What is the difference between a port and a socket

Question

This was a question raised by one of the software engineers in my organisation. I'm interested in the broadest definition.

Answer 1

They are terms from two different domains: 'port' is a concept from TCP/IP networking, 'socket' is an API (programming) thing. A 'socket' is made (in code) by taking a port and a hostname or network adapter and combining them into a data structure that you can use to send or receive data.

Answer 2

In a broad sense, Socket - is just that, a socket, just like your electrical, cable or telephone socket. A point where "requisite stuff" (power, signal, information) can go out and come in from. It hides a lot of detailed stuff, which is not required for the use of the "requisite stuff". In software parlance, it provides a generic way of defining a mechanism of communication between two entities (those entities could be anything - two applications, two physically separate devices, User & Kernel space within an OS, etc)

A Port is an endpoint discriminator. It differentiates one endpoint from another. At networking level, it differentiates one application from another, so that the networking stack can pass on information to the appropriate application.

Answer 3

A socket = IP Address + a port (numeric address)
Together they identify an end-point for a network connection on a machine. (Did I just flunk network 101?)

Answer 4

A socket is a structure in your software. It's more-or-less a file; it has operations like read and write. It isn't a physical thing; it's a way for your software to refer to physical things.

A port is a device-like thing. Each host has one or more networks (those are physical); a host has an address on each network. Each address can have thousands of ports.

One socket only may be using a port at an address. The socket allocates the port approximately like allocating a device for file system I/O. Once the port is allocated, no other socket can connect to that port. The port will be freed when the socket is closed.

Take a look at TCP/IP Terminology.

Answer 5

I know that there are lot of explanations. But, there is one more easy way to understand with practical example. We all can connect to HTTP port 80, but does it mean only one user can connect to that port at a time?. The answer is obviously 'no'. Multiple users for multiple purposes can access HTTP port 80 but they still get proper response they are waiting for, from the server, can't they?. Now think about it for a minute, how?. Yes you are correct, its IP address that uniquely identifies different users who contacts for different purposes. If you would have read the previous answers before reaching here, you would know that IP address is a part of information that socket consists. Think about it, is it possible to have a communication without sockets?. The answer is 'Yes' but you cannot run more than one application in a port but we know that we are not a 'Dump' switch that runs on just hardware.

Answer 6

Port and socket can be compared to the Bank Branch.

The building number of the "Bank" is analogous to IP address. A bank has got different sections like:

1. Savings account department
2. Personal loan department
3. Home loan department
4. Grievance department

So 1 (savings account department), 2 (personal loan department), 3 (home loan department) and 4 (grievance department) are ports.

Now let us say you go to open a savings account, you go to the bank (IP address), then you go to "savings account department" (port number 1), then you meet one of the employees working under "savings account department". Let us call him SAVINGACCOUNT_EMPLOYEE1 for opening account.

SAVINGACCOUNT_EMPLOYEE1 is your socket descriptor, so there may be SAVINGACCOUNT_EMPLOYEE1 to SAVINGACCOUNT_EMPLOYEEN. These are all socket descriptors.

Likewise, other departments will be having employess working under them and they are analogous to socket.