What is – MAC Address, MAC Filtering, MAC Spoofing

MAC Address or Media Access Control Address (physical address/ hardware address) is the permanent address embedded in NIC (Network Interface Cards) and Wireless Adapters. In this article, you can read a short introduction to What is MAC address, MAC filtering & MAC spoofing.

What is a MAC Address?

A MAC address is a permanent address which is assigned to the network interface of every network connected device (NIC Cards, Wireless Adapters, etc) by the hardware manufacturers. Even though every network connected device has an IP address to identify them at the network layer (L3), the IP address is frequently changed (by a DHCP Server, for example). In contrast, MAC addresses are fixed and they function at the Data Link Layer(L2). A MAC address is also known as the physical address or the hardware address of a device.

A network device (like a computer, server, etc) can have multiple Network Interface Cards and each of them is assigned a unique MAC address. The ARP Table (Address Resolution Protocol Table) maintained by network devices contains the mapping between IP address and its corresponding MAC address, in order to identify and enable the network devices to communicate with each other. So, even though you identify and send a packet to a network device using its IP address, the IP address is mapped to its corresponding permanent MAC address.

A MAC Address has a standard naming convention overseen by the IEEE which enables all the hardware manufacturers to assign unique MAC Addresses to their device. This popular convention is referred to as MAC-48 (for network hardware) and each MAC address consists of a 12-digit hexadecimal number. These twelve digits are further broken into six sets of two hexadecimal numbers each separated by a ‘:’ or ‘-‘ . So, the MAC address looks like hh:hh:hh:hh:hh:hh where h refers to a hexadecimal digit. So, a MAC address can look like this: 05-b6-12-28-7c-da.

What is MAC Filtering?

In Wireless Network devices like Wireless Access Points / Wireless Routers, etc there is an option for MAC Filtering. The Wireless Routers / Access points connect to only those devices whose MAC addresses have already been approved to connect to them (Using a list of White Listed MAC addresses that is already stored inside them). This provides some basic level security and can prevent casual network browsers from connecting to the wireless network. But MAC filtering does not give adequate security for wireless networks due to MAC Spoofing which is discussed below.

In fact, MAC filtering is also employed to provide selective access to other types of network devices like wired switches, etc. Even multiple VLAN ‘s (Virtual LAN) can be formed, each containing a group of devices with certain MAC addresses. When using a corporate directory authentication like LDAP /RADIUS /Active Directory, it is possible to verify both user id / password (and) device MAC address before giving network access to a user.

What is MAC Spoofing?

MAC Spoofing refers to the ability of changing your computer’s MAC address to any MAC address you want and then connecting to the networks that have MAC filtering in place. This method is used by hackers to sniff a valid MAC address used in a wireless network and connect to the Wireless LAN after having changed their own MAC address to that valid MAC address.

A wireless network can be monitored from a near-by place where the wireless network signals are available and a valid MAC address used in that network can be identified using freely available programs on the Internet like Nmap. After that, it is simple to change the MAC address to any MAC address desired by you, using commands like ifconfig in Linux, MAC, BSD (or) changing the Windows Registry entry for MAC address in Windows (or) using freely available software programs.

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