Managing Cisco Network Security, Second Edition
A completely updated sourcebook on Cisco Security Management.
TABLE OF CONTENTS Managing Cisco Network Security, Second Edition
MAC Filtering
In order to fully discuss the advantages and disadvantages of MAC filtering, let's have a short review on what a MAC address is. The term MAC stands for Media Access Control, and forms the lower layer in the Data-Link layer of the OSI model. The purpose of the MAC sublayer is to present a uniform interface between the physical networking media (copper/fiber/radio frequency) and the Logical Link Control portion of the Data-Link layer. These two layers are found onboard a NIC, whether integrated into a device or used as an add-on (PCI card or PCMCIA card).
What Is a MAC Address?
In order to facilitate delivery of network traffic, the MAC layer is assigned a unique address, which is programmed into the NIC at the time of manufacture. The operating system will associate an IP address with this MAC address, which allows the device to participate in an IP network. Because no other NIC in the world should have the same MAC address, it is easy to see why it could be a secure way to equate a specific user with the MAC address on his or her machine.
Now, let's look at an actual MAC address. For example, my laptop has a MAC address of 00-00-86-4C-75-48. The first three octets are called the organizationally unique identifier (OUI). The Institute of Electrical and Electronic Engineers controls these OUIs and assigns them to companies as needed. If you look up the 00-00-86 OUI on the IEEE's Web site...
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