CIT 161 Intro to Networking Chapter 15 - Application Layer

What part of the URL, http://www.cisco.com/index.html, represents the top-level DNS domain?

.com Topic 15.4.0 - The components of the URL http://www.cisco.com/index.html are as follows: http = protocol www = part of the server name cisco = part of the domain name index = file name com = the top-level domain

What is the complete range of TCP and UDP well-known ports?

0 to 1023 Topic 14.4.0 - There are three ranges of TCP and UDP ports. The well-know range of port numbers is from 0 - 1023.

Assume a host with IP address 10.1.1.10 wants to request web services from a server at 10.1.1.254. Which of the following would display the correct socket pair?

10.1.1.10:1099, 10.1.1.254:80. 1. The socket pair for a host with IP address 10.1.1.10 requesting web services from a server at 10.1.1.254 would be 10.1.1.10:1099, 10.1.1.254:80.

Which number or set of numbers represents a socket?

192.168.1.1:80 Topic 14.4.0 - A socket is defined by the combination of an IP address and a port number, and uniquely identifies a particular communication.

How many connections are required by FTP between client and server?

2 1. FTP requires two connections between the client and the server. One connection is over port 21 for client commands and server replies. The other connection is over port 20 for data transfer.

Which of these ports are used by FTP? (Choose two.)

20 21 3. Ports 20 and 21 are used by FTP.

Which of the following DNS record types is used to resolve IPv6 addresses?

AAAA 1. DNS AAAA records are used to resolve names to IPv6 addresses.

Which two flags in the TCP header are used in a TCP three-way handshake to establish connectivity between two network devices? (Choose two.)

ACK SYN Topic 14.5.0 - TCP uses the SYN and ACK flags in order to establish connectivity between two network devices.

Which peer-to-peer application allows users to share pieces of many files with each other at the same time?

BitTorrent 3. BitTorrent clients use a torrent file to locate other clients that are sharing pieces of needed files. In this way, many files can be shared between clients at the same time

The netstat Command Unexplained TCP connections can pose a major security threat. They can indicate that something or someone is connected to the local host. Sometimes it is necessary to know which active TCP connections are open and running on a networked host. Netstat is an important network utility that can be used to verify those connections. As shown below, enter the command netstat to list the protocols in use, the local address and port numbers, the foreign address and port numbers, and the connection state.

By default, the netstat command will attempt to resolve IP addresses to domain names and port numbers to well-known applications. The -n option can be used to display IP addresses and port numbers in their numerical form.

A wireless host needs to request an IPv4 address. What protocol would be used to process the request?

DHCP Topic 15.4.0 - The DHCP protocol is used to request, issue, and manage IP addressing information. CSMA/CD is the access method used with wired Ethernet. ICMP is used to test connectivity. SNMP is used with network management and FTP is used for file transfer.

Which two are protocols that belong in the OSI application layer?

DNS SMTP 4. The application layer of the OSI model provides an interface between applications protocols exchanging data between hosts. Protocols at the application layer include DNS, HTTP, SMTP, FTP, and IMAP.

Which two services or protocols use the preferred UDP protocol for fast transmission and low overhead? (Choose two)

DNS VoIP Topic 14.3.0 - Both DNS and VolP use UDP to provide low overhead services within a network implementation.

Which two fields are the same in a TCP and UDP header? (Choose two.)

Destination port number Source port number 4. Both TCP and UDP headers include a source and destination port number fields.

How does a networked server manage requests from multiple clients for different services?

Each request has a combination of source and destination port numbers, coming from a unique IP address. Topic 14.4.0 - Each service provided by a server, such as email or file transfers, uses a specific port number. The source port number of a service request identifies the client that is requesting services. The destination port number identifies the specific service. Servers do not use address information to provide services. Routers and switches use addressing information to move traffic through the network.

3. Which two applications would use the TCP transport layer protocol? (Choose two.)

FTP HTTP 3. FTP and HTTP require the use of the TCP transport layer protocol.

True or false? The peer-to-peer networking model requires the implementation of a dedicated server for data access.

False 1. The correct answer is False. In the peer-to-peer model, clients can share resources without using a dedicated server.

True or false? A DNS server that receives a request for a name resolution that is not within its DNS zone will send a failure message to the requesting client.

False 2. The correct answer is False. When a DNS server receives a name resolution request for a name not within its zone, the serve will forward the request to another DNS server.

