1. Cisco three layer model
   1. Core layer
      1. Backbone
         1. Transports large amounts of traffic reliably and quickly
         2. If it fails, every user is affected
         3. Speed and latency key, MUST NOT be slowed down
         4. Design for high reliability
            1. EG: FDDI, Fast Ethernet, ATM
         5. Design with speed in mind
         6. Use protocols with little convergence time
   2. Distribution layer
      1. Routing
         1. Determine best path for service and passes to core layer
         2. Implement access list
         3. Implement security
         4. Redistribution between routing protocols
         5. Routing between VLAN's
         6. Define broadcast and multicast domain
   3. Access layer
      1. Switching
         1. Controls user access and internetwork resources
         2. Used for local traffic
         3. Continued use of access control and policies
         4. Segmentation (collision domain)
         5. Workgroup connectivity to distribution layer
2. Internetwok connections
   1. Router
      1. Don't forward Broadcasts by default
      2. Use logical addressing (IP)
      3. Use Access lists
      4. Can provide layer 2 switching
      5. Provides connections to VLAN's
      6. Provide QoS for some network traffic
   2. Switch
      1. Segments network into Collision Domain
      2. Forwards and filters frames
      3. Uses filter lists
      4. Uses MAC addressing
   3. Hub
      1. Does not segment network in any way
      2. Connects multiple hosts together
3. OSI model
   1. 7: Application Layer
      1. Interacts with user interface
   2. 6: Presentation layer
      1. Presents data
      2. Handles processes like encryption
   3. 5: Session layer
      1. Keep different application data separate
   4. 4: Transport layer
      1. Provides reliable or unreliable delivery
         1. Connection oriented communication
            1. Uses a virtual circuit
            2. Uses sequensing
            3. Uses acknowledgements
            4. Uses flow control
            5. Prevents hosts overwhelming receiver
            6. Ensures:
            7. Received segments are acknowledge
            8. Any segments not received is retransmitted
            9. Segments are ordered upon arrival
            10. A manageable data flow is maintained
      2. Performs error correction before retransmission
   5. 3: Network layer
      1. Provides logical addressing
         1. Data packets
            1. Routed protocols
            2. IPv4
            3. IPv6
         2. Route update packets
            1. Routing protocols
            2. Distributes and update routing tables
            3. RIP
            4. RIPv2
            5. EIGRP
            6. OSPF
   6. 2: Data link layer
      1. Provides access to media with MAC address
         1. MAC 802.3
            1. Defines how packets are placed on the media
         2. LLC 802.2
            1. ID's network layer protocols and encapsulating them
      2. Provides error detection, not correction
   7. 1: Physical layer
      1. Move bits between devices
         1. CSMA/CD
            1. Helps share bandwidth without collisions
            2. Host checks media
            3. If clear, sends data
            4. If not, waits
            5. If collision occurs, all hosts stop transmitting
            6. Each host waits a set amount of time before retransmitting
         2. Half/full duplex
            1. Half duplex
            2. One wire
            3. Transmit one way at a time
            4. Uses CSMA/CD
            5. If hub involved, will run with switch
            6. Full Duplex
            7. Uses 2 wires
            8. One for transmitting
            9. On for sending
            10. No CSMA/CD needed
            11. Data transfer much faster
            12. Used:
            13. Connection from switch to host
            14. Connection from switch to switch
            15. Connection from host to host with x-over cable
4. LAN traffic problems
   1. Too many hosts
   2. Broadcast storm
   3. Multicasting
   4. Low bandwidth
   5. Adding hubs
   6. Too much AR & IPX traffic
5. Encapsulation
   1. Protocol Data Unit
      1. Segment at Transport layer
         1. TCP header added
      2. Packet at Network
         1. IP header added
      3. Frames at data link layer
         1. MAC/LLC header and FCS footer added
      4. Bits at physical layer