CCENT ?'s - sec 1

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  1. Name the seven layers of the OSI model.
    • Physical
    • Data Link
    • Network
    • Transport
    • Session
    • Presentation
    • Application
  2. What is/are the main purpose(s) of Layer 7?
    Application - provides standardized services to applications. {Web Browser, HTTP}
  3. What is/are the main purpose(s) of Layer 6?
    Presentation - defines data formats, compression, and possibly encryption
  4. What is/are the main purpose(s) of Layer 5?
    Session - controls the conversation between two endpoints. Ensures that not only communication, but also useful sets of communication between endpoints is accomplished
  5. What is/are the main purpose(s) of Layer 4?
    Transport - provides end-to-end recovery, if requested {TCP/UDP}
  6. What is/are the main purpose(s) of Layer 3?
    Network - defines logical addressing and routing as a means of delivering data across an entire network. {IP, IPX}
  7. What is/are the main purpose(s) of Layer 2?
    Data Link - defines addressing specific to a particular medium as part of the means of providing delivery of data across that medium. Includes protocols used to determine what device(s) accesses the media at any point in time.
  8. What is/are the main purpose(s) of Layer 1?
    Physical - responsible for encoding energy signals onto the medium and interpreting a received energy signal. Also defines connector and cabling details
  9. Describe the process of data encapsulation as data is processed from creation until it exits a physical interface to a network. Use the OSI model as an example.
    Data encapsulation represents the process of a layer adding a header (and possibly a trailer) to the data as it is processed by progressively lower layers in the protocol specification. In the context of the OSI, each layer could add a header so that, other than the true application data, there would be six other headers (Layer 2 to 7) and a trailer for Layer 2, with the L2PDU being encoded by the physical layer onto the network media.
  10. Name three benefits to layering networking protocol specifications.
    • Reduced complexity
    • Standardized interfaces
    • Modular engineering
    • Interoperable technology
    • Accelerated evolution
    • Simplified teaching and learning
  11. What header or trailer does a router discard as a side effect of routing?
    The data link header/trailer
  12. What OSI layer typically encapsulates using both a header and a trailer?
    The data link layer. Also, the trailer typically includes a frame check sequence (FCS) to perform error detection.
  13. What terms are used to describe the contents of the data encapsulated by the data link, network, and transport layers, respectively?
    Frames, Packets, Segments
  14. Explain the meaning of the term L5PDU.
    • Layer 5 Protocol Data Unit
    • PDU is the entity that includes headers and trailers created by a particular networking layer, plus any encapsulated data.
  15. Explain how Layer x on one computer communicates with Layer x on another computer.
    The protocol defined by each layer uses a header that is transmitted between the computers to communicate between the same layer on each device
  16. List the terms behind the acronym TCP/IP.
    • Transmission Control Protocol
    • Internet Protocol
  17. List the terms behind the acronym OSI.
    Open Systems Interconnection
  18. What does MAC stand for?
    Media Access Control
  19. Name three terms popularly used as a synonym for MAC address
    • NIC Address
    • Card Address
    • LAN Address
    • Hardware Address
    • Ethernet Address
    • Burned-In Address
  20. What portion of a MAC address encodes an identifier representing the manufacturer of the card?
    The first 3 bytes, called the Organizationally Unique Identifier (OUI)
  21. Are MAC addresses defined by a Layer 2 or Layer 3 protocol?
    Layer 2 (defined in the 802.3 specification)
  22. How many bits are present in a MAC address?
  23. Name the two main parts of a MAC address. Which part identifies which “group” this address is a member of?
    Trick Question - there are no official "groups" in the MAC address
  24. What OSI layer typically encapsulates using both a header and a trailer?
    Data Link (Layer 2)
  25. If a Fast Ethernet NIC currently is receiving a frame, can it begin sending a frame?
    Yes, if it is operating in Full-Duplex
  26. What are the two key differences between a 10-Mbps NIC and a 10/100-Mbps NIC?
    • The 10/100-Mbps NIC can operate at 100 Mbps speed
    • The 10/100-Mbps NIC can auto negotiate both speed and duplex between itself and the device it is cabled to, typically a LAN switch
  27. How fast is Fast Ethernet?
    100 Mbps
  28. How many bytes long is a MAC address?
    6 bytes (48 bits)
  29. Define the difference between broadcast and multicast MAC addresses.
    • Broadcast always implies ALL devices on the LAN (FFFF:FFFF:FFFF)
    • Multicast implies some subnet of all devices (0100.5e00.0001)
  30. Explain the function of the loopback and collision-detection features of an Ethernet NIC in relation to half-duplex and full-duplex operations.
