• In a broadcast link, filtering by address is necessary since frames are sent to every node, and some frames may not be directed towards each node.

• 1 hexadecimal number is equivalent of 4 digits of binary number.
• The first 3 bytes (24 bits, 6 hexadecimal digits) of the MAC address indicates the vendor of the adaptor.
• Broadcast Address: reserved address used to broadcast a frame in my network.
• Virtual machine can create its own MAC addresss.

Ethernet

• Ether is the medium that nodes are connected to.

• 802.3 is the standard produced by IEEE that defines physical and link layer's MAC or wired ethernet.

• Type field determines to which network-layer protocols the frame should be sent to - multiplexing and demultiplexing.

• enables us to receive the frame without any error
• Why is there a need for a clock?
• How does the preamble tell the receiver the width of a bit?
• Why is it important if there is a long string of bits of the same value?

• NIC does not sent ack / nak, however it has CSMA/CD, retransmitting data due to collision.

• The above is a bus topology.
• The original Ethernet had one backbone cable that connects all the nodes.
• This carries a lot of risks, since if the cable is damaged, the entire network will fail.
• And it is slow.

• Hub topology.
• Dumb and simple.
• What does it mean when the hub re-creates the bits?
• What does it mean when it boosts the energy strength?
• Why does it need to act on individual bits rather than frames?
  • I guess due to technological limitation back then - now switches deal with frames.

• Easier to maintain, because you only need to switch the hub or connect to different ports (interface).
• Still using the broadcasting method, which is slow and therefore not ideal for larger networks.

• Switch is predominant now.
• Instead of dealing with bits, it now deals with frames.
  • This is what Layer-2 means?

• Transparent: hosts need not know the MAC of the switches.
  • This means that even when the switches are changed, there is no need for customers to change accordingly.

• Each interface (like interface 1 through 6 in the image above) has buffer dedicated to it, and the transmissions can be done simultaneously.

  • Means no collision and time efficient.
  • This is a major development from hub, where every node is using the same device .

  

• As long as the frames do not go through routers, the communication between two nodes in a LAN is a single hop communication.

• Don't quite understand the filtering part.
  • Are we assuming that the filtering is done on the switch with interfaces 1 through 4?
  • Why does it mean that the other switch already has the frame if the frame we are sending is on interface 2?
• Flooding is done when there is no entry of the destination MAC in the table - sending the frame to every other interfaces.

• The IP address is check on the network layer.

ARP

• ARP table maps IP addresses to MAC addresses.
• pinging the IP address that is not in the ARP table will send a query to that IP address for the MAC address, filling up the ARP table.

• If A knows B' MAC address, then just create a frame with it and send.
  
• If A doesn't know, broadcast ARP query.
  • Only B' will respond.
  • A then caches B's mapping in its ARP table.

• Sending frame to a different subnet would not work if the MAC dest is the one in a different subnet, since none of the switches would recognize it.
  • What's needed instead is to set the destination MAC address as the router's interface.
  • Then when it gets out of the router, the src MAC address is set to the router's interface.
  • The destination MAC address is set to the one in the other subnet.