NAT (Network Address Translation) is well-known as one of the short-term solutions of IPv4 address exhaustion. NAT is a technique that shares a single IP address in several PCs, and is widely used for alleviating the IPv4 address exhaustion and as a security solution. However, when a backbone network has access control function for PCs based on their IP addresses, it cannot identify the PCs under a NAT router since their original IP addresses are hidden by the NAT router. In this research, we focus on MAC address which identifies PC on datalink layer and propose a NAT router which relays the MAC addresses of PCs inside of a LAN to the outside. Since the source MAC addresses of packets sent from PCs are preserved even after being relayed by the NAT router, a LAN access control server outside of the NAT router can still identify these PCs based on their MAC addresses instead of their IP addresses.