In which scenario is BGP preferred over OSPF for routing?

BGP, or Border Gateway Protocol, is specifically designed for inter-domain routing, meaning it is used to exchange routing information between different autonomous systems (ASes). This capability is essential when connecting to multiple Internet Service Providers (ISPs) or managing connections with other autonomous systems. BGP is highly scalable and allows for the management of large networks, making it suitable for scenarios where multiple external connections exist.

In contrast, OSPF (Open Shortest Path First) is an interior gateway protocol meant for routing within a single autonomous system and is better suited for local network routing. While it efficiently handles routing within a local area network, it does not have the capabilities needed to manage external connections or advanced features such as path attributes and route policies that BGP provides.

The other scenarios outlined in the options are not ideal for BGP. For instance, distributing network load across servers typically employs load balancers or application delivery approaches rather than a routing protocol. Likewise, simple routing in a local area network is more effectively handled by OSPF due to its design for such environments, and prioritizing data packets based on size would more commonly involve Quality of Service (QoS) mechanisms rather than relying on a routing decision between BGP and OSPF.