Introduction to Port Numbers
- Port numbers are essential for TCP and UDP communication, helping
identify services on a network.
- Critical for troubleshooting communication issues and firewall
configuration (firewalls use port numbers to allow or block traffic).
- Memorizing key port numbers is required for A+ certification and becomes intuitive
with practice.
- Understand the port number, protocol, and purpose
of each service.
File Transfer Protocol (FTP)
- Used for transferring files between devices across different operating systems.
- TCP Port 20: Active data transfer (data channel).
- TCP Port 21: Control/administration (command channel).
- Supports authentication (username/password) or anonymous login.
- Features include file listing, renaming, deleting, and directory management.
Secure Shell (SSH) and Telnet
- SSH (Secure Shell): Encrypted remote command-line access over TCP Port
22.
- Replaced the insecure Telnet protocol for secure administration.
- Telnet (Telecommunications Network): Unencrypted remote access over TCP
Port 23.
- Telnet sends all data in clear text, making it insecure for modern use.
- Always use SSH for secure remote administration.
Email Protocols
- SMTP (Simple Mail Transfer Protocol): Sends email between servers or from clients
to servers over TCP Port 25.
- POP3 (Post Office Protocol v3): Retrieves email to a local client over TCP
Port 110.
- IMAP4 (Internet Message Access Protocol v4): Advanced email retrieval with
multi-device synchronization over TCP Port 143.
- IMAP supports folder management, server-side storage, and
multi-client access.
Domain Name System (DNS)
- Translates domain names (e.g.,
example.com) to IP
addresses (e.g., 192.0.2.1).
- Uses UDP Port 53 for standard queries.
- Critical for internet functionality; often deployed with redundant DNS servers.
Dynamic Host Configuration Protocol (DHCP)
- Automatically assigns IP addresses, subnet masks, default
gateways, and DNS servers to devices.
- Uses UDP Port 67 (server) and UDP Port 68 (client).
- IP addresses are leased temporarily; devices can renew or release them.
- Supports reserved IP addresses for specific devices (e.g., printers, servers).
Hypertext Transfer Protocol (HTTP/HTTPS)
- HTTP: Unencrypted web traffic over TCP Port 80.
- HTTPS: Encrypted web traffic over TCP Port 443 (secure version of
HTTP).
- Most modern websites use HTTPS for security.
Server Message Block (SMB) and NetBIOS
- SMB (Server Message Block): Used for file/printer sharing in Windows (TCP
Port 445).
- Also known as CIFS (Common Internet File System).
- NetBIOS: Older Windows protocol for name resolution and session setup.
- UDP Port 137: NetBIOS Name Service (similar to DNS).
- TCP Port 139: NetBIOS Session Service (file transfers).
- Modern Windows systems use direct SMB over TCP 445 (NetBIOS-less).
Lightweight Directory Access Protocol (LDAP)
- Accesses and manages directory services (e.g., user databases, organizational
units).
- LDAP: Unencrypted over TCP Port 389.
- LDAPS (LDAP Secure): Encrypted version (often over TCP Port 636).
- Used in Microsoft Active Directory and other directory services.
- Organizes data into OUs (Organizational Units), CNs (Common
Names), etc.
Remote Desktop Protocol (RDP)
- Provides remote desktop access to Windows systems over TCP Port
3389.
- Allows full control of a remote machine or single-application access.
- Compatible with Windows, macOS, Linux, and mobile devices.