automatic Protection Switching (APS) mode defined in RFC 7271. The updates provide rules related to the initialization of the Protection State Coordination (PSC) Control Logic, in which the state machine resides, when operating in APS mode, and clarify some operation related to state transition table lookup. 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 December 5, 2017. Copyright Notice Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. Ryoo, et al. Expires December 5, 2017 [Page 1] Internet-Draft Updates to MPLS-TP LP in APS mode June 2017 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 2. Conventions Used in This Document . . . . . . . . . . . . . . 3 3. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. Updates . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 4.1. Initialization Behavior . . . . . . . . . . . . . . . . . 4 4.2. State Transition Modification . . . . . . . . . . . . . . 5 4.3. Operation related to State Transition Table Lookup . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 8.1. Normative References . . . . . . . . . . . . . . . . . . 8 8.2. Informative References . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction MPLS Transport Profile (MPLS-TP) linear protection in Automatic Protection Switching (APS) mode is defined in RFC 7271 [RFC7271]. It defines a set of alternate and additional mechanisms to perform some of the functions of linear protection described in RFC 6378 [RFC6378]. The actions performed at initialization of the Protection State Coordination (PSC) Control Logic are not described in either [RFC7271] or [RFC6378]. Although it is a common perception that the state machine starts at the Normal state, this is not explicitly specified in any of the documents and various questions have been raised by implementers and in discussions on the MPLS working group mailing list concerning the detailed actions that the PSC Control Logic should take. The state machine described in [RFC7271] operates under the assumption that both end nodes of a linear protection domain start in the Normal state. In the case that one node reboots while the other node is still in operation, various scenarios may arise resulting in problematic situations. This document resolves all the problematic cases and minimizes traffic disruptions related to initialization Ryoo, et al. Expires December 5, 2017 [Page 2] Internet-Draft Updates to MPLS-TP LP in APS mode June 2017 including both cold and warm reboots that require re-initialization of the PSC Control Logic. This document contains updates to the MPLS-TP linear protection in APS mode defined in [RFC7271]. The updates provide rules related to initialization of the PSC Control Logic, in which the state machine resides, when operating in APS mode. The updates also include modifications to the state transition table defined in Section 11.2 of [RFC7271]. The changes in the state transition table have been examined to make sure that they do not introduce any new problems. This document does not introduce backward compatibility issues with implementations of [RFC7271]. In case a node implementing this document restarts, the new state changes will not cause problems at the remote node implementing [RFC7271] and the two ends will converge to the same local and remote states. In case a node implementing [RFC7271] restarts, the two ends behave as today. This document also provides some clarifications on the operation related to state transition table lookup. The reader of this document is assumed to be familiar with [RFC7271]. 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 RFC 2119 [RFC2119]. 3. Acronyms Ryoo, et al. Expires December 5, 2017 [Page 3] Internet-Draft Updates to MPLS-TP LP in APS mode June 2017 This document uses the following acronyms: APS Automatic Protection Switching DNR Do-not-Revert E::R Exercise state due to remote EXER message EXER Exercise MS-P Manual Switch to Protection path MS-W Manual Switch to Working path MPLS-TP MPLS Transport Profile NR No Request PF:DW:R Protecting Failure state due to remote SD-W message PF:W:L Protecting Failure state due to local SF-W PF:W:R Protecting Failure state due to remote SF-W message PSC Protection State Coordination RR Reverse Request SA:MP:R Switching Administrative state due to remote MS-P message SA:MW:R Switching Administrative state due to remote MS-W message SD Signal Degrade SF-P Signal Fail on Protection path SF-W Signal Fail on Working path UA:P:L Unavailable state due to local SF-P WTR Wait-to-Restore 4. Updates This section specifies the actions that will be performed at the initialization of the PSC Control Logic and the modifications of the state transition table defined in Section 11.2 of [RFC7271]. Some clarifications on the operation related to state transition table lookup are also provided. 4.1. Initialization Behavior This section defines initialization behavior that is not described in [RFC7271]. When the PSC Control Logic is initialized, the following actions MUST be performed: o Stop the WTR timer if it is running. o Clear any operator command in the Local Request Logic. o If an SF-W or SF-P exists as the highest local request, the node being initialized starts at the PF:W:L or UA:P:L state, respectively. o If the node being initialized has no local request: Ryoo, et al. Expires December 5, 2017 [Page 4] Internet-Draft Updates to MPLS-TP LP in APS mode June 2017 * If the node being initialized does not remember the active path or if the node being initialized remembers the working path as the active path, the node starts at the Normal state. * Else (the node being initialized remembers the protection path as the active path), the node starts at the WTR state sending NR(0,1) or at the DNR state sending DNR(0,1) depending on the configuration that allows or prevents automatic reversion to the Normal state. o In case any local SD exists, the local SD MUST be considered as