Final answer:
MPLS (Multiprotocol Label Switching) is a type of network commonly used by service providers, where forwarding decisions are based on a label contained in a 32-bit header.
Step-by-step explanation:
The type of network, commonly used by service providers, that makes forwarding decisions based on a label contained in a 32-bit header is MPLS (Multiprotocol Label Switching). MPLS is a protocol for efficient traffic routing in a network, where packets are assigned labels and routers use these labels to make forwarding decisions. This helps in optimizing network performance and ensuring the efficient delivery of data. MPLS can encapsulate packets of various network protocols, especially in service provider environments.