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Questions and Answers

What is the purpose of the Sequence Number field in a TCP header?

To facilitate data reassembly. (correct)

To signify that data has been successfully received.

To track the total number of bytes that can be sent.

To indicate the destination application by port number.

Which statement correctly describes the window size field in a TCP header?

It indicates the priority of the TCP segment.

It specifies the duration for which data can be held in the buffer.

It represents the amount of data the sender can send without receiving an acknowledgment. (correct)

It defines the maximum size of the TCP header.

What characteristic of UDP makes it different from TCP?

It does not maintain state information between transactions. (correct)

It has a larger header size compared to TCP.

It establishes a connection before sending data.

It provides reliability and guarantees data delivery.

Which field in a TCP header is reserved for future use?

Reserved. Signup and view all the answers

What does the Checksum field in a TCP header do?

Provides error checking for the segment header and data. Signup and view all the answers

Which statement describes the nature of UDP's delivery mechanism?

It functions as a best-effort delivery protocol. Signup and view all the answers

What is the primary purpose of the three-way handshake in TCP?

To establish a communication session between hosts Signup and view all the answers

What denotes the urgency of data in a TCP header?

Urgent. Signup and view all the answers

Which TCP control flag is primarily used to signal that the sender has finished sending data?

FIN Signup and view all the answers

Which of the following TCP header fields is specifically responsible for indicating that data has been received?

Acknowledgment Number. Signup and view all the answers

How does TCP ensure reliable and ordered delivery of segments?

By using sequence numbers and acknowledgments Signup and view all the answers

What is indicated by the ACK control flag in a TCP segment?

A segment has been successfully received Signup and view all the answers

Which of the following scenarios would likely result in the RST (reset) flag being utilized?

Unexpected data being received for an inactive session Signup and view all the answers

What indicates that the destination device has an active service accepting requests on a specific port during the handshake process?

The SYN flag is sent Signup and view all the answers

What is the role of sequence numbers in TCP segments?

To determine the order of segments Signup and view all the answers

Which TCP control bit allows a sender to push data immediately to the receiving application?

PSH Signup and view all the answers

What is the main purpose of selective acknowledgment (SACK) in TCP?

To acknowledge only the segments that were received. Signup and view all the answers

How does TCP determine the amount of data it can send before requiring an acknowledgment?

Through the window size defined in the TCP header. Signup and view all the answers

What happens to the flow of data in TCP once the source receives an acknowledgment?

The source is permitted to send additional data based on the current window size. Signup and view all the answers

During the three-way handshake of a TCP connection, what is established?

The initial window size for data flow control. Signup and view all the answers

What role does the acknowledgment number play in TCP communications?

It indicates the next expected byte by the receiver. Signup and view all the answers

In TCP, what happens if the window size of the destination is modified?

The new window size will be included in every TCP segment. Signup and view all the answers

What is the effect of flow control on TCP transmission?

It allows the receiver to manipulate the sender's behavior based on processing capabilities. Signup and view all the answers

What does the TCP header's window size field indicate?

The number of unacknowledged bytes that can be sent. Signup and view all the answers

What is the primary advantage of IPv6 over IPv4 regarding address space?

Offers 128-bit addressing as opposed to 32-bit with IPv4 Signup and view all the answers

How does IPv6 improve packet handling compared to IPv4?

By using a simplified header format with fewer fields Signup and view all the answers

What issue does the elimination of NAT in IPv6 resolve?

It allows each device to have its unique address for end-to-end connectivity Signup and view all the answers

Which field in the IPv6 header is primarily responsible for suggesting handling by routers?

Flow Label Signup and view all the answers

What is a consequence of increasing the number of routes in a routing table?

Slower performance of the router Signup and view all the answers

What advantage does the hierarchical network architecture of IPv6 provide?

Enhances routing efficiency Signup and view all the answers

What characterizes the Traffic Class field in the IPv6 header?

It is an 8-bit field equivalent to the IPv4 Differentiated Services field Signup and view all the answers

Why was IPv6 developed in the early '90s?

To replace IPv4 and address its limitations Signup and view all the answers

What does the 16-bit field in an IPv6 packet indicate?

The length of the data payload in the packet Signup and view all the answers

Which field in an IPv6 packet replaces the IPv4 TTL field?

Hop Limit Signup and view all the answers

How does a host determine if the destination is a local or remote network?

By comparing the source IPv4 address with the destination IPv4 address and subnet mask Signup and view all the answers

What do the source and destination IPv6 address fields identify?

The sending and receiving hosts' IPv6 addresses Signup and view all the answers

What happens to an IPv6 packet when its Hop Limit reaches zero?

The packet is discarded Signup and view all the answers

Which address is referred to as the loopback interface?

