Network Working Group L. Jin(ed.) Internet-Draft ZTE Updates: 4447 6073(if approved) R. Key(ed.) Intended status: Standards Track Huawei Expires: December 17, 2012 S. Delord Alcatel-Lucent T. Nadeau Juniper S. Boutros Cisco Systems, Inc. June 15, 2012 Pseudowire Control Word Negotiation Mechanism Update draft-ietf-pwe3-cbit-negotiation-04.txt Abstract The control word negotiation mechanism specified in RFC4447 has a problem when PE changes the preference for the use of control word from PREFERRED to NOT-PREFERRED. This draft updates RFC4447 by introducing a message exchanging mechanism to resolve this control word negotiation issue. 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 17, 2012. Copyright Notice Copyright (c) 2012 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 Jin, et al. Expires December 17, 2012 [Page 1] Internet-Draft draft-ietf-pwe3-cbit-negotiation-04 June 2012 (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 . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Problem Statement . . . . . . . . . . . . . . . . . . . . . . . 3 3. Control word re-negotiation by label request message . . . . . 4 3.1. Control word re-negotiation use case . . . . . . . . . . . 5 4. Backward Compatibility . . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6 8. Contributing Authors . . . . . . . . . . . . . . . . . . . . . 6 9. Normative references . . . . . . . . . . . . . . . . . . . . . 7 Appendix A. Updated C-bit Handling Procedures Diagram . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 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]. Jin, et al. Expires December 17, 2012 [Page 2] Internet-Draft draft-ietf-pwe3-cbit-negotiation-04 June 2012 1. Introduction The control word negotiation mechanism specified in [RFC4447] section 6.2 has a problem when PE changes the preference for the use of control word from PREFERRED to NOT-PREFERRED. There would be a wrong negotiated result of the control word as "not used" while both ends of pseudowire PE have the use of control word as PREFERRED. This draft updates [RFC4447] by introducing a message exchanging mechanism to resolve this negotiation issue. 2. Problem Statement [RFC4447] section 6 describes the control word negotiation mechanism. Each PW endpoint has the capability of being configurable with a parameter that specifies whether the use of the control word is PREFERRED or NOT PREFERRED. While in some case of control word negotiation, PE will advertise C-bit=0 in label mapping message with its locally configured use of control word as PREFERRED. This kind of behavior will cause some problem when peer PE changes the use of control word from NOT PREFERRED to PREFERRED. The following case will describe the negotiation problem in detail: +-------+ +-------+ | | PW | | | PE1 |====================| PE2 | | | | | +-------+ +-------+ Figure 1 1. Initially, the use of control word on PE1 is configured as PREFERRED, and on PE2 as NOT PREFERRED. 2. The negotiation result for the control word of this PW is used, and PE1 sends label mapping with C-bit=0 finally according to [RFC4447] section 6.2. 3. PE2 then changes its use of control word configuration to PREFERRED. 4. PE2 will then send label withdraw message to PE1. 5. According to the control word negotiation mechanism, the received label mapping on PE2 from PE1 indicates C-bit=0, therefore PE2 will still send label mapping with C-bit=0. Jin, et al. Expires December 17, 2012 [Page 3] Internet-Draft draft-ietf-pwe3-cbit-negotiation-04 June 2012 The negotiation result for the control word is still not used, even though the use of control word configuration on both PE1 and PE2 is PREFERRED. 3. Control word re-negotiation by label request message In order to resolve above problem, the control word re-negotiation mechanism as described in [RFC4447] section 6 is updated by adding label request message. When Local PE changes its use of control word from NOT PREFERRED to PREFERRED and only if it already received the remote label mapping message with C-bit=0, additional procedure will be added as follow: -i. Local PE MUST send a label withdraw message to remote PE if it has previously sent a label mapping, and label release message to remote PE, and wait until receiving a label release from the remote PE. -ii. Local PE MUST send a label request message to remote PE, and wait until receiving a label mapping message containing the remote PE locally configured preference for use of control word. -iii. After receiving remote PE label mapping with C-bit, Local PE MUST follow procedures defined in [RFC4447] section 6 when sending its label mapping message. When the remote PE successfully processed the label withdraw and label release, and removed the remote label binding, it MUST reset its use of control word with the locally configured preference, and send label mapping as a response of label request with locally configured preference for use of control word. Note: the FEC element in label request message should be the PE's local FEC element. Only if FEC element in label request message could bind together with peer PE's local FEC element, the peer PE sends label mapping with its bound local FEC element and label as a response. The label request message format and procedure is described in [RFC5036]. The multi-segment PW case for T-PE is same. S-PE SHOULD assume an initial passive role as defined in [RFC6073]. When an S-PE receives a label request message from one of its adjacent PEs (be it S-PE or another T-PE), it MUST send a matching label request message to other adjacent PE (again, it may be an S-PE or a T-PE). This is necessary since S-PE does not have full information of interface parameter field in the FEC advertisement. When S-PE receives a label release Jin, et al. Expires December 17, 2012 [Page 4] Internet-Draft draft-ietf-pwe3-cbit-negotiation-04 June 2012 message from remote PE, it MUST send a corresponding label release to the other remote PE where it has received label mapping. As local T-PE will send label withdraw before sending label request to remote peer, the S-PE MUST send the label withdraw upstream before it advertises the label request. When S-PE receives the label withdraw, it should process this message to send a label release as a response and a label withdraw to upstream S-PE/T-PE, then process the next LDP message, e.g. the label request message. When Local PE changes the use of control word from PREFERRED to NOT PREFERRED, Local PE would be able to re-negotiate the Control Word to be not used following the procedures defined in [RFC4447], and no label request message to peer PE will be needed. In that case, Local PE will always send new label mapping with C-bit reflecting the locally configured preference for use of Control Word. The diagram in Appendix A in this document updates the control word negotiation diagram in [RFC4447] Appendix A. 3.1. Control word re-negotiation use case The procedure of PE1 and PE2 for the use case in figure 1 should be as follows: 1. PE2 changes locally configured preference for use of control word to PREFERRED. 