A network socket application programming interface (API) running on a communication device is operative to provide, to applications running on the device, information about the performance of communication links used by sockets for communicating across a network. The socket API receives packets associated with sockets, and retrieves from the packets performance information for corresponding communication links. In response to receiving a request from an application for performance information associated with a particular socket, the API identifies performance information for the particular socket and returns the retrieved information to the application. A performance monitoring network device provides the performance information. The performance monitoring device stores information about the performance of a plurality of communication links used by sockets of communications devices in the network, and inserts the performance information for particular sockets into associated packets before transmitting the packets to corresponding communication devices.