MAC Addressing

• It is a 12 digit hex code that consists of 6 pairs of characters.
• Each pair is 1 byte, so Total MAC address size is 6 bytes (48 bits)

It has two parts:

1. Organizational Unique Identifier(OUI) : Identifies the [Manufacturer]
2. Network Interface Controller(NIC) : Unique identifier for each [NIC]

Ethernet Frame (L2)

Frame Header

1. [Destination(MAC)]: When unknown -> find via ARP
3. [Length:]
   • Total length of frame (Header + Data + Trailer) should be ≥ 64 bytes,
   • Where 18 bytes consists of the header and trailer, rest is packet.
   • A “padding” is added to the frame if the total length ≤ 64 bytes. i.e streams of 0s at the end of the frame.

Frame Switching

1. When frames have to go from source to destination, they are provided the three following things: [1. Source IP | 2. Source MAC | 3. Destination IP] Here, goal is to find the machine with [IP = Destination IP], and once that is found we store that found device’s MAC as Destination MAC.

2. [Store & Forward Switching:] Frames are moved forward, and as switches forward these frames, they store the MAC addresses of all the encountered devices. This is later on used for Frame forwarding & ARP.

Frames travelling pathway can be divided into two modes:

• 1. Frame Flooding (Broadcast) —> When Unknown: When device with matched IP is not yet found, frame is broadcasted to all devices except the source at all nodes.

  [CASE 1]: Frame is received by the destination IP → Return an “ARP Reply” as an indicator [CASE 2]: Frame is NOT yet received to dest. → Ignore the frame, move it forward.

• 2. Frame Forwarding (Unicast) —> When Known: When device with matched IP is known(already found). Then frame is moved along the path from source to destination easily.