2. PE2 will then send label withdraw and release messages to PE1, and wait until receiving label release from PE1. 3. PE1 will send label release in reply to label withdraw message from PE2. After that and processing the label release from PE2, it would reset the use of control word to the locally configured preference as PREFERRED. 4. Upon receipt of Label release message from PE1, PE2 would reset use of control word to the locally configured preference as PREFERRED, and MUST send label request message to PE1, and wait until receiving a label mapping message. 5. PE1 must send label mapping message with C-bit=1 again to PE2 as response of label request. 6. PE2 receives the label mapping from PE1 and gets the remote label binding information. PE2 should wait for PE1 label binding before sending its label binding with C-bit set. Jin, et al. Expires December 17, 2012 [Page 5] Internet-Draft draft-ietf-pwe3-cbit-negotiation-04 June 2012 7. PE2 will send label mapping to PE1 with C-bit=1, and follow procedures defined in [RFC4447] section 6. It is to be noted that the above assume that PE1 is configured to prefer the use of control word, however in step 5 if PE1 doesn't prefer or support control word, PE1 would send the label mapping message with C-bit=0, this would result in PE2 in step 7 sending a label mapping with C-bit=0 as per [RFC4447] section 6. By sending label request message, PE2 will get the locally configured preference for use of control word of peer PE1 in the received label mapping message. By using the new C-bit from label mapping message received from peer PE1 and locally configured preference for use of control word, PE2 should determine the use of PW control word according to [RFC4447] section 6. 4. Backward Compatibility Since control word negotiation mechanism is updated by adding label request message, and still follows the basic procedure described in [RFC4447] section 6, it is fully compatible with existing implementations. The remote PE (PE1 in figure 1) which already implement label request message could be compatible with the PE (PE2 in figure 1) following the mechanism of this document. 5. Security Considerations This document does not introduce any additional security constraints. 6. IANA Considerations This document does not require IANA assignment. 7. Acknowledgements The authors would like to thank Stewart Bryant, Andrew Malis, Nick Del Regno, Luca Martini, Venkatesan Mahalingam, Alexander Vainshtein, Adrian Farrel and Spike Curtis for their discussion and comments. 8. Contributing Authors Vishwas Manral Hewlett-Packard Co. Jin, et al. Expires December 17, 2012 [Page 6] Internet-Draft draft-ietf-pwe3-cbit-negotiation-04 June 2012 19111 Pruneridge Ave, Bldg 44, Cupertino, CA 95014-0691 Email: vishwas.manral@hp.com Reshad Rahman Cisco Systems, Inc. 2000 Innovation Drive Ottawa, Ontario K2K 3E8 CANADA Email: rrahman@cisco.com 9. Normative references [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [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. [RFC6073] Martini, L., Metz, C., Nadeau, T., Bocci, M., and M. Aissaoui, "Segmented Pseudowire", RFC 6073, January 2011. Appendix A. Updated C-bit Handling Procedures Diagram ----------------------------------- | | | ------------------ | Y | Received Label | N | -------| Mapping Msg? |-------------- | | ------------------ | | -------------- | | | | | | ------- ------- | | | C=0 | | C=1 | | | ------- ------- | | | | | | | ---------------- | | | | Control Word | N | | | | Capable? |----------- | | | ---------------- | | | | Y | | | | | | | | | | ---------------- | | Jin, et al. Expires December 17, 2012 [Page 7] Internet-Draft draft-ietf-pwe3-cbit-negotiation-04 June 2012 | | | Control Word | N | | | | | Preferred? |---- | | | | ---------------- | | | | | Y | | | | | --------------------- | | | | | | Control Word | | | | ---------------- | | change Preferred | | | | | Control Word | | | to not-Preferred? | | | | | Preferred? | | --------------------- | | | ---------------- | Y | | N | | | N | Y | | | | | | | | | | | Send Send Send Send Send Send | | C=0 C=1 C=0 C=0 C=0 C=1 | | | | | | | ------------------- ---------------------------------- | | Send withdraw | | If receive the same as sent, | | | if already sent | | PW setup is complete. If not: | | | label mapping, | ---------------------------------- | | and release msg | | | | | | ------------------- ------------------- ----------- | | | Receive | | Receive | | ------------------- | C=1 | | C=0 | | | Receiving label | ------------------- ----------- | | release message | | | | ------------------- Wait for the Send | | next message Wrong C-bit | ------------------- | | | Send label | Send Label | | request message | Mapping Message | ------------------- | | ------------- Authors' Addresses Lizhong Jin (editor) ZTE Corporation 889, Bibo Road Shanghai, 201203, China Email: lizhong.jin@zte.com.cn Jin, et al. Expires December 17, 2012 [Page 8] Internet-Draft draft-ietf-pwe3-cbit-negotiation-04 June 2012 Raymond Key (editor) Huawei Email: raymond.key@ieee.org Simon Delord Alcatel-Lucent Email: simon.delord@gmail.com Thomas Nadeau Juniper Email: tnadeau@juniper.net Sami Boutros Cisco Systems, Inc. 3750 Cisco Way San Jose, California 95134, USA Email: sboutros@cisco.com Jin, et al. Expires December 17, 2012 [Page 9]