What is an explicit-null label

The explicit-null label is label 0, which takes effect only at the bottom of the stack. An LSR must pop up the label stack and forward the explicit-null label based on the IPv4 header information.

The penultimate hop attaches label 0 to the bottom of the stack and forwards the stack to the egress node. The egress node does not search in the ILM if a packet has label 0. It pops the label 0 and determines the forwarding path based on the IP header information (if the label stack has only one layer).

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