tcp port number 21

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External Resources SANS Internet Storm Center: port 21

Notes: Port numbers in computer networking represent communication endpoints. Ports are unsigned 16-bit integers (0-65535) that identify a specific process, or network service. IANA is responsible for internet protocol resources, including the registration of commonly used port numbers for well-known internet services. Well Known Ports: 0 through 1023. Registered Ports: 1024 through 49151. Dynamic/Private : 49152 through 65535. TCP ports use the Transmission Control Protocol, the most commonly used protocol on the Internet and any TCP/IP network. TCP enables two hosts to establish a connection and exchange streams of data. TCP guarantees delivery of data and that packets will be delivered in the same order in which they were sent. Guaranteed communication/delivery is the key difference between TCP and UDP. UDP ports use the Datagram Protocol. Like TCP, UDP is used in combination with IP (the Internet Protocol) and facilitates the transmission of datagrams from one computer to applications on another computer, but unlike TCP, UDP is connectionless and does not guarantee reliable communication; it's up to the application that received the message to process any errors and verify correct delivery. UDP is often used with time-sensitive applications, such as audio/video streaming and realtime gaming, where dropping some packets is preferable to waiting for delayed data. When troubleshooting unknown open ports, it is useful to find exactly what services/processes are listening to them. This can be accomplished in both Windows command prompt and Linux variants using the "netstat -aon" command. We also recommend runnig multiple anti-virus/anti-malware scans to rule out the possibility of active malicious software. For more detailed and personalized help please use our forums.

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Sherpa Guide Kami Rita Sets Record for Most Times Scaling Mount Everest

Top un court orders israel to halt military operation in rafah, here’s why you won’t see much of the royal family for the next 6 weeks, young missionary couple from u.s. among 3 killed by gunmen in haiti’s capital, family says, egypt agrees to send u.n. aid trucks through israeli crossing to gaza — but impact is unclear, israeli airstrike kills dozens of palestinians in rafah, medics say, uvalde families sue meta, call of duty maker on second anniversary of school massacre, nicki minaj detained at amsterdam airport for allegedly carrying drugs, two-time pga tour winner grayson murray dies at age 30, a day after withdrawing from colonial, pga tour says, $900,000 settlement after ‘psychological torture’ spurs false murder confession, tcp port number 21 and how it works with ftp.

TCP Port Number 21 is the standardized port number used by FTP (File Transfer Protocol) for managing communication between FTP clients and servers. It’s a part of the Transmission Control Protocol (TCP), which is responsible for regulating and managing data transfer between devices on the internet.

FTP is one of the oldest and most common ways of transferring files between devices on a network, whether it be between servers or between a server and an end-user’s computer. FTP allows users to create, manage, and delete files, as well as move them from one device to another, providing the user with an unparalleled level of control and flexibility over their data.

When a user initiates an FTP session, their computer first connects to the server at the TCP port 21. Any traffic sent over this port will typically be used for FTP control commands, including messages relating to login credentials, directory changes, and file transfers. If an FTP client wants to transfer a file to the server, it will use port 21 to inform the server that it wishes to transfer a file, along with information about the file’s name and its intended destination.

However, while the FTP control protocol relies on port 21, it’s important to note that file transfers themselves are typically handled through a separate data connection. FTP utilizes two ports: the control port (usually port 21) and the data port (sometimes called the “passive port” or “active port”), with the data port typically being a randomly assigned port number.

When a file transfer request is initiated, the server responds with a port number on which the data connection can be established, and the client typically proceeds to connect to that port to begin the file transfer itself. This process of opening and using a separate data connection is called “passive mode,” and it’s the most commonly used mode in modern FTP implementations.

In summary, TCP Port Number 21 plays a vital role in FTP communication, transmitting commands and control messages between the client and server. However, it’s just one part of a larger picture, and file transfers themselves are typically handled through separate data connections on dynamically assigned port numbers, allowing for maximum flexibility and bandwidth efficiency.

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TCP/IP Ports and Sockets Explained

The IP address identifies the device e.g. computer.

However an IP address alone is not sufficient for running network applications, as a computer can run multiple applications and/or services .

Just as the IP address identifies the computer, The network port identifies the application or service running on the computer.

The use of ports allow computers/devices to run multiple services/applications .

The diagram below shows a computer to computer connection and identifies the IP addresses and ports.

If you use a house or apartment block analogy the IP address corresponds to the street address.

All of the apartments share the same street address.

However each apartment also has an apartment number which corresponds to the Port number.

Port Number Ranges and Well Known Ports

A port number uses 16 bits and so can therefore have a value from 0 to 65535 decimal

Port numbers are divided into ranges as follows:

Port numbers 0-1023 – Well known ports. These are allocated to server services by the Internet Assigned Numbers Authority (IANA). e.g Web servers normally use port 80 and SMTP servers use port 25 (see diagram above).

Ports 1024-49151- Registered Port -These can be registered for services with the IANA and should be treated as semi-reserved. User written programs should not use these ports.

Ports 49152-65535 – These are used by client programs and you are free to use these in client programs. When a Web browser connects to a web server the browser will allocate itself a port in this range. Also known as ephemeral ports .

TCP Sockets

A connection between two computers uses a socket.

A socket is the combination of IP address plus port

Imagine sitting on your PC at home, and you have two browser windows open.

One looking at the Google website, and the other at the Yahoo website.

