2.1 Net. Intro/Ports CompTIA A+ 220 - 1201

Network Data Transmission Analogy (Moving Vans)

Think of sending data across a network like moving boxes using trucks on roads.

• Roads = Network infrastructure

  • Examples: Ethernet, DSL, cable networks

• Truck = Internet Protocol (IP)

  • Responsible for delivering packets across networks

• Boxes = Transmission Control Protocol (TCP) or User Datagram Protocol (UDP)

  • These contain the data being transported

• Contents inside the boxes = Application data

  • Examples: web pages, email, files

Where are TCP and UDP encapsulated?

Inside the IP

TCP

Transmission Control Protocol

• Connection-oriented

• Reliable delivery

• Error recovery & retransmission

• Receiver controls the flow of data

UDP

User Datagram Protocol

• Connectionless

• No reliability or error correction

• No flow control/ the sender controls the flow

• Faster, lower overhead than Transmission Control Protocol (TCP)

UDP use case

• Speed is more important than reliability

• Real-time communication is required

• Applications handle packet loss themselves

  • Ignore it

  • Request new data

  • Continue without it

TCP Use Case

• Connection-oriented protocols

• Require reliable delivery

• Example protocols: HTTPS, SSH

• TCP handles error recovery, ordering, and retransmission

Port Analogy

• Internet Protocol (IP) delivers data from one IP address to another

  • Similar to a truck delivering packages between houses

• IP address = the house address

  • Identifies the device on the network

• Ports = the rooms in the house

  • Each service or application listens on a specific port

• When data arrives:

  • The IP address gets the data to the correct computer

  • The port number sends it to the correct application

Define IPv4 sockets and it’s parts

A socket identifies a specific connection between two nodes using

Server/Client IP address + Protocol (TCP/UDP) + Port

Ex. Client: 192.168.1.10 : 53021
Server: 142.250.0.5 : 443
Protocol: TCP

Non-ephemeral ports

“Well-know”/permanent ports that don’t change

0-1023

Usually on a server or service

Examples:

• HTTP – 80

• HTTPS – 443

• DNS – 53

Ephemeral ports

Temporary port numbers

Created automatically by the client at the start of a connection

1024 – 65,535

How many total TCP and UDP ports are there for each?

The TCP and UDP ports can have numbers 0 - 65,535

TCP port 80 is not UDP port 80

What is FTP and its ports

File Transfer Protocol

TCP/20 = active mode data

TCP/21 = control

• Transfers files between systems

• Full-featured: list, upload, download, delete files

TCP 20 TCP 21

Port for FTP = File Transfer Protocol

SSH

Secure Shell

TCP 22

• Provides encrypted remote login

• Functions like Telnet but secure

• Preferred for production systems

TCP 22

Port for SSH = Secure Shell

Telnet

• Port: TCP 23

• Remote login / console access

• Communication in plaintext (not encrypted)

• Not recommended for production systems

TCP 23

Port for Telnet

SMTP

• Simple Mail Transfer Protocol

• Port: TCP 25

• Used for server-to-server email delivery

• Also used by email clients to ONLY send outgoing mail

• Receiving email uses other protocols:

  • POP3

  • IMAP

TCP 25

Port for SMTP =Simple Mail Transfer Protocol

DNS

Domain Name System

• Port: UDP 53

• Translates domain names → IP addresses

  • Example: google.com → 142.251.116.101

• Mission-critical service, usually deployed with redundant DNS servers

UDP 53

• DNS = Domain Name System

• DNS → UDP 53 normally

  • TCP 53 → zone transfers or large responses

What does DHCP assign? (4 things)

Dynamic Host Configuration

• Automatically assigns network configuration to devices:

  • IP address

  • Subnet mask

  • Default gateway

  • DNS server

UDP 67/68

DHCP = Dynamic Host Configuration Protocol

HTTP/HTTPS

Hypertext Transfer Protocol/Secure

Browsers use HTTP/HTTPS to load websites.

• HTTP TCP 80 Web traffic (unencrypted)

• HTTPS TCP 443 Secure web traffic (encrypted)

TCP 80

HTTP = Hypertext Transfer Protocol

TCP 443

HTTPS = Hypertext Transfer Protocol Secure

POP3

• Post Office Protocol 3

• Port: TCP 110

• Basic email retrieval

• Emails are downloaded to the device

• Often removed from the server

TCP 110

POP3 = Post Office Protocol 3

IMAP4

Internet Message Access Protocol

• Port: TCP 143

• More advanced email management

• Emails stay on the server

• Supports multiple devices accessing the same mailbox

TCP 143

IMAP(4) = Internet Message Access Protocol

What is SMB used for, and what ports does it use?

Server Message Block

SMB is a protocol used by Microsoft Windows for file sharing and printer sharing. Like when you access a shared drive.

Ports:

• TCP 445 — Direct SMB communication (modern method)

• Legacy Method

  • UDP 137 — NetBIOS name service

  • TCP 139 — NetBIOS session service

Also called Common Internet File System (CIFS)

TCP 445

SMB = Server Message Block

What is Common Internet File System (CIFS)?

Another name for SMB, commonly used in older Windows systems.

UDP 137
TCP 139

NetBIOS

UDP 137 – Name service
TCP 139 – Session service

What is NetBIOS?

NetBIOS (Network Basic Input/Output System) is a protocol that allows applications on different computers to communicate over a local network.

It was commonly used by Microsoft Windows for:

• Device naming

• Session communication

• File and printer sharing

Often used with Server Message Block (SMB) on older networks.

It’s mostly legacy now.

LDAP

Lightweight Directory Access Protocol

LDAP is a protocol used to store and retrieve information from a directory service.

Commonly used in Microsoft Active Directory to manage:

• Users

• Groups

• Devices

• Permissions

Ports

• TCP 389 — LDAP

• TCP 636 — LDAP over SSL (LDAPS) for encrypted communication

TCP 389

LDAP = Lightweight Directory Access Protocol

TCP 636

LDAP over SSL (LDAPS)

What is RDP and what is it used for?

RDP allows you to share and control a desktop or application remotely over a network.

• Port: TCP 3389

• Can connect to:

  • Full desktop

  • Single application

TCP 3389

RDP = Remote Desk Protocol