这是我所在组织的一位软件工程师提出的问题。我感兴趣的是最广义的定义。
当前回答
这个问题已经有了理论上的答案。我想举一个实际的例子来解释这个问题,让大家对Socket和Port有一个更清晰的理解。
我在这里找到的
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.wiley.com into the address bar. Your web browser uses a Domain Name System (DNS) server to look up the name www.wiley.com to identify its IP address is. For this example, the address is 192.0.2.100. Firefox makes a connection to the 192.0.2.100 address and to the port where the application layer web server is operating. Firefox knows what port to expect because it is a well-known port . The well-known port for a web server is TCP port 80. The destination socket that Firefox attempts to connect is written as socket:port, or in this example, 192.0.2.100:80. 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 192.168.1.25, and a randomly chosen dynamic port number. The socket associated with Firefox looks like 192.168.1.25:49175. Because web servers operate on TCP port 80, both of these sockets are TCP sockets, whereas if you were connecting to a server operating on a UDP port, both the server and client sockets would be UDP sockets.
其他回答
套接字= IP地址+端口(数字地址) 它们一起标识机器上网络连接的端点。(我刚刚是不是网络基础课不及格?)
I know that there are lot of explanations. But, there is one more easy way to understand with practical example. We all can connect to HTTP port 80, but does it mean only one user can connect to that port at a time?. The answer is obviously 'no'. Multiple users for multiple purposes can access HTTP port 80 but they still get proper response they are waiting for, from the server, can't they?. Now think about it for a minute, how?. Yes you are correct, its IP address that uniquely identifies different users who contacts for different purposes. If you would have read the previous answers before reaching here, you would know that IP address is a part of information that socket consists. Think about it, is it possible to have a communication without sockets?. The answer is 'Yes' but you cannot run more than one application in a port but we know that we are not a 'Dump' switch that runs on just hardware.
端口和插座可以比作银行分行。
“银行”的门牌号与IP地址类似。 银行有不同的部分,比如:
储蓄帐务部 个人贷款部 房屋贷款部 投诉部门
因此,1(储蓄账户部)、2(个人贷款部)、3(住房贷款部)和4(申诉部)是端口。
现在让我们假设你要开一个储蓄账户,你去了银行(IP地址),然后你去了“储蓄账户部门”(端口号1),然后你遇到了在“储蓄账户部门”工作的一名员工。让我们称他为SAVINGACCOUNT_EMPLOYEE1,用于开户。
SAVINGACCOUNT_EMPLOYEE1是套接字描述符,因此可能存在 SAVINGACCOUNT_EMPLOYEE1到SAVINGACCOUNT_EMPLOYEEN。这些都是套接字描述符。
同样地,其他部门将有员工在他们之下工作,他们类似于插座。
Socket is an abstraction provided by kernel to user applications for data I/O. A socket type is defined by the protocol it's handling, an IPC communication etc. So if somebody creates a TCP socket he can do manipulations like reading data to socket and writing data to it by simple methods and the lower level protocol handling like TCP conversions and forwarding packets to lower level network protocols is done by the particular socket implementation in the kernel. The advantage is that user need not worry about handling protocol specific nitigrities and should just read and write data to socket like a normal buffer. Same is true in case of IPC, user just reads and writes data to socket and kernel handles all lower level details based on the type of socket created.
端口和IP一起就像给套接字提供一个地址,虽然不是必需的,但它有助于网络通信。
首先,我认为我们应该先了解一下什么构成了从a到B的数据包。
网络的一个常见定义是使用OSI模型,该模型根据目的将网络分离为许多层。有几个重要的,我们将在这里介绍:
The data link layer. This layer is responsible for getting packets of data from one network device to another and is just above the layer that actually does the transmitting. It talks about MAC addresses and knows how to find hosts based on their MAC (hardware) address, but nothing more. The network layer is the layer that allows you to transport data across machines and over physical boundaries, such as physical devices. The network layer must essentially support an additional address based mechanism which relates somehow to the physical address; enter the Internet Protocol (IPv4). An IP address can get your packet from A to B over the internet, but knows nothing about how to traverse individual hops. This is handled by the layer above in accordance with routing information. The transport layer. This layer is responsible for defining the way information gets from A to B and any restrictions, checks or errors on that behaviour. For example, TCP adds additional information to a packet such that it is possible to deduce if packets have been lost.
TCP包含了端口的概念。这些实际上是Internet套接字(AF_INET)可以绑定到的同一IP地址上的不同数据端点。
UDP和其他传输层协议也是如此。从技术上讲,它们不需要以端口为特色,但这些端口确实为上层的多个应用程序提供了一种使用同一台计算机接收(实际上是发出)传出连接的方法。
这就把我们带到了TCP或UDP连接的解剖。每个都有一个源端口和地址,以及一个目标端口和地址。这样,在任何给定的会话中,目标应用程序都可以从源进行响应和接收。
因此,端口本质上是一种规范强制的方式,允许多个并发连接共享相同的地址。
现在,我们需要看看如何从应用程序的角度与外部世界通信。要做到这一点,你需要询问你的操作系统,因为大多数操作系统都支持伯克利套接字的方式来做事情,我们看到我们可以从应用程序创建包含端口的套接字,像这样:
int fd = socket(AF_INET, SOCK_STREAM, 0); // tcp socket
int fd = socket(AF_INET, SOCK_DGRAM, 0); // udp socket
// later we bind...
太棒了!因此,在sockaddr结构中,我们将指定端口,bam!完成工作!嗯,差不多了,除了:
int fd = socket(AF_UNIX, SOCK_STREAM, 0);
也是可能的。啊,这可真是个麻烦!
好吧,实际上并没有。我们所需要做的就是想出一些合适的定义:
internet套接字是IP地址、协议及其相关端口号的组合,服务可以在其上提供数据。tcp端口80,stackoverflow.com是一个互联网套接字。 unix套接字是一个在文件系统中表示的IPC端点,例如/var/run/database.sock。 套接字API是一种请求应用程序能够向套接字读写数据的方法。
瞧!这样就把事情整理好了。在我们的方案中,
端口是一个数字标识符,作为传输层协议的一部分,标识应该响应给定请求的服务号。
因此,端口实际上是形成互联网套接字所需的一个子集。不幸的是,“套接字”这个词的意思恰好被应用到几个不同的概念中。所以我衷心建议你为你的下一个项目命名套接字,只是为了增加混乱;)
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