Switch

• It is an L2 device
• It takes decisions based on L2 header only
• use and maintain MAC address table

Functions

• Learning
• Flooding
• Forwarding

MAC Address Table

• Mapping of Switch Ports to MAC addresses

Switch Port	MAC Address
5	a1a1
6	c3c3
7	b2b2
8	d4d4

Working

• Source: a1a1 wants to send data to Destination: d4d4 via switch
• The frame is sent to switch (Learning)
  • switch updates the mapping: 5 ⇒ a1a1
• The frame is duplicated to all the switch ports except source (Flooding)
• The frame is dropped by c3c3, b2b2 but received by d4d4
• d4d4 sends the response to switch
  • switch updates the mapping: 8 ⇒ d4d4
• Switch sends to port 5 (Forwarding)
  • It looks at existing mapping of: 5 ⇒ a1a1
• The response is received by a1a1

Switch MAC and IP

• Switch’s MAC address and IP address is only used if we sending traffic TO the switch
• It will act as a host in the network and follow all the host communication rules
• If traffic is sent THROUGH the switch then its MAC address and IP address is not involved at all

Unicast and Broadcast

• Unicast frame
  • Flooded only if the MAC address table is not populated
• Broadcast frame
  • destination MAC: FF:FF:FF:FF:FF:FF
  • Always flooded and no lookup/update in MAC address table