True or false? Resource sharing over SMB is only supported on Microsoft operating systems.

False 4. The correct answer is False. Resource sharing over SMB is also supported by Apple Macintosh. Linux and Unix operating systems use a version of SMB called SAMBA.

True or false? HTTP is a secure protocol.

False 5. The correct answer is False. HTTP sends information in plaintext and is not considered secure. If security is desired, HTTP Secure (HTTPS) should be used.

What message type is used by an HTTP client to request data from a web server?

GET Topic 15.3.0 - HTTP clients send GET messages to request data from web servers.

Which three protocols or standards are used at the application layer of the TCP/IP model? (Choose three.)

GIF HTTP MPEG Topic 15.1.0 - HTTP, MPEG, and GIF operate at the application layer of the TCP/IP model. TCP and UDP operate at the transport layer. IP operates at the internet layer.​

This protocol is used by a web browser to establish a connection to a web server.

HTTP 2. Web browsers connect to web servers over HTTP. IMAP and SMTP are email protocols. SSL is an encryption protocol used with HTTPS.

Which protocol uses encryption?

HTTPS Topic 15.1.0 - HTTPS uses Secure Socket Layer (SSL) to encrypt traffic accessed from a web server.

When retrieving email messages, which protocol allows for easy, centralized storage and backup of emails that would be desirable for a small- to medium-sized business?

IMAP Topic 15.3.0 - IMAP is preferred for small-to medium-sized businesses as IMAP allows centralized storage and backup of emails, with copies of the emails being forwarded to clients. POP delivers the emails to the clients and deletes them on the email server. SMTP is used to send emails and not to receive them. HTTPS is not used for secure web browsing.

2. Which TCP header statement is true?

It consists of 10 fields in a 20-byte header. 2. The TCP header consists of 10 fields in a 20-byte header.

Which UDP header statement is true?

It consists of 4 fields in an 8-byte header. 2. The UDP header consists of four fields in an 8-byte header.

Which is a feature of IMAP?

It downloads a copy of email messages leaving the original on the server 4. IMAP is a protocol for clients to retrieve copies of email messages from an IMAP server. The original messages remain on the server until manually deleted.

Why is DHCP for IPv4 preferred for use on large networks?

It is a more efficient way to manage IPv4 addresses than static address assignment is. Topic 15.4.0 - Static IPv4 address assignment requires personnel to configure each network host with addresses manually. Large networks can change frequently and have many more hosts to configure than do small networks. DHCP provides a much more efficient means of configuring and managing IPv4 addresses on large networks than does static address assignment.

Why is UDP desirable for protocols that make a simple request and reply transactions?

Low overhead 1. UDP is desirable for protocols that make simple request and reply transactions because of its low overhead.

Which of the following DNS resource record types resolves authoritative name servers?

NS 4. NS records resolve authoritative name servers. DNS A records resolve IPv4 addresses. AAAA records resolve IPv6 addresses, and MX records resolve mail exchange servers.

Which protocol can be used to transfer messages from an email server to an email client?

POP3 Topic 15.3.0 - SMTP is used to send mail from the client to the server but POP3 is used to download mail from the server to the client. HTTP and SNMP are protocols that are unrelated to email.

This message type is used when uploading data files to a web server.

POST 1. HTTP uses the POST message to upload data files to a web server. The GET message is used by clients to request data and the PUT message is used to upload content such as images.

The Internet Assigned Numbers Authority (IANA) is the standards organization responsible for assigning various addressing standards, including the 16-bit port numbers. The 16 bits used to identify the source and destination port numbers provides a range of ports from 0 through 65535. The IANA has divided the range of numbers into the following three port groups.

Port Group - Number Range - Description Well-known Ports - 0 to 1,023 * These port numbers are reserved for common or popular services and applications such as web browsers, email clients, and remote access clients. * Defined well-known ports for common server applications enables clients to easily identify the associated service required. Registered Ports - 1,024 to 49,151 * These port numbers are assigned by IANA to a requesting entity to use with specific processes or applications. * These processes are primarily individual applications that a user has chosen to install, rather than common applications that would receive a well-known port number. * For example, Cisco has registered port 1812 for its RADIUS server authentication process. Private and/or Dynamic Ports - 49,152 to 65,535 * These ports are also known as ephemeral ports. * The client's OS usually assign port numbers dynamically when a connection to a service is initiated. * The dynamic port is then used to identify the client application during communication. Note: Some client operating systems may use registered port numbers instead of dynamic port numbers for assigning source ports.

