Application Layer Study Guide

What is an application layer?

it provides the interface between the applications used to communicate, and the underlying network over which messages are transmitted

Application layer protocols are used to

exchange data between programs running on the source and destination hosts.

What are the three primary functions in the presentation Layer?

Formatting, or presenting, data at the source device into a compatible format for receipt by the destination device., Compressing data in a way that can be decompressed by the destination device., Encrypting data for transmission and decrypting data upon receipt.

The presentation layer formats data for the application layer, and

it sets standards for file formats

What are some well-known standard formats that the presentation layer uses?

MKV, MPG, MOV, FIG, JPG, and PNG.

What does the session layer do?

create and maintain dialogs between source and destination applications

The session layer handles

the exchange of information to initiate dialogs, keep them active, and to restart sessions that are disrupted or idle for a long period of time.

The TCP/IP application protocols specify

the format and control information necessary for many common internet communication functions.

Application layer protocols are used by

both the source and destination devices during a communication session.

For the communications to be successful,

the application layer protocols that are implemented on the source and destination host must be compatible.

True or False: Trivial File Transfer Protocol is a connectionless file transfer protocol with best-effort, unacknowledged file deliver that is less overhead than FTP and used port UDP 69

True

HTTP or HyperText Transfer Protocol is

a set of rules for exchanging text, graphic images, sound, video, and other multimedia files on the World Wide Web and uses TCP 80, 8080

HTTP Secure is the same as HTTP but has

The browser uses encryption to secure HTTP communications and authenticates the website to which you are connecting your browser in addition uses TCP or UDP port number 443.

In the client/server model, the device requesting the information is called a

client

The device responding to the request is called a

server.

The client is a hardware/software combination that people use to

directly access the resources that are stored on the server.

Client and server processes are considered to be

in the application layer

Application layer protocols describe the format of the requests and responses between

clients and servers

Data transfer from a client to a server is referred to as an

upload

data from a server to a client as a

download.

In a P2P network, two or more computers are connected via

a network and can share resources (such as printers and files) without having a dedicated server.

Every connected end device (known as a peer) can function as

both a server and a client.

One computer might assume the role of server for one transaction while

simultaneously serving as a client for another.

The roles of client and server are set on a

per request basis.

P2P applications require that each end device

provide a user interface and run a background service.

In a hybrid system, each peer accesses an index server to get the

location of a resource stored on another peer.

Gnutella-compatible client software allows users to connect to Gnutella services over the internet, and to

locate and access resources shared by other Gnutella peers

What common P2P networks are included?

BitTorrent, Direct Connect, eDonkey, and Freent (which some are based on Gnutella protocol).

Clients ask for pieces from multiple users at the same time. This is known as

a swarm and the technology is called BitTorrent

Many P2P applications allow users to

share pieces of many files with each other at the same time.

Clients use a torrent file to locate other users who have pieces that they need so that

they can then connect directly to them

HTTP is a

request/response protocol.

When a client, typically a web browser, sends a request to a web server,

HTTP specifies the message types used for that communication.

What does the GET message type do?

This is a client request for data. A client (web browser) sends the GET message to the web server to request HTML pages.

What does the POST message type do?

This uploads data files to the web server, such as form data.

What does the PUT message type do?

This uploads resources or content to the web server, such as an image.

HTTPS uses

authentication and encryption to secure data as it travels between the client and server

HTTPS uses the same client request-server response process as HTTP, but the data stream is encrypted with

Transport Layer Security (TLS) or its predecessor Secure Socket Layer (SSL) before being transported across the network.

Email is a

store-and-forward method of sending, storing, and retrieving electronic messages across a network.

Email messages are stored in

databases on mail servers.

Email clients communicate with mail servers to

send and receive email.

Mail servers communicate with other mail servers to

transport messages from one domain to another.

An email client does not communicate directly with

another email client when sending email. Instead, both clients rely on the mail server to transport messages.

SMTP message formats require a

message header and a message body.

Although the message body can contain any amount of text,

the message header must have a properly formatted recipient email address and a sender address.

If the message is still not delivered after a predetermined expiration time,

it is returned to the sender as undeliverable.

POP is used by an

application to retrieve mail from a mail server.

True or False: With POP, mail is downloaded from the server to the client and then deleted on the server. This is the default operation of POP.