The connection to Google would be:

Your PC – IP1 +port 60200 ——– Google IP2 +port 80 (standard port)

The combination IP1+60200 = the socket on the client computer and IP2 + port 80 = destination socket on the Google server.

The connection to Yahoo would be:

your PC – IP1 +port 60401 ——–Yahoo IP3 +port 80 (standard port)

The combination IP1+60401 = the socket on the client computer and IP3 + port 80 = destination socket on the Yahoo server.

Notes : IP1 is the IP address of your PC. Client port numbers are dynamically assigned, and can be reused once the session is closed.

TCP and UDP -The Transport Layer

Note : You may find reading the article on the TCP/IP protocol suite useful to understand the following

IP addresses are implemented at the networking layer which is the IP layer.

Ports are implemented at the transport layer as part of the TCP or UDP header as shown in the schematic below:

The TCP/IP protocol supports two types of port- TCP Port and UDP Port .

TCP – is for connection orientated applications. It has built in error checking and will re transmit missing packets.

UDP – is for connection less applications. It has no has built in error checking and will not re transmit missing packets.

Applications are designed to use either the UDP or TCP transport layer protocol depending on the type of connection they require.

For example a web server normally uses TCP port 80 .

It can use any port, but the web server application is designed to use a TCP connection. See TCP vs UDP

Here is a very good video that explains ports and sockets really well

Checking For Open Ports

Windows and Linux systems have a utility called netstat which will give you a list of open ports on your computer.

These articles show you how to use netstat on windows and on linux .

You can check the port status of remote machines using a port scanner line nmap .

You can install NMAP on windows,Linux and Apple. It can be used with a graphical user interface of as a command line tool.

Here is a useful article on using NMAP from the command line .

Here is a good video on using Nmap and also covers TCP/IP connection procedures which is useful for understanding ports.

References and resources:

TCP and UDP basics -Connecting to a website- This is for programmers but there is no coding just an explanation of ports and sockets.

Connection states – if you are wondering what established and listening and the other state descriptions mean. here is a good state diagram that it refers to.

Online port tester Collection of tools for port scanning and web server testing.

Related Articles:

• TCP/IP protocol suite explained
• Port Forwarding Explained
• IPv4 Basics

70 comments

I created an inbound UDP port (10512); but I am not able to see this port. I also tried creating other ports in the noted range with out any success. Registered Ports: 1024 through 49151 portqry —-> UDP port 10512 (unknown service): NOT LISTENING Thanks for any clarification

Have you tried writing a program to send/receive data on that port.What utility are you using to view the ports. Rgds

Sorry, no time to research and develop a program. it would nice. I am trying to use online tools. I think that I just learned that portqry works great for TCP. I am trying to use iperf3; however not enough hands on as of yet. I see that iperf3 created inbound rule TCP and UDP. I deleted the TCP. I need more flying hours. iperf3 -s -p 10512 ———————————————————– Server listening on 10512 ———————————————————– I am also trying to use netstat to see if the port is listening; however no progress on that end. netstat -ab

netsh firewall show state netsh will show UDP port on client computer with Win 11 PRO but not on the server 2019.

thanks for any input

client side >iperf3 -c 10.241.71.38 -u -p 10512 -b 10M

I’ve decided to try to mess around with port forwarding as a means to try to get me and my friend who live in the same town and use the same internet provider (Spectrum) to be able to connect to each other in games that do not have dedicated servers. Spectrum’s peer-to-peer is absolute trash, and we can never connect to each other playing games like Risk of Rain 2, Elden Ring, etc. I’m trying to find a port that would help us overcome the connection issues. Any advice?

I’m not a gamer and so I have never experienced these issues. However games have their own ports have you checked on the required ports for these games? Rgds Steve

Hi Steve, I have a requirement. We have a web application which is connected to a mobile/Android POS device. This web application connects via TCPIP. As of today, we have the connections that are initiated from the device. the URL and port # of the web server is configured in the device and the connection is initiated from the device. Web application will respond to a request from the device. We now want to initiate the request from the server. Can we add another port # for this new communication? Similarly, there is a 3rd communication that happens from the device on timed intervals. For this, we want to use a 3rd port. Is this a possible solution for this? Happy to discuss this separately too.

I assume that you are talking about a web server. A web server cannot start a connection. Rgds Steve

Respected Sir Thank you so much for this informative article. I am a first year IT student. Sir , if I visit any particular website for 15 minutes and visit various sections of this website (feedback/ contact us / about us etc) in such case, does my visit to various sections is considered as a single connection/ single session or they are considered as multiple connections / multiple sessions to this website? Also what is the role of session ID in TCP IP communication along with port and socket Thank you Sir Bhavesh

It is a single TCP/IP connection. If you close the tab and then revisit by typing in the url then you will get a new connection.

Just out of curiosity, if the user visits different pages on the website, won’t these be over a new TCP connection every time unless a long-lived HTTP is used?

No they will be a single connection just a different get command. HTTP now hold the connection open by default until you close the browser tab. Rgds Steve

Thanks Steve for making it vividly simple.

I have a problem with an application that uses fixed source ports in the communication with the server. If the communication ends for some reason the clients tries to put the communication up again using the same source port. The problem is that the server have not gotten a fin packet that takes down the communication and it still listens for the communication from the client in a ESTABLISHED status if you run netstat -a on the server. If the client had not used fixed ports I would think that the communication would reconnect with a new session because the client had used “+1” on its source port and the server would connect the communication with a new socket.

