Ch. 9 Transport Layer & Ch. 10 Application Layer

Three responsibilities of the transport layer

Tracking individual conversations Segmenting data and reassembling segments Identifying the applications

Which number or set of numbers represents a socket?

192.168.1.1:80

Why is DHCP preferred for use on large networks?

It is a more efficient way to manage IP addresses than static address assignment.

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.

What is true about a client-server network?

The network includes a dedicated server.

Which command is used to manually query a DNS server to resolve a specific host name?

nslookup

A UDP datagram includes

source and destination ports, length field, and checksum (error checking) 8 bytes of overhead above application layer data

TCP is a ______________ protocol, which is a protocol that keeps track of the state of the communication session.

stateful

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

to keep track of multiple conversations between devices

The sequence number represents the first data byte of the TCP segment (T or F)

True

A TCP segment includes

*20 bytes of overhead* above application layer data source and destination ports (ID's the application) sequence # (for data reassembly) acknowledgment # (indicates data has been received and the next byte expected from the source) header length (data "offset" indicates length of the TCP segment header) reserved (field reserved for future) control bits (indicate purpose of the TCP segment aka flags) window size (indicates # of bytes that can be accepted at one time) checksum (used for error checking) urgent (indicates if data is urgent)

The presentation layer's three primary functions:

1) Formatting, or presenting, data at the source device into a compatible form for receipt by the destination device 2) Compressing data in a way that can be decompressed by the destination device 3) Encrypting data for transmission and decrypting data upon receipt the protocols: MPEG, GIF, and JPEG

Three parts of the URL:

1) http (the protocol or scheme) 2) www.cisco.com (the server name) 3) index.html (the specific filename requested) http://www.cisco.com/index.html

Which three fields are used in a UDP segment header?

A UDP header consists of only the Source Port, Destination Port, Length, and Checksum fields. Sequence Number, Acknowledgment Number, and Window Size are TCP header fields.

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

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

DHCP client and server communication

DHCP client ---> server DHCPDISCOVER DHCP server ---> client DHCPOFFER DHCP client ---> server DHCPREQUEST DHCP server --> client DHCPACK DHCPv6 messages are SOLICIT, ADVERTISE, INFORMATION REQUEST, and REPLY

Both TCP and UDP can be used with what applications?

DNS and SNMP

A user is attempting to access http://www.cisco.com/ without success. Which two configuration values must be set on the host to allow this access?

DNS server default gateway

DNS uses different message formats for all types of client queries and server responses, error messages, and the transfer of resource record information between servers (T or F)

FALSE, DNS uses the *same* message format for client queries, server responses, error messages, and resource record information.

FTP

File transfer process- application layer protocol to allow for data transfers between a client and a server. FTP client is an application that runs on a computer that is used to push and pull data from an FTP server. two connections needed: control connection for control traffic and data connection for data traffic

What is a common protocol that is used with peer-to-peer applications such as WireShare, Bearshare, and Shareaza?

Gnutella

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

HTTP MPEG GIF

HTTPS

HTTP Secure is used for secure communication across the Internet. HTTPS uses authentication and encryption to secure data as it travels between the client and server. data stream is encrypted with *SSL* (secure socket layer)

Applications that use TCP

HTTP, FTP, SMTP, Telnet all use TCP which in turn works with IP at the internet layer

Port numbers

IANA standards body for port numbers 0-1023 are well-known ports (for applications) 1024 to 49151 are registered ports (assigned by IANA) 49152 to 65535 are private/dynamic ports (ephemeral ports, used to ID client application)

Peer-to-Peer Networks

In the peer-to-peer (P2P) networking model, the data is accessed from a peer device without the use of a dedicated server. every connected end device (known as a peer) can function as both a server and a client.