an input to the Local Request Logic only after the local node has received the first protocol message from the remote node and completed the processing (i.e., updated the PSC Control Logic and decided which action, if any, to be sent to the PSC Message Generator). o If the local node receives an EXER message as the first protocol message after initialization and the remote EXER becomes the top- priority global request, the local node MUST set the position of the bridge and selector according to the Path value in the EXER message and transit to the E::R state. Remembering the active path in case of no local request minimizes traffic switchovers in cases where the remote node is still in operation. This approach does not cause a problem even if the remembered active path is no longer valid due to any local input that occurred at the remote node while the initializing node was out of operation. It is worth noting that in some restart scenarios (e.g., cold rebooting) no valid SF/SD indications may be present at the input of the Local Request logic. In this case, the PSC Control Logic would restart as if no local requests are present. If a valid SF/SD indication is detected later, this would be notified to the PSC Control Logic and trigger state change. 4.2. State Transition Modification In addition to the initialization behavior described in Section 4.1, four cells of the remote state transition table need to be changed to make two end nodes converge after initialization. State transition by remote message defined in Section 11.2 of [RFC7271] is modified as follows (only modified cells are shown): Ryoo, et al. Expires December 5, 2017 [Page 5] Internet-Draft Updates to MPLS-TP LP in APS mode June 2017 | MS-W | MS-P | WTR | EXER | RR | DNR | NR --------+---------+---------+-----+------+----+------+---- N | | | (13)| | | DNR | PF:W:R | | | | | | DNR | PF:DW:R | | | | | | DNR | The changes in two rows of remote protecting failure states lead to the replacement of note (10) with DNR, therefore note (10) is no longer needed. The resultant three rows read: | MS-W | MS-P | WTR | EXER | RR | DNR | NR --------+---------+---------+-----+------+----+------+---- N | SA:MW:R | SA:MP:R | (13)| E::R | i | DNR | i PF:W:R | SA:MW:R | SA:MP:R | (9) | E::R | i | DNR | (11) PF:DW:R | SA:MW:R | SA:MP:R | (9) | E::R | i | DNR | (11) In the tables above, the letters 'i' and 'N' stand for "ignore" and "Normal state", respectively. Other acronyms can be found in Section 3. 4.3. Operation related to State Transition Table Lookup In addition to the rules related to the state transition table lookup listed in Section 11 of [RFC7271], the following rule is also applied to the operation related to the state transition table lookup: o When the local SF-P is cleared and the priorities of the local and remote requests are re-evaluated, the last received remote message may not be valid any more due to the previous failure of the protection path. Therefore, the last received message MUST be treated as if it were NR and only the local request shall be evaluated. The last paragraph in Section 11 of [RFC7271] is modified as follows: Ryoo, et al. Expires December 5, 2017 [Page 6] Internet-Draft Updates to MPLS-TP LP in APS mode June 2017 --------- Old text: --------- In the state transition tables below, the letter 'i' stands for "ignore" and is an indication to remain in the current state and continue transmitting the current PSC message. --------- New text: --------- In the state transition tables below, the letter 'i' is the "ignore" flag, and if it is set it means that the top-priority global request is ignored. If re-evaluation is triggered, it is checked if the ignore flag is set. If it is, the state machine will transit to the supposed state, which can be Normal or DNR as indicated in the footnotes to the state transition tables. If the ignore flag is not set, the state machine will transit to the state indicated in the cell of the state transition table. If re-evaluation is not triggered, it is checked if the ignore flag is set. If it is, the state machine will remain in the current state, and the current PSC message continues to be transmitted. If the ignore flag is not set, the state machine will transit to the state indicated in the cell of the state transition table. 5. Security Considerations No specific security issue is raised in addition to those ones already documented in [RFC7271]. It may be noted that tightening the description of initializing behavior may help to protect networks from re-start attacks. 6. IANA Considerations This document makes no request of IANA. Note to RFC Editor: this section may be removed on publication as an RFC. 7. Acknowledgements The authors would like to thank Joaquim Serra for bringing up the issue related to initialization of the PSC Control Logic at the very beginning. The authors would also like to thank Adrian Farrel and Loa Andersson for their valuable comments and suggestions on this document. Ryoo, et al. Expires December 5, 2017 [Page 7] Internet-Draft Updates to MPLS-TP LP in APS mode June 2017 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC7271] Ryoo, J., Ed., Gray, E., Ed., 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, DOI 10.17487/RFC7271, June 2014, . 8.2. Informative References [RFC6378] Weingarten, Y., Ed., Bryant, S., Osborne, E., Sprecher, N., and A. Fulignoli, Ed., "MPLS Transport Profile (MPLS- TP) Linear Protection", RFC 6378, DOI 10.17487/RFC6378, October 2011, . Authors' Addresses Jeong-dong Ryoo ETRI EMail: ryoo@etri.re.kr Taesik Cheung ETRI EMail: cts@etri.re.kr Huub Van Helvoort Hai Gaoming BV EMail: huubatwork@gmail.com Italo Busi Huawei Technologies EMail: Italo.Busi@huawei.com Ryoo, et al. Expires December 5, 2017 [Page 8] Internet-Draft Updates to MPLS-TP LP in APS mode June 2017 Guangjuan Wen Huawei Technologies EMail: wenguangjuan@huawei.com Ryoo, et al. Expires December 5, 2017 [Page 9]