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Chapter 5 : Ethernet, DIFFA MAHARANI NINGTYAS, 201710893, JARINGAN…

- - - - Ethernet
        Most widely used LAN technology, operates in the data link layer and the physical layer, Family of networking technologies that are defined in the IEEE 802.2 and 802.3 standards, and Supports data bandwidths of 10, 100, 1000, 10,000, 40,000, and 100,000 Mbps (100 Gbps)
      - Ethernet standards
        Define Layer 2 protocols and Layer 1 technologies, two separate sub layers of the data link layer to operate - Logical link control (LLC) and the MAC sublayers
      - Ethernet is defined by Data Link layer and Physical layer protocols.
        Application, presentation, session, transport, network, data link, physical
      - LLC
        Handles communication between upper and lower layers and takes the network protocol data and adds control information to help deliver the packet to the destination
      - MAC
        Constitutes the lower sublayer of the data link layer, Implemented by hardware, typically in the computer NIC, Two primary responsibilities:
        
        Data encapsulation
        
        Media access control
    - - Data encapsulation
        Frame assembly before transmission and frame disassembly upon reception of a frame, MAC layer adds a header and trailer to the network layer PDU
      - Provides three primary functions:
        
        Frame delimiting – identifies a group of bits that make up a frame, synchronization between the transmitting and receiving nodes
        
        Addressing – each Ethernet header added in the frame contains the physical address (MAC address) that enables a frame to be delivered to a destination node
      - Media Access Control
        
        Responsible for the placement of frames on the media and the removal of frames from the media, Communicates directly with the physical layer, If multiple devices on a single medium attempt to forward data simultaneously, the data will collide resulting in corrupted, unusable data, and Ethernet provides a method for controlling how the nodes share access through the use a Carrier Sense Multiple Access (CSMA) technology
        
        Carrier Sense Multiple Access (CSMA) process
        Used to first detect if the media is carrying a signal, If no carrier signal is detected, the device transmits its data and If two devices transmit at the same time - data collision
        
        CSMA/Collision Detection
        The device monitors the media for the presence of a data signal, If a data signal is absent, indicating that the media is free, the device transmits the data, If signals are then detected that show another device was transmitting at the same time, all devices stop sending and try again later, While Ethernet networks are designed with CSMA/CD technology, with today’s intermediate devices, collisions do not occur and the processes utilized by CSMA/CD are really unnecessary, and Wireless connections in a LAN environment still have to take collisions into account
        
        CSMA/Collision Avoidance (CSMA/CA) media access method
        Device examines the media for the presence of data signal - if the media is free, the device sends a notification across the media of its intent to use it , The device then sends the data, and Used by 802.11 wireless networking technologies
    - - MAC addresses assigned to workstations, servers, printers, switches, and routers
      - Example MACs: 00-05-9A-3C-78-00, 00:05:9A:3C:78:00, or 0005.9A3C.7800.
      - Forwarded message to an Ethernet network, attaches header information to the packet, contains the source and destination MAC address
      - Each NIC views information to see if the destination MAC address in the frame matches the device’s physical MAC address stored in RAM
      - No match, the device discards the frame
      - Matches the destination MAC of the frame, the NIC passes the frame up the OSI layers, where the decapsulation process takes place
- - - - Layer 2 LAN switch
        Connects end devices to a central intermediate device on most Ethernet networks, Performs switching and filtering based only on the MAC address, Builds a MAC address table that it uses to make forwarding decisions, and Depends on routers to pass data between IP subnetworks
    - - The switch receives a broadcast frame from PC 1 on Port 1.
      - The switch enters the source MAC address and the switch port that received the frame into the address table.
      - Because the destination address is a broadcast, the switch floods the frame to all ports, except the port on which it received the frame.
      - The destination device replies to the broadcast with a unicast frame addressed to PC 1.
      - The switch enters the source MAC address of PC 2 and the port number of the switch port that received the frame into the address table. The destination address of the frame and its associated port is found in the MAC address table
      - The switch can now forward frames between source and destination devices without flooding, because it has entries in the address table that identify the associated ports.
    - - Half Duplex (CSMA/CD)
        Unidirectional data flow, higher potential for collision, and hub connectivity
      - Full Duplex
        Point-to-point only, attached to dedicated switched port, requires full-duplex support on both ends, collision-free and collision detect circuit disabled.
    - - Store-and-forward
        A store-and-forward switch receives the entire frame, and computes the CRC. If the CRC is valid, the switch looks up the destination address, which determines the outgoing interface. The frame is then forwarded out the correct port.
    - - Cut-through
        A cut-through switch forwards the frame before it is entirely received. At a minimum, the destination address of the frame must be read before the frame can be forwarded.
        
        Two variants:
        
        Fast-forward switching:
        Lowest level of latency immediately forwards a packet after reading the destination address, typical cut-through method of switching
        
        Fragment-free switching:
        Switch stores the first 64 bytes of the frame before forwarding, most network errors and collisions occur during the first 64 bytes
    - - Port-based memory
        In port-based memory buffering, frames are stored in queues that are linked to specific incoming and outgoing ports.
      - Shared memory
        Shared memory buffering depositd all frames into a common memory buffer, which all the ports on the switch share.
  - - - Forwarding information base (FIB)
      - Conceptually similar to a routing table
      - A networking device uses this lookup table to make destination-based switching decisions during Cisco Express Forwarding operation
      - Updated when changes occur in the network and contains all routes known at the time
      - Adjacency tables
        Maintain layer 2 next-hop addresses for all FIB entries
  - - - Switch Virtual Interface (SVI) – Logical interface on a switch associated with a virtual local area network (VLAN).
      - Routed Port – Physical port on a Layer 3 switch configured to act as a router port. Configure routed ports by putting the interface into Layer 3 mode with the no switchport interface configuration command.
      - Layer 3 EtherChannel – Logical interface on a Cisco device associated with a bundle of routed ports