The table displays some common well-known port numbers and their associated applications. Well-Known Port Numbers

Port Number - Protocol - Application 20 -TCP - File Transfer Protocol (FTP) - Data 21 TCP - File Transfer Protocol (FTP) - Control 22 TCP - Secure Shell (SSH) 23 TCP - Telnet 25 TCP - Simple Mail Transfer Protocol (SMTP) 53 UDP, TCP - Domain Name System (DNS) 67 UDP - Dynamic Host Configuration Protocol (DHCP) - Server 68 UDP - Dynamic Host Configuration Protocol - Client 69 UDP - Trivial File Transfer Protocol (TFTP) 80 TCP - Hypertext Transfer Protocol (HTTP) 110 TCP - Post Office Protocol version 3 (POP3) 143 TCP - Internet Message Access Protocol (IMAP) 161 UDP - Simple Network Management Protocol (SNMP) 443 TCP - Hypertext Transfer Protocol Secure (HTTPS)

Which application layer protocol is used to provide file-sharing and print services to Microsoft applications?

SMB Topic 15.5.0 - SMB is used in Microsoft networking for file-sharing and print services. The Linux operating system provides a method of sharing resources with Microsoft networks by using a version of SMB called SAMBA.

This protocol is used by a client to send email to a mail server.

SMTP 3. Email clients connect to SMTP servers over port 25 to send email. POP and IMAP are used by clients to receive email. HTTP is used between web browsers and web servers.

2. Which control bit flags are used during the three-way handshake?

SYN and ACK 2. The three-way handshake consists of a three message exchanges with the following control bit flags: SYN, SYN ACK, and ACK.

What TCP mechanism is used to enhance performance by allowing a device to continuously send a steady stream of segments as long as the device is also receiving necessary acknowledgements?

Sliding window Topic 14.6.0 - TCP uses windows to attempt to manage the rate of transmission to the maximum flow that the network and destination device can support while minimizing loss and retransmissions. When overwhelmed with data, the destination can send a request to reduce the of the window. The process of the destination sending acknowledgments as it processes bytes received and the continual adjustment of the source send window is known as sliding windows.

Which of the following would be valid source and destination ports for a host connecting to an email server?

Source: 49152, Destination: 25 1. The destination port is the well-known port for Simple Mail Transport Protocol, which is 25. This is the port that the mail server will be listening on. The source port is dynamically selected by the requesting client and can be 49152.

Which of the following would be valid source and destination ports for a host connecting to a DNS server?

Source: 49152, Destination: 53 3. The correct valid source and destination ports for a host requesting DNS service is Source: 49152, Destination: 53.

1. Which transport layer protocol ensures reliable same-order delivery?

TCP 1. The TCP transport layer protocol ensures reliable same-order delivery.

Which transport layer feature is used to establish a connection-oriented session?

TCP 3-way handshake Topic 14.5.0 - TCP uses the 3-way handshake. UDP does not use this feature. The 3-way handshake ensures there is connectivity between the source and destination devices before transmission occurs.

Which two applications would use the UDP transport layer protocol? (Choose two.)

TFTP VolP 3. TFTP and VolP require the use of the UDP transport layer protocol.

Which statement is true about FTP?

The client can download data from or upload data to the server Topic 15.5.0 - FTP is a client/server protocol. FTP requires two connections between the client and the server and uses TCP to provide reliable connections. With FTP, data transfer can happen in either direction. The client can download (pull) data from the server or upload (push) data to the server.

Which action is performed by a client when establishing communication with a server via the use of UDP at the transport layer?

The client randomly selects a source port number. Topic 14.7.0 - Because a session does not have to be established for UDP, the client selects a random source port to begin a connection. The random port number selected is inserted into the source port field of the UDP header.

What happens if part of an FTP message is not delivered to the destination?

The message is lost because FTP does not use a reliable delivery method Topic 14.6.0 - Because FTP uses TCP as its transport layer protocol, sequence and acknowledgment numbers will identify the missing segments, which will be re-sent to complete the message.

What happens when a sending host senses there is congestion?

The sending host reduces the number of bytes it sends before receiving an acknowledgment from the destination host. 3. When a sending host senses congestion, it reduces the number of bytes it sends before receiving an acknowledgment from the destination host.

