Physical MAC address

1. MAC address
The MAC address of the NIC is not defined at will, and its composition structure.
 
 
 
 
1> the last three bytes represent the serial number of a network product (such as a NIC) manufactured by the manufacturer. The first three bytes represent the serial number of the network hardware manufacturer, it is allocated by IEEE (Association of Electrical and Electronics Engineers)
 
2> the ethernet address is 48 bits, which are uniformly allocated to the NIC manufacturer by IEEE. Each NIC address must be globally unique. Length of 6 bytes in total. FF: FF is the broadcast address. It can only be used in the destination address segment and cannot be used as the source address segment. Packets whose destination address is a broadcast address can be received by all network cards in a LAN. The valid ethernet address 32nd-bit multicast flag must be 0. For example:
 
X0: XX
 
X2: XX
 
X4: XX
 
X6: XX
 
X8: XX
 
XA: XX
 
XC: XX
 
XE: XX
 
Valid ethernet address. The preceding X represents any one of 0-f.
 
Address
 
X1: XX
 
X3: XX
 
X5: XX
 
X7: XX
 
X9: XX
 
XB: XX
 
XD: XX
 
XF: XX
 
It is a multicast address and can only be used as the destination address. It cannot be used as the source address. A multicast address can be received by a network card that supports this multicast address. Multicast addresses are mainly used in video broadcast, Remote Wake-up (by sending a special packet to enable the NIC to generate an interrupt signal and start the computer), and games (games played by multiple people on the LAN.
 
2 Nic MAC Application
1> the following are some specific multicast addresses:
 
Address range: 01: 00: 5E: 00: 00: 00---01: 00: 5E: 7F: FF is used for ip address multicast. Other multicast addresses have nothing to do with TCP/IP, we will not introduce it.
 
2> the NIC can receive data packets from the following addresses:
 
The first type of destination address is the same as the network card address;
 
Data Packets whose destination address is FF: FF broadcast address;
 
The third destination address is a packet with the same range as the multicast address.
 
3> in Ethernet applications, if you want your data packets to be sent to only one Nic, use the peer NIC address as the destination address;
 
4> if you want to send data packets to all NICs, use the broadcast address as the destination address;
 
5> if you want to send data packets to a group of NICs, use the multicast address as the destination address.
 
3. extended knowledge (MAC security issues)
 
1> the MAC address can be modified:
 
In some cases, you need to modify the MAC address. For example, if you assume that you are an official user in the network, you need to modify the MAC address of the NIC. To modify the MAC address, you can use the hardware method, that is, using the program provided by the NIC manufacturer to burn the ENI's EEPROM (Electrically ically Erasable Programmable Read-OnlyMemory, Electrically Erasable Programmable Read-only memory) this is feasible, but it is easy to make mistakes. You can also use another method: when Windows is installed, it will automatically read the MAC address from the NIC, store it in the MAC address in the registry, and store it in the Registry for backup. When data is transmitted over the network, a source MAC address is required in the packets sent from the network adapter. This MAC address is read from the Registry (not from the network adapter). Therefore, if you modify the MAC address in the registry, it is equivalent to changing the MAC address in the nic eeprom. The actual effect is the same.