Application layer protocols:

Name system protocol: DNS (domain name system) Host configuration protocols: BOOTP (bootstrap protocol) and DHCP (dynamic host configuration protocol) email protocols: SMTP (simple mail transfer protocol), POP (post office protocol) and IMAP (internet message access protocol) file transfer protocols: FTP (file transfer protocol) and TFTP (trivial file transfer protocol) web protocols: HTTP (hypertext transfer protocol) and HTTPS (hypertext transfer protocol secure)

Peer-to-Peer Applications

P2P applications require that each end device provide a user interface and run a background service. common P2P applications: bittorrent and bitcoin

POP operates

POP is used by an application to retrieve mail from a mail server. With POP, mail is downloaded from the server to the client and then deleted on the server. not good if you need back up!

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

POP3

What is an advantage of SMB over FTP?​

SMB clients can establish a long-term connection to the server.​

SMB

Server Message Block is a client/server file sharing protocol that describes the structure of shared network resources, such as directories, files, printers, and serial ports. request-response protocol. long-term connection to servers

Three protocols supporting email operation

Simple Mail Transfer Protocol (SMTP) *sends mail* Post Office Protocol (POP) and IMAP *receive mail*

A TCP connection is established in three steps:

Step 1 - The initiating client requests a client-to-server communication session with the server. Step 2 - The server acknowledges the client-to-server communication session and requests a server-to-client communication session. Step 3 - The initiating client acknowledges the server-to-client communication session.

A TCP conversation is terminated in four steps:

Step 1 - When the client has no more data to send in the stream, it sends a segment with the FIN flag set. Step 2 - The server sends an ACK to acknowledge the receipt of the FIN to terminate the session from client to server. Step 3 - The server sends a FIN to the client to terminate the server-to-client session. Step 4 - The client responds with an ACK to acknowledge the FIN from the server.

SMTP/POP, HTTP, databases, web browsers, and email clients use what transport protocol?

TCP because they require that all data that is sent arrives at the destination in its original condition. stored audio and video use TCP ("buffering")

Which transport layer feature is used to guarantee session establishment?

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.

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.

What are three responsibilities of the transport layer?

The transport layer has several responsibilities. Some of the primary responsibilities include the following: Tracking the individual communication streams between applications on the source and destination Segmenting data at the source and reassembling the data at the destination Identifying the proper application for each communication stream through the use of port numbers Multiplexing the communications of multiple users or applications over a single network Managing the reliability requirements of applications

The transport layer services:

The transport layer provides transport-related services by: -Dividing data received from an application into segments -Adding a header to identify and manage each segment -Using the header information to reassemble the segments back into application data -Passing the assembled data to the correct application

What does the value of the window size specify?

The window size specifies the amount of data that can be sent before an acknowledgment is received from the receiver. This value specifies the highest number of bytes, not the required number of bytes.

HTTP is flexible, but it is not secure. The request messages send information to the server in plain text that can be intercepted and read. The server responses, typically HTML pages, are also unencrypted. (T or F)

True

True or False? In FTP transactions, an FTP client uses the pull method to download files from an FTP server.

True

Uniform Resource Identifiers (URIs) and Uniform Resource Locators (URLs) are the names most people associate with web addresses (T or F).

True

Streaming live video, live audio, VoIP use what transport protocol?

UDP because these applications can tolerate some data loss during transmission over the network, but delays in transmission are unacceptable. UDP is the better choice for these applications because less network overhead is required.

What is an advantage of UDP over TCP?

UDP communication requires less overhead. TCP is a more reliable protocol and uses sequence numbers to realign packets that arrive out of order at the destination. Both UDP and TCP use port numbers to identify applications. UDP has less overhead than TCP because the UDP header has fewer bytes and UDP does not confirm the receipt of packets.

GET

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

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

a home router

TCP

a reliable full-featured transport layer protocol which ensures that all of the data arrives at the destination. requires additional fields in the TCP header which increases the size of the packet and also increases delay Three basic operations of reliability: 1) Numbering and tracking data segments transmitted to a specific host from a specific application 2) Acknowledging received data 3) Retransmitting any unacknowledged data after a certain period of time

HTTP

a request/response protocol. when a client sends a request to a web server, HTTP specifies the message types used for that communication. the three message types are *GET, POST, and PUT*

IMAP

another way to retrieve email messages. when the user connects to an IMAP-capable server, copies of the messages are downloaded to the client application. the original messages are kept on the server until manually deleted

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

application layer

What type of applications are best suited for using UDP?

applications that are sensitive to delay

Upload v download

data transferred from a client to a server is referred to as an upload and data from a server to a client as a download.