Network congestion has resulted in the source learning of the loss of TCP segments that were sent to the destination. What is one way that the TCP protocol addresses this?

The source decreases the amount of data that it transmits before it receives an acknowledgement from the destination. Topic 14.6.0 - If the source determines that the TCP segments are either not being acknowledged or are not acknowledged in a timely manner, then it can reduce the number of bytes it sends before receiving an acknowledgment. This does not involve changing the window in the segment header. The source does not decrease the window that is sent in the segment header. The window in the segment header is adjusted by the destination host when it is receiving data faster than it can process it, not when network congestion is encountered.

True or false? In a peer-to-peer network environment every peer can function as both a client and a server.

True 2. The correct answer is True. A peer-to-peer network does not require a dedicated server because each peer can function as both a client and as a server.

True or false? FTP data transfers take place from client to server (push) and from server to client (pull).

True 2. The correct answer is True. Data transfer over FTP can take place in either direction, uploads from client to server, or downloads from server to client.

Which of the following is a stateless best-effort delivery transport layer protocol?

UDP 1. UDP is a stateless best-effort delivery transport layer protocol.

3. Which transport layer protocol statement is true?

UDP is a best-effort delivery protocol. UDP is a best-effort delivery protocol while TCP is a reliable transport protocol.

Which UDP datagram reassembly statement is true?

UDP reassembles the data in the order that it was received. 2. UDP reassembles the data in the order that it was received.

The six bits in the Control Bits field of the TCP segment header are also known as flags. A flag is a bit that is set to either on or off. The six control bits flags are as follows:

URG - Urgent pointer field significant ACK - Acknowledgment flag used in connection establishment and session termination PSH - Push function RST - Reset the connection when an error or timeout occurs SYN - Synchronize sequence numbers used in connection establishment FIN - No more data from sender and used in session termination Search the internet to learn more about the PSH and URG flags.

Which of the following is a feature of the Gnutella protocol?

Users can share whole files with other users 4. Gnutella is a peer-to-peer protocol that allows users to share whole files with other users.

4. Which transport layer protocol would be used for VolP applications?

VolP Transfer Protocol UDP would be used by time sensitive VoIP applications.

The nslookup Command

When configuring a network device, one or more DNS Server addresses are provided that the DNS client can use for name resolution. Usually the ISP provides the addresses to use for the DNS servers. When a user application requests to connect to a remote device by name, the requesting DNS client queries the name server to resolve the name to a numeric address. Computer operating systems also have a utility called Nslookup that allows the user to manually query the name servers to resolve a given host name. This utility can also be used to troubleshoot name resolution issues and to verify the current status of the name servers. In this figure, when the nslookup command is issued, the default DNS server configured for your host is displayed. The name of a host or domain can be entered at the nslookup prompt. The Nslookup utility has many options available for extensive testing and verification of the DNS process.

On a home network, which device is most likely to provide dynamic IPv4 addressing to clients on the home network?

a home router Topic 15.4.0 - On a home network, a home router usually serves as the DHCP server. The home router is responsible for dynamically assigning IPv4 addresses to clients on the home network. ISPs also use DHCP, but it usually assigns an IPv4 address to the Internet interface of the home router, not the clients on the home network. In businesses, it is common to have a file or other dedicated server provide DHCP services to the network. Finally, a DNS server is responsible for finding the IP address for a URL, not for providing dynamic addressing to network clients.

Which two operations are provided by TCP but not by UDP? (Choose two.)

acknowledging received data retransmitting any unacknowledged data Topic 14.1.0 - Numbering and tracking data segments, acknowledging received data, and retransmitting any unacknowledged data are reliability operations to ensure that all of the data arrives at the destination. UDP does not provide reliability. Both TCP and UDP identify the applications and track individual conversations. UDP does not number data segments and reconstructs data in the order that it is received.

This layer of the OSI model is concerned with the protocols that exchange data between programs running on hosts.

application 1. The application layer of the OSI model is the layer that is closest to the end user. It provides an interface between application protocols exchanging data between hosts.

Which TCP/IP model layer is closest to the end user?

application Topic 15.1.0 - End users use applications to interact with and use the network. The application layer of the TCP/IP model is closest to the end user. Application layer protocols are used to communicate and exchange messages with other network devices and applications. The layers of the TCP/IP model are from top to bottom (memory aid - ATIN): application, transport, internet, network access

These three OSI layers define the same functions as the TCP/IP model application layer.

application presentation session 3. The upper three OSI layers; application, presentation, and session, define the application layer functions of the TCP/IP model.

