It only takes a minute to sign up. If there is a limit on the number of ports one machine can have and a socket can only bind to an unused port number, how do servers experiencing extremely high amounts more than the max port number of requests handle this? Is it just done by making the system distributed, i. You misunderstand port numbers quite severely: a server listens only on one port and can have large numbers of open sockets from clients connecting to that one port.
On the TCP level the tuple source ip, source port, destination ip, destination port must be unique for each simultaneous connection. That means a single client cannot open more than simultaneous connections to a server. But a server can theoretically server simultaneous connections per client. So in practice the server is only limited by how much CPU power, memory etc.
When offering network services, 1. IP So although practically a client will not use a port already in use for a connection to open a connection to a different destination IP address, port number depletion is going to be the least of your problems for nearly any application - be it on the server or client side.
The problem is a very real one with NAT gateways routers serving clients with a high number of open outbound connections e. In this case the NAT gateway is unable to create any additional associations, thus effectively cutting clients off the internet. There are multiple ways to share load across multiple servers; DNS round robin is one; there are others.
Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. How do high traffic sites service more than TCP connections? Ask Question. Asked 6 years, 7 months ago. Active 6 years, 6 months ago. Viewed 27k times. Active Oldest Votes. Dennis Kaarsemaker Dennis Kaarsemaker 17k 39 39 silver badges 66 66 bronze badges.
TheLQ Without CGN each client cannot open more than connections to the same server, no client should need nearly that many connections to the same server. Whether the CGN can simultaneously open connections to one server and connections to another server is an implementation detail, which can vary between different CGN implementations. But you can also just deploy dual stack.
TCP / HTTP Listening On Ports: How Can Many Users Share the Same Port
Then connections to servers with IPv6 support won't go through the CGN, so they won't be consuming precious port numbers. Dennis Kaarsemaker, can you also please have a look at this question? You are mistaken - the socket's uniqueness is determined by four factors: the local IP address the local port number the remote IP address the remote port number When offering network services, 1.
There are multiple ways to share load across multiple servers; DNS round robin is one; there are others Deploy "carrier-grade NAT" which a friend derisively and correctly in my view refers to as "crummier-grade NAT". If you read more than the title, you'll see that this question is about port exhaustion and the OP was mistaken about how it works. How exactly does this answer add anything new of value to that? The OP asks explicitly and not just in the headline "how do servers experiencing extremely high amounts Leaving aside the confusion over how sockets work, that's a valid question.When you connect a laptop, a couple of PCsand some smartphones to your network, it's harder to stream Netflix or Hulu on your TV.
That's because as more devices connect to a network, it takes more bandwidth. The router determines where capacity is needed and where it's being used the most. It then pulls indiscriminately to keep all devices working at some level. Each access point has limits for the number of connections and the amount of network load it can handle.
By integrating multiple access points into a larger network, the overall scale is increased. The speed rating of access points represents the maximum theoretical network bandwidth each can support. If you're not sure what your router can support, do a web search for the model number, and you should be able to find it that way. Most people only use their network connection occasionally, and a router shifts its available bandwidth to the devices that need it.
Those shifts depend on what a particular device needs at a particular time. Most people don't have anywhere near the maximum number of devices a typical router can hold. That's a good thing, because connecting devices to a single Wi-Fi access point, while theoretically possible, is not feasible for a few reasons.
The performance degrades as more devices join the network and use it simultaneously. Even a handful of active devices streaming video or downloading files can quickly max out a shared internet link. Access points overheat and stop working when operating at extreme loads for extended periods, even if handling only local traffic and not accessing the internet.
Radio interference among Wi-Fi devices degrades network performance due to frequent re-broadcasting of messages that fail to reach their destination and eventually causes connection drops. Some home routers include a feature that allows administrators to control the number of clients that can simultaneously connect. Many Linksys routers, for example, set a default maximum of 50 devices. Installing a second router or access point on a home network can help distribute the network load.
By adding more access points to the network, any number of devices can be supported. Something else you can do if you have one or more routers that support a large number of devices is to increase the bandwidth available to each simultaneously connected device by upping your subscription with your ISP. For example, if your network devices and internet subscription download at 1 Gbps, having 50 devices connected at once lets each device consume up to 20 megabits of data per second.
Some people use mesh networks to improve wireless network coverage in their homes. These networks provide better coverage because they consist of interlocked routers that supply internet coverage over a broad area, which most traditional, single router networks can't offer. What Does Wireless Really Mean?
Tweet Share Email. Administrators often keep limits in place to keep the routers and networks running reliably. More from Lifewire.TCP and UDP operate at the host-to-host layer in the IP communication model and provide host-to-host communication services for the application layer protocol.
This means an application layer protocol is on one IP host connecting to an application layer protocol on another IP host. In most situations, these host-to-host connections have a sever process running on one host and a client process running on the other host. Think of them as receptacles on an old-fashioned telephone switchboard. By associating the application layer server to use a specific port, you have created a destination that a remote IP host can connect to.