Is there a “best practice” rfc that explains why it is not a good idea to use fixed ports?

Not that I am aware.

Wonderful, I’ve sent it over email along with some info It runs on Ubuntu Thank you for your time on this and God bless Al

I have a software which creates 4 sockets with apparently random numbers (the person who developed left no documentation)

However, the client which connects to it only sends over port 9091

Is there a way to interconnect those random number sockets and port 9091 so the client is able to connect to the software?

Thanks in advance and God bless

Hi It sounds like the software is supposed to be a server which usually has fixed ports. What does the software do?

It receives video data, connects to a MariaDB server, and serves as an API to it, receiving calls from a mobile app and sending customer data back

I wonder if the reason why it opens 4 sockets is to receive and send video data and receive and send customer data

Either way, the problem is that it creates sockets of random numbers instead of a 9091 port which is what the android app uses

Below its log, hope that sheds some light and thanks

[0121/06/01 12:55:01][0000-00000001] SDSS int server v1.2.0 – b6 (01/03/2021) run up at Thu Jul 1 12:55:01 2021 [0121/06/01 12:55:01][0000-00000002] debug level set to 99 [0121/06/01 12:55:01][0000-00000003] args[ ./dvis -d99 ] [0121/06/01 12:55:01][0000-00000004] startup info follows: [0121/06/01 12:55:01][0000-00000005] stdin handle 0 [0121/06/01 12:55:01][0000-00000006] openSQL( 0x5f687580 ) [0121/06/01 12:55:01][0000-00000007] openSQL: Connection successful to ‘127.0.0.1’ as ‘sa’ [0121/06/01 12:55:01][0000-00000008] hostname being used is ‘stipra.com’ [0121/06/01 12:55:01][0000-00000009] get_ipaddress() [0121/06/01 12:55:01][0000-00000010] lo IP Address 127.0.0.1 [0121/06/01 12:55:01][0000-00000011] wlo1 IP Address 192.168.1.142 [0121/06/01 12:55:01][0000-00000012] lo IP Address ::1 [0121/06/01 12:55:01][0000-00000013] wlo1 IP Address fe80::d6a7:186d:aa86:5311 [0121/06/01 12:55:01][0000-00000014] get_ipaddress: returning an IP4 address of 192.168.1.142 [0121/06/01 12:55:01][0000-00000015] Running on server stipra.com IP address 192.168.1.142 [0121/06/01 12:55:01][0000-00000016] setsockopt returned 0, errno 11 [0121/06/01 12:55:01][0000-00000017] sockets created [0121/06/01 12:55:01][0000-00000018] 63420 [0121/06/01 12:55:01][0000-00000019] 29616 [0121/06/01 12:55:01][0000-00000020] 6052 [0121/06/01 12:55:01][0000-00000021] 43464 [0121/06/01 12:55:01][0000-00000022] wait_for_cmd(0x1) [0121/06/01 12:55:01][0000-00000023] stdin(0) [0121/06/01 12:55:01][0000-00000024] recv_d( 0, 0x7f90fdd4e010, 8 ) [0121/06/01 12:56:01][0000-00000025] recv_d: Select timeout, retrying [0121/06/01 12:57:01][0000-00000026] recv_d: Select timeout, retrying [0121/06/01 12:58:01][0000-00000027] recv_d: Select timeout, retrying [0121/06/01 12:59:01][0000-00000028] recv_d: Select timeout, retrying [0121/06/01 13:00:01][0000-00000029] recv_d: Select timeout, retrying [0121/06/01 13:01:01][0000-00000030] recv_d: Select timeout, retrying [0121/06/01 13:02:01][0000-00000031] recv_d: Select timeout, retrying [0121/06/01 13:03:01][0000-00000032] recv_d: Select timeout, retrying [0121/06/01 13:04:01][0000-00000033] recv_d: Select timeout, retrying [0121/06/01 13:05:01][0000-00000034] recv_d: Select timeout, retrying [0121/06/01 13:06:01][0000-00000035] recv_d: Select timeout, retrying [0121/06/01 13:07:01][0000-00000036] recv_d: Select timeout, retrying [0121/06/01 13:08:01][0000-00000037] recv_d: Select timeout, retrying [0121/06/01 13:09:01][0000-00000038] recv_d: Select timeout, retrying [0121/06/01 13:10:01][0000-00000039] recv_d: Select timeout, retrying [0121/06/01 13:10:01][0000-00000040] wait_for_cmd: Initial receive is not 8 bytes [0121/06/01 13:10:01][0000-00000041] pipe broken exiting

Sorry don’t know, It looks like it is creating client connections but not sure what to. When you say it receives video data I assume that that is coming in on a port. The database would need another. The mobile app is used to view the video I assume. Is any part of it working. Where is the mobile App located(internet or same network). Is this a standard kit or is it put together by yourself? Rgds Steve

The software creates 4 sockets with random port numbers but none of them are the port 9091 which the APP uses. The mobile App is on the internet.

