Run the command netstat -a This will give you a list of all of the network conne
ID: 3864875 • Letter: R
Question
Run the command netstat -aThis will give you a list of all of the network connections your system knows about. How many do you see that are listening (meaning, there are programs that are waiting for connections from other systems)? Run the command netstat -a
This will give you a list of all of the network connections your system knows about. How many do you see that are listening (meaning, there are programs that are waiting for connections from other systems)? Run the command netstat -a
This will give you a list of all of the network connections your system knows about. How many do you see that are listening (meaning, there are programs that are waiting for connections from other systems)?
Explanation / Answer
is allowed to drop packets; i.e., it is an unreliable protocol. There are no acknowledgements and no retransmissions. There is no flow-control such as there is in a RS-232 serial interface.
One way to think of IP communication is by analogy to communications via a letter. You write the letter (this is the data you are sending); put the letter inside an envelope (the IP packet); address the envelope (using an IP address); put your return address on the envelope (your local IP address); and then you send the letter. Like a real letter, you have no way of knowing whether an IP packet was received. If you send a second letter one day after the first, the second one may be received before the first. Or, the second one may never be received.
UDP (User Datagram Protocol) is a connectionless protocol sitting on top of IP that provides unreliable packet delivery. It essentially provides user-level access to the low-level IP hardware. But adds port numbers and checksumming for error handling (UDP can drop bad packets).
Useful for games (sending position), network time services, internet telephony, DNS, streaming video.
UDP is much faster than TCP.
TCP (Transmission Control Protocol) is another protocol, a reliable but slower one, sitting on top of IP. TCP provides reliable, stream-oriented connections; can treat the connection like a stream/file rather than packets. Packets are ordered into the proper sequence at the target machine via use of sequence numbers. TCP automatically deals with lost packets before delivering a complete "file" to a recipient. Control-flow prevents buffer overflows etc...
TCP is like a phone connection versus the simple "fire and forget" letter stateless style of UDP. TCP sockets are open for the duration of a communication (i.e., until you close the connection).
Unlike UDP, the destination host and port number is not sufficient to identify a recipient of a TCP connection. There are five distinct elements that make a TCP connection unique:
If the IP address is like an office building main phone number, a socket is like the extension numbers for offices. So the IP and socket, often called the port, uniquely identify an "office" (server process). You will see unique identifiers like 192.168.2.100:80 where 80 is the port. Just like in an office, it is possible no process is listening at a port. That is, there is no server waiting for requests at that port.
Ports run from 1..65535. 1..1024 require root privileges to use and ports 1..255 are reserved for common processes like:
Continuing the office analogy further, just because you can open a connection to a port doesn't mean you can speak the right language. Processes at ports all speak a specific, predefined, agreed-upon protocol like HTTP.
If the IP address is like an office building main phone number, a socket is like the extension numbers for offices. So the IP and socket, often called the port, uniquely identify an "office" (server process). You will see unique identifiers like 192.168.2.100:80 where 80 is the port. Just like in an office, it is possible no process is listening at a port. That is, there is no server waiting for requests at that port.
Ports run from 1..65535. 1..1024 require root privileges to use and ports 1..255 are reserved for common processes like:
Continuing the office analogy further, just because you can open a connection to a port doesn't mean you can speak the right language. Processes at ports all speak a specific, predefined, agreed-upon protocol like HTTP.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.