Packet data contains a special number in its header, called port. The typical use of the port in the computer is to map data to a specific process running on it.
To be more precise the port is defined with the following example.
Let us suppose that the IP addresses are the street addresses of an apartment building and the port number is a specific apartment of that building. If we dispatch a letter to building without mentioning the specific apartment number so how would one that that actually should belong to this letter? Same is the case with the IP address and the port number. The ender has to make sure that the port number is also mentioned along with the address in order to make the letter carry to the right domicile.
A server using various server processes will provide both SMTP for sending and POP3 for receiving while sending and receiving an e-mail. The port number will specify the association of a certain data with a certain process. Network ports are not used by all networks. ICMP is the example of a network not using ports. The source port and the destination port are specified by the packet header in both TCP and UDP each of which ranges 0 to 65535. It also specifies the IP numbers in other things. A port may bind to a specifics process for sending or receiving the data means the incoming packet number whose destination number matches to it will be listened by it as well as the sending of an outgoing packet whose destination number matches to it. The process can bind to multiple ports. Application that can be implemented for the common services will accept some specific port numbers which have been defined for use with the available protocol by conversion. This ensures the security to avoid the unreliable process working on a system.
The process possessed by the super user can listen to port numbers ranging 0 to 1023 in UNIX. The port number is readily interpreted by the sending, receiving as well as the other aspect of the networking infrastructure because it forms the part of packet header. Firewalls are thought to respond differently to respond to port number in the lights of their paths and sources.
An application of this is port forwarding. The port scanning is the effort to connect a broad range of services in sequence in a single computer.
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