Common Network Ports - CompTIA A+ 220-1101 - 2.1

Introduction to Port Numbers

In this section, we will discuss the concept of port numbers and their importance in communication between devices. We will explore well-known port numbers and their significance for both servers, clients, and firewalls.

Well-Known Port Numbers

• Port numbers are used by services to enable communication between devices.

• Well-known port numbers are important for both servers and clients to know which port number to use for communication.

• Firewalls also rely on port numbers to allow or disallow traffic.

• Memorizing port numbers may seem like rote memorization at first, but they become easier with practice.

• It is crucial to know the protocols associated with specific port numbers and when to use them.

FTP (File Transfer Protocol)

• FTP is a protocol used for transferring files between devices.

• TCP port 20 is used for data transfers, while TCP port 21 is used for controlling the data transfer.

• FTP often requires authentication, such as a username and password, to access remote devices.

• FTP includes file management functions like listing files, adding, deleting, renaming files on an FTP server.

SSH (Secure Shell) and Telnet

• SSH provides a secure terminal connection to a remote device over TCP using port 22. Communication is encrypted.

• Telnet also offers a text-based console front end but communicates over TCP using port 23. Communication is not encrypted.

• It is recommended to use SSH instead of Telnet for secure terminal communication due to the lack of encryption in Telnet.

SMTP (Simple Mail Transfer Protocol)

• SMTP is used by email servers to communicate with each other over TCP using port 25.

• SMTP can also be used by mail clients to send emails through an email server.

• Receiving mail typically involves different protocols like IMAP or POP3.

DNS (Domain Name System)

• DNS is responsible for resolving IP addresses from fully qualified domain names.

• DNS uses UDP port 53 for communication between clients and DNS servers.

• It is a critical resource as it allows us to use domain names instead of memorizing IP addresses.

DHCP (Dynamic Host Configuration Protocol)

• DHCP automatically assigns IP addresses to devices on a network.

• DHCP uses UDP port 67 and UDP port 68 as well-known ports.

• Leasing system is used, allowing temporary usage of an IP address. Administrators can also assign specific IP addresses.

Conclusion

In this section, we learned about the importance of port numbers in communication between devices. We explored various well-known port numbers associated with different protocols such as FTP, SSH, Telnet, SMTP, DNS, and DHCP. Understanding these port numbers and their corresponding protocols is essential for effective network communication.

DHCP Server Configuration

This section discusses how to make changes to devices' configurations on a DHCP server, allowing for easy management without accessing individual devices.

Making Changes on the DHCP Server

• Changes to device configurations can be made directly on the DHCP server.

• When a device requests a DHCP address, it will receive the new configuration automatically.

HTTP and HTTPS Protocols

This section explains the difference between HTTP and HTTPS protocols used by web browsers for communication with web servers.

HTTP Protocol

• HTTP (Hypertext Transfer Protocol) is commonly used by web browsers to communicate with web servers.

• It uses TCP and port 80 for non-encrypted communication.

HTTPS Protocol

• HTTPS (Hypertext Transfer Protocol Secure) is used when communicating over an encrypted connection.

• It uses TCP port 443 for secure communication.

Email Protocols: SMTP, POP3, and IMAP

This section covers different email protocols used for sending and receiving email messages.

SMTP (Simple Mail Transfer Protocol)

• SMTP is used for sending email messages.

• It commonly uses TCP port 25.

POP3 (Post Office Protocol version 3)

• POP3 is used to retrieve email messages from an email client.

• It commonly uses TCP port 110.

• Designed for single-client use, not suitable for multiple email clients.

IMAP4 (Internet Message Access Protocol version 4)

• IMAP4 is used to synchronize mailboxes across multiple devices.

• It commonly uses TCP port 143.

File Transfer Protocols: SMB/CIFS

This section discusses file transfer protocols commonly used in operating systems like Windows.

SMB (Server Message Block)

• SMB is the protocol commonly used by Microsoft Windows for file transfer and printer sharing.

• It is also referred to as CIFS (Common Internet File System).

• Uses various protocols for communication.

NetBIOS over TCP/IP

• NetBIOS (Network Basic Input Output System) is used by older Windows machines.

• It uses UDP port 137 for name service function and TCP port 139 to set up a session and transfer data.

Direct SMB Connection

• Modern versions of Windows use direct SMB connections using TCP port 445.

• Allows direct communication between devices using only TCP/IP.

SNMP (Simple Network Management Protocol)

This section introduces SNMP, a protocol used for network management and monitoring.

SNMP Overview

• SNMP allows network management devices to query infrastructure devices for performance details.

• It uses UDP port 161 for queries.

Traps

• Infrastructure devices can send alerts, known as traps, to the management station.

• Traps use UDP port 162.

SNMP Versions

• SNMP supports version 1, version 2, and version 3.

• Version 1 sends information in clear text.

• Version 2 allows bulk transfers but still in non-encrypted form.

• Version 3 provides encryption, message integrity, authentication, and encryption of all SNMP data.

LDAP (Lightweight Directory Access Protocol)

This section explains LDAP, a protocol commonly used to query directories like Microsoft Active Directory.

LDAP Protocol

• LDAP is used to query directories on modern networks.

• It commonly uses TCP port 389.

RDP (Remote Desktop Protocol)

This section discusses RDP, a protocol used for remote desktop sharing on Windows systems.

RDP Protocol

• RDP is the standard protocol used by Windows for remote desktop sharing.

• It commonly uses TCP port 3389.

• Available in many editions of Windows and compatible with various operating systems.

Conclusion

These are the key protocols discussed in the transcript:

• DHCP for server configuration

• HTTP and HTTPS for web communication

• SMTP, POP3, and IMAP for email protocols

• SMB/CIFS for file transfer

• SNMP for network management

• LDAP for directory access

• RDP for remote desktop sharing