Automated selection of an optimal path between a core switch and teamed network resources of a computer system

A NIC teaming intermediate driver running on a computer system binds NIC resources into teams to provide a physical interface for the computer system to the network. When configuring a team, the teaming driver assigns one of the team members to be the primary resource and the others to be secondary. When one or more members of the team are coupled to more than one path through a layer 2 network to a core switch, the intermediate driver listens to frames transmitted over the layer 2 network regarding the cost (i.e. the bandwidth) of various connections between switches in the network and chooses the primary member to be that member coupled to the lowest cost path (i.e. highest bandwidth).