Transport layer protocols

describe how the transport layer header information is used to reassemble the data pieces into streams to be passed to the application layer.

Client-server model

device requesting information is the client and the device responding to the request is the server. these processes are in the application layer

DNS

domain name service- created to convert the numeric IP address into a simple, recognizable name. ex. www.cisco.com vs. 198.133.219.25

DHCP

dynamic host configuration protocol- for IPv4 service- DHCP automates the assignment of IPv4 addresses, subnet masks, gateways, and other IPv4 networking parameters. DHCPv6 (DHCP for IPv6) provides similar services for IPv6 clients. One important difference is that *DHCPv6 does not provide a default gateway address*. used mainly for end user devices

4 features of TCP

establishing a session reliable delivery same-order delivery flow control

SMTP

format requires message header (recipient email address and sender address) and message body facilitates sending emails. makes connection w server, sends message, server places message in local account or forwards it to another mail server for delivery.

A header

is added to each block of data and used for reassembly and to track the data stream.

Applications that use UDP

live video and multimedia applications simple request and reply applications (DNS and DHCP) applications that handle reliability themselves (SNMP and TFTP)

A wired laser printer is attached to a home computer. That printer has been shared so that other computers on the home network can also use the printer. What networking model is in use?

peer-to-peer (P2P)

Segmentation

segmenting the data into smaller chunks enables many different communications, from many different users, to be interleaved (multiplexed) on the same network.

Which three layers of the OSI model provide similar network services to those provided by the application layer of the TCP/IP model?

session, presentation, application

A client application needs to terminate a TCP communication session with a server. The termination process steps in the order that they will occur are

step 1: client sends FIN step 2: server sends ACK step 3: server sends FIN step 4: client sends ACK

The TCP/IP application layer consists of what layers of the OSI model

the application, presentation, and session layers of the OSI model

A socket is

the combination of the source IP address and the source port number OR the destination IP address and destination port number it is used to ID the server and service being requested by the client ex. 192.168.1.5:1099, 192.168.1.7:80

What type of information is contained in a DNS MX record?

the domain name mapped to mail exchange servers

The OSI transport layer

the processes described in the OSI transport layer accept data from the application layer and prepare it for addressing at the network layer. think of a shipping department preparing a single order of multiple packages for delivery. The transport layer is responsible for establishing a temporary communication session between two applications and delivering data between them.

Segment identification

the transport layer adds a header containing binary data organized into several fields. the values in these fields enable various transport layer protocols

How does the transport layer identify the different applications?

the transport layer assigns each application an identifier called a *port number* source port (dynamically generated by the sending device) and destination port (tells what service is being requested)

Transport layer reliability

the transport layer is also responsible for managing reliability requirements of a conversation. TCP/IP provides two transport layer protocols: TCP and UDP (user datagram protocol) *TCP is reliable*

What is the purpose of the TCP sliding window?

to request that a source decrease the rate at which it transmits data The TCP sliding window allows a destination device to inform a source to slow down the rate of transmission. To do this, the destination device reduces the value contained in the window field of the segment. It is acknowledgment numbers that are used to specify retransmission from a specific point forward. It is sequence numbers that are used to ensure segments arrive in order. Finally, it is a FIN control bit that is used to end a communication session.

What OSI layer is responsible for establishing a temporary communication session between two applications and ensuring that transmitted data can be reassembled in proper sequence?

transport layer

POST

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

PUT

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

Static addressing

used for network devices, such as gateways, switches, servers, and printers.

UDP

user datagram protocol- DOES NOT provide for reliability and is simpler than TCP. Fewer fields and is faster than TCP. *best-effort* delivery protocol... no acknowledgment that data is received at destination

Netstat command

verifies which active TCP connections are open and running on a networked host

nslookup

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