The software connects to a tunnel connection 10.8.0.0, which leads me to believe it requires the creation of some kind of tunnel to capture anything received from the internet on port 9091 from 192.168.1.142 and forward it to those 4 sockets through some kind of dynamic port forwarding thing or something like that

I tried to use ssh -D 192.168.1.142:9091 -N -f [email protected] and I am able to telnet 192.168.1.142 and connect the app, but no data seems to go or come back 🙁

The software connects to the database, and that’s actually the only thing it is doing well

Does it have any setup instructions. Is it off the shelf software and does it have a website that I can take a look at. Rgds Steve

It is a bespoke software made by a person who left the company and never left any documentation. It is developed in C++ 32 bits I can send it to your email which I believe is [email protected] as it is rather small, along with how to run itm (the little I know at least)

That email will work is it for windows or linux?

Hi, I have a question, is it possible for me to run 2 applications and connect to different ip but using same port number (example 6000) ?

Yes you are doing that when you connect to two different websites as they both use port 80 rgds steve

So I have a question. Let’s say there is a webserver A which hosts a website and that server A has the port 443 open and let’s say I have written a code as part of a webpage on that website and that code connects to a remote server B to get some data. Can server A somehow restrict me and only allow connections to the port 443 on the remote server B and not allow me to connect me to any other port on remote server B? Have you seen such a restriction before and if yes then what would be the reason behind such a restriction? Thank you

Not quite sure exactly what restriction you mean but you can restrict on destination port and ip and source port and IP if that helps rgds steve

Hi Steve, So here is the scenario. The webserver A has the port 443 open for any incoming requests. The webserver A hosts a website and one of the pages of that website has C# code which makes API calls to a remote server B. I was told by the network admin of Webserver A that the C# API call should be made only to the port 443 of the remote server B. Currently the remote server B has port 7093 open and it’s listening to any API requests on that port. So my questions are:- 1. Is it possible for the network admin to disallow API calls to ports other than 443? 2. What could be the reason for such a restriction? After all, how can restricting a destination port give you any sort of advantage? Port is just a number on which the server listens. Please help. Thank you

Yes you can filter incoming traffic on port, ip address and protocol even on basic firewalls. Restricting ports is for security reasons Rgds Steve

Minor formatting issue: “{outline]Each end of the connection will have a socket.{/outline]”

Tks for pointing that out. Rgds Steve

Very well explained, thanks a lot!

Steve, this was very well explained, thank you.

Thank you very much! Realy clear explanation.

I want to read a data from a machine which supports open protocol if the machine is in network and if I know IP address and port number(socket) how can I read a data from it(I know it send and receive data in packet format )

Hi not sure what you mean by supports open protocol. Rgds Steve

Thank you, Steve! Is it possible with TCP/IP sockets to send requests to one IP:PORT and listen for responses on a different IP:PORT. E.g. we want to send to a load balancer IP but listen for response on localhost.

Hi Not quite sure of what you mean exactly but load balancing is quite common. This might help https://www.citrix.com/glossary/load-balancing.html

Question: When a program on your computer sends or receives data over the Internet it sends that data to an ip address and a specific port on the remote computer. How does my computer know what port a specific application is working on another computer to populate the TCP Header?

When Machine A connects to machine B. The source ip and port are contained in the connection packet as well as the destination port and IP address. The IP packet contains the ip addresses and the tcp layer contains the port numbers see https://en.wikipedia.org/wiki/IPv4 https://en.wikipedia.org/wiki/Transmission_Control_Protocol

Hi Steve, Thanks for the tutorial can you please help me with the following issue I have multiple devices connected to the same network and I want to transfer data across them, how can I transmit the data the IP of some devices changes after a particular time I can keep the port number constant but the devices don’t know each others IP address and also I don’t want to use UDP because it is not reliable

Hi You need to use DNS.Because the IP changes you need dynamic DNS. Most devices have MDNS enabled. See this article on my other site https://stevessmarthomeguide.com/name-resolution-and-dns-on-home-networks/ To seen if mdns is working try ping computer_name.local However the easiest solution is to give them static IP addresses. Rgds Steve

Great site. I have a quick question. If I receive a UDP datagram using recvmsg(), will the msghdr structure be filled out with the sender’s IP and port (in the msg_name field, which is a sockaddr struct)?

Many thanks.

Hi Haven’t programmed c with UDP but according to IBM then yes for ip address but doesn’t mention the port. https://www.ibm.com/support/knowledgecenter/en/SSLTBW_2.1.0/com.ibm.zos.v2r1.hala001/rcvm.htm rgds steve

hi ,I have some questions When using TCP protocol, the client must use in its message the IP address and Port number of the server. And it must also include its own IP address and port number. why?

4- When using UDP protocol, the client is required to use in its message the IP address and Port number of the server. But it is not required to include its own IP address and port number.why?

TCP is a connection orientated protocol and so the destination device needs to know who to send a reply to. UDP is connectionless and so doesn’t require a response and hence the source IP address is optional. Rgds Steve

really very useful..thanks for your explanation

Can Server and client share the port number, eg : Server is listening at port num : 51001 and client also listens on the same port num : 510001 .

Can you pls explain this

Yes providing they are on different hardware. A port is simply a door into the machine the numbers themselves aren’t really important except for the conventions already adopted and standardised. Machines use 16bits for the port numbers hence the limitation of 64,000.

16 bits = 1+2+4+8+16+32+64+128+256+512+1024+2048+4096+8192+16384+32768 = 65535

Good job Steve. I have a question, and it goes like this: if i have 2 browsers from my PC connecting to the same service, for example both browsers are connecting to google.com, does that mean that the two browsers from my computer are connecting to the same socket in the google server? Meaning can more than one socket connect to a socket at the same time?

