Ports and Protocols You Must Know to Pass the CompTIA A+ 1101


Ports are virtual channels that facilitate communication between devices or applications over a network. Acting as logical communication endpoints, they enable the transmission of data packets. Inbound ports, also known as listening ports, receive incoming data packets, allowing external devices to establish connections for communication and data exchange. Conversely, outbound ports initiate outgoing connections, sending data packets from a device or application to a specific destination. Ports can be any number between 0 and 65,535.

Ports are specified by appending them to the end of an IP address, separated by a colon, to indicate the specific endpoint for communication and data exchange.

Well-Known Ports

Assigned by the Internet Assigned Numbers Authority (IANA), ports 0-1023 are reserved for commonly used protocols.

Registered Ports

Ports 1024-49151 are reserved for proprietary protocols that must be registered with IANA.

Dynamic and Private Ports

Ports 49152-65535 can be used by any application without having to register with IANA, used for temporary outbound connections.

Ports You Need to Know

FTP (File Transfer Protocol) – Ports 20/21 – Provides insecure (no encryption) file transfers.

SSH (Secure Shell) – Port 22 – Provides secure remote control of another machine using a text-based environment.

SFTP (Secure File Transfer Protocol) – Port 22 – Provides secure file transfer, uses SSH to transfer files.

Telnet – Port 23 – Provides insecure remote control of another machine using a text-based environment.

SMTP (Simple Mail Transfer Protocol) – Port 25 – Provides the ability to send emails over the network.

DNS (Domain Name Service) – Port 53 – Converts domain names to IP addresses and vise versa.

DHCP (Dynamic Host Configuration Protocol) – Port 67/68 – Automatically provides network parameters to clients, such as assigned IP addresses, subnet mask, default gateway, and the DNS server they should be using.

TFTP (Trivial File Transfer Protocol) – Port 69 – Insecure file transfer protocol which uses UDP (faster), no authentication or encryption.

HTTP (Hypertext Transfer Protocol) – Port 80 – Used for insecure web browsing.

POP3 (Post Office Protocol Version Three) – Port 110 – Used for receiving incoming emails.

NetBIOS (Network Basic Input/Output System) – Port 137/139 – Used for file or printer sharing in a Windows network.

IMAP (Internet Mail Application Protocol) – Port 143 – A newer method of retrieving incoming emails which improves on POP3.

SNMP (Simple Network Management Protocol) – Port 161/162 – Used to collect data about network devices and monitor their status.

LDAP (Lightweight Directory Access Protocol) – Port 389 – Provides directory services to the network.

HTTPS (Hypertext Transfer Protocol – Secure) – Port 443 – Used as a secure and encrypted version of web browsing.

SMB (Server Message Block) – Port 445 – Used for Windows file and printer sharing services.

RDP (Remote Desktop Protocol) – Port 3389 – Provides a graphical remote control of another client or server.


Welcome to your Port Numbers

Which protocol uses ports 20/21 for file transfers?

What ports does NetBIOS use (select two)?

What port does IMAP use for retrieving incoming emails?

What is SNMP used for?

What port does SFTP use for secure file transfers?

What is RDP (Remote Desktop Protocol) used for?

What port does SMB (Server Message Block) use for Windows file and printer sharing services?

What is HTTPS (Hypertext Transfer Protocol - Secure) used for?

What port does LDAP (Lightweight Directory Access Protocol) use for providing directory services?

What is NetBIOS (Network Basic Input/Output System) used for?

What port does POP3 (Post Office Protocol Version Three) use for receiving incoming emails?

What port does TFTP (Trivial File Transfer Protocol) use for insecure file transfers?

What is DHCP (Dynamic Host Configuration Protocol) used for?

What port does DNS (Domain Name Service) use for domain name conversion?

What port does Telnet use for insecure remote control?

What ports does DHCP use (select two)?

What port does RDP use?