Intro to Networks Chapter 5

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  1. LLC
    Logical Link Control 802.2   Handles the communication between the upper layers and the lower layers.  LLC can be considered the driver software for the NIC
  2. MAC sublayer
    • The lower sublayer of the data link layer. 802.3   MAC is implemented by hardware, typically in the computer NIC
    • 2 responsibilities
    • data encapsulation
    • media access control
  3. Data encapsulation
    process includes frame assembly before transmission and frame disassembly upon reception of a frame
  4. Data encapsulation provides 3 primary functions
    • Frame delimiting - 
    • Addressing
    • Error detection
  5. Frame delimiting -
    The framing process provides important delimiters that are used to identify a group of bits that make up a frame..  Provides synchronization between the transmitting and receiving nodes.
  6. Addressing
    The encapsulaiton process also provides for data link layer addressing.
  7. Error detection
    Each ethernet frame contains a trailer with a cyclic redundancy check (CRC) of the frame contents.    After reception of a frame, the receiving node creates a CRC to compare to the one in the frame.  The the CRC calculations match it can be trusted
  8. Media Access Control
    Responsible for the placement of frames on the media and the removal of frames from the media  

    This sublayer communicates directly with the physical layer.
  9. Carrier Sense Multiple Access  CSMA
    Detects is the media is carrying a signal.  If it does it will wait and try again after a short time period.  If no carrier signal is detected the device transmits its data
  10. CSMA / Collsion Detection
    The device monitors the media for the presence of a data signal.  If no data signal, it will transmit, if signal is present will wait and retry
  11. CSMA / Collision Avoidance
    The device will examine the media for a data signal.  If media is free the device sends a notification across the media of its intent to use it.  The data is then sent  Used by 802.11 wireless technologies
  12. MAC Address Structure
    a 48 bit value expressed as 12 hexadecimal digits.  First the bytes (24 bits) are the vendors code, called the OUI   Organizationally Unique Identifier
  13. MAC address structure
    Must be globally unique  first 3 bytes are manufacturer last 3 bytes are vendor code or serial number
  14. Ethernet size
    64 bytes and the max of 1518 bytes (includes all the bytes from the destination MAC address gield trhough the Frame Check Sequence Field  (FCS)
  15. Runt Frame
    Any frame less than 64 bytes in length 

    Automatically discarded by receiving stations
  16. VLAN  stands for
    Virtual Local Area Network
  17. Preamble and Start Frame Delimiter Fields
    • Preamble (7 bytes)  
    • Start Frame Delimiter (1 byte)

    used for synchronization between the sending and receiving devices.  These 1st 8 bytes get tthe attention of the receiving nodes.
  18. Destination MAC Address Field
    6 byte field is the identifier for the intended receipt
  19. Source MAC Address Field
    This 6 byte field identifies the frame's originating NIC or interface
  20. Length Field
    Used to describe which higher layer protocol is present
  21. Data Field
    This field (46-1500) bytes contains the encapsulated data from a higher layer
  22. Frame Check Sequence Field
    4 bytes, is used to detect errors in a frame  The sending device receives the frame and generates a CRC to look for errors.  If the calculations match, no error occurred.  If calculation do not match the frame is dropped
  23. Unicase MAC address
    A unique address used when a frame is sent from a single transmitting device to a single destination device
  24. Broadcast packet
    Contains a destination IP address that has all ones in the host portion.

    all hosts on the local network will receive and  process the packet.
  25. Multicase addresses
    allow a source device to send a packet to a group of devices.   Devices that belong to a multicast group are assigned a multicast group IP address

    Remote gaming, video conferencing
  26. Physical address aka
    MAC address
  27. Logical address
    the IP address
  28. DNS aka
    Domain Name Service  -  which an ip address is associated to a domain name
  29. ARP  aka
    Address Resolution Protocol
  30. ARP's have 2 functions
    Resolving IPv4 addresses to MAC addresses

    Maintaining a table of mappngs
  31. 2 ARP Issues
    May be initially slow while the ARP address is being aquired

    ARP spoofing/.poisioning
  32. Half Duplex
    Relies on unidirectional data flow where sending and receiving data are no performed at the same time.  

    Typical of a hub  slows data flow
  33. Full Duplex
    data flow is bidirectional

    • Point to point only-pc1 to switch, switch to pc 2 
    • requires full duplex suppoer on both ends
    • collision free
  34. auto-MDIX
    A feature on the switch which detects the required cable type for copper Ethernet connections and configures the interfaces accordingly.  You may use crossover or straight thru for connections
  35. Store and forward switching
    when the switch receives the frame it stores the data n buffers until the complete frame is received.  During storage the switch determines destination and also preforms Cyclic Redundancy Check CRC.
  36. CRC aka
    Cyclic Redundancy Check uses a mathmetical formula based on the number of bits in the frame to determine whether the received frame has an error.
  37. cut through switching
    the switch acts upon the data as soon as it is received.  The switch buffers just enough of the frame to read the dest. MAC address so that it can determine to which port to forward the data.  NO ERROR CHECKING IS PREFORMED
  38. Two types of cut through switching
    Fast forward switching - immediately forwars a packet after reading the dest. address

    Fragment free switching - stores the first 64 bytes of the frame before forwarding.  Preforms a small error check on the first 64 bytes (where most errors occur)
  39. Port Memory Buffering
    Frames are stored n ques that are linked to specific incoming and outgoing ports.  A frame is transmitted to the outgoing port only when all the frames ahead of it in the queue have been successfully transmitted.
  40. Shared Memory Buffering
    deposits all frames into a common memory buffer that all the ports on the switch share.   This allows the packet to be received on one port and then transmitted on another port without moving it to a different que
  41. asymmetric switching
    allows for different data rates on different ports which allows more bandwidth to be dedicated to certain ports such as a port connected to a server.
  42. PoE aka and what it does
    Power over ethernet   -  supplies power from switch to device such as a phone over ethernet cable
  43. Fixed configuration Swtiches
    Fixed in their configuration, can't add features or options to the switch beyond those that originally came with the switch.
  44. Modular Switches
    Typically come with different sized chassis that allow for the installation of different numbers of modular line cards.  The line cards actually contain the ports.
  45. Cisco Express Forwarding
    cisco devices which support layer 3 switching

    • Two main components of CEF
    • Forwarding Information Base
    • Adjacency tables
  46. Forwarding Information Base
    Used in Layer 3 switches

    Similar to a routing table
  47. Adjacency tables
    maintain layer 2 next hop addresses for all FIB entries
  48. Switch Virtual Interface
    Logical interface on a switch associated with a virtual local area network VLAN
  49. Routed Port
    Physical port on a layer 3 switch configured to act as a router port
  50. Layer 3 EtherChannel
    Logical interface on a cisco device associated with a bundle of routed ports
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Intro to Networks Chapter 5
2015-02-09 16:18:03
CCNA Chapter

Terms and misc Chapter 5
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