Yes they use the same IP and port on the Google server but different ports on the client. rgds steve

Hi, Thanks for this information sharing. It is very well explained. I have following doubt, What I understand is TCP protocol takes care of data transmission error that duplication of packets or packet in true form delivered to other end. This is not done in UDP protocol. But when I see the Schematic of TCP, UDP & IP in your article I do not find any block for error checking in TCP where as UDP has checksum. Could you please clear my doubt.

The TCP packet also has a checksum which isn’t shown in my schematic you can see the full structure on wiki https://en.wikipedia.org/wiki/Transmission_Control_Protocol However it is the ack and nack messages that are responsible or making sure all of the data is received. Rgds Steve

In above example, google application/service and yahoo application/service both uses same port number i.e:80. Then there should be ambiguity that is to which application/service it should refer to either google or yahoo ;How it knows that it is google or yahoo as both has same port number? Answer will help me alot.

Google and Yaoo have different IP addresses. When you connect to google you use Google_IP +port 80. When you connect to Yahoo you connect to Yahoo_IP + port 80. Does that make sense? rgds steve

The IP is the who and the Port is part of the how.

The IP address of google and yahoo is different. say for google 172.13.73.130 and for yahoo 172.23.73.128 so even accessing the same port the two sockets will be totally different and hence different connections.

using the real world analogy two rooms of two different apartments may have the same room number and hence two server system may have same port number as well.

The port number 80 is the open port of server.here Google server had an open port (80) also Yahoo had an open port (80).

Both Google and Yahoo had different IP addresses.

If I want to connect Google server,I will open a new port,for example I will open port 5000, at the same time I will open another port 5002 to connect with Yahoo server.

My IP + 5000 — connects — Google IP + 80

My IP + 5002 — connects — Yahoo IP + 80

Great work!

Good Job!! Well Explained

Hi! keep up the good work. I have few doubts though, hope you can clear them: 1. Can you tell if a server uses a single port 80 on all of its connections to clients? Or is it used only by the Welcoming socket? Can port 80 handle multiple connections simultaneously?

A port (e.g port 80) can handle multiple connections each connection is a socket and will have a different source IP address and port number.

No… a session needs to be established at said layer. A is lessening on port 443 (SSL) for incoming packets and firewall infront is in addition to alllowing 443 to A also policing 25, 80 etc Whatever….

Excellent explanation. Thankyou!

very good information

The way you explain ed it, now it’s very easy understand the whole thing thanks alot sir .

Complete details about the TCP / IP ports and the sockets. in this article .The infographic is so good that anybody can understand at a glance. I request the author to post more articles on networking.

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FTP and FTPS ports: an overview

by Kyle Lapaglia | Mar 5, 2024 | FTP Basics , Informational

Transferring files securely requires a comprehensive understanding of the connections, ports, and IP addresses utilized by FTP (File Transfer Protocol) and FTPS (FTP over TLS/SSL). The FTP protocol and its secure version, FTPS, operate over TCP (Transmission Control Protocol). This guide provides an in-depth look at these protocols’ commonly used control and data ports, their differences, and firewall considerations.

Understanding FTPS and FTP Port Connections

FTP and FTPS connections primarily consist of two types: the control connection and the data connection . The client initializes these connections, which  are vital for data transfer.

The Control Connection

The control connection is the initial link, also known as the control channel, established when a client connects to an FTP server using the server’s IP address. Its purpose is to grant clients access to the server and enable them to send commands (FTP commands) and receive server responses.

• TCP Port 21 is the default control connection port for FTP, often called FTP port 21.
• Port 990 is the default control connection port for FTPS.

These ports are where the server side initiates an FTP session. However, these default ports are not set in stone. As a server administrator, you are free to adjust the listener to any open port on the system. But if you’re running a software-based firewall, ensure your router doesn’t block the chosen port. If blocked, your FTP or FTPS server will be invisible and inaccessible to users.

The Data Connection

The data connection is the pathway through which the FTP server exchanges file listings (like directory listings in ASCII format) and transfers files. This is where the FTP client instructs the server to send a file listing or transfer a file.

• Port 20 is the most common data connection port for FTP.
• Port 989 is the default data connection port for FTPS.

Understanding and managing data connections can be challenging for server administrators, as this is where most complications arise. Two modes, active FTP and passive FTP (PASV), dictate how the client and server establish these connections.

In active mode, the client opens a random port, sends the FTP server the information via a PORT command, and waits for the server to initiate the connection. However, active FTP often faces issues with firewalls blocking incoming connections.

In passive mode FTP, after authentication, the server opens a random port, sends this port number back to the client via the PASV command, and waits for the client to initiate the data connection. Passive mode is generally more firewall-friendly, as the connections are all initiated from the client side.

FTP vs. FTPS Port Connection Usage – Implicit vs. Explicit

FTP and FTPS use different ports, and these choices dictate the security behavior of clients and servers. FTPS can operate in two modes: Explicit FTPS and Implicit FTPS.

In Implicit FTPS, connections established via Port 990 will automatically perform an SSL/TLS (Secure Sockets Layer/Transport Layer Security) handshake, implying a secure connection.

On the other hand, in Explicit FTPS, connections established via Port 21 need an additional AUTH command to enable security, i.e., to start the SSL/TLS session. The security features of FTPS protect your data from being sent as plain text or unencrypted over the network protocol.

