CompTIA Network+ Preparation · lesson 29 of 30 · 25 min
Well-Known Ports
Port numbers identify specific services on a host. Well-known ports are 0–1023 (assigned by IANA). Registered ports are 1024–49151. Dynamic/ephemeral ports are 49152–65535 (used by clients for source ports).
The Network+ exam requires memorising the most common port numbers and their protocols.
Protocol Comparisons
FTP vs SFTP vs FTPS: FTP (ports 20/21) is unencrypted. SFTP (port 22) runs over SSH — encrypted. FTPS adds TLS to FTP (ports 990/989).
Telnet vs SSH: Both provide remote CLI access. Telnet (port 23) sends everything in plaintext — never use on production. SSH (port 22) encrypts all traffic.
HTTP vs HTTPS: HTTP (port 80) is unencrypted. HTTPS (port 443) uses TLS — encrypts the connection. All modern web traffic should use HTTPS.
POP3 vs IMAP: POP3 (port 110) downloads email to the client and typically deletes from server. IMAP (port 143) keeps email on the server — synced across devices.
SNMP versions: SNMPv1/v2c use community strings (plaintext — insecure). SNMPv3 adds authentication and encryption — use in production.
Exam Tip
Memorise the port table — Net+ questions frequently ask “which port does X use?” Focus on: 22 SSH, 23 Telnet, 25 SMTP, 53 DNS, 80 HTTP, 443 HTTPS, 3389 RDP, 161 SNMP, 67/68 DHCP.
Key Terms
Key Terms
Knowledge Check — 10 Questions
Network+ — Protocols and Ports
Which port does SSH use?
- 21
- 22
- 23
- 25
Answer: 22
SSH = port 22. Telnet = 23. FTP control = 21. SMTP = 25. SSH replaced Telnet for secure remote access.
HTTPS uses which port?
- 80
- 8080
- 443
- 8443
Answer: 443
HTTPS = TCP port 443. HTTP = TCP port 80. HTTPS encrypts traffic with TLS.
RDP (Remote Desktop Protocol) uses port:
- 22
- 3306
- 3389
- 5900
- Answer: 3389
RDP = TCP port 3389. Provides graphical remote access to Windows systems. Should be protected by VPN or NLA.
SNMP traps are sent on which port?
- 161
- 162
- 514
- 123
Answer: 162
SNMP: port 161 for queries (manager polls agent), port 162 for traps (agent sends unsolicited alerts to manager).
Which email protocol keeps messages on the server?
- POP3
- SMTP
- IMAP
- MIME
Answer: IMAP
IMAP (port 143) keeps email on the server — synced across all devices. POP3 (port 110) downloads and typically deletes from server.
TFTP differs from FTP because TFTP:
- Uses TCP
- Requires authentication
- Uses UDP and has no authentication
- Supports encryption
- Answer: Uses UDP and has no authentication
TFTP (port 69) uses UDP and has no authentication — simple and fast. Used for network device firmware updates and PXE boot.
NTP uses which port?
- 53
- 67
- 123
- 161
Answer: 123
NTP (Network Time Protocol) uses UDP port 123. Accurate time is critical for authentication, logging, and certificate validation.
SMB file sharing uses port:
- 139
- 389
- 445
- 636
- Answer: 445
SMB uses TCP port 445 for direct hosting. Port 139 was used with NetBIOS. Port 445 is the modern SMB port.
Which is the secure version of LDAP?
- LDAP on port 389
- LDAPS on port 636
- LDAP on port 443
- LDAP with SNMPv3
Answer: LDAPS on port 636
LDAPS (LDAP Secure) uses TLS on port 636. Standard LDAP on port 389 is unencrypted.
FTP uses port 21 for control and port _____ for data transfer.
Answer: 20
FTP uses two channels: port 21 for control (commands) and port 20 for active mode data transfer.
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