The label-withdraw-delay command enables a node to delay sending Label Withdraw messages.
The undo label-withdraw-delay command disables a node from delaying sending Label Withdraw messages.
By default, the label withdraw delay function is disabled.
Usage Scenario
If a route change causes an LDP label switched path (LSP) failure, the upstream node of the faulty node may detect the route change and send a Label Withdraw message to instruct the ingress to tear down the LSP before receiving an LSP Down Reason message from the faulty node. When the LSP Down Reason message arrives at the upstream node, this node discards the message because the LSP has been torn down. As a result, the ingress cannot obtain fault information carried in the LSP Down Reason message. To help the ingress obtain the fault cause, run the label-withdraw-delay command on each node of the LDP LSP to delay sending Label Withdraw messages.
The label withdraw delay function prevents downstream LSP flapping from spreading to upstream nodes. For example, an LSP on a local node flaps because an LDP session between the node and its downstream peer flaps, a route flaps, or an LDP policy is modified. The local node repeatedly sends Label Withdraw and Label Mapping messages in sequence to upstream nodes. This causes the upstream nodes to repeatedly tear down and reestablish LSPs. As a result, the entire LDP LSP flaps. The label withdraw delay function can be enabled on each node of the LDP LSP to suppress the spread of LSP flapping.
Follow-up Procedure
Use the default delay time of 5s or run the label-withdraw-delay timer command to set the delay time.