ICND1-2-Understanding TCPIP-44c.txt

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ICND1-2-Understanding TCPIP-44c.txt
2013-07-25 17:24:24

Cisco - ICND1-2-Understanding TCPIP
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  1. What is the Internet Protocol (IP)?
    • IP is a connectionless protocol that provides best-effort delivery routing of packets.
    • IP has the following characteristics:
    • - Operates at Layer 3 of the Open Systems Interconnection (OSI) (network) and TCP/IP (Internet) model
    • - Is connectionless
    • - Uses hierarchical addressing
    • - Provides best-effort delivery of packets
    • - Has no built-in data recovery
  2. What is an IP address used for?
    An IP address uniquely identifies a device on an IP network
  3. How many bits are in an IPv4 address? In an IPv6 address?
    • IPv4: 32 bits
    • IPv6: 128 bits
  4. An IP address is a hierarchical address that consists of what two parts?
    • An IP address is a hierarchical address that consists of the following two parts:
    • - Network ID: Describes the network to which the IP address or device belongs
    • - Host ID: The ID that identifies a specific host
  5. What are the different classes of IP addressing and the address ranges of each class?
    • The different classes of IP addressing and their ranges are as follows:
    • - Class A: to
    • - Class B: to
    • - Class C: to
    • - Class D: to (Multicasting)
    • - Class E: to (Reserved)
  6. What does RFC 1918 define?
    • RFC 1918 defines reserved (private) networks and addresses that are not routed on the Internet.
    • These addresses are as follows:
    • - to
    • - to
    • - to
  7. If an IP wants to communicate with all devices on the local network, what is the destination IP address of its broadcast?
    • This address is also called the local broadcast address.
  8. What is special about IP address
    • is the loopback address.
    • The loopback address lets the host send a message to itself to see whether TCP/IP was properly bounded to the network card.
  9. In a Class A network, how many octets are used for host addresses?
    3. One octet consists of 8 bits; thus a Class A network reserves 24 bits for host addresses. The maximum number of hosts a Class A network can have is 16,777,214 (224 [ms] 2).
  10. How many hosts are available for use in a Class B network?
    65,534. A Class B network reserves 16 bits for host addresses; thus 216 [ms] 2 = 65,534.
  11. How many hosts are available for use in a Class C network?
    254. A Class C network reserves 8 bits for host addresses. Thus 28 [ms] 2 = 254.
  12. What is DHCP?
    Dynamic Host Configuration Protocol (DHCP) allows a host to obtain an IP address automatically and to set TCP/IP stack configuration parameters such as subnet mask, default gateway, and DNS addresses.
  13. What is DNS?
    • The Domain Name System (DNS) converts names into IP addresses.
    • Instead of having to remember a host's IP address, DNS allows you to use a friendly name to access the host. For example, it is easier to remember http://www.cisco.com than
  14. On a Windows XP computer, what command can you use to view the IP information assigned to the PC?
    • ipconfig.
    • To release the IP address: ipconfig /release
    • To request a new address: ipconfig /renew
  15. What two protocols function at the transport layer of the TCP/IP model?
    • Two protocols that function at the transport layer of the TCP/IP model are as follows:
    • - TCP (Transmission Control Protocol): A connection-oriented, reliable protocol
    • - UDP (User Datagram Protocol): A connectionless and unacknowledged protocol
  16. Which has more overhead, UDP or TCP?
    TCP. Because UDP segments are not acknowledged, they do not carry the overhead that TCP does, thus allowing faster transmissions and greater efficiency.
  17. What are the protocol numbers for TCP and UDP?
    • TCP: 6
    • UDP: 17
  18. What is reliable versus best-effort delivery?
    Reliable delivery is connection oriented, and best-effort is connectionless.
  19. What are TCP and UDP port numbers?
    To pass information (such as e-mail) to upper layers, TCP and UDP use port numbers. These port numbers are predefined and keep track of different conversations among different hosts at the same time. Originating source port numbers are dynamically assigned by the source host using a number in the range of 49,152 to 65,535.
  20. What are well-known port numbers?
    Well-known port numbers are used for fundamental applications on the Internet such as e-mail and DNS. They have a range from 1 to 1023.
  21. What is the port number for SMTP?
  22. What is the port number for DNS?
  23. What are the port numbers for FTP?
    • 20 and 21.