Firewall Considerations

When using FTPS, specific firewall ports must be open to ensure smooth file transfers. The command and data channels must be open on the client and server. Understanding the range of ports to open can be complex, requiring careful configuration of your port range and endpoints.

In some cases, you may also need to facilitate FTP port forwarding. Hence the need for intelligent FTPS servers like Cerberus FTP Server.

Understanding FTP and FTPS ports is crucial for secure file transfers. The choice between FTP and FTPS and the preferred port numbers often depends on your specific security needs and system configurations.

Apps and command-line tools help implement and manage these protocols, ensuring permissions are correctly set and public key authentication is used when needed. Using a secure, turnkey   file transfer solution like Cerberus will make this much easier on you with its robust set of management features. Feel free to download a trial  to experience secure file transfer like never before. Your first 25 days are free.

Frequently Asked Questions

What port does ftp use.

FTP uses port 21 for the command port and port 20 for the data port. In addition to ports 21 and 20, FTP can be configured to use a range of passive ports for data transfer, typically between 1024 and 65535.

What port does FTPS use?

When operating in explicit FTPS mode, FTPS typically uses port 990 for the command port and port 989 for the data port. However, implicit FTPS mode typically uses port 990 for both command and data connections.

Is FTPS port 21 or 990?

FTPS typically uses port 990 for control connections and port 989 for data connections under implicit security. However, FTPS can also use port 21 when operating under explicit security.

Learn more about the   difference between FTPS vs HTTPS for secure file transfers.

Does FTPS use port 22?

No, FTPS does not use port 22. This port is primarily associated with SFTP (SSH File Transfer Protocol, part of Secure Shell).

Read more about the differences in SCP vs SFTP on our blog.

What is the difference between port 21 and 990?

Port 21 is FTP’s default control connection port, while port 990 is the same for FTPS. The main difference lies in their expected security behavior. Port 990 implies implicit security, whereas port 21 can be used with explicit security.

Read our blog post on how secure is FTP to learn more about these differences.

What port is FTP and FTPS?

FTP uses port 21 for control connections and port 20 for data connections. FTPS uses port 990 for control connections and port 989 for data connections under implicit security. When using explicit security, FTPS can also use port 21.

Learn more about securing an FTP or SFTP server on our blog.

Remember, knowledge about these protocols, ports and RFC 959 (the original FTP standard) can help you secure and manage file transfers effectively.

Download a risk-free 25 day free trial of Cerberus FTP Server for Secure File Transfers today which supports for FTP and FTPS, along with many other protocols. Download now

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TCP/IP Port Numbers

In computer networking, a port is a communications socket/endpoint in a computer’s operating system. A port is associated with an IP address of the host , as well as the type of protocol used for communication. A port in conjunction with the IP address is known as a socket or endpoint.

The Transport Layer protocols, such as the Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP), are the primary users of TCP/IP ports. The sockets created by each host that is used in the communication session are known as socket pairs or endpoint pairs.

These sockets or endpoints allow hosts to create more than one session to allow for multiple communication channels to be active at any given time between various hosts.

Port Ranges

There are clearly defined port numbers for every popular or well-known TCP/IP application. A port number is a 16-bit value between 0 and 65,535. Within this range of ports, some port numbers are established for specific services , some are reserved for certain applications , and others are available for temporary use by applications .

Web servers, for example, use port number 80 because client browsers are developed to connect to web servers using the HTTP protocol on port 80 . Port numbers from 0 to 1023 are called well-known ports and are reserved for specific TCP/IP application services. The range of port numbers from 1024 to 49151 are the Registered, also known as User ports .

These ports are assigned by IANA for specific services upon application by a requesting entity. The range from 49152 to 65535 are above the registered ports. This range is reserved for the Dynamic and/or Private ports that cannot be registered with IANA. This range is used for custom or temporary purposes and for automatic allocation of ephemeral ports.

Well-Known Ports

The port numbers in the range from 0 to 1023 are the well-known, also known as System ports . They are used by system processes that provide widely-used types of network services. Examples of some of the most common well-known ports are:

If we take the example of a host system trying to access a web server, the source system will craft a packet to send to the destination IP address on port 80 . Since port 80 is a well-known port for HTTP, in most cases, if you wanted to host a web server, you would not change the web server’s default port.

If you did configure the web server to run on a different port , you would have to communicate this information to your users since the client applications that they are using (web browsers) are expecting to connect to the web server on port 80.

In this scenario, the client that established this connection with the web server will use a port in the Private/Dynamic range. For example, the source IP:source port may be 192.168.1.1:50125 for the client. When the web server sends back a packet to the client it will send it back to this IP and port (socket/endpoint).

For more information about port numbers or to get a complete listing of reserved and registered ports, please visit the Service Name and Transport Protocol Port Number Registry .

