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2.1 Common Network Ports - CompTia A+ 220-1101

Network Communication Basics

  • Connecting to a server requires knowledge of the port number of the service running on that device, commonly referred to as well-known port numbers.

  • This understanding is crucial for configuring firewall rules, which involve adding an IP address and a corresponding port number to control traffic.

  • Memorization of port numbers may initially seem like rote memorization, but practical experience improves retention.

Key Protocols and Their Port Numbers

FTP (File Transfer Protocol)

  • Purpose: Used for transferring files and managing file systems.

  • Port Numbers:

    • TCP Port 20: Active mode data transfer.

    • TCP Port 21: Control connection for FTP commands.

  • Authentication: Often uses username and password; some servers allow anonymous logins.

  • Capabilities: List, add, and delete files and folders on the server.

SSH (Secure Shell)

  • Purpose: Provides secure access to the command line of a remote device.

  • Port Number: TCP Port 22.

  • Features: Encrypted communication, making it secure compared to Telnet.

Telnet

  • Purpose: Provides console or terminal access to devices using a text-based interface.

  • Port Number: TCP Port 23.

  • Security Note: Unencrypted communications make it insecure; prefer SSH when possible.

SMTP (Simple Mail Transfer Protocol)

  • Purpose: Used to send emails between devices.

  • Port Number: TCP Port 25.

  • Functionality: Sends mail from client to mail server and between mail servers.

DNS (Domain Name System)

  • Purpose: Converts fully qualified domain names into IP addresses.

  • Port Number: UDP Port 53.

DHCP (Dynamic Host Configuration Protocol)

  • Purpose: Automatically assigns IP addresses and other network configuration settings to devices.

  • Port Numbers:

    • UDP Port 67: Server-side.

    • UDP Port 68: Client-side.

  • Functionality: Provides real-time IP address assignments with a lease time; supports IP address reservations based on MAC addresses.

HTTP and HTTPS

  • HTTP (Hypertext Transfer Protocol)

    • Purpose: Used for web browsing, transmitting data between client and web server.

    • Port Number: TCP Port 80.

  • HTTPS (HTTP Secure)

    • Purpose: Secure version of HTTP with encrypted data transmission.

    • Port Number: TCP Port 443.

POP3 and IMAP

  • POP3 (Post Office Protocol version 3)

    • Purpose: Retrieves emails from a server.

    • Port Number: TCP Port 110.

    • Limitation: Lacks synchronization capabilities across multiple devices.

  • IMAP (Internet Message Access Protocol version 4)

    • Purpose: Retrieves and synchronizes emails across devices.

    • Port Number: TCP Port 143.

SMB (Server Message Block)

  • Purpose: Protocol for file and printer sharing, primarily associated with Windows.

  • Port Numbers:

    • TCP Port 445: Direct SMB over IP.

    • Legacy usage of NetBIOS now rarely implemented (UDP Port 137, TCP Port 139).

SNMP (Simple Network Management Protocol)

  • Purpose: Monitors and manages network devices.

  • Port Numbers:

    • UDP Port 161: Queries for device performance data.

    • UDP Port 162: SNMP traps for proactive device monitoring.

  • Versions:

    • SNMPv1: Basic single queries, no security.

    • SNMPv2: Bulk data transfer, still unsecured.

    • SNMPv3: Enhanced security with encryption.

LDAP (Lightweight Directory Access Protocol)

  • Purpose: Accesses directory services like Microsoft Active Directory.

  • Port Number: TCP Port 389.

RDP (Remote Desktop Protocol)

  • Purpose: Provides remote desktop access to Windows machines.

  • Port Number: TCP Port 3389.

  • Functionality: Allows full control of the desktop or access to specific applications; supports various operating systems as RDP clients.