Packet Forwarding

Network Device Communication

The main function of a network is provide connectivity between devices.

  • Each layer describes a specific function.
  • Each layer can be modified or changed without requiring changes to the layers above or below it.

Layer 2 Forwarding

Collision Domains

  • Second layer of OSI model.
  • Ethernet use MAC (Media Access Control) addresses.
MAC address
  • MAC address FF:FF:FF:FF:FF:FF will be processed by all network devices.
  • By default broadcast are not forwarded beyond a Layer 3.
  • Ethernet use CSMA/CD (Carrier Sense Multiple Access / Collision Detect).
  • Hub: Repeat traffic out of every port –> Half duplex.
  • Switch: Maintain a table associated with the host’s MAC connected to the port –> Full duplex.
Collisions and Broadcast Domains
Local Area Network
  • A frame is received by the switch and checks if the source MAC is in the MAC Table, if not its added.
  • If the destination MAC of the frame is in the MAC table then is forwarded, if not it is flooded to all ports except the source port (no matter if already those ports have a MAC address in the MAC table).
  • CAM is a high-speed memory.
Network Traffic Types

Virtual LANs