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6.1 Describe the purpose and usage of MAC addresses and VLANs

  • LAN is a network confined within a building or campus
  • traffic stays local and can be transferred between devices by a switch
  • switch = network device that operates at L2 (Data Link layer)

Ethernet

  • L2 protocol defined by IEEE
  • guidelines and standards that specify:
    • cabling and signaling formats at L1 and L2
    • voltage levels
    • max distance signal can travel
    • format of Ethernet frame

MAC Addresses

  • Media Access Control
  • used to enable comm between devices connected to a local network
  • accomodates 3 different network communications:
    • Unicast: one sender and one receiver
    • Broadcast: data sent from one source to all other devices
    • Multicast: info sent from one device to a specific group of devices
  • IEEE has defined MAC addresses for each type:
    • when least significant bit (LSB) is 0, it means its unicast
    • when LSB is 1, it means its multicast
    • when all bits are set to 1, its means its broadcast
  • Each device that needs to exchange data on Ethernet network needs to have unique MAC Address
  • MAC address is burned into the NIC and is also known as burned-in-address (BIA)
  • 48 bits organized as 12 hexadecimal numbers
  • Mac Address has 2 components:
    • Organizationally unique identifier (OUI): 24-bit number identifies manufacturer of NIC
    • Vendor-assigned address: 24-bit number uniquely identifies Ethernet hardware

VLANS

  • group of devices on an Ethernet network logically segmented by function, team, application
  • students grouped into student VLAN, faculty into faculty VLAN, etc
  • standard 802.1q integrated as an 802.1q header in the Ethernet frame
    • 12 bits dedicated to VLAN identifier
  • max 4094 VLANS per network
  • VLAN IDs 0 and 4095 are reserved
  • each VLAN defines its own broadcast domain
  • no matter what location device is in, it can be a part of the same VLAN

Benefits of VLANS

  • creating VLANS and assigning devices to them reduces the size of broadcast domains which reduces chances of broadcast storms
  • Easier troubleshooting with logically-grouped devices
  • easier to enforce security policies and limit access between VLANS than doing it port-by-port on a switch