WHAT IS MAC ADDRESS.

MAC address (Media Access Control address) is a quasi-unique identifier consists of a six byte number that attached to most network adapter card or network interface card (NIC). As such, all network cards, whether it’s of Ethernet NIC, Gigabit Ethernet NIC or wireless 802.11a/b/g/n WiFi or HiperLAN adapter, should have different MAC addresses, which also known as Ethernet Hardware Address (EHA) or adapter address.

In operating system, MAC address is often represented in 12-digit hexadecimal number. For example, 1A-2B-3C-4D-5E-6F. In practical usage, layer 2 MAC address is converted from layer 3 protocol addresses such as Internet Protocol (IP address) by ARP (Address Resolution Protocol), which then allowed each host to be uniquely identified and frames to be marked for specific hosts on broadcast networks, such as Ethernet. After translated (or when a host on LAN sends its MAC address to another machine which does n ot configured not to accept unrequested ARP replies on the network for preemptive caching), MAC address is cached on source PC ARP table for later use. Content of ARP table on each computer can be viewed by typingarp -a in Windows or arp in Linux. MAC address thus forms the basis of most of the layer 2 networking upon which higher OSI Layer protocols are built to produce complex, functioning networks.

There are many reasons or possibilities that an user may want to change the MAC address or a network adapter, which also known as MAC spoofing. For example, to bypass the MAC address filtering on firewall or router. The trick can be used to get pass the network access restriction by emulating a new unrestricted MAC address, or to gain access connection by spoof an authorized MAC address after sniffing the legitimate MAC address out of the air in MAC filtering Wi-Fi network.

Beside, hackers or enthusiasts also spoofing another host’s MAC address as their own in order to receive traffic packets not meant for them, although ARP poisoning technique is more commonly used. However, changing MAC address can still keep the real information from been detected and logged by various services such as IDS, firewall, DHCP server, wireless access points and etc, and is essential protect user’s privacy. MAC spoofing also potentially trigger a Denial of Service (DoS) attack by causing routing problem with duplicating MAC address exists in the network, especially those similar with gateway and AP router’s BSSID (Basic Service Set Identifier.)

Whatever the reason, it’s pretty easy to change the MAC address or perform MAC spoofing on most of today’s hardware, listed below. Actually, the original MAC address is burnt and imprinted to the network card, and cannot be changed. However, operating system can spoof as if there is different MAC address for the network interface card using tricks below.