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From the command line type - netstat -a
Sockets
Logical construct offered by the operating combining the IP and Port. It’s analogous to a socket that you put in a wall and the socket itself.
There are two types of sockets, server sockets, and client sockets. One server socket communicates with 1 or more client sockets.
An application that is acting in a server capacity creates a server socket. The server socket must bind to a port on the host that it is running on. When client applications want to communicate with a server socket they do this by opening a client socket and sending a bind request to the host and port that the server is running. The server can respond by creating a client socket so that two-way communications can begin between the two endpoints.
DNS (Domain Name Server)
Given that computing nodes on a network have IP addresses, there may be 100s - 10000s of nodes in a network, and that the IP addresses can change. Using IP addresses as a point of reference in code of any kind is not scaleable or good design, it leads to brittle designs.
A better approach is to attach to the IP (which is a changeable value) an identifier that is more persistent. Such an identifier could be a human-readable value like a name, something that is more memorable than IP addresses. This is the purpose of a DNS. It follows the NVList pattern (Name/Value List). For each IP address, you associate with it a human-readable name.
When you want to locate a node on the network, simply request its IP address from the DNS by passing it the human-readable name.
This model leads to more scaleable and decoupled systems.
ARP (Address Resolution Protocol)
Used to convert an IP address to its corresponding physical address(i.e., MAC Address).
ARP is used by the Data Link Layer (ISO 7-layer) to identify the MAC address of a target node.