A logical communication endpoint that exists on a computer or server
TCP and UDP both has 65,536 ports

Port that is listening for a connection from a client (Specific Port)

Port created to call out to a server that is listening for a connection (High Random Port)

Port Types

Port TypePort NumbersDescription
Well Known Ports0 - 1023Assigned to well know protocols
Registered Ports1024 - 49,151Registered to specific protocols
Dynamic and Private Ports49,152 - 65,535Not registered and can be used for any purpose

Ports in Action
PC (High Random Port) → Web Server (Specific Port)
PC (High Random Port) ← Web Server (Specific Port)

Common Protocol Ports

Protocols: Rules governing device communication and data exchange

FTP (File Transfer Protocol)21TCPProvides insecure file transfers
SSH (Secure Shell Protocol)22TCPProvides secure remote control of another machine using text-based environment
SCP (Secure Copy Protocol)22TCPProvides secure copy features
SFTP (Secure File Transfer Protocol)22TCPProvides secure file transfers
Telnet23TCPProvides insecure remote control of another machine using text-based environment
SMTP (Simple Mail Transfer Protocol)25TCPProvides ability to send emails over the network
DNS (Domain Name Service)53TCP, UDPConverts domain names to IP Addresses and IP Addresses to domain names
DHCP (Dynamic Host Control Protocol)67, 68Assigns IP Address, Subnet Mask, Default Gateway and DNS Server to clients on network
TFTP (Trivial File Transfer Protocol)69UDPLightweight file transfer method for sending config files or networking booting of OS
HTTP (Hypertext Transfer Protocol)80TCPUsed for insecure web browsing
Kerberos88UDPNetwork authentication protocol
POP3 (Post Office Protocol v3)110TCPUsed for receiving incoming emails
Network News Transfer Protocol (NNTP)119TCPUsed for accessing newsgroups
NTP (Network Time Protocol)123Used to keep accurate time for clients on a network
Remote Procedure Call (RPC)135TCP, UDPFacilitates communication between different system processes
NetBIOS (Network Basic Input/ Output System)137, 138, 139TCP, UDPUsed for file or printer sharing in Windows environment
IMAP4 (Internet Mail Application Protocol v4)143TCPA newer method of retrieving incoming mails
SNMP (Simple Network Management Protocol)161UDPUsed to collect data about network devices and monitor their status
SNMP Trap162UDPResponsible for sending SNMP trap messages
LDAP (Lightweight Directory Access Protocol)389TCPUsed to provide directory services to the network
HTTPS (HTTP Secure)443TCPUsed for secure web browsing
SMB (Server Message Block)445TCPUsed for Windows file and printer sharing
SMTP Secure (SMTPS)465, 587TCPSecure and encrypted way to send emails
Syslog (System Logging Protocol)514UDPUsed to send logging data to a central server
LDAP Secure (LDAPS)636TCPProvides secure directory services
IMAP over SSL993TCPSecure and encrypted way to receive email
POP3 over SSL995TCPSecure and encrypted way to receive email
MSSQL Server Protocol1433TCPUsed to communicate with database engine
SQLnet Protocol1521Used to communicate with Oracle database engine
RADIUS TCP1645, 1646TCPUsed for remote authentication, authorization and accounting
RADIUS TCP1812, 1813UDPUsed for remote authentication and accounting as defined by IETF
MySQL Protocol3306Used to communicate with MySQL database engine
RDP (Remote Desktop Protocol)3389TCPProvides graphical remote control over another device
SIP (Session Initiation Protocol)5060, 5061Used to initiate VoIP and video calls
Syslog TLS6514TCPSecure transfer of syslog’s over the network

TFTP: Does not support authentication. It is a stripped down version of FTP
IMAP: Allows to view emails without having to download them to local device. Email server keeps emails synced across devices
LDAP: AD is an proprietary version of LDAP. It also uses port 389
SMB: Works along with NetBIOS which performs the authentication on Port 139 and then hands over control to SMB for resource sharing