MAC Addresses

A Media Access Control (MAC) is an address that uniquely identifies a network node. The manufacture hard codes a the MAC address into physical Network Interface Card. A device can not connect to a local area segment without a MAC address.

It is six octets in length which is defined by the IEEE, the first three octets are the Organization Unique Identifier and the second set of three octets are Network Interface Controller specific. The Organization Unique Identifier is assigned by the IEEE

Unicast Addresses

Used when a frame is intended for a single recipient.


Used when the frame is intended for all devices on the LAN, it has a values of FFFF.FFFF.FFFF.


Used when the frame is intended for more than one but not all nodes on the LAN.


  • Preamble (7 bytes)
  • Start Frame Delimiter (1 byte)
  • Destination MAC Address (6 bytes)
  • Source MAC Address (6 bytes)
  • Length (2 byte)
  • Type (2 bytes)
  • Data (46-1500 bytes)
  • Frame Check sequence (4 bytes)

Note Either the length or the type is present but not both.

Note If jumbo frames is enabled the maximum frame size can be increased to nine thousand bytes.

Collision Domains

A collision domain is an area of the network where two of more frames could electrically collide if more than an single frame is transmitted at the same time.


Are a network device that divides a LAN into multiple segments. They are used to reduce network traffic by dividing an network into two segments, recording all the maC addresses on the network and only forwarding frames to the segment that contains the destination address.


Are a network device that acts like a multi-port bridge.

Broadcast domain

Is the collection of nodes that receive the same broadcast messages. They span bridges and switches but not routers