What happens to an unlabeled IP packet that arrives at an LSR router and the intended outgoing interface is MPLS-enabled?

What happens to an unlabeled IP packet that arrives at an LSR router and the intended outgoing interface is MPLS-enabled?

• A label is added and the packet is forwarded.
• The packet is sent to the LFIB for a forwarding decision.
• The packet is forwarded without a label to the next hop LSR.
• An error code is sent to the source CE router and the packet is dropped.

Explanation: The data plane of an LSR consists of an IP forwarding table (FIB) and a label forwarding table (LFIB). The FIB makes forwarding decisions for unlabelled packets. The LFIB makes forwarding decisions for labeled packets. When an unlabeled IP packet arrives on an interface, if the outgoing interface is MPLS enabled, a label is added and the packet forwarded out the MPLS-enabeled interface.

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