Which protocol allows for the distribution of labels in an MPLS network?

In an MPLS (Multiprotocol Label Switching) network, the distribution of labels is primarily handled by the Border Gateway Protocol (BGP), particularly in MPLS implementations that involve inter-domain label distribution or when connecting different service provider networks. BGP facilitates the exchange of routing information and labels between different routers, enabling them to maintain a consistent and up-to-date mapping of labels to routes.

Labels in MPLS are crucial for efficient data forwarding, as they allow routers to make forwarding decisions based on the shortest path rather than having to inspect packet headers at every hop. BGP, when utilized in conjunction with extensions like Label Distribution Protocol (LDP) or Resource Reservation Protocol (RSVP), allows for the dynamic allocation of labels to routes being used across the network.

The other protocols mentioned in the options serve different purposes. IGMP (Internet Group Management Protocol) is used for managing multicast group memberships, while STP (Spanning Tree Protocol) and RSTP (Rapid Spanning Tree Protocol) are related to preventing loops in Ethernet networks and are not concerned with label distribution in MPLS. Thus, BGP is the correct and relevant choice for label distribution within an MPLS environment.