127.0.0.1 Signup and view all the answers

Which of the following best describes a local host?

A host sharing the same network address as the sending host Signup and view all the answers

What does the Next Header field in an IPv6 packet indicate?

The type of the next encapsulated protocol Signup and view all the answers

What does the default gateway do?

Routes traffic to other networks when the destination is not local Signup and view all the answers

How does a host obtain the address of its default gateway?

It is received via DHCP or can be manually configured Signup and view all the answers

What command needs to be executed to view the routing table on a Windows host?

route print Signup and view all the answers

What section is NOT part of a Windows host's routing table?

Protocol Usage Table Signup and view all the answers

What role does the routing table play when sending packets to a remote network?

It determines the route the packet will take to a remote network Signup and view all the answers

Which of the following is true about the default gateway in a host's routing table?

It creates a default route for all outgoing traffic Signup and view all the answers

What information is NOT typically displayed in the Interface List of a Windows host's routing table?

IP address of the default gateway Signup and view all the answers

What occurs when a packet's destination is not on the same local network as the sending host?

The packet is sent to the default gateway for routing Signup and view all the answers

Study Notes

Application Layer

Supports end-user applications
Works with session and presentation layers to provide network services
Well-known protocols interact with end-user applications
TCP/IP application layer protocols operate
Web and email protocols operate
DNS and DHCP operate
File transfer protocols operate

Application, Presentation, and Session

Application Layer: closest to the end user, used to exchange data between programs running on source and destination hosts
Presentation Layer: formats data for the receiving device, compresses data, encrypts data
Session Layer: creates and maintains dialogues between source and destination applications

TCP/IP Application Layer Protocols

Domain Name Server (DNS): TCP, UDP 53 - translates domain names into IP addresses.
Bootstrap Protocol (BOOTP): Being superseded by DHCP.
Dynamic Host Configuration Protocol (DHCP): UDP 68, server 67 - dynamically assigns IP addresses to client stations at start-up.
Simple Mail Transfer Protocol (SMTP): TCP 25 - enables clients to send email to a mail server.
Post Office Protocol (POP): TCP 110 - enables clients to retrieve email from a mail server.
Internet Message Access Protocol (IMAP): TCP 143 - enables clients to retrieve email from mail server, maintains email on server.
File Transfer Protocol (FTP): TCP 20 and 21 - reliable, connection-oriented, and acknowledged file delivery protocol.
Trivial File Transfer Protocol (TFTP): UDP 69 - simple connectionless file transfer protocol.
Hypertext Transfer Protocol (HTTP): TCP 80, 8080 - rules for exchanging text, graphic images on the World Wide Web.
Hypertext Transfer Protocol Secure (HTTPS): TCP, UDP 443 - uses encryption and authentication to secure communication.

Client-Server Model

Client and server processes in the application layer
Application layer protocols describe the format of requests and responses between clients and servers
Example: using an ISP's email service to send, receive, and store email

Peer-to-Peer Networks

Data accessed from a peer device without a dedicated server
Each device can function as a server and client
A P2P application allows a device to act as a client and server within the same communication.
P2P applications require each end device provide a user interface and run a background service.

Common P2P Applications

Common P2P networks include: G2, Bitcoin, BitTorrent, eDonkey
Some P2P applications are based on the Gnutella protocol, where each user shares whole files.
Many P2P applications allow users to share parts of many files at the same time - this is bittorrent technology.

Web and Email Protocols

Hypertext Transfer Protocol (HTTP): request/response protocol
- Common types: GET (request data), POST (upload data to server), PUT (upload resources or content to server)
HTTP Secure (HTTPS): uses encryption and authentication to secure data.
Email Protocols:
- Simple Mail Transfer Protocol (SMTP): sending email
- Post Office Protocol (POP): retrieving email
- Internet Message Access Protocol (IMAP): retrieving email

IP Addressing Services

Domain Name Service (DNS): converts numeric addresses into simple, recognizable names.
DNS protocol defines an automated service that matches resource names with required numeric network address.
DNS Message Format:
- Header
- Question
- Answer
- Authority
- Additional
DNS Hierarchy: client, local DNS server, secondary level domain servers, top-level domain servers, and root DNS servers
nslookup command: utility to manually query name servers to resolve a given host.
TCP/IP Application Layer Protocols (Cont.)
Configures clients to send email to a mail server
Enables clients to retrieve email from a mail server

Dynamic Host Configuration Protocol (DHCP)

DHCP automates the assignment of IPv4 addresses, subnet masks, gateways, and other parameters.
DHCP-distributed addresses are leased for a set period of time.
DHCP is typically used for end-user devices. Static addressing is used for network devices like gateways, switches, servers, and printers.

