networking fr

What are the two main Transport Layer protocols?

TCP and UDP

Why is UDP commonly used for streaming and real-time communication?

It has low overhead without acknowledgements or retransmissions

What is the function of the Transport Layer?

It segments data and assigns port numbers for communication

What does the destination port represent?

The receiving service’s port such as DNS on 53 or HTTP on 80

Why is UDP considered unreliable?

It provides no delivery guarantee

Why does UDP work well for real-time apps?

Retransmission delays would be more disruptive than small packet loss

How does TCP ensure reliable delivery?

It uses sequence numbers and acknowledgements to confirm receipt

What is the purpose of TCP sequence numbers?

They let the receiver reorder segments correctly

What is an acknowledgement in TCP?

A receiver signal confirming which bytes or segments were received

What is the main difference between TCP and UDP?

TCP is reliable and ordered while UDP is faster without guarantees

When is UDP preferred over TCP?

When low latency matters more than reliability such as voice or video streaming

What is the purpose of port numbers at the Transport Layer?

They identify specific conversations and applications between source and destination devices

What are well-known ports?

Ports 1–1023 reserved for common network services like HTTP

What port does a web server use?

TCP port 80

What port does an FTP server use?

TCP port 21 and TCP port 20

What port does a mail server use?

TCP port 25

How do clients know which port to use when connecting to a service?

Clients like web browsers are preconfigured with default port numbers for common services

What are dynamically assigned or ephemeral ports?

Ports 49152 to 65535 randomly chosen by a host for temporary use as source ports

How does a client distinguish multiple simultaneous connections?

Each application uses a unique source port combined with its IP address forming a unique socket

What is a socket?

The combination of an IP address and a port number identifying one end of a network connection

What is a socket pair?

The combination of the client’s IP and port with the server’s IP and port (e.g.

What is a source port?

A temporary random port used as the return address in a session.

How do TCP and UDP ports allow multiple apps to run at once?

They allow each process to use a unique port number so data can be directed to the correct application

What port is used for DNS?

UDP and TCP port 53

What port is used for DHCP server responses?

UDP port 67

What port is used for DHCP client requests?

UDP port 68

What port is used for TFTP?

UDP port 69

What port is used for HTTPS?

TCP port 443

What are registered ports?

ports 1024–49151, assigned for specific applications

What is the purpose of the netstat command?

It displays active network connections and listening ports on a host

What does the netstat command show?

Protocols in use, local and foreign IP addresses, port numbers, and connection states

Why is netstat important for network security?

It helps identify unexplained or suspicious TCP connections that may indicate unauthorized access

What option in netstat prevents name resolution and displays numeric IP addresses and ports?

-n

Why might resolving IP addresses and port numbers be disabled?

To speed up output and show raw network details for troubleshooting or security checks

What are foreign addresses in the netstat output?

They represent remote hosts or devices connected to the local machine

What does the connection state column indicate in netstat?

The current status of each TCP connection such as ESTABLISHED or LISTENING

What protocol header information is used at the transport layer to identify a target application?

Port Number

What is a server?

A host running software that provides information or services to clients on a network

What is a client?

A device or application that requests and uses services from a server

What ensures servers and clients can communicate properly?

They rely on standardized protocols and communication rules

What does a TCP connection establish between client and server?

A reliable session defined by source and destination IP addresses and port numbers

Why are random source ports used on clients?

They allow multiple simultaneous connections to different servers or services

What is the function of the transport layer in web communication?

It manages ports and connections so multiple apps can send and receive data at once

What is a URI?

A Uniform Resource Identifier that names or locates a resource on a network

What are the two types of URIs?

Uniform Resource Name (URN) and Uniform Resource Locator (URL)

What does a URL specify?

The protocol

How does a web page request process begin?

The client performs a DNS lookup

What is SSH used for?

To securely access and manage servers and network devices remotely

What is SMTP used for?

To send email messages and attachments from clients to servers and between email servers

What is POP used for?

To allow email clients to retrieve messages from a remote mail server

What is IMAP used for?

To let email clients access and manage emails stored on a remote server

What does DHCP do?

Automatically assigns IP addresses and network configuration to devices

What is HTTP used for?

To transfer web pages and related files between web browsers and web servers

What is FTP used for?

To transfer files between a client and a server

What is the main function of a DNS server?

To associate domain names or hostnames with their corresponding IP addresses

What does the client do after receiving the IP address?

It uses the IP address to contact the web server and load the webpage

What command can you use to find a domain’s IP address?

nslookup

On which systems can you use the nslookup command?

Both Windows and Linux

What was the original purpose of Telnet?

To let users remotely access and control computers over a network like a local terminal

What does Telnet emulate?

A text-based terminal connection to a remote system

What TCP port does Telnet use?

TCP port 23

What is a virtual terminal (vty) session?

A Telnet-based software session that provides command-line access to a remote device

What are the main functions a Telnet user can perform?

Execute commands

Why is Telnet considered insecure?

Because it sends all login credentials and data in plaintext without encryption

What protocol replaced Telnet for secure remote access?

SSH (Secure Shell)

How does SSH improve security over Telnet?

It encrypts all transmitted data and provides stronger authentication

When should Telnet be used instead of SSH?

Only in controlled lab or learning environments where security is not a concern

Which protocol is used to send email messages?

SMTP (Simple Mail Transfer Protocol)

What port does SMTP use?

TCP port 25*

Which protocol allows clients to download messages and remove them from the server?

POP3 (Post Office Protocol version 3)

What port does POP3 use?

TCP port 110

Which protocol allows clients to read and manage mail stored on the server?

IMAP4 (Internet Message Access Protocol version 4)

What port does IMAP4 use?

TCP port 143

How does IMAP differ from POP3?

IMAP keeps messages on the server unless deleted

What is VoIP?

Voice over IP

How does VoIP work?

It converts analog voice into digital data and sends it as IP packets through the network

What is needed to call a regular phone using VoIP?

A gateway to connect to the Public Switched Telephone Network (PSTN)

What does ipconfig /all additonally display?

MAC address, IP of default gateway and DNS servers, DHCP status and address, and lease information.

What does ipconfig /release do?

Releases the current DHCP bindings

What does ipconfig /renew do?

Request fresh configuration information from the DHCP server

Echo request

The packet sent during a ping

Echo Reply

The reponse packet during a ping

What does the ping command test?

Connectivity between a source and destination network device using ICMP echo requests and replies

What happens when you ping a domain name?

A DNS query is sent first to resolve the name to an IP address before sending echo requests

What does it indicate if a ping to the IP address succeeds but a ping to the domain name fails?

There is likely a problem with DNS resolution

What does it indicate if pings to both the name and IP address succeed but the application still fails?

The issue is likely with the destination application or service not running

What does it indicate if both pings to the name and IP address fail?

There is most likely a network connectivity problem along the path

Why is it common to ping the default gateway when troubleshooting?

To verify whether the problem is on the local network or beyond it

What does it mean if a ping to the default gateway is successful?

The problem is not on the local network and may be farther along the route

What does it mean if a ping to the default gateway fails?

The issue is local

Why might a ping fail even when network connectivity is fine?

Because a firewall or router may be blocking ICMP packets

How many echo requests does the ping command typically send by default?

Four

What is bandwidth?

The theoretical capacity of a link

what is throughput?

the actual data rate observed

What is latency?

The time it takes for data to travel from source to destination (delay)

What are the three signal types used in networks?

Electrical, optical, wireless

What units are used to express digital bandwidth?

Kbps

What is a host?

Any device that participates directly in network communication