Just some concept about TCP Socket, let's say there are 100 clients simultaneously communicating with a traditional HTTP/TCP web server. How many sockets are respectively at the server and at each client? Do all of the sockets at the server
have the same server-side port number?
The question is generic, so the answer is going to be as well.
For traditional TCP-based HTTP server, there will be 100 sockets on the server (one for each client), and one socket on every client. All server sockets will be bound to the same server port.
This answer doesn't take into account the fact that in modern HTTP model a client usually opens more than one socket to serve a single request.
Usually a web server is listening to any incoming connection through port 80. So, my question is that shouldn't it be that in general concept of socket programming is that port 80 is for listen for incoming connection. But then after the server accepted the connection, it will use another port e.g port 12345 to communicate with the client. But, when I look into the wireshark, the server is always using port 80 during the communication. I am confused here.
So what if https://www.facebook.com:443, it has hundreds of thousands of connection to the it at a second. Is it possible for a single port to handle such a large amount of traffic?
A particular socket is uniquely identified by a 5-tuple (i.e. a list of 5 particular properties.) Those properties are:
Source IP Address
Destination IP Address
Source Port Number
Destination Port Number
Transport Protocol (usually TCP or UDP)
These parameters must be unique for sockets that are open at the same time. Where you're probably getting confused here is what happens on the client side vs. what happens on the server side in TCP. Regardless of the application protocol in question (HTTP, FTP, SMTP, whatever,) TCP behaves the same way.
When you open a socket on the client side, it will select a random high-number port for the new outgoing connection. This is required, otherwise you would be unable to open two separate sockets on the same computer to the same server. Since it's entirely reasonable to want to do that (and it's very common in the case of web servers, such as having stackoverflow.com open in two separate tabs) and the 5-tuple for each socket must be unique, a random high-number port is used as the source port. However, each of those sockets will connect to port 80 at stackoverflow.com's webserver.
On the server side of things, stackoverflow.com can already distinguish between those two different sockets from your client, again, because they already have different client-side port numbers. When it sees an incoming request packet from your browser, it knows which of the sockets it has open with you to respond to because of the different source port number. Similarly, when it wants to send a response packet to you, it can send it to the correct endpoint on your side by setting the destination port number to the client-side port number it got the request from.
The bottom line is that it's unnecessary for each client connection to have a separate port number on the server's side because the server can already uniquely identify each client connection by its client IP address and client-side port number. This is the way TCP (and UDP) sockets work regardless of application-layer protocol.
shouldn't it be that in general concept of socket programming is that port 80 is for listen for incoming connection. But then after the server accepted the connection, it will use another port e.g port 12345 to communicate with the client.
No.
But, when I look into the wireshark, the server is always using port 80 during the communication.
Yes.
I am confused here.
Only because your 'general concept' isn't correct. An accepted socket uses the same local port as the listening socket.
So what if https://www.facebook.com:443, it has hundreds of thousands of connection to the it at a second. Is it possible for a single port to handle such a large amount of traffic?
A port is only a number. It isn't a physical thing. It isn't handling anything. TCP is identifying connections based on the tuple {source IP, source port, target IP, target port}. There's no problem as long as the entire tuple is unique.
Ports are a virtual concept, not a hardware ressource, it's no harder to handle 10 000 connection on 1 port than 1 connection each on 10 000 port (it's probably much faster even)
Not all servers are web servers listening on port 80, nor do all servers maintain lasting connections. Web servers in particular are stateless.
Your suggestion to open a new port for further communication is exactly what happens when using the FTP protocol, but as you have seen this is not necessary.
Ports are not a physical concept, they exist in a standardised form to allow multiple servers to be reachable on the same host without specialised multiplexing software. Such software does still exist, but for entirely different reasons (see: sshttp). What you see as a response from the server on port 80, the server sees as a reply to you on a not-so-random port the OS assigned your connection.
When a server listening socket accepts a TCP request in the first time ,the function such as Socket java.net.ServerSocket.accept() will return a new communication socket whoes port number is the same as the port from java.net.ServerSocket.ServerSocket(int port).
Here are the screen shots.
I have an application (essentially a game) that is broadcasting game state data via UDP to many connected clients on a private LAN.
UDP works fine for broadcasting game state. Not having to configure the clients is important for this app. The client just read the UDP datagram stream and build up state as it goes.
But now I need the clients to reliably download a few pieces large data payload from the server. TCP is way better then UDP for that.
But we still rather not have to configure each and every clients with the host info.
It would be better to just embed an service advertisement in the broadcast UDP stream and then have each client see the advertisement and connect to the TCP host with no extra configuration on the endpoints.
Is there an standard way, or better, example code of advertising a TCP service via UDP. Preferably in C++.
The client needs to know the IP and port of the TCP server, that is all. If you can embed that info into your protocol it will work.
Actually, the UDP clients probably know the IP already because the UDP packets have a sender IP. Maybe this fact can help you.
One of the options here (maybe not for just a game but for some "enterprise" service) is setting up SRV records in local DNS.
Is there anyway in which I can check if a server supports XMPP protocol or not?
I am very new to XMPP, and I am dealing with a shared server. I am supposed to use XMPP to create a chatting system. But as I read about XMPP, I am supposed to install openfire and I have no access to the server itself.
So I want to check if the server supports xmpp or not.
Here's the XMPP RFC which includes recommended port numbers:
https://www.rfc-editor.org/rfc/rfc3920#section-15.9
So you could try connecting to port 5222 on a server (with a proper XMPP client, a plain socket in C, the telnet program, or whatever). Note also that port 5223 is used by some XMPP servers for SSL/TLS (as noted in appendix D.1. of the RFC).
I currently have issues with SIP User Agents behind a symmetric NAT connecting to my SIP client, which is an IVR voice service.
I read that Asterisk has a solution for this in the sip.conf, where I can set attribute
nat=yes
and this will ignore the IP and Port in the SIP headers and use the one for the SIP request and also waits for an incoming RTP stream to reply to.
I'd like to make use of this feature as we already have an Asterix server installed for AIX requests.
What would be the minimum configuration required for Asterix to act as the man in the middle on a new port as 5060 will still be used to connect directly to the SIP client? I don't care about authentication etc. I just need the Asterix to act as a SIP relay.
Thanks
K
You may also need to have "canreinvite=no" in the [general] section of your sip.conf.
That setting keeps Asterisk in the call path, otherwise voice traffic may be sent directly from one endpoint to the other.