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Various TCP and UDP ports

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Transportation layer conventions utilize the idea of ports and multiplexing/demultiplexing to convey information to individual services listening on network nodes. These ports are spoken to by a solitary 16-bit number, implying that they can constitute a range of numbers 0-65535. This range has been separated by the IANA (Internet Assigned Numbers Authority) into several different segments : 

• Port 0 is not used for internet/network traffic, but it’s sometimes utilized in communications going down between different programs on identical computers.
• Ports 1-1023 are alluded to as system ports. These ports speak to official ports for most notable system administrations and many common network services. HTTP usually communicates at port 80, while FTP at port 21. In most working frameworks/OS, administrative-level access is expected to begin a program that tunes in on a system port.
• Ports 1024-49151 are known as registered ports. These ports are utilized for a bunch of different network functions and services that probably won’t be very frequently used as ones that are on system ports. A genuine case of a registered port is 3306, which is a port that numerous databases tune in on. Registered ports are in some cases formally enlisted and recognized by IANA, yet this is not certain to always be the case. On most operating systems, any client of any entry-level can run a program tuning in on a Registered port.
• Lastly, there is a range of ports from port 49152-65535. These are known as Ephemeral ports (or private ports). Ephemeral ports can’t be enlisted with IANA and are commonly utilized for setting up outbound network traffic and connections. All TCP traffic needs one destination port and one source port to establish a connection. At the point when a client needs to speak with a server, the client will be appointed an ephemeral port to be utilized for simply that one connection, while the server tunes in on a static system framework or registered port.

Not every single working operating system follows ephemeral port proposals of IANA. The ephemeral ports utilized for outbound associations comprise ports 49152 through 65535. Yet, this range of ports can change as per the operating system and framework you’re dealing with. Quite a few times registered ports are utilized, however, no modern operating system will ever utilize a system port for outbound connections. 

Here are some commonly used ports for reference:  

The transport layer has a lot of ports to accommodate various application protocols simultaneously. The ports are dictated by the type of transport layer connectivity.  Also, remember that there are lots of protocols in the application layer but not all of them require port numbers (like TCP or UDP). Internet Control Message Protocol (ICMP) is one of them. 

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About TCP/UDP Ports

• Port 0 to 1023: These TCP/UDP port numbers are considered as well-known ports. These ports are assigned to specific server sevice by the Internet Assigned Numbers Authority (IANA). For example, port 80 is used by web servers.
• Port 1024 to 49151: These are ports that an organization, such as application developers, can register with IAMA to be used for a particular service. These should be treated as semi-reserved.
• Port 49152 to 65535: These are port numbers used by client programs, such as a web browser. When you visit a web site, your web browser will assign that session a port number from within this range. As an application developer, you are free to use any of these ports.
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How to check open tcp/ip ports in windows.

Everything that connects to the Internet uses ports in one way or another,

Hannah Stryker / How-To Geek

Read update, quick links, how do ports work, use built-in tools to see what is listening on a port, use nirsoft currports to view what is listening on a port, key takeaways.

• Run the command "netstat -ab" in an elevated Command Prompt, PowerShell, or Terminal window to see a list of applications and their associated ports. This works in Windows 11 too.
• Checking open ports can be done using built-in tools like Command Prompt or PowerShell, which list active ports and the associated process names or identifiers.
• The freeware application CurrPorts by NirSoft provides an easier way to view what is listening on a port, displaying detailed information about the process and allowing for better management of ports.

Whenever an application wants to make itself accessible over the network, it claims a TCP/IP port, which means that port can't be used by anything else. So how do you check open ports to see what application is already using it?

We've tested this process and confirmed that all of the steps are up-to-date, and that they all work in Windows 11, too.

An IP address specifies a computer — or other network device — on a network. When one device sends traffic to another, the IP address is used to route that traffic to the appropriate place. Once the traffic reaches the right place, the device needs to know which app or service to send the traffic on to. That's where ports come in.

If the IP address is akin to a street address on a piece of mail, the port is something like the name of the person at that residence who gets the mail. For the most part, you don't need to worry about ports. But once in a while, you might encounter an app that's set to listen for traffic on the same port that another app already has in use. In that case, you'll need to identify the app that already has that port in use.

There are a number of ways to tell what application has a port locked, but we're going to walk you through a couple of built-in ways that use the Command Prompt , PowerShell , or the Terminal , and then show you a great freeware application that makes it even easier. All these methods should work no matter which version of Windows you use.

We've got two commands to show you. The first lists active ports along with the name of the process that's using them. Most of the time, that command will work fine. Sometimes, though, the process name won't help you identify what app or service actually has a port tied up. For those times, you'll need to list active ports along with their process identifier numbers and then look those processes up in Task Manager.

Option One: View Port Use Along with Process Names

First, you'll need to open the Command Prompt in administrator mode. Hit Start, and then type "command" into the search box. When you see "Command Prompt" appear in the results, right-click it and choose "Run as administrator," or click "Run as Administrator" on the right.

You can also use PowerShell or Terminal for this.

At the Command Prompt, type the following text and then hit Enter:

netstat -ab

After you hit Enter, the results may take a minute or two to fully display, so be patient. Scroll through the list to find the port (which is listed after the colon to the right of the local IP address), and you'll see the process name listed under that line. If you'd like to make things a little easier, remember that you can also pipe the results of the command to a text file . You could then just search the text file for the port number you're after.

Here, for example, you can see that port 49902 is tied up by a process named picpick.exe. PicPick is an image editor on our system, so we can assume the port is actually tied up by the process that regularly checks for updates to the app.

Option Two: View Port Use Along with Process Identifiers

If the name of the process for the port number you're looking up makes it difficult to tell what the related app is, you can try a version of the command that shows process identifiers (PIDs) rather than names. Type the following text at the Command Prompt, and then hit Enter:

netstat -aon

The column at the far right lists PIDs, so just find the one that's bound to the port that you're trying to troubleshoot.

