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hardware address是mac地址吗( 三 )

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If the least significant bit of the most significant byte is set to a 0, the packet is meant to reach only one receiving NIC. This is called unicast. If the least significant bit of the most significant byte is set to a 1, the packet is meant to be sent only once but still reach several NICs. This is called multicast.
MAC-48 and EUI-48 addresses are usually shown in hexadecimal format, with each octet separated by a dash or colon. An example of a MAC-48 address would be "00-08-74-4C-7F-1D". If you cross-reference the first three octets with IEEE's OUI assignments,[3] you can see that this MAC address came from Dell Computer Corp. The last three octets represent the serial number assigned to the adapter by the manufacturer.
The following technologies use the MAC-48 identifier format:
Ethernet
802.11 wireless networks
Bluetooth
IEEE 802.5 token ring
most other IEEE 802 networks
FDDI
ATM (switched virtual connections only, as part of an NSAP address)
Fibre Channel and Serial Attached SCSI (as part of a World Wide Name)
The distinction between EUI-48 and MAC-48 identifiers is purely semantic: MAC-48 is used for network hardware; EUI-48 is used to identify other devices and software. (Thus, by definition, an EUI-48 is not in fact a "MAC address", although it is syntactically indistinguishable from one and assigned from the same numbering space.)
The IEEE now considers the label MAC-48 to be an obsolete term which was previously used to refer to a specific type of EUI-48 identifier used to address hardware interfaces within existing 802-based networking applications and should not be used in the future. Instead, the term EUI-48 should be used for this purpose.
EUI-64 identifiers are used in:
FireWire
IPv6 (as the low-order 64 bits of a unicast network address when temporary addresses are not being used)
ZigBee / 802.15.4 wireless personal-area networks
The IEEE has built in several special address types to allow more than one Network Interface Card to be addressed at one time:
Packets sent to the broadcast address, all one bits, are received by all stations on a local area network. In hexadecimal the broadcast address would be "FF:FF:FF:FF:FF:FF".
Packets sent to a multicast address are received by all stations on a LAN that have been configured to receive packets sent to that address.
Functional addresses identify one of more Token Ring NICs that provide a particular service, defined in IEEE 802.5.
These are "group addresses", as opposed to "individual addresses"; the least significant bit of the first octet of a MAC address distinguishes individual addresses from group addresses. That bit is set to 0 in individual addresses and 1 in group addresses. Group addresses, like individual addresses, can be universally administered or locally administered.
In addition, the EUI-64 numbering system encompasses both MAC-48 and EUI-48 identifiers by a simple translation mechanism. To convert a MAC-48 into an EUI-64, copy the OUI, append the two octets "FF-FF", and then copy the organization-specified part. To convert an EUI-48 into an EUI-64, the same process is used, but the sequence inserted is "FF-FE". In both cases, the process can be trivially reversed when necessary. Organizations issuing EUI-64s are cautioned against issuing identifiers that could be confused with these forms. The IEEE policy is to discourage new uses of 48-bit identifiers in favor of the EUI-64 system.
IPv6—one of the most prominent standards that uses EUI-64—applies these rules inconsistently. Due to an error in the appendix to the specification of IPv6 addressing, it is standard practice to extend MAC-48 addresses (such as IEEE 802 MAC address) to EUI-64 using "FF-FE" rather than "FF-FF."
[edit] Individual address block
An Individual Address Block comprises a 24-bit OUI managed by the IEEE Registration Authority, followed by 12 IEEE-provided bits (identifying the organization), and 12 bits for the owner to assign to individual devices. An IAB is ideal for organizations requiring fewer than 4097 unique 48-bit numbers (EUI-48).[4]
[edit] Bit-reversed notation
The standard transmission order notation for MAC addresses, as seen in the output of the ifconfig command for example, is also called canonical format.
However, since IEEE 802.3 (Ethernet) and IEEE 802.4 (Token Bus) send the bits over the wire with least significant bit first, while IEEE 802.5 (Token Ring) and IEEE 802.6 send the bits over the wire with most significant bit first, confusion may arise where an address in the latter scenario is represented with bits reversed from the canonical representation. So for instance, an address whose canonical form is 12-34-56-78-9A-BC would be transmitted over the wire as bits 01001000 00101100 01101010 00011110 01011001 00111101 in the standard transmission order (least significant bit first). But for Token Ring networks, it would be transmitted as bits 00010010 00110100 01010110 01111000 10011010 10111100 in most significant bit first order. If care is not taken to translate correctly and consistently to the canonical representation, the latter might be displayed as 482C6A1E593D, which could cause confusion. This would be referred to as "Bit-reversed order", "Non-canonical form", "MSB format", "IBM format", or "Token Ring format" as explained by RFC 2469. Canonical form is preferred[who?].


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