Ports and Protocol Decision Table
Key Takeaways
- Port knowledge is most useful when tied to use case, transport, and secure alternatives.
- TCP is connection-oriented; UDP is connectionless and common for low-latency or query-response services.
- Secure protocol choices often replace cleartext management or transfer protocols.
- Network+ scenarios may ask which port to allow, which service is failing, or which protocol best fits a requirement.
- Do not memorize ports in isolation; connect them to symptoms and design decisions.
Last updated: April 2026
Ports Become Useful in Context
Port questions are rarely just flashcards. You may need to choose a secure management protocol, identify a blocked service, or decide which firewall rule supports a requirement.
| Protocol | Port(s) | Transport | Common use | Exam decision clue |
|---|---|---|---|---|
| FTP data/control | 20/21 | TCP | File transfer | Legacy and cleartext; prefer SFTP/FTPS when security matters |
| SSH/SFTP | 22 | TCP | Secure shell and secure file transfer | Secure remote administration |
| Telnet | 23 | TCP | Remote terminal | Insecure cleartext; avoid for management |
| SMTP | 25 | TCP | Mail transfer between servers | Mail relay traffic |
| DNS | 53 | UDP/TCP | Name resolution and zone transfers | UDP for typical queries, TCP for zone transfers or large responses |
| DHCP | 67/68 | UDP | Dynamic client addressing | Client cannot obtain lease |
| TFTP | 69 | UDP | Simple file transfer | Lightweight, no authentication, often network boot/device files |
| HTTP | 80 | TCP | Web traffic | Cleartext web |
| Kerberos | 88 | TCP/UDP | Authentication | Time-sensitive authentication in directory environments |
| POP3 | 110 | TCP | Mail retrieval | Older mailbox download protocol |
| NTP | 123 | UDP | Time synchronization | Clock drift affects logs, certificates, Kerberos |
| IMAP | 143 | TCP | Mail access | Mail stays on server |
| SNMP | 161/162 | UDP | Monitoring and traps | Device monitoring; prefer SNMPv3 |
| LDAP | 389 | TCP/UDP | Directory access | Directory queries; LDAPS is encrypted |
| HTTPS | 443 | TCP | Encrypted web | Secure web applications |
| SMB | 445 | TCP | Windows file sharing | File shares and domain-related access |
| Syslog | 514 | UDP/TCP | Log forwarding | Central logging; secure variants may use TLS |
| LDAPS | 636 | TCP | Encrypted directory access | Secure LDAP |
| SQL Server | 1433 | TCP | Microsoft SQL Server | Database access |
| RDP | 3389 | TCP/UDP | Remote desktop | Remote GUI administration; restrict and protect |
| SIP | 5060/5061 | UDP/TCP/TLS | VoIP signaling | 5061 commonly indicates TLS-secured SIP |
Secure Replacement Table
| Insecure or weaker choice | Better choice when supported | Why |
|---|---|---|
| Telnet | SSH | Encrypts remote administration |
| FTP | SFTP or FTPS | Protects credentials and file contents |
| HTTP | HTTPS | Uses TLS for web confidentiality and integrity |
| SNMPv1/v2c | SNMPv3 | Adds stronger authentication and encryption options |
| LDAP | LDAPS or LDAP with StartTLS | Protects directory queries and credentials |
TCP or UDP Decision Cues
| Need | Often fits |
|---|---|
| Reliable ordered delivery and session control | TCP |
| Low overhead query/response or real-time traffic | UDP |
| Name lookup | DNS over UDP for typical queries, TCP in specific cases |
| Address lease | DHCP over UDP |
| Time sync | NTP over UDP |
| Web session | HTTP/HTTPS over TCP |
Scenario Decisions
| Scenario | Best protocol or port focus |
|---|---|
| Secure CLI administration of a switch | SSH TCP 22 |
| Users cannot receive DHCP leases | UDP 67/68 and DHCP relay/scope |
| Monitoring system cannot poll router interface counters securely | SNMPv3, typically UDP 161 |
| Internal site must protect credentials in transit | HTTPS TCP 443 |
| Directory bind exposes credentials | LDAPS TCP 636 or StartTLS |
Memorize the core ports, but always attach them to an operational story. That is how they appear in troubleshooting and firewall-rule questions.
Test Your Knowledge
Which protocol is the best secure replacement for Telnet when administering a router CLI?
A
B
C
D
Test Your KnowledgeMulti-Select
Which protocol and port pairings are correct? Select all that apply.
Select all that apply
DNS: port 53
HTTPS: port 443
DHCP: UDP ports 67 and 68
RDP: port 25
SSH: port 22
Test Your KnowledgeMatching
Match each requirement to the best protocol choice.
Match each item on the left with the correct item on the right
1
Encrypted web application access
2
Secure remote CLI administration
3
Dynamic IP address leasing
4
Network time synchronization
5
Secure directory access