When the remote IP host connects to an application layer server, the connection the host makes is to a port operating on a specific IP host identified by an IP address. This pairing of an IP address and a port as a connection endpoint is a socket. Think of these connectors as the ports, but because the port is associated with a phone, together they make a socket, such as the TCP or UDP port, when paired with an IP address is a socket. With IP, the client application has a port that it operates on, so on the client host, there is an IP address and port for the client side of the connection; this is a socket.
On the server side of the connection is an IP address for the server and a port to make a socket on the server host. To establish a connection between the client application layer and the server application layer is a virtual connection between these two sockets.
This example will walk you thru the process of connecting to a website, such as Wiley. You would open your web browser like Mozilla Firefox and type www. For this example, the address is Firefox makes a connection to the Firefox knows what port to expect because it is a well-known port. The well-known port for a web server is TCP port The destination socket that Firefox attempts to connect is written as socket:port, or in this example, This is the server side of the connect, but the server needs to know where to send the web page you want to view in Mozilla Firefox, so you have a socket for the client side of the connection also.
The client side connection is made up of your IP address, such as The socket associated with Firefox looks like About the Book Author Edward Tetz has worked with computers as a sales associate, support tech, trainer, and consultant.In computer networkinga port is a communication endpoint.
At the software level, within an operating systema port is a logical construct that identifies a specific process or a type of network service. Ports are identified for each protocol and address combination by bit unsigned numbers, commonly known as the port number. A port number is always associated with an IP address of a host and the protocol type of the communication.
It completes the destination or origination network address of a message. Specific port numbers are commonly reserved to identify specific services, so that an arriving packet can be easily forwarded to a running application.
For this purpose, the lowest numbered port numbers identify the historically most commonly used services, and are called the well-known port numbers. Higher-numbered ports are available for general use by applications and are known as ephemeral ports.
When used as a service enumeration, ports provide a multiplexing service for multiple services or multiple communication sessions at one network address. In the client—server model of application architecture multiple simultaneous communication sessions may be initiated for the same service. A port number is a bit unsigned integer, thus ranging from 0 to For TCPport number 0 is reserved and cannot be used, while for UDPthe source port is optional and a value of zero means no port.
A process associates its input or output channels via an Internet socketwhich is a type of file descriptorwith a transport protocolan IP addressand a port number. This is known as bindingand enables the process to send and receive data via the network. The operating system's networking software has the task of transmitting outgoing data from all application ports onto the network, and forwarding arriving network packets to processes by matching the packet's IP address and port number.
Common application failures, sometimes called port conflictsoccur when multiple programs attempt to use the same port number on the same IP address with the same protocol. Applications implementing common services often use specifically reserved well-known port numbers for receiving service requests from clients. This process is known as listeningand involves the receipt of a request on the well-known port and establishing a one-to-one server-client dialog, using the same local port number.
Other clients may continue to connect to the listening port; this works because a TCP connection is identified by a tuple consisting of the local address, the local port, the remote address, and the remote port. The core network services, such as the World Wide Webtypically use well-known port numbers. In many operating systems special privileges are required for applications to bind to these ports, because these are often deemed critical to the operation of IP networks.
The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I understand the basics of how ports work. However, what I don't get is how multiple clients can simultaneously connect to say port I know each client has a unique for their machine port.
Does the server reply back from an available port to the client, and simply state the reply came from 80? How does this work? First off, a "port" is just a number.
All a "connection to a port" really represents is a packet which has that number specified in its "destination port" header field. Now, there are two answers to your question, one for stateful protocols and one for stateless protocols. For a stateless protocol ie UDPthere is no problem because "connections" don't exist - multiple people can send packets to the same port, and their packets will arrive in whatever sequence.
Nobody is ever in the "connected" state. For a stateful protocol like TCPa connection is identified by a 4-tuple consisting of source and destination ports and source and destination IP addresses. So, if two different machines connect to the same port on a third machine, there are two distinct connections because the source IPs differ. If the same machine or two behind NAT or otherwise sharing the same IP address connects twice to a single remote end, the connections are differentiated by source port which is generally a random high-numbered port.
Simply, if I connect to the same web server twice from my client, the two connections will have different source ports from my perspective and destination ports from the web server's. So there is no ambiguity, even though both connections have the same source and destination IP addresses. Unless an application defines its own higher-level protocol, there is no way to multiplex a port.
If two connections using the same protocol simultaneously have identical source and destination IPs and identical source and destination ports, they must be the same connection. I'm sorry to say that the response from "Borealid" is imprecise and somewhat incorrect - firstly there is no relation to statefulness or statelessness to answer this question, and most importantly the definition of the tuple for a socket is incorrect.
This means host A connects to server X's port 80 and another host B also connects to same server X to the same port Now, how the server handles these two sockets depends on if the server is single threaded or multiple threaded I'll explain this later.
