Which device adds MPLS labels to packets that enter a service provider network?

The device that adds MPLS labels to packets entering a service provider network is known as an ingress Label Edge Router (iLER). This function is crucial in MPLS (Multiprotocol Label Switching) networks as it designates the starting point in the MPLS architecture, where data packets are tagged with labels for efficient routing through the network.

The iLER plays a vital role by examining incoming packets and appending labels based on predefined policies, allowing subsequent MPLS routers (usually core routers) to make forwarding decisions based solely on these labels, rather than having to inspect the entire packet. This helps streamline operations and enhance performance within the service provider's infrastructure.

In the context of other device types mentioned, while edge routers might perform different roles such as routing between different network segments, the specific task of labeling packets as they enter the MPLS network is distinctly managed by the ingress routers.