CODEWITHSUNDEEP
c#socketsnetwork-programming
Avi Thalker
Avi Thalker

Reputation: 59

How many tcp connections on different ports a sever can handle?

I am designing a server client app in C#. the client connect and communicate with the sever threw tcp socket.

in the server side I am using the socket.accept() method in order to handle new connection from client. when client is connecting, the server use a random port in order to communicate with the client.

so my question is.. how many clients the server can receive in this kind of form? is there another form that I should use in order to handle lots of clients?

Upvotes: 1

Views: 2418

Answers (4)

tigrou
tigrou

Reputation: 4526

On Windows, you can run those commands to find the maximum amount of ports that can be used (which limits maximum amount of connections) :

netsh int ipv4 show dynamicport tcp
netsh int ipv4 show dynamicport udp
netsh int ipv6 show dynamicport tcp
netsh int ipv6 show dynamicport udp

It should be 16384 (starting Windows Vista and Windows Server 2008). Before, it was approximately 4000.

More info : the default dynamic port range for TCP/IP has changed since Windows Vista and in Windows Server 2008 and troubleshoot port exhaustion issues.

This limit can be changed by creating a new DWORD entry in registry (need computer reboot) : HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters > MaxUserPort

Please kind in mind that a connection will go into TIME_WAIT state after being closed and thus will still use a port for a while (120 seconds by default). This can also limit the number of connections that can be established.

Upvotes: -1

david.pfx
david.pfx

Reputation: 10863

You may like to see this question I asked in similar vein: https://softwareengineering.stackexchange.com/questions/234672/is-there-are-problem-holding-large-numbers-of-open-socket-connections-for-length, and particularly some of the comments.

The answer seems to be that there is no practical limit. The combination of receive port and send port must be unique, and each of them can have 64K values. The total number of combinations is extremely large. There really are servers out there with extremely large numbers of open connections, but to get there you have to solve a number of other interesting problems. The question above contains a link to an article about a million connection server. See also How to retain one million simultaneous TCP connections?. And do a web search for the C10K problem.

What you probably cannot do is use synchronous ports and threads because you run into thread limits, not port limits. You have to use asynchronous ports and a thread pool. And you will have to write one to throw away, just to find out how to do it.

Upvotes: -1

user207421
user207421

Reputation: 311039

in the server side i am using the socket.accept() method in order to handle new connection from client. when client is connecting, the server use a random port in order to communicate with the client.

Not unless you open another, pointless, connection from server to client, and you won't be doing that for firewall reasons. The accepted socket uses the same local port number as the listening socket. Contrary to several answers and comments here.

Your question is therefore founded on a misconception. Whatever you run out of, and it could be memory, thread handles, socket handles, socket buffer space, CPUs, CPU power, virtual memory, disk space, ..., it won't be TCP ports.

EDIT Adherents of the new-random-port theory need to explain the following netstat output:

TCP    127.0.0.4:8009         0.0.0.0:0              LISTENING
TCP    127.0.0.4:8009         127.0.0.1:53777        ESTABLISHED
TCP    127.0.0.4:8009         127.0.0.1:53793        ESTABLISHED
TCP    127.0.0.4:8009         127.0.0.1:53794        ESTABLISHED
TCP    127.0.0.4:8009         127.0.0.1:53795        ESTABLISHED
TCP    127.0.0.4:8009         127.0.0.1:53796        ESTABLISHED
TCP    127.0.0.4:8009         127.0.0.1:53798        ESTABLISHED
TCP    127.0.0.4:8009         127.0.0.1:53935        ESTABLISHED

and show where in RFC 793 it says anything about allocating a new port to an accepted socket, and where in the TCP connect-handshake exchange the new port number is conveyed.

Upvotes: 2

usr
usr

Reputation: 171246

This is practically limited by the OS. You have to test this. On Windows you must use fully asynchronous socket IO at this scale. You will probably be limited by memory usage.

On a TCP level there is no practical limit. There can be one connection for each combination of (server port, server ip, client port, client ip). So with one server port and one server ip you can serve an unlimited amount of clients as long as they have less than 65k connections per client.

You do not need to pick a random port on the server. This is a common misconception.

Upvotes: 3

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