Next, open up Task Manager by right-clicking any open space on your taskbar and choosing " Task Manager ." You can also hit Ctrl+Shift+Esc.

If you're using Windows 8, 10, or 11 switch to the "Details" tab in Task Manager.

In older versions of Windows, you'll see this information on the "Processes" tab. Sort the list of process by the "PID" column and find the PID associated with the port you're investigating. You might be able to tell more about what app or service has the port tied up by looking at the "Description" column.

If not, right-click the process and choose "Open file location." The location of the file will likely give you clues as to what app is involved.

When Once you're there, you can use the End Process, Open File Location, or Go to Service(s) options to control the process or stop it.

If you aren't really the Command Prompt type — or you'd rather just use a simple utility to do all this in one step — we recommend the excellent freeware CurrPorts utility by NirSoft. Go ahead and download the tool. Just make sure you get the right version (the regular version is for 32-bit Windows and the x64 version is for 64-bit Windows). It's a portable app , so you won't need to install it. Just unzip the download folder and run executable.

In the CurrPorts window, sort by the "Local Port" column, find the port you're investigating, and you can see everything — the process name, PID, port, the full path to the process, and so on.

To make it even easier, double-click on any process to see every single detail in one window.

When you've determined what app or service has the port you're investigating tied up, it's up to you how to handle it. If it's an app, you may have the option to specify a different port number. If it's a service — or you don't have the option to specify a different port number — you'll likely have to stop the service or remove the app.

What Are TCP Ports and Why Are They Important?

Quick Definition of TCP:  Transmission Control Protocol  (TCP) is a global communication standard that devices use to reliably transmit data. TCP is defined by being connection-oriented, which means that both the client and the server have to be established before the data gets sent. This means the data is reliable, ordered and error-checked in transit. It is one of the main protocols of the Internet protocol suite — and the entire suite is often referred to as TCP/IP.

Quick Definition of TCP Ports:  A "port" is a logical distinction in computer networking. Ports are numbered and used as global standards to identify specific processes or types of network services.

Much like before shipping something to a foreign country, you'd agree where you'd be shipping out of and where you'd have it arriving, TCP ports allow for standardized communication between devices. One device can receive information for many different processes and services, and which port the information flows on helps to keep it organized.

An Overview of TCP Ports [VIDEO]

In this video, Tim Warner covers what TCP ports are as well as where and how TCP port numbers are used. He further describes how you can use the netstat command-line tool to find port use information. He also explains how, on Windows computers, you can use a free GUI-based tool called TCPView to better view and work with this information.

How Do TCP and TCP Ports Work?

Transmission Control Protocol is a key component of the TCP/IP protocol stack . TCP is a connection-oriented protocol that requires a connection or a circuit between the source sending computer and the destination one. TCP is one of the two main ways to transmit data in a TCP/IP network. UDP, which is a best-effort connectionless protocol, is the other one.

For devices to communicate via TCP, they use TCP ports. Generally, a TCP port represents an application or service-specific endpoint identifier.

Think of opening a web browser. When you type in "CBTNuggets.com", your browser translates that to "http://www.cbtnuggets.com". And with that, you're specifying the hypertext transfer protocol — and hopefully, you get the page without issue. That happens because CBT Nuggets' web server aka its HTTP server is listening for incoming connections on a particular port address.

The well-known port for HTTP is 80. By contrast, you might download some software from ftp.microsoft.com, their FTP server is going to be listening on the well-known Port 23. And so forth. Protip: If you're planning to earn an IT certification exam, you may need to have many of the most common TCP ports memorized.

How Many TCP Ports Are There?

A TCP port is a 16-bit, unsigned value, so there's a finite number of TCP ports available in the world. Specifically, there are 65,535 available TCP ports.

You've probably heard that the world is moving from IPv4 to IPv6  due to address depletion. It's also entirely likely that the time will come when we'll have to expand the port range to accommodate additional services.

That said, the first 1,024 TCP ports are called well-known port numbers, and they're agreed upon among technology vendors. So if you and I were to go into business and sell a really nice FTP client software, we'd agree to work with the standard, well-known FTP port numbers.

How Do Sockets Work with TCP Connections?

A socket allows for a connection to another system that's already running some TCP server software. A socket takes a combination of an IP address and a port number. That means a single host can host multiple instances of the same service by using different port numbers.

For instance, we can set up a web server that has "Site 1" listening on the default port of 80 and another web server. That is to say another website on the same server with the same IP address, "Site 2", but listening on Port 8080.

Where and How Do We Use Port Numbers?

One place is during server application configuration. Enterprise apps like Oracle , SQL, SharePoint, all require you to set up services on discrete port numbers. Which is also why working with your network administrator to allow for that traffic to flow on those port IDs are important. Firewalls monitor ports to keep systems secure.

Service addressing is another way to use port numbers. Once we install our enterprise application, we advertise the service using, generally speaking, a hostname and the port number. For example, "http://cbtnuggets:1988". We wouldn't have to do that if it were a well-known port. If it's well known, we can leave it off.

We use port numbers for troubleshooting purposes. Specifically, we can troubleshoot malware and identify rogue processes.

Firewall configuration often uses rules that denote both aspects of a socket. You might create allowances or traffic blocks based on IP addresses, port numbers, