The present invention is in the field of virtualization of Network Interface Cards and Controllers (NIC) that connect to for example a host computer that can have multiple functions and OS's (referred to as guest functions and guest-OS's) running on it simultaneously and, in particular, relates to the virtualization of the operation of a single NIC such that it can be used simultaneously by multiple guests in such a manner that memory references due to the network traffic originating from and destined to a particular guest is kept separate from other network traffic, and that allows the Media Access Controller (MAC) within the NIC to operate such that it only accepts network packets that are destined to one of the guest-functions or guest-OS's, and the MAC is not required to operate in promiscuous mode where it accepts all incoming packets in order to implement the virtualization features.