VCCV Extensions for Segmented Pseudo-Wire draft-hart-pwe3-segmented-pw-vccv-00.txt Neil Hart, Mustapha A - PowerPoint PPT Presentation

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VCCV Extensions for Segmented Pseudo-Wire draft-hart-pwe3-segmented-pw-vccv-00.txt Neil Hart, Mustapha A

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S-PE pops the outer label and decrements TTL of the inner label ... It is a requirement that each S-PE decrement the PW label TTL correctly ... – PowerPoint PPT presentation

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Title: VCCV Extensions for Segmented Pseudo-Wire draft-hart-pwe3-segmented-pw-vccv-00.txt Neil Hart, Mustapha A


1
VCCV Extensions for Segmented Pseudo-Wiredraft-ha
rt-pwe3-segmented-pw-vccv-00.txtNeil Hart,
Mustapha Aïssaoui, Matthew Bocci, Tiberiu
Grigoriu Alcatel
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-0
    2 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., TTL1
    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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