PORT NUMBERS

PORT

• Logical (not physical) connection to computer (server).
• One hardware link: Many ports.
• One host (physical server) can run many services (listening processes) at different addresses.
• IP address = Address of a host.
• IP address + port = Address of a process (service) on a host.
• List of ports. 1 to 65535 (16 bit no). 

• Server machine may run multiple server processes, each contactable on different port. 
• Conversely, multiple clients may want to contact same port (e.g. Web server).
• Client creates socket at its end. Sends request to server (at port no). Server creates socket at its end dedicated to that client. 
• One port: Many sockets to that port.
• Port scanner - look at some machines in DCU to find ports that are "open" - providing a service.
• Does this by trying to open a socket to that port.  
  NOTE: Port use is regulated by the Internet Corporation for Assigning Names and Numbers (ICANN).

  TYPES OF PORT NUMBERS

By ICANN there are three categories for ports: 

• 0 to 1023 – well known ports assigned to common protocols and services. 
• 1024 to 49151 – registered ports assigned by ICANN to a specific service. 
• 49152 to 65 535 – dynamic (private, high) ports range from 49,152 to 65,535

COMMONLY USED PORTS