What is important is that one server can listen to multiple sockets simultaneously. Irrespective of stateful or stateless protocols, two clients can connect to same server port because for each client we can assign a different socket as client IP will definitely differ. To answer the second part of the question on how a server knows which socket to answer. First understand that for a single server process that is listening to same port, there could be more than one sockets may be from same client or from different clients.
Now as long as a server knows which request is associated with which socket, it can always respond to appropriate client using the same socket. Thus a server never needs to open another port in its own node than the original one on which client initially tried to connect. If any server allocates different server-ports after a socket is bound, then in my opinion the server is wasting its resource and it must be needing the client to connect again to the new port assigned.
Example 2: It's a very interesting question: "can two different processes on a server listen to the same port". If you do not consider protocol as one of parameter defining socket then the answer is no.
This is so because we can say that in such case, a single client trying to connect to a server-port will not have any mechanism to mention which of the two listening processes the client intends to connect to. This is the same theme asserted by rule 2.Multiple Chat Clients: One Thread (in C++)
Thus two processes in same node can listen to same port only if they are using different protocol. For example two unrelated clients say one is using TCP and another is using UDP can connect and communicate to the same server node and to the same port but they must be served by two different server-processes.
When a server's processes listening to a port that means multiple sockets can simultaneously connect and communicate with the same server-process.In the last socket programming in Java post, I described how to build a single server and a single client connection using Java socket APIs.
In this post, I explore the techniques needed to build a multi-clients, single server scheme in Java. We need to build a multithreaded server. The modifications only need to happen in the server side. The key here is that once server. That is if you run the original EchoServer, EchoClient program, the first client would work, but the second client would be blocked without a response.
In order to get around this, I have to create a thread for each socketServer. This way, multiple client requests can be served simultaneously. To do this, we first implemented a ClientWorker class. It encapsulates the things we want to do after we established a connection.
Single Server With Multiple Clients: A Simple C++ Implementation
In this case, just send back to the client the original message the client. The next step is using separate threads in EchoServer to invade the ClientWorker to handle incoming requests. The key components of the class is here. The other parts of the class is here.
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You are commenting using your Twitter account. You are commenting using your Facebook account. Notify me of new comments via email. Notify me of new posts via email. Yunming Zhang's Blog. Skip to content. Like this: Like LoadingAfter reading this article, you will be able to build your own server that is able to handle multiple clients at the same time. Several key classes are developed in this article, and hopefully, you will have the chance to use these classes in your daily development work.
The first one is myTcpSocketthis class hides the details of socket programming by providing a simple and easy-to-use interface, it is used to build both the server and client. The second class is myThread class whose main purpose is to make server to handle multiple clients simultaneously: for each incoming client call, the server will create a separate thread to communicate with this client, therefore it can handle as many incoming clients as there are.
In a multi-thread environment like this, however, synchronization of these threads is always an important issue. To solve this problem, we need our last major class, namely, mySemaphore. Well, here is the answer for you, hope you have a chance to see this article too. Hope this gives you the motivation to read this article. The server will be started first and after it is started, we want the server to wait for the incoming client calls, and periodically report its status: how many clients have been connected with the server and how many clients have been disconnected with the server.
TCP and UDP server using select
Meanwhile, once an incoming call is detected and accepted, the server will create a separate thread to handle this client, it will therefore create as many separate sessions as there are incoming clients and it should be able to "talk" with any one of these clients.
You can download the source code and the following. After downloading these files, you can then build two projects: one for the server and one for the client. After compiling, you should start the server first.
Successfully starting the server will show the following console screen:. This assumes that you are using your local PC as the server, therefore, Name should show your domain name or, in some cases, your PC's name, like in this exampleand Address should show your current IP address depending on your ISP, your IP address can change from time to time. At the time I was running the server, this IP address was Clearly, in order to communicate with your server, you need to let your client know the IP address of your server.
To do so, you need to create a simple text file named serverConfig. So add You can start as many clients as you want and you can send messages from server to any of these clients by typing on the keyboard, also, you can send messages from any client to the server again by typing a string on the keyboard. To end a client, send the message Quit or quit from the client to server, this client will be terminated. In this section, myTcpSocket class is described.
In fact, article 1 presents a rather detailed description about this class, so here let us only show the key methods of this class by using the following examples. In a nutshell, this class encapsulates socket-related system calls into a single class to offer a simple and easy-to-use interface, a typical usage of this class as a server is shown as follows:.
Besides these major methods in myTcpSocket class, there are other methods you can use to manipulate the socket, for example:.
However, the following problems still exist in this basic model:. To solve these problems, we need two more classes, namely, myThread and mySemaphore. These classes are discussed in the next section.
Here is the improved but also simplified main function on the server side don't worry about the details :. Therefore, the main function is free to do any other processing you might want to do, for instance, reporting the status of the server you can see the details in the source files you downloaded.