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On my previous assignment for a networking class, I compared answers with a classmate regarding Source Address Table for a problem that had 3 devices connected to a switch.

Device A + B were connected to a hub that was connected to the switch. Device C was directly connected to the switch.

Apparently, in the MAC forwarding table, there should be 4 MAC addresses/3 ports listed...why? I thought a hub had no MAC address...

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Hubs and Switches

The fundamental function of Hubs and Switches is to connect multiple devices to one Network.

Although they perform the same basic function, there are some key differences between them.

The term Switch commonly refers to a network bridge that processes and routes data at OSI Model Layer 2 (Data Link).

Switches that additionally process data at OSI Model Layer 3 (Network) and above are often referred to as "Layer 3 Switches" or Multilayer Switches.

A Hub is an OSI Layer 1 (Physical) Device and is used in a wired Network to connect Ethernet cables from a number of devices together.

Note that OSI Model Layer 2 (used by Switches) has a MAC sublayer:

The Media access control (MAC) sublayer is responsible for:

  • Multiple access protocols for channel-access control, for example CSMA/CD protocols for collision detection and re-transmission in Ethernet bus networks and hub networks, or the CSMA/CA protocol for collision avoidance in wireless networks.
  • Physical addressing (MAC addressing)
  • LAN switching (packet switching) including MAC filtering and spanning tree protocol
  • Data packet queuing or scheduling
  • Store-and-forward switching or cut-through switching
  • Quality of Service (QoS) control
  • Virtual LANs (VLAN)

Summary

  • Hubs don't have MAC addresses
  • Switches have a MAC address and know about the MAC address of attached devices.
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Probably the assignment also calculated in a mac address for the switch, because indeed: a hub does not have a mac (nor ip) address, a hub works on a lower level with the data.

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