    • Loopback feature copies the transmitted frame back onto the receive pins on the NIC interface.
    • Collision-detection logic compares the received frame to the transmitted frame during transmission; if the signals do not match, a collision is occurring.
    • With full-duplex operation, collisions cannot occur, so the loopback and collision-detection features are purposefully disabled, and concurrent transmission and reception is allowed
  31. Are DLCI addresses defined by a Layer 2 or Layer 3 protocol?
    Layer 2 (Data Link)
  32. Define the terms DCE and DTE in the context of the physical layer and a point-to-point serial link.
    • At the physical layer, DTE refers to the device that receives clocking from the device at the other end of the cable on a link.
    • The DCE supplies that clocking.
  33. Which layer or layers of OSI are most closely related to the functions of Frame Relay? Why?
    • Layer 2
    • Frame Relay depends on other well-known physical layer specifications. Frame Relay defines headers for delivery across the Frame Relay cloud, making it a Layer 2 protocol. Frame Relay does not include any routing or logical addressing specifications, so it is not a Layer 3 protocol
  34. True or false: “A leased line between two routers provides a constant amount of bandwidth—never more and never less.” Defend your answer.
    • True
    • A leased line creates the cabling equivalent of having a cable between two routers, with the speed (clock rate) defined by the telco. Even when the routers have no data to send, the full bandwidth is available to be used.
  35. Do HDLC and PPP, as implemented by Cisco routers, support Protocol Type fields and error detection? Explain your answer.
    Both protocols support a Protocol Type field and an FCS field to perform error detection. PPP defines both fields as part of the PPP standard; the HDLC standard includes the FCS field, but Cisco added a Protocol Type field to the standard HDLC header.
  36. What are some of the main similarities between Frame Relay and ATM?
    • Both use an access link to access the service provider
    • Both use the concept of a virtual circuit between DTE devices.
    • Both allow multiple VCs to cross a single access link
  37. What are the two main functions of each OSI Layer 3–equivalent protocol?
    • Path selection (routing)
    • Logical addressing
  38. Assume that PC1 sends data to PC2, and PC2 is separated from PC1 by at least one router. Are the IP addresses of the PCs in the same IP subnet? Explain your answer.
    • They must be in different subnets.
    • IP addressing rules require that IP hosts separated by a router must be in different subnets
  39. How many bits are present in an IP Version 4 address?
    32 bits (IPv6 = 128)
  40. Name the two main parts of an IP address. Which part identifies which group this address is a member of?
    • Network
    • Host
    • Subnet identifies group
  41. PC1 sends data to PC2 using TCP/IP. Three routers separate PC1 and PC2. Explain why the statement “PC1 sends an Ethernet frame to PC2” is true or false.
    • False.
    • Packets are delivered from end-to-end, but frames are simply passed between devices on each common physical network (frames are replaced at each router)
  42. In IP addressing, how many octets are in 1 byte?
  43. Describe the differences between a routed protocol and a routing protocol.
    • Routed protocol defines the addressing and Layer 3 header in the packet that actually is forwarded by a router.
    • Routing protocol defines the process of routers exchanging topology data so that the routers know how to forward the data.
  44. Imagine an IP host on an Ethernet, with a single router attached to the same segment. In which cases does an IP host choose to send a packet to this router instead of directly to the destination host, and how does this IP host know about that single router?
    Typically an IP host knows what router to send a packet based on its configured default router. If the destination of the packet is in another subnet, the host sends the packet to the default router. Otherwise, the host sends the packet directly to the destination host because it is in the same subnet and, by definition, must be on the same data link.
