CompTIA A+ | Protocols and Ports

20/21

FTP (TCP) - File Transfer Protocol. 20 = data, 21 = control. Unencrypted file transfer

22

SSH (TCP) - Secure Shell. Encrypted remote command line. Also used by SFTP

23

Telnet (TCP) - Unencrypted remote command line. Also used by SFTP

25

SMTP (TCP) - Simple Mail Transfer Protocol. SENDS email.

53

DNS (TCP/UDP) - Domain Name System. Resolves name to IP addresses

67/68

DHCP (UDP) - Automatically assigns IP addresses. 67 = server, 68 = client.

80

HTTP (TCP) - Unencrypted web traffic.

110

POP3 (TCP) - RECEIVES email by downloading it to one device.

137-139

NetBIOS/NetBT (TCP/UDP) - Legacy Windows name and file sharing services.

143

IMAP (TCP) - RECEIVES email and keeps it synced across devices.

161/162

SNMP (UDP) - Monitors and manages netword devices. 162 = traps (alerts).

389

LDAP (TCP/UDP) - Access directory services like Active Directory.

443

HTTPS (TCP) - Encrypted web traffic.

445

SMB/CIFS (TCP) - Windows file and printer sharing.

3389

RDP (TCP) - Remote Desktop Protocol. Graphical remote access to Windows.

A user wants email synced on their phone and laptop. Which protocol and port?

IMAP, port 143

A tech needs to securely access a server’s command line. Which protocol and port?

SSH, port 22

A website shows “Not Secure” in the browser. Which protocol and port is it likely using?

HTTP, port 80

A user can’t access a shared folder on a Windows network. Which port should be checked?

445 (SMB)

A tech needs to remotely control a Windows desktop with a graphical interface. Which protocol and port?

RDP, port 3389

Which protocol and ports would an email client use to send a message?

SMTP, port 25

Which ports are insecure and have encrypted replacements?

Telnet 23 → SSH 22, HTTP 80 → HTTPS 443, FTP 21 → SFTP 22

Which port-based protocols use UDP only?

DHCP (67/68) and SNMP (161/162)