In one embodiment, a system includes a hardware processor and logic integrated with and/or executable by the processor or media access control (MAC) functionality of a network port. The logic is configured to negotiate a credit aging duration during initialization of a link between a receiving endpoint and a sending endpoint, the receiving and sending endpoints being connected in a network fabric. The link includes at least one virtual link. The logic is also configured to receive an amount of available flow credits from the receiving endpoint and transmit one or more packets to the receiving endpoint. The amount of available flow credits are used to determine a capacity to process packets at the receiving endpoint. The exchange of flow credits is performed on a per virtual link basis. Other systems, methods, and computer program products are presented according to more embodiments.