Network Working Group Lizhong Jin (ed.), ZTE Internet-Draft Raymond Key (ed.), Telstra Updates: 4447 (if approved) Simon Delord, Alcatel-Lucent Category: Standards Track Thomas Nadeau, Huawei Expires: October 12, 2011 Vishwas Manral, IPInfusion Sami Boutros, Cisco Reshad Rahman, Cisco April 12, 2011 Pseudowire Control Word Negotiation Mechanism Update draft-ietf-pwe3-cbit-negotiation-00 Abstract This document describes the problem of control word negotiation mechanism specified in [RFC4447]. Based on the problem analysis, a message exchanging mechanism is introduced to solve this control word negotiation issue. This document is to update [RFC4447] control word negotiation mechanism. 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 October 12, 2011. Jin, et al. Expires October 2011 [Page 1] Internet-Draft draft-ietf-pwe3-cbit-negotiation-00 April 2011 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 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 4. Backward Compatibility . . . . . . . . . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 8.1. Normative References . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Appendix A. Updated C-bit Handling Procedures Diagram . . . . . . . 8 Appendix B. Alternative proposal by "Label Release" message . . . . 9 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 October 2011 [Page 2] Internet-Draft draft-ietf-pwe3-cbit-negotiation-00 April 2011 1. Introduction This document describes the problem of control word negotiation mechanism specified in [RFC4447]. Based on the problem analysis, a message exchanging mechanism is introduced to solve this negotiation issue. The control word negotiation mechanism in this document is to update [RFC4447] section 6.2 "PW Types for Which the Control Word is NOT Mandatory". 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 control word PREFERRED. This kind of behavior will cause some problem when peer PE changes its control word from NOT PREFERRED to PREFERRED. This following case will describe the negotiation problem in detail: +-------+ +-------+ | | PW | | | PE1 |====================| PE2 | | | | | +-------+ +-------+ Figure 1 1. Initially, the control word on PE1 is configured to PREFERRED, and on PE2 to NOT PREFERRED. 2. The negotiation result for the control word for this PW is "not supported", and PE1 send label mapping with C-bit=0 finally. 3. PE2 then changes its 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. The negotiation result for the PW control word is still "not supported", even though the control word configuration on both PE1 and PE2 is set to PREFERRED. Jin, et al. Expires October 2011 [Page 3] Internet-Draft draft-ietf-pwe3-cbit-negotiation-00 April 2011 3. Control word re-negotiation by label request message In order to solve this problem, the control word re-negotiation is operated by adding label request message. The control word negotiation mechanism can still follow the procedure described in [RFC4447] section 6. When Local PE changes its 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 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 configured control word setting. -iii. After receiving remote PE label mapping with control word setting, Local PE MUST follow procedures defined in [RFC4447] section 6 when sending its label mapping message. When the peer PE successfully processed the label withdraw and removed the remote label binding, it MUST send label mapping as a response of label request with locally configured control word parameter. 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, and the request message MUST be processed in ordered mode. When S-PE receives a label request message from a remote peer, it MUST advertise the request message to the other remote PE. This is necessary since S-PE does not have full information of interface parameter field in the FEC advertisement. 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. Jin, et al. Expires October 2011 [Page 4] Internet-Draft draft-ietf-pwe3-cbit-negotiation-00 April 2011 When Local PE changes its control word from PREFERRED to NOT PREFERRED, Local PE would be able to re-negotiate the Control Word to be NOT PREFERRED 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 local Control Word configuration. The procedure of PE1 and PE2 for the case in figure 1 should be as follows: 1. PE2 changes locally configured control word to PREFERRED. 2. PE2 will then send label withdraw message to PE1. 3. PE1 will send label release in reply to label withdraw message from PE2. 4. Upon receipt of Label release message from PE1, PE2 MUST send label request messages to PE1 although it already received the label mapping with C-bit=0. 5. PE1 MUST send label mapping message with C-bit=1 again to PE2 (Note: PE1 MUST send label mapping with locally configured CW parameter). 6. PE2 receives the label mapping from PE1 and updates the remote label binding information. PE2 MUST wait for PE1 label binding before sending its label binding with C-bit set, only if it previously had a label binding with C-bit=0 from PE1. 