 | Copyright © 2009, Juniper Networks, Inc. All rights reserved. Trademark Notice. | |
A MAC address is the serial number permanently stored in a device adapter to uniquely identify the device. MAC addresses operate at the data link layer, while IP addresses operate at the network layer. The IP address of a device can change as the device is moved around a network to different IP subnets, but the MAC address remains the same, because it is physically tied to the device.
Within an IP network, devices match each MAC address to its corresponding configured IP address by means of the Address Resolution Protocol (ARP). ARP maintains a table with a mapping for each MAC address in the network.
Most Layer 2 networks use one of three primary numbering spaces—MAC-48, EUI-48 (Extended Unique Identifier), and EUI-64—which are all globally unique. MAC-48 and EUI-48 spaces each use 48-bit addresses, and EUI-64 spaces use a 64-bit addresses, but all three use the same numbering format. MAC-48 addresses identify network hardware, and EUI-48 addresses identify other devices and software.
The Ethernet and ATM technologies supported on devices use the MAC-48 address space. IPv6 uses the EUI-64 address space.
MAC-48 addresses are the most commonly used MAC addresses in most networks. These addresses are 12-digit hexadecimal numbers (48 bits in length) that typically appear in one of the following formats:
The first three octets (MM:MM:MM or MM-MM-MM) are the ID number of the hardware manufacturer. Manufacturer ID numbers are assigned by the Institute of Electrical and Electronics Engineers (IEEE). The last three octets (SS:SS:SS or SS-SS-SS) make up the serial number for the device, which is assigned by the manufacturer. For example, an Ethernet interface card might have a MAC address of 00:05:85:c1:a6:a0.
| Copyright © 2009, Juniper Networks, Inc. All rights reserved. Trademark Notice. | |