What type of applications are best suited for using UDP?

applications that are sensitive to delay Topic 14.3.0 - UDP is not a connection-oriented protocol and does not provide retransmission, sequencing, or flow control mechanisms. It provides basic transport layer functions with a much lower overhead than TCP. Lower overhead makes UDP suitable for applications which are sensitive to delay.

An author is uploading one chapter document from a personal computer to a file server of a book publisher. What role is the personal computer assuming in this network model?

client Topic 15.2.0 - In the client/server network model, a network device assumes the role of server in order to provide a particular service such as file transfer and storage. The device requesting the service assumes the role of client. In the client/server network model, a dedicated server does not have to be used, but if one is present, the network model being used is the client/server model. In contrast, the peer-to-peer network model does not have a dedicated server.

What are two characteristics of the application layer of the TCP/IP model? (Choose two.)

closest to the end user the creation and maintenance of dialogue between source and destination applications Topic 15.1.0 - The application layer of the TCP/IP model is the layer that is closest to the end user, providing the interface between the applications. It is responsible for formatting, compressing, and encrypting data, and is used to create and maintain dialog between source and destination applications.

2. Which three are transport layer responsibilities? (Choose three.)

conversation multiplexing segmenting data and reassembling segments tracking individual conversations The transport layer is responsible for conversation multiplexing, segmenting data and reassembling segments, and tracking individual conversations.

This is a function of the OSI session layer.

exchange of information to initiate dialog between peers 5. The session layer of the OSI model creates and maintains the dialogs, or sessions, between two communicating hosts.

Which two tasks can be performed by a local DNS server? (Choose two.)

forwarding name resolution requests between servers mapping name-to-IP addresses for internal hosts Topic 15.4.0 - Two important functions of DNS are to (1) provide IP addresses for domain names such as www.cisco.com, and (2) forward requests that cannot be resolved to other servers in order to provide domain name to IP address translation. DHCP provides IP addressing information to local devices. A file transfer protocol such as FTP, SFTP, or TFTP provides file sharing services. IMAP or POP can be used to retrieve an email message from a server.

How many exchanges are needed to end both sessions between two hosts?

four exchanges 3. There are four exchanges to end both sessions between two hosts. (1) Host A sends a FIN. (2) Host B sends an ACK. (3) Host B sends a FIN. (4) Host A sends an ACK.

Which Windows command would display the protocols in use, the local address and port numbers, the foreign address and port numbers, and the connection state?

netstat 3. The netstat Windows command would display protocols in use, the local address and port numbers, the foreign address and port numbers, and the connection state.

MKV, GIF, and JPG standards are associated with which OSI layer?

presentation 2. The presentation layer is concerned with formatting and presenting data in a format that is compatible with the destination device. Examples of presentation layer standards are MKV, GIF, JPG, MOV, and PNG.

What field is used by the destination host to reassemble segments into the original order?

sequence number 1. The sequence number field is used by the destination host to reassemble segments into the original order.

What is a socket?

the combination of a source IP address and port number or a destination IP address and port number Topic 14.4.0 - A socket is a combination of the source IP address and source port or the destination IP address and the destination port number.

Which of the following is displayed by the nslookup utility?

the configured default DNS server 3. By issuing the nslookup command, the default DNS server that is configured is displayed.

What is the purpose of using a source port number in a TCP communication?

to keep track of multiple conversations between devices Topic 14.4.0 - The source port number in a segment header is used to keep track of multiple conversations between devices. It is also used to keep an open entry for the response from the server. The incorrect options are more related to flow control and guaranteed delivery.

What is a responsibility of transport layer protocols?

tracking individual conversations Topic 14.1.0 - There are three main responsibilities for transport layer protocols TCP and UDP: o Tracking individual conversations o Segmenting data and reassembling segments o Identifying the applications

1. Which layer is responsible for establishing a temporary communication session between the source and destination host applications?

transport layer The transport layer is responsible for establishing a temporary communication session between the source and destination host applications.

Which port group includes port numbers for FTP, HTTP, and TFTP applications?

well-known ports 2. FTP, HTTP, and TFTP applications port numbers are defined in the well-known port numbers group.

What field is used to provide flow control?

window size 2. The Window Size field is used to provide flow control.