LDP Graceful Restart for Pseudowire

Kan. HuJian. LuoBo. Wu

ZTE Corporation

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

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)

• 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.

PE1 PE2CE2CE1

ACACPseudowire

Problem statement (II)

1. PE2 restarts its control plane.2. PE1 detects that its LDP session with a neighbor went

down.3. PE1 retains the LSP-FEC and PW-FEC label bindings,

and continue traffic forwarding.4. PE2 will not retain PW-FEC in the data plane, and

remove the label and PW-FEC binding. 5. The traffic black hole will be caused on PE1 until

recovery time out

PE1 PE2CE2CE1

ACACPseudowire

LSP GRLSP&PW GR

Problem statement (III)

Black hole time =

PE1 LDP session established time +

Minimum {FT Recovery Time, Maximum Recovery Time}

PE1 PE2CE2CE1

ACACPseudowire

LSP GRLSP&PW 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

1. 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.

2. 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".

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

PE1 PE2CE2CE1

ACACPseudowire

LSP GRLSP&PW GR

Next steps

• Need comments from work group

Thank you