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VCCV Extensions for Segmented PW: Enhanced Ping and Trace

This document proposes a method to extend VCCV to operate over a segmented PW, allowing for improved ping and trace functionality. It ensures compatibility with existing VCCV and LSP Ping/Trace operations.

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VCCV Extensions for Segmented PW: Enhanced Ping and Trace

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  1. VCCV Extensions for Segmented Pseudo-Wiredraft-hart-pwe3-segmented-pw-vccv-00.txtNeil Hart, Mustapha Aïssaoui, Matthew Bocci, Tiberiu GrigoriuAlcatel

  2. Objective • Provide a method to extend VCCV to operate over a segmented PW • Allow both ping and trace of a PW FEC • Compatible with operation of VCCV in SS-PW • Current proposal in draft-ietf-pwe3-segmented-pw-02 defines a new VCCV sub-TLV in the PW switching point and a new MS-PW VCCV control word with a TTL field • Compatible with operation of LSP Ping and LSP trace which examine TTL to determine if VCCV message should be terminated and processed at S-PE • Current proposal requires processing of the new MS-PW control word to determine this

  3. Principles of Operation - Control Plane • T-PEs and S-PEs negotiate the common use of Control Word for VCCV end to end • VCCV parameter included in the interface parameter field of the PW ID FEC TLV or the sub-TLV interface parameter of the Generalized PW ID FEC TLV • S-PE will not pass other CC types, i.e., TTL=1 and Route Alert, in the PW FEC as currently specified in draft-ietf-pwe3-segmented-pw-02

  4. Principles of Operation – Data plane • PW FEC Ping: • T-PE sets inner PW label TTL to a large enough value to allow the packet to reach the far end T-PE • T-PE sends a VCCV packet that will follow the exact same data path at each S-PE as that taken by data packets, • S-PE performs an outer label pop, an inner label swap with TTL decrement, and new outer label push. • there is no requirement for the S-PE to inspect the CW • VCCV packet is diverted to VCCV control processing at the destination T-PE • T-PE replies using the specified reply mode, i.e., reverse PW path or IGP path

  5. Principles of Operation – Data plane (II) • PW FEC Trace: • the TTL of the PW label is used to force the VCCV message to 'pop out' at an S-PE • S-PE pops the outer label and decrements TTL of the inner label • If the TTL expires, the S-PE determines that the packet is a VCCV packet by checking the control word • S-PE diverts the packet to VCCV control processing • S-PE replies using the specified reply mode

  6. Design Considerations • It is a requirement that each S-PE decrement the PW label TTL correctly • Manipulation of the PW label TTL by a penultimate LSR between S-PEs, or between an S-PE and a T-PE, may cause the VCCV message not to emerge from the MS-PW at the correct S-PE

  7. Next Step • Authors would like to request more feedback on mailing list

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