True

With POP, email messages are downloaded to the client and removed from the server, so there is

no centralized location where email messages are kept

True or False: POP4 is the most commonly used version

False

IMAP is another protocol that

describes a method to retrieve email messages

Unlike POP, when the user connects to an IMAP-capable server,

copies of the messages are downloaded to the client application

True or False: The original messages are kept on the server until manually deleted. Users view copies of the messages in their email client software.

True

True or False: Users can create a file hierarchy on the server to organize and store mail. That file structure is not duplicated on the email client as well.

False

When a user decides to delete a message,

the server synchronizes that action and deletes the message from the server.

Domain names were created to

convert the numeric address into a simple, recognizable name.

True or False: On the internet, fully-qualified domain names (FQDNs), such as http://www.cisco.com, are much easier for people to remember than 198.133.219.25, which is the actual numeric address for this server.

True

True or False: If Cisco decides to change the numeric address of www.cisco.com, it is immediate to the user because the domain name is different.

False

The DNS protocol communications use

a single format called a message.

This message format is used for

all types of client queries and server responses, error messages, and the transfer of resource record information between servers.

What are some of the resource records that a DNS server will use?

A, NS, AAAA, MX

What is the meaning of A in the resource records at a DNS server?

An end device IPv4 address

What is the meaning of NS in the resource records at a DNS server?

An authoritative name server

What is the meaning of AAAA in the resource records at a DNS server?

An end device IPv6 address (pronounced quad-A)

What is the meaning of MX in the resource records at a DNS server?

A mail exchange record

True or False: When a client makes a query, the server DNS process first looks at its own records to resolve the name.

True

If it is unable to resolve the name by using its stored records,

it contacts other servers to resolve the name

True or False: After a match is found and returned to the original requesting server, the server temporarily deletes the numbered address in the event that the same name is requested again.

False

What is the description of the Question in the DNS message section?

The question for the name server

What is the description of Answer in the DNS message section?

Resource Records answering the question

What is the description of Authority in the DNS message section?

Resource Records pointing toward an authority

What is the description of Additional in the DNS message section?

Resource Records holding additional information

The DNS protocol uses a

hierarchical system to create a database to provide name resolution

True or False: DNS is scalable because hostname resolution is spread across multiple servers.

True

Each DNS server maintains a specific database file and is only responsible for managing name-to-IP mappings

for that small portion of the entire DNS structure.

What does the top-level domain (.com) represents?

A business or industry

What does the top-level domain (.org) represent?

A non-profit organization

What does the top-level domain (.edu) represent?

education

What does the top-level domain (.co) represent?

Colombia

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.

The Dynamic Host Configuration Protocol (DHCP) for IPv4 service automates

the assignment of IPv4 addresses, subnet masks, gateways, and other IPv4 networking parameters

True or False: When using static addressing, the network administrator manually enters IP address information on hosts.

True

True or False: When a host connects to the network, the DHCP server is not contacted, and an address is not requested

False

The DHCP server chooses an address from a configured range of addresses called

a pool and assigns (leases) it to the host.

True or False: On smaller networks, or where the user population changes little, DHCP is preferred for address assignment.

False

DHCP can allocate IP addresses

for a configurable period of time, called a lease period.

DHCP is used for

general purpose hosts, such as end user devices

Static addressing is used for

network devices, such as gateway routers, switches, servers, and printers.

True or False: One important difference is that DHCPv6 does not provide a default gateway address.

True

What are the four messaging types that DHCP used?

DHCPDISCOVER, DHCPOFFER, DHCPREQUEST, DHCPACK

What are the four messaging types that DHCPv6 uses?

SOLICIT, ADVERTISE, INFORMATION REQUEST, REPLY.

An FTP client is an application which runs

on a computer that is being used to push and pull data from an FTP server.

What is the first step when using the FTP protocol?

The client establishes the first connection to the server for control traffic using TCP port 21. The traffic consists of client commands and server replies.

What is the second step when using the FTP protocol?

The client establishes the second connection to the server for the actual data transfer using TCP port 20. This connection is created every time there is data to be transferred.

What is the third step when using the FTP protocol?

The data transfer can happen in either direction. The client can download (pull) data from the server, or the client can upload (push) data to the server.

True or False: Server Message Block is NOT a request-response protocol

True

The Server Message Block (SMB) is a client/server file sharing protocol that

describes the structure of shared network resources, such as directories, files, printers, and serial ports.

Whare are the three function of SMB messages?

Start, authenticate, and terminate sessions., Control file and printer access., Allow an application to send or receive message to or from another device.

True or False: After the FTP connection is established, the user of the client can access the resources on the server as though the resource is local to the client host.

True