MAC(Media Access Control) Address

• Hub: Is a repeater, it takes signal coming from one port and creates multiple copies of that send it out to all other ports(connected to cable)

• Frame by itself doesn't contain source and destination address, that is where MAC address comes in picture

cat /sys/class/net/
br-a22840597dd6/ crc/             crc-nic/         docker0/         lo/              virbr0/          virbr0-nic/      wlp0s20f3/       

cat /sys/class/net/wlp0s20f3/address 
20:1e:88:6d:99:f3

• MAC Address - have 12 hexadecimal chars and each hex is of size 4 bits(total size - 12 * 4 = 48bits)

• First 3 groups of 2 are issued to the Manufacturer.

• In the above shown MAC Addr 20:1e:88 has Intel as Vendor. ref

• These first 3 pairs are called OEM(Original Equipment Manufacturer)

• The second 3 pairs are called Unique Identifier(UID)

• Sender's and receiver's MAC addresses are attached with the frame and when receiver receives a frame it checks if its receiver's MAC addr matches machines NIC MAC addr and sends to the application or else discards it.