1.4 - Ports and protocols

Network+ N10-009 objective 1.4 is heavy on memorising ports, protocols and what each does. HTTPS uses TCP 443, SSH uses 22 for secure remote administration, and DNS uses 53 to resolve names. For email, IMAP on 143 retrieves messages while leaving them on the server and syncing across devices, POP3 uses 110, and SMTP uses 25. Other must-know entries include FTP (20/21), Telnet (23), DHCP (67/68), TFTP (69), HTTP (80), NTP (123), SNMP (161/162), LDAP (389), SMB (445) and RDP (3389). You should know both the number and the protocol's purpose, and whether it runs over TCP or UDP. Expect direct questions that give a protocol and ask its port, or give a port and ask the service - so drill these with flashcards until recall is instant.

Memory hook
HTTPS 443, SSH 22, DNS 53, IMAP 143 (POP3 110, SMTP 25), FTP 20/21, HTTP 80, NTP 123, SNMP 161/162, LDAP 389, SMB 445, RDP 3389. Know number, purpose and TCP/UDP. Drill with flashcards.

Practice questions

1. Which TCP port does HTTPS use by default?

  • 22
  • 80
  • 443 (correct answer)
  • 3389

HTTPS (HTTP over TLS) uses TCP 443. 22 is SSH, 80 is plain HTTP, 3389 is RDP.

2. Which protocol resolves an IPv4 address to a MAC address on a LAN?

  • DNS
  • DHCP
  • ARP (correct answer)
  • ICMP

ARP (Address Resolution Protocol) maps an IP to a MAC within the local subnet. DNS maps names to IPs, DHCP leases IPs, ICMP is for diagnostics (ping).

3. Traffic addressed to every host on a subnet at once is called:

  • Unicast
  • Multicast
  • Anycast
  • Broadcast (correct answer)

Broadcast reaches all hosts on the subnet (e.g., 255.255.255.255). Unicast = one to one, multicast = one to a group, anycast = one to nearest of a group.

4. Which port does SSH use for secure remote administration?

  • 21
  • 22 (correct answer)
  • 23
  • 25

SSH uses TCP 22 for encrypted remote shells and SFTP/SCP. 21 is FTP control, 23 is unencrypted Telnet, 25 is SMTP.

5. Which UDP ports does DHCP use for client and server messages?

  • 53 and 54
  • 110 and 143
  • 67 and 68 (correct answer)
  • 161 and 162

DHCP uses UDP 67 (server) and 68 (client). 53 is DNS, 110/143 are POP3/IMAP, 161/162 are SNMP.

6. Which port does LDAP use for directory queries by default?

  • 25
  • 53
  • 389 (correct answer)
  • 445

LDAP uses TCP 389 (LDAPS is 636). 25 is SMTP, 53 is DNS, 445 is SMB.

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