File Transfer Protocol (FTP)

FTP requires two connections between client and server.
One for commands and replies (TCP port 21)
One for actual file transfer (TCP port 20)

Server Message Block (SMB)

Client/server file sharing protocol
SMB file-sharing and print services are a mainstay of Microsoft networking.
Clients establish a long-term connection to servers and can access resources as if local.

Transport Layer

Link between application layer and lower layers for network transmission
Protocols: TCP, UDP
Track conversations
Segment data
Reassemble segments
Add segment header information
Identify applications.
Multiplexing conversations

TCP (Transmission Control Protocol)

Reliable, full-featured transport layer protocol; ensuring all data arrives at destination
Includes fields for delivery of data, requiring additional processing by sending and receiving hosts.
Analogous to sending tracked packages
Provides reliability and flow control using operations like:
- Numbering and tracking data segments
- Acknowledging received data
- Retransmitting unacknowledged data
- Sequencing data (if it arrives out-of-order)
- Sending data at an acceptable rate
TCP divides data into segments

UDP (User Datagram Protocol)

Simpler, connectionless transport layer protocol with fewer header fields.
Faster processing compared to TCP.
Handles basic functions for delivering datagrams between applications with minimal overhead and checking.
Stateless protocol; does not track communications between client and server.
Commonly used for live video and audio applications

Socket Pairs

Source and destination ports within a TCP segment within an IP packet
Source IP address and port number, or destination IP address and port number—known as a socket—enable multiple processes on a client and multiple connections to a server to distinguish themselves.
Source port acts as a return address for the requesting application. Transport layer keeps record of this port/application, enabling forwarding responses to the correct application.

Transport Layer Session Establishment

Each application process on a server is configured to use a unique port number.
A host cannot have two services assigned to the same port number.
An active service on a port is open and processes addressed segments to that port.
Data is passed to the appropriate server application.

TCP Connection Establishment

Three-way handshake process:
- Step 1 (SYN): Client requests communication
- Step 2 (SYN, ACK): Server acknowledges client request, requesting server-to-client communication
- Step 3 (ACK): Client acknowledges server-to-client request. Connection is established

TCP Session Termination

FIN (Finish) control flag used to close a connection
Two-way handshake to end each TCP session:
- FIN segment
- ACK segment
Four exchanges are needed to fully terminate a TCP conversation (either client or server can initiate).

TCP Reliability—Guaranteed and Ordered Delivery

TCP ensures all data segments arrive at destination in their original order.
Segments are assigned sequence numbers in the header, enabling reassembly at the destination.
Initial sequence number (ISN) for each session is set; numbers increment as data is sent.
Missing segments are identified and retransmitted.

TCP Reliability—Data Loss and Retransmission

TCP methods manage segment losses by retransmitting for unacknowledged data.
Sequence (SEQ) and acknowledgement (ACK) numbers confirm receipt of data.
The SEQ number identifies the first byte of data in a segment.
The ACK number in the return indicates the next expected byte.

TCP Flow Control—Window Size and Acknowledgments

Flow control manages the rate of data between source and destination.
Window size in the TCP header determines the amount of data sent before expecting an acknowledgement.
Acknowledgment number is the next expected byte number.

TCP Flow Control—Maximum Segment Size (MSS)

MSS defines the largest amount of data allowed in a TCP segment.
Calculated by subtracting the IP and TCP header sizes from the maximum transmission unit (MTU) of the network.

TCP Flow Control—Congestion Avoidance

Packets are discarded during congestion on a network, resulting in unacknowledged TCP segments.
TCP estimates network congestion based on the rate of sent segments vs. acknowledged segments.
Retransmission of lost segments can worsen congestion.
TCP employs algorithms, timers, and mechanisms to handle congestion and avoid further congestion.

Network Layer

Responsible for end-to-end transport.
Protocols: IPv4, IPv6
Four processes: addressing of end devices (IP addresses), encapsulation, routing of packets to other networks, and de-encapsulation (at destination)

Characteristics of IP

Connectionless: no end-to-end connections established prior to packet sending; similar to sending a letter via mail.
Best-effort delivery: not guaranteed all sent packets will be received; upper layers handle missing/incorrect packets.
Media independent: works with various communication mediums.

IPv4 Packet Header

Contains fields with binary numbers identifying settings of the IP packet.
Important fields include:
- Version
- Header Length
- Differentiated Services (DS)
- Time to Live (TTL)
- Protocol
- Source IP Address
- Destination IP Address

IPv6 Packet

Simpler header format compared to IPv4.
Advantages over IPv4 include increased address space (128-bit addressing), improved packet handling (fewer fields), elimination of the need for network address translation (NAT).
Handles multiple simultaneous conversations, offering significant improvements to the internet

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