VCCV Extensions for Multi-Segment Pseudo-Wire draft-hart-pwe3-segmented-pw-vccv-01.txt draft-ietf-pwe3-segmented-pw-04.txt Mustapha A

1
VCCV Extensions for Multi-Segment
Pseudo-Wiredraft-hart-pwe3-segmented-pw-vccv-01.t
xtdraft-ietf-pwe3-segmented-pw-04.txtMustapha
Aïssaoui, AlcatelTom Nadeau, Cisco
2
Introduction

• Requirements
• when a switching point exists between PE nodes,
  it is required to be able to continue operating
  VCCV end-to-end across a S-PE and,
• to provide the ability to trace the path of the
  MS-PW over any number of segments
• Two proposed methods to achieve these objectives
• The first method is based on re-using the
  existing VCCV CW and decrementing the TTL of the
  PW label at each hop in the path of the MS-PW
• described in draft-hart-pwe3-segmented-pw-vccv-01.
  txt
• suitable to deployments where T-PE nodes continue
  to use the SS-PW control word
• requires S-PE nodes capable of decrementing the
  TTL field for all PW packets
• The second method is based on using a new MH-VCCV
  control word and decrementing the TTL field in
  the control word
• described in draft-ietf-pwe3-segmented-pw-03.txt
• suitable to deployments where S-PE nodes cannot
  rely the TTL in the PW label to identify if a
  VCCV packet is destined to this node or not
• requires upgrade to T-PE and S-PE user and
  control plane to use the new MH-VCCV CW

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Proposal to Move Forward

• Authors believe both methods are required based
  on existing deployments
• Initial text describing both methods added to
  draft-ietf-pwe3-segmented-pw-04.txt
• Will be published shortly
• Both methods will provide the following
  capabilities
• End-to-end VCCV (ping mode)
• Partial tracing from T-PE (ping mode)
• Partial Tracing between S-PEs (ping mode)
• Automated VCCV Trace from T-PE (trace mode)

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Signaling MS-PW VCCV Capability

• Like in SS-PW, MS-PW VCCV capabilities are
  signaled using the 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
• When using the SS-PW VCCV CW method, T-PE signals
  CC type 1
• When using the MH-VCCV CW method, T-PE signals
  the new CC type 4
• S-PE nodes processing of the VCCV parameter
  removes CC Types specified by the originating
  T-PE, except CC Types 1 and 4 which are passed
  unchanged
• The far end T-PE, T-PE2, receives the VCCV
  parameter indicating that one or both Control
  Word CC types only if they are supported by the
  sending T-PE (T-PE1) and all S-PEs along the
  MS-PW path
• If T-PE1 signaled both types and T-PE2 also
  supports them, T-PE2 uses the SS-PW CW CC type in
  preference

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New VCCV Control Channel Type 4

• The new MH-VCCV CW requires a new CC Type
• 0 1 2
  3
• 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
  4 5 6 7 8 9 0 1 0
• ------------------------
  --------
• 0x0c 0x04 CC Types
  CV Types
• ------------------------
  --------
• 0x01 Type 1 PWE3 control word with 0001 as
  first nibble
• 0x02 Type 2 MPLS Router Alert Label.
• 0x04 Type 3 MPLS PW Demultiplexor Label
  TTL 1 (Type 3).
• 0x08 Type 4 MH-VCCV Control Word

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Packet Encapsulation with MH-VCCV CW

• A new PW associated channel type is defined to
  distinguish VCCV packets with new MH-VCCV CW from
  existing VCCV CW
• 0 1 2
  3
• 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2
  3 4 5 6 7 8 9 0 1
• -----------------------
  ---------
• 0 0 0 1 0x00 Reserved 0
  Channel Type TBD
• -----------------------
  ---------
• MH-TTL MH-VCCV sub-TLV
  
• -----------------------
  ---------
• Three new values are required
• One for IPv4 control channel
• One for IPv6 control channel
• One for BFD packets without IP/UDP headers

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Control Plane Processing of an MS-PW VCCV Echo
Message

• Native lt------------Pseudo
  Wire------------gt Native
• Service
  Service
• (AC) lt-PSN1--gt
  lt-PSN2--gt (AC)
• V V V V
  V V
• ----- -----
  -----
• ---- T-PE1S-PE1
  T-PE2 ----
• -------......PW1-Seg1........PW1-Se
  g2......-------
• CE1
  CE2
• ----- -----
  -----
• ---- ----

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Ping Mode of Operation

• Single operation to check MS-PW FEC at an S-PE or
  destination T-PE
• Sending a VCCV Echo Request Message
• The sender of the echo request message requires
  the FEC of the last segment to the target
  S-PE/T-PE node
• This information can be configured manually or
  can be obtained by inspecting the corresponding
  sub-TLV's of the PW switching point TLV
• Receiving a VCCV Echo Request Message
• Target node validates the request and responds
  with a VCCV echo reply
• If target node is an S-PE for the MS-PW, it
  responds with an echo reply containing a FEC TLV
  with the FEC of the next downstream segment and a
  return code of 8 (label switched at stack-depth)
• If target node is the egress T-PE of the MS-PW,
  it responds with an echo reply with a return code
  of 3 (egress router) and no FEC TLV is included
• Receiving a VCCV Echo Reply Message
• The sender node may choose to ignore the
  information in the FEC TLV in the echo reply and
  report only the return code to the operator

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Trace Mode of Operation

• Automated path tracing capability that
  iteratively probes the segments the MS-PW to
  learn the target FEC information
• Sending a VCCV Echo Request Message
• The sender of the echo request message (T-PE)
  learns the target FEC by probing one by one the
  hops of the MS-PW path
• Receiving a VCCV Echo Request Message
• Same as in ping mode
• Receiving a VCCV Echo Reply Message
• the node builds the subsequent VCCV echo request
  message by incrementing TTL field in PW label or
  in MH-VCCV CW and using the downstream FEC it
  received in the echo request message
• It sends the echo request message to the next
  downstream PW segment

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Next Step

• Add details of control plane processing and
  automated trace into draft-ietf-pwe3-segmented-pw-
  04.txt
• Authors would like to request WG feedback on
  mailing list