Ethernet Logical Addressing

Ethernet Logical Addressing

In Ethernet, LAN devices must have a unique identifier on that specific domain. LAN devices use a Media Access Control (MAC) address for such purpose. MAC addresses are also referred to as hardware addresses or burned-in addresses because they are usually programmed into the Ethernet adapter by the manufacturer of the hardware.

The format of a MAC address is a 48-bit hexadecimal address. Because hexadecimal uses the digits 0-9 and the letters a-f (for numbers 10-15), this yields a 12-digit address. MAC addresses are represented in any one of four formats. All the formats properly identify a MAC address and differ only in the field separators, as follows:

• Dashes between each two characters: 00-01-03-23-31-DD

• Colons instead of dashes between each two characters: 00:01:03:23:31:DD

• Periods between each fourth character: 0001.0323.31DD

• The digits without dashes, periods, or colons: 0001032331DD

Cisco routers typically use the 0001.0323.31DD formatting, while Cisco switches running Catalyst Operation System (Catalyst OS) images use 00:01:03:23:31:DD to represent the same address.