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Analysis and Update of Control Word Negotiation Mechanism for PWE3 at IETF79

This draft presents an analysis of control word negotiation mechanisms based on discussions with industry experts. It highlights flaws in the current methodology as described in RFC 4447 and explores various options for improvement, including control word re-negotiation and optional configurations. The document aims to clarify problems with label mapping and propose enhancements that align with service provider requirements. Recognizing the necessity for robust control word capabilities, it invites community feedback on which proposed options should be adopted moving forward.

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Analysis and Update of Control Word Negotiation Mechanism for PWE3 at IETF79

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  1. Pseudowire Control Word Negotiation Mechanism Analysis and Update PWE3 IETF79 draft-jin-pwe3-cbit-negotiation-01

  2. Introduction • This draft is an outcome from many face-to-face and email discussions with: • Stewart Bryant, Andrew Malis, Nick Del Regno, Sami Boutros, Luca Martini, Venkatesan Mahalingam, Alexander Vainshtein, Adrian Farrel, and etc. • This draft describes the problem of control word negotiation mechanism specified in [RFC4447].

  3. Relations with other draft • draft-delregno-pwe3-mandatory-control-word also solve the problem of control word negotiation, and briefly described in option 4 in this draft.

  4. Problem Statement Label Map: Cbit=0 CW: PREFERRED CW: NOT-PREFERRED PW Negotiated Cbit=0 Label Map: Cbit=0 Configuration changed to Label Withdraw CW: PREFERRED 1 Label Map: Cbit=0 PW Negotiated Cbit=0 Wrong 1 According to the control word negotiation mechanism, the received label mapping on PE2 from PE1 indicates Cbit=0, therefore PE2 will still send label mapping with Cbit=0.

  5. Option 1: Control Word Re-Negotiation by Label Request Label Map: Cbit=0 CW: PREFERRED CW: NOT-PREFERRED PW Negotiated Cbit=0 Label Map: Cbit=0 Configuration changed to Label Withdraw CW: PREFERRED Label Request Label Map: Cbit=1 Label Map: Cbit=1 PW Negotiated Cbit=1 5

  6. Option 1: Control Word Re-Negotiation by Label Request • When PE doing the CW changing operation, it should send label request to peer PE, even if it has already received the label mapping message. • Request message processing for PW: • The request message should be processed in ordered mode in MS-PW case. • PE1 SHOULD send label mapping with locally configured CW parameter. • Option1 is backward compatible.

  7. Option 2: Make CW Non-Configurable • Option 2: Make CW Non-Configurable • Default value is PREFERRED which can be degraded to NOT PREFERRED by negotiation automatically; • But: there is explicit requirement from service providers to allow control word to be configurable.

  8. Option 3: Manual Configuration Process for CW Label Map: Cbit=0 CW: PREFERRED CW: NOT-PREFERRED Label Map: Cbit=1 Configuration changed to PW Negotiated Cbit = 0 AND 1 = 0 Label Withdraw CW: PREFERRED Label Map: Cbit=1 PW Negotiated Cbit = 1 AND 1 = 1 • 1. Abandon the control word negotiation mechanism described in [RFC4447]; • 2. Local PE should simply do “AND” operation between receiving CW with local configuration (PREFERRED or not-PREFERRED). 8

  9. Option 4: Make CW Capability Mandatory • Option 4: Make CW Capability Mandatory • The PW will only be in operation UP when both PW end-points support control word capability.

  10. Next steps • Which option should be accepted? • Need comments from work group Thank you

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