Media access control (MAC) addressing

Ethernet designates the frame format and the speed of the data travelling over the physical network. However, there is still a need for controlling how individual hosts (workstations) attached to the physical network locate each other. The answer is the media access control (MAC) address. Every host connected to the network has a unique MAC address associated with its NIC. This MAC address, via the NIC, uniquely identifies the host.

MAC addresses are generally built into the NIC itself, but TCP/IP on z/OS does allow MAC addresses of OSA cards to be manually altered.

Note: The address assigned to a NIC might also be referred to as a "universally administered address", because all NICs sold worldwide (within a protocol group, such as Ethernet) must be uniquely addressed. If the address of a NIC has been manually overridden, it is considered to be a "locally administered address."