The server sends its reply back to whatever port number it finds in the Source Port field of the request. Key Concept: In most TCP/IP client/server communications, the client uses a random ephemeral port number and sends a request to the appropriate reserved port number at the servers IP address. The server sends its reply back to that port number, which it reads from the request. Its port number for this exchange is the pseudo-randomly-selected 3,022. The client is making an HTTP request and sends it to the server at HTTPs well-known port number, 80. This highly simplified example shows how clients and servers use port numbers for a request.reply exchange. This example isįigure 199: TCP/IP Client/Server Application Port Mechanics The two processes can exchange information back and forth Įach time the source port number and destination port number are swappedĪlong with the source and destination IP addresses. It back to 177.41.72.6, using Destination Port 3,022 and Source That process generates a reply, and sends HTTP request arrives at the Web server it is conveyed to port 80 where The Source Port number is allocatedįrom a pool of ephemeral ports let's say it's port 3,022. Is sent using TCP, with a Destination Port number of 80 (the To a particular Web site at IP address 41.199.222.3. Our Web browser, with IP address 177.41.72.6 wants to send an HTTP request Registered port number on the server process, back to the ephemeral port number on the client machine. So, the server's reply is sent from the well-known or Port numbers, just as it does the source and destination IP addresses. In forming this response message, it swaps the source and destination The server receives the request, and then generates a reply. Port number, it is used as the source port in the client's request TCP/UDP Port Number Use During a Client/Server ExchangeĬlient/server application message exchange. TCP/IP Client (Ephemeral) Ports and Client/Server Application Port Use TCP/IP Sockets and Socket Pairs: Process and Connection Identification TCP/IP Application Assignments and Server Port Number Ranges: Well-Known, Registered and Dynamic/Private Ports Then click "Add Filter." at the bottom, and add this string: Then just click OK.ĩ TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)ĩ Transmission Control Protocol (TCP) and User Datagram Protocol (UDP)ĩ TCP/IP Transport Layer Protocol (TCP and UDP) Addressing: Ports and Sockets Or go to the Tools menu and select "Adblock Plus Preferences.". To do so, just open the Adblock menu and select "Disable on ". If you want to use this site for free, I'd be grateful if you could add the site to the whitelist for Adblock. It's priced very economically and you can read all of it in a convenient format without ads. If you like The TCP/IP Guide, please consider the download version. ![]() And I have a family to support, just like you. ![]() ![]() I don't want to go to a pay-only model like some sites, but when more and more people block ads, I end up working for free. But please understand that I am providing premium content for free that takes hundreds of hours of time to research and write. The TCP/IP Guide - TCP/IP Client (Ephemeral) Ports and Client/Server Application Port Use
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