  45. Name three items in an entry in any routing table.
    • A number that identifies a group of addresses {i.e., subnet numbers}
    • The interface out which to forward the packet {i.e., outgoing interface}
    • The Layer 3 address of the the next router to which to send the packet {i.e., next-hop router}
  46. Name the parts of an IP address when subnetting is used.
    • Network
    • Subnet
    • Host
    • {sometimes only referred to in two parts: Subnet & Host}
  47. How many valid IP addresses exist in an unsubnetted Class A network? (You may refer to the formula if you do not know the exact number.)
    (2^24) -2
  48. How many valid IP addresses exist in an unsubnetted Class B network? (You may refer to the formula if you do not know the exact number.)
    (2^16) -2
  49. How many valid IP addresses exist in an unsubnetted Class C network? (You may refer to the formula if you do not know the exact number.)
    (2^8) -2
  50. What values can a Class A network have in the first octet?
  51. What values can a Class B network have in the first octet?
  52. What values can a Class C network have in the first octet?
  53. When subnetting a Class B network, do you create the subnet field by taking bits from the network part of the address or the host part?
    Host part
  54. When subnetting a Class B network, using the entire third octet for the subnet part, describe the number of possible subnets created.
    • 2^8 with 8 bits, or 256
    • The host part consists of a full octet in this case, which is 8 bits long
  55. When subnetting a Class A network using the entire second octet for the subnet part, describe the number of hosts in each subnet.
    • 2^16 with 16 bits, or 65,536
    • The host part consists of two entire octets in the case, which is 16 bits long
  56. When a router hears about multiple routes to the same subnet, how does it choose which route to use?
    Routing protocols use a metric to describe how good each route is. The lower the metric is, the better the route.
  57. What is the primary purpose of a routing protocol?
    Routing protocols discover the routes in a network and build routing tables.
  58. True or false: “Routing protocols are required to learn routes of directly connected subnets.”
    False. Routers add routes to directly connected subnets when the interfaces initialize. No routing protocols are needed.
  59. List the similarities and differences between ARP and DNS.
    • Both send messages with one piece of information, hoping to learn another piece of information. DNS requests are unicast IP packets sent specifically to the DNS server, whereas ARP uses a LAN broadcast frame.
    • DNS queries supply a name, expecting to hear the corresponding IP address back from the server. ARP requests supply an IP address, hoping to hear a corresponding MAC address not from a server, but from the host that uses that IP address
  60. Describe the features required for a protocol to be considered connectionless.
    Connectionless protocols allow communication to occur without any previous configuration or dynamic protocol messages between the two devices.
  61. Describe the features required for a protocol to be considered connection oriented.
    Either the protocol must exchange messages with another device before data is allowed to be sent, or some pre-established correlation between the two endpoints must be defined.
  62. In a particular error-recovering protocol, the sender sends three frames, labeled 2, 3, and 4. On its next sent frame, the receiver of these frames sets an Acknowledgment field to 4. What does this typically imply?
    Frames through number 3 were received successfully. The receiver might not have received Frame 4, or Frame 4 might not have passed the FCS check.
  63. Describe how TCP performs error recovery. What role do the routers play?
    TCP numbers the first byte in each segment with a sequence number. The receiving host uses the Acknowledgement field in segments that it sends back to acknowledge receipt of the data. If the receiver sends an acknowledgement number that is a smaller number than the sender expected, the sender believes that the intervening bytes were lost, so the sender resends them. The router plays no role unless the TCP connection ends in the router (for example, a Telnet into a router).
  64. How many TCP segments are exchanged to establish a TCP connection? How many are required to terminate a TCP connection?
    A three-way connection establishment sequence is used, and a four-way connection-termination sequence is used.
  65. Describe the purpose of the Port Number field in a TCP header. Give one example.
    The port numbers are used to help computers multiplex received data.
  66. How many UDP segments must be sent to establish a UDP connection? How many are used with normal UDP connection termination?
    UDP does not establish connections because it is not connection oriented.
Card Set
CCENT ?'s - sec 1
Open ended questions for section 1 of Cisco's CCNA/CCENT ICND1
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