7. PE2 will send label mapping to PE1 with C-bit=1. It is to be noted that the above assume that PE1 is configured to support CW, however in step 5 if PE1 doesn't support CW, 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] CW negotiation procedure. By sending label request message, PE2 will get the configured CW parameter of peer PE1 in the received label mapping message. By using the new CW parameter from label mapping message received from peer PE1 and locally configured CW, PE2 should determine the PW CW parameter according to [RFC4447] section 6. The diagram in Appendix A in this document updates the control word negotiation diagram in [RFC4447] Appendix A. Jin, et al. Expires October 2011 [Page 5] Internet-Draft draft-ietf-pwe3-cbit-negotiation-00 April 2011 4. Backward Compatibility Since control word re-negotiation is operated by adding label request message, and still follows the 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. References 8.1. Normative References [RFC2119] Bradner, S., Key words for use in RFCs to Indicate Requirement Levels, BCP 14, RFC 2119, March 1997 [RFC4447] Martini, L., and al, Pseudowire Setup and Maintenance Using the Label Distribution Protocol (LDP), RFC 4447, April 2006 [RFC5036] Andersson, L., Minei, I., and Thomas B., LDP Specification, RFC 5036, October 2007 Jin, et al. Expires October 2011 [Page 6] Internet-Draft draft-ietf-pwe3-cbit-negotiation-00 April 2011 Authors' Addresses Lizhong Jin (editor) ZTE Corporation 889, Bibo Road Shanghai, 201203, China Email: lizhong.jin@zte.com.cn Raymond Key (editor) Telstra Email: raymond.key@ieee.org Simon Delord Alcatel-Lucent Email: simon.delord@gmail.com Thomas Nadeau Huawei Email: tnadeau@lucidvision.com Vishwas Manral IPInfusion Email: vishwas@ipinfusion.com Sami Boutros Cisco Systems, Inc. 3750 Cisco Way San Jose, California 95134 USA Email: sboutros@cisco.com Reshad Rahman Cisco Systems, Inc. 2000 Innovation Drive Ottawa, Ontario K2K 3E8 CANADA Email: rrahman@cisco.com Jin, et al. Expires October 2011 [Page 7] Internet-Draft draft-ietf-pwe3-cbit-negotiation-00 April 2011 Appendix A. Updated C-bit Handling Procedures Diagram ----------------------------------- | | | ------------------ | Y | Received Label | N | -------| Mapping Msg? |-------------- | | ------------------ | | -------------- | | | | | | ------- ------- | | | C=0 | | C=1 | | | ------- ------- | | | | | | | ---------------- | | | | Control Word | N | | | | Capable? |----------- | | | ---------------- | | | | Y | | | | | | | | | | ---------------- | | | | | 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 wait until | | | | | | | receiving label | ------------------- ----------- | | release | | Receive | | Receive | | ------------------- | C=1 | | C=0 | | | ------------------- ----------- | ------------------- | | | | Send label | Wait for the Send | | request message | next message Wrong C-bit | ------------------- | | | Send Label | | Mapping Message ------------- Jin, et al. Expires October 2011 [Page 8] Internet-Draft draft-ietf-pwe3-cbit-negotiation-00 April 2011 Appendix B. Alternative proposal by "Label Release" message We refer to the proposal in section 3 as "Label Request" message proposal. There is an alternative proposal to re-negotiate control word by sending label release with a new LDP status error code "PW Reset C-bit negotiation". When this label release is received by the S-PE in MS-PW case, it must forward it back to the T-PE. When the T-PE receives the label release with this error code, it must send a label withdraw followed by a new label mapping even if its C-bit remains the same. The procedure of PE1 and PE2 for the case in figure 1 should be as follows: 1. PE2 changes locally configured control word to PREFERRED. 2. PE2 will then send label withdraw message to PE1, and label release with a new LDP status error code "PW Reset C-bit negotiation" to PE1. 3. PE2 will then send label mapping with C-bit=1 as per RFC4447. 4. PE1 will send label release in reply to label withdraw message from PE2. 5. Upon receipt of label release with error code "PW Reset C-bit negotiation" from PE2, PE1 MUST withdraw its label mapping and re-advertise with the configured C-bit=1. 6. PE2 receives the label mapping from PE1 with C-bit=1, and re-negotiates to get the result of C-bit=1 as per RFC4447. Both "Label Request" and "Label Release" message proposals work to resolve the control word negotiation problem described in this document. We do not choose the "Label Release" message proposal for the following backward compatible reasons: 1. PE1 always needs to be updated, while the "label request" message proposal has better backward compatibility as described in section 4. 2. S-PE needs to be updated in MS-PW case, while it is not necessary in the "label request" message proposal. Jin, et al. Expires October 2011 [Page 9] Internet-Draft draft-ietf-pwe3-cbit-negotiation-00 April 2011 The following table makes a simple comparison between the two proposals. +---------+------------+-----------+---------+---------+ | Has new | Change | PE1 | PE2 | S-PE | | Defined | LDP | need | need | need | | Status? | RFC5036? | update? | update? | update? | +----------+---------+------------+-----------+---------+---------+ | Label | | Yes (add | No (see | | | | Request | No | FEC update | section 4)| Yes | No | | Proposal | | at PE2) | | | | +----------+---------+------------+-----------+---------+---------+ | Label | | Yes (change| | | | | Release | Yes | label-rel | Yes | Yes | Yes | | Proposal | | procedure) | | | | +----------+---------+------------+-----------+---------+---------+ Jin, et al. Expires October 2011 [Page 10]