Bridge

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An Ethernet bridge establishes separate physical network segments while keeping all nodes in the same logical network.

• works at Data Link layer
• reduces the number of collisions caused by having too many nodes contending for access

• bridge creates separate collision domains
  • nodes in one segment don’t slow or contend with nodes on the other
• enables communication between the separate collision domains as an entire broadcast domain
  • forwards only the right traffic
• creates a single logical network
  • called a layer 2 broadcast domain
• builds forwarding database to track which addresses are associated with which of its ports
  • when a bridge is initialized, the database is empty
  • builds up as bridge listens to the connected segments
  • entries are flushed out of the table after a period of time to ensure the information remains current
• if no record of the MAC address exists or if the frame is a broadcast or multicast:
  • bridge floods the frame to all segments except for the source segments
    • acts like a hub