Ldp graceful restart for pseudowire
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LDP Graceful Restart for Pseudowire. draft-jiang-pwe3-ldp-gr-01.txt. Kan. Hu Jian. Luo Bo. Wu ZTE Corporation. Introduction. LDP graceful restart mechanism defined in [RFC 3478] can be applied to pseudowire graceful restart.

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LDP Graceful Restart for Pseudowire

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LDP Graceful Restart for Pseudowire

draft-jiang-pwe3-ldp-gr-01.txt

Kan. Hu

Jian. Luo

Bo. Wu

ZTE Corporation


Introduction

  • LDP graceful restart mechanism defined in [RFC 3478] can be applied to pseudowire graceful restart.

  • Pseudowire graceful restart (GR) mechanism can be optimized by extending capability negotiation in [RFC 3478] .


Problem statement (I)

Pseudowire

  • PE1 support both LSP-FEC and PW-FEC graceful restart.

  • PE2 only support graceful restart for LSP-FEC.

  • Through Fault Tolerant (FT) Session TLV in the LDP Initialization message, negotiated result is:

    • PE1 will assume PE2 also supports graceful restart for both LSP-FEC and PW-FEC.

    • PE2 will assume PE1 only supports graceful restart for LSP-FEC.

AC

AC

CE1

CE2

PE1

PE2


Problem statement (II)

Pseudowire

  • PE2 restarts its control plane.

  • PE1 detects that its LDP session with a neighbor went down.

  • PE1 retains the LSP-FEC and PW-FEC label bindings, and continue traffic forwarding.

  • PE2 will not retain PW-FEC in the data plane, and remove the label and PW-FEC binding.

  • The traffic black hole will be caused on PE1 until recovery time out

AC

AC

CE1

CE2

PE1

PE2

LSP&PW GR

LSP GR


Problem statement (III)

Pseudowire

Black hole time =

PE1 LDP session established time +

Minimum {FT Recovery Time, Maximum Recovery Time}

AC

AC

CE1

CE2

PE1

PE2

LSP&PW GR

LSP GR


LDP graceful restart capability encoding

  • FT FEC type TLV

    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

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    |1|0| FT FEC type TLV (tbd) | Length (= 4) |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    |F| Reserved | FEC Element | Reserved |

    | | Flag | Type | |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

  • This draft defines FT FEC type TLV to indicate the FEC element type that support graceful restart.

  • FEC element type: One octet FEC Element Type that specifies the FEC Element Type that supports graceful restart. Please see section 3.4.1 of RFC5036, and RFC4447.


LDP graceful restart capability encoding

  • Several FT FEC type TLVs can be appended behind FT Session TLV

  • Each FT FEC type TLV will carry a FEC element type which indicates the FEC that support graceful restart.

    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

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    |1|0| FT Session TLV (0x0503) | Length (= 12) |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    | FT Flags | Reserved |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    | FT Reconnect Timeout (in milliseconds) |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    | Recovery Time (in milliseconds) |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    |1|0| FT FEC type TLV (tbd) | Length (= 4) |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    |F| Reserved | FEC Element | Reserved |

    | | Flag | Type | |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    | ................. |

    ~ ~

    | |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    |1|0| FT FEC type TLV (tbd) | Length (= 4) |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

    |F| Reserved | FEC Element | Reserved |

    | | Flag | Type | |

    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


PE operation during restart with the extension

Pseudowire

  • PE1 detects that its LDP session with PE2 went down. It already knew that the neighbor is only capable of preserving its LSP-FEC forwarding state across the restart By negotiating through FT FEC type TLV.

  • PE1 will delete the PW-FEC and label binding immediately, but it will retains the LSP-FEC and label bindings received via that session and marks them as "stale".

  • PE1 will notify CE1 that network side is down, and CE1 will not send traffic toPE1.

AC

AC

CE1

CE2

PE1

PE2

LSP&PW GR

LSP GR


Next steps

  • Need comments from work group

Thank you


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