portInfoPhyIfPhysAddress 1.3.6.1.4.1.11.2.3.7.11.33.4.2.1.3.2.1.1.9

The interface's address at the protocol layer immediately `below' the network layer in the protocol stack. For interfaces which do not have such an address (e.g., a serial line), this object should contain an octet string of zero length.