Transportation layer conventions utilize an idea of ports and multiplexing/demultiplexing to convey information to individual services listening on network nodes. These ports are spoken to by a solitary 16-bit number, implying that they can constitute a range of numbers 0-65535. This range has been separated by the IANA (Internet Assigned Numbers Authority) into several different segments :
- Port 0 is not used for internet/network traffic, but it’s sometimes utilized in communications going down between different programs on identical computer.
- Ports 1-1023 are alluded to as system ports. These ports speak to official ports for most notable system administrations and many common network services. HTTP usually communicates at port 80, while FTP at port 21. In most working frameworks/OS, administrative-level access is expected to begin a program that tunes in on a system port.
- Ports 1024-49151 are known as registered ports. These ports are utilized for a bunch of different network functionality and services that probably won’t be very frequently used as ones that are on system ports. A genuine case of a registered port is 3306, which is port that numerous databases tune in on. Registered ports are in some cases formally enlisted and recognized by IANA, yet this is not certain to always be case. On most operating systems, any client of any entry-level can run a program tuning in on a Registered port.
- Lastly, there is a range of ports from port 49152-65535. These are known as Ephemeral ports (or private ports). Ephemeral ports can’t be enlisted with IANA and are commonly utilized for setting up outbound network traffic and connections. All TCP traffic needs one destination port and one source port to establish a connection. At the point when a client needs to speak with a server, client will be appointed an ephemeral port to be utilized for simply that one connection, while server tunes in on a static system framework or registered port.
Not every single working operating system follows ephemeral port proposals of IANA. The ephemeral ports utilized for outbound associations comprise of ports 49152 through 65535. Yet, this range of ports can change as per operating system and framework you’re dealing with. Quite a few times registered ports are utilized, however, no modern operating system will ever utilize a system port for outbound connections.
Here are some commonly used ports for reference:
|7||Echo||Port just echoes whatever is sent to it. This feature can be used in many attacks, such as Smurf/Fraggle.||TCP and UDP|
|20 /21||File Transfer Protocol (FTP)||Port used by FTP protocol to send data to client||TCP|
|22||Secure Shell (SSH)||Used as secure replacement protocol for Telnet||TCP and UDP|
|23||Telnet||Port used by Telnet to remotely connect to a workstation or server(unsecured)||TCP|
|25||Simple Mail Transfer Protocol (SMTP)||Used to send E-Mail over intenet||TCP|
|53||Domain Name System (DNS)||Port for DNS requests, network routing and zone transfers||TCP and UDP|
|67 /68||Dynamic Host Configuration Protocol (DHCP)||Used on networks that do not use static IP address assignment.||UDP|
|80||Hyper Text Transfer Protocol (HTTP)||Used for browsing web-pages on a browser||TCP|
|110||Post Office Protocol (POP3)||Port used to retrieve complete contents of a server mailbox||TCP|
|143||Internet Message Access Protocol (IMAP4)||Internet Message Access Protocol (IMAP4) is a new protocol to read email with wider range of operations||TCP and UDP|
|194||Internet Relay Chat Protocol(IRC)||allows communication in form of text between multiple parties, one or more clients can connect to a centralized server.||TCP and UDP|
|443||HTTP with Secure Sockets Layer (SSL)||Port used for secure web traffic||TCP and UDP|
|3389||Remote Desktop Protocol(RDP)||Port used by remote desktop to remotely manage other windows system||TCP and UDP|
The transport layer has a lot of ports to accommodate lots of various applications protocols simultaneously. The ports are dictated by the type of transport layer connectivity.
Also, remember that there are lots of protocols in the application layer but not all of them require port numbers (like TCP or UDP). Internet Control Message Protocol (ICMP) is one of them.
To become more familiar with ports, and to see a rundown of what ports have been appointed to different services, check out IANA Service Name and Transport Protocol Port Number Registry. A comparable list of ports and corresponding services is on Wikipedia, which is a rather brief and easier read. Check it out, as well!.
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