Hello, we know that MAC addresses are addresses used in the media access layer, also known as physical addresses, hardware addresses, or link addresses, which are written inside the hardware when manufactured by network device manufacturers. Today I want to introduce MAC related knowledge, let's start.
MAC Foundation
Definition:
The MAC (Media Access Control) address defines the location of the network device.
Composition:
MAC addresses are composed of 48-bit long, 12-bit, 16-bit digits. Starting from left to right, 0 to 23 bits is the code used by the manufacturer to identify the manufacturer from IETF, etc. 24 to 47 bits are assigned by the manufacturer itself and are a unique number for all network cards manufactured by each manufacturer.
MAC address classification:
Unicast (physical) MAC address:
The 8th bit of a MAC address is a unicast MAC address, which uniquely identifies a terminal on an Ethernet network and is the only hardware address in the world.
Broadcast MAC address:
The MAC address of all 1 (FF-FF-FF-FF-FF-FF-FF) used to represent all terminal devices on a LAN.
Multicast MAC address:
In addition to the broadcast address, the MAC address with bit 8 of 1 is a multicast MAC address (for example, 01-00-00-00-00), which represents a set of terminals on a LAN.
MAC address table:
The corresponding relationship between the MAC address, interface number and the VLAN ID to which the connected device belongs is recorded. When forwarding data, the routing device queries the MAC address table based on the destination MAC address and VLAN ID of the message to quickly locate the interface, thereby reducing broadcasting. Classification of MAC address tables:
Dynamic table items:
The interface learns from the source MAC address in the received message, and the table entry has an aging time.
Static table items:
Configured manually by the user and sent down to each interface panel, the table items do not age.
Black hole table entries:
Indicates that data frames containing a specific source or destination MAC address are discarded, manually configured by the user, and sent to each interface panel without aging the table entries.
Determined by the way of networking, the more popular way to access the Internet today (and the direction of future development) is to organize hosts together through a local area network, and then connect through switches and the Internet. This raises the question of how to distinguish specific users and prevent theft. Because IP is only a logical identity, anyone can modify it at will, so it cannot be used to identify users. MAC address is not, it is solidified inside the network card. Theoretically, there is no way to impersonate your hardware (network card) unless you steal it. So that's why you need a MAC address.