    • FTP uses port 20 for data transfer; port 21 is the command port
  24. What is the port number for TFTP?
  25. What is the port number for Telnet?
  26. What is a socket?
    • A socket is an IP address combined with a TCP or UDP port number.
    • When a host wants to talk to another host, it sends its IP address along with the application (port number) it wants to communicate with. For example, if host wants to talk to host by e-mail, host sends its IP address and destination port number ( to host with the port number it wants to communicate with (
  27. What are the three mechanisms TCP uses to accomplish a connection-oriented connection?
    • The three mechanisms TCP uses to accomplish a connection-oriented connection are as follows:
    • - Packet sequencing
    • - Acknowledgments, checksums, and timers
    • - Windowing
  28. What are the steps for the TCP three-way handshake?
    • The steps for the TCP three-way handshake are as follows:Step 1. The source host sends a SYN to the destination host.
    • Step 2. The destination host replies to the source with an ACK. At the same time, it sends a SYN to the source host.
    • Step 3. The source host replies with an ACK.
  29. What is the purpose of flow control?
    • Flow control provides a mechanism for the receiver to control the transmission speed.
    • TCP implements flow control by using the SYN and ACK fields in the TCP header, along with the Window field. The Window field is a number that implies the maximum number of unacknowledged bytes allowed outstanding at any time.
  30. What is a TCP window?
    A TCP window is the amount of data that can be sent before an acknowledgment is required.
  31. What is the purpose of a three-way handshake?
    The three-way handshake initiates communication by establishing an initial sequence number and window size.
  32. What is the purpose of TCP sequencing?
    The purpose of sequencing is to provide reliability by requiring the recipient to acknowledge receipt of a group of segments before a timer expires.
  33. What fields are included in the TCP header?
    • The fields included in the TCP header are as follows:
    • - Acknowledgment Number
    • - Sequence Number
    • - Source/Destination Port
    • - Window Size
    • - TCP Checksum
  34. What is an example of a Layer 2 address?
    • MAC address.
    • MAC addresses are assigned to end devices and are used for communication over the local network. MAC addresses are hard-coded into the network card.
  35. What is the Address Resolution Protocol (ARP)?
    ARP is used to resolve a known IP address to a MAC address. For a host to communicate with another host, it must know the MAC address of the destination host (if they are on the same network) or next-hop router. This is the reason for ARP.
  36. What is the ARP table?
    • The ARP table stores the reference of each known IP address to its MAC address.
    • The ARP table is created and maintained dynamically.
  37. What is the purpose of the default gateway?
    • The default gateway allows hosts to communicate to hosts that are on a different network (segment).
    • All data that is not destined for the same network is sent to the default gateway for delivery.
  38. A host computer has been correctly configured with a static IP address, but the default gateway is incorrect. Which layer of the OSI model is first affected by this misconfiguration?
    • Layer 3.
    • The default gateway sends IP packets to a remote network and functions at Layer 3 of the OSI model.
  39. What three configuration settings does a host on a TCP/IP network require to communicate with hosts on a remote TCP/IP network?
    • The configuration settings are as follows:
    • - IP address
    • - Subnet mask
    • - Default gateway address
  40. You want to test TCP/IP connectivity between two hosts. What IP tool can you use to do this?
    Ping. Ping is a tool that is part of IP that sends Internet Control Message Protocol (ICMP) packets to test network layer connectivity between two hosts. Ping sends an "echo request" packet to the target host and listens for an ICMP "echo response."
  41. What two utilities test IP connectivity?
    • Ping and traceroute (tracert).
    • Ping and traceroute are ICMP utilities. ICMP can test only Layer 3 connectivity.
    • Note: These tests will fail if a firewall senses an asymetric route (stateful packet inspection)
  42. List four functions of ICMP.
    • Four functions of ICMP are as follows:
    • - Flow control
    • - Detect unreachable destinations
    • - Redirect routes
    • - Check remote hosts
  43. While troubleshooting a computer with network connectivity problems, you notice steady link lights on both the computer and the switch port the computer is connected to. However, when you issue the ping command from the computer, you receive a "Request timed out" message. On what layer of the OSI model does the problem most likely exist?
    • The network layer.
    • Because the link lights on the computer network interface card (NIC) and workstation port are on, the physical connection is working properly. Because you are getting a "Request timed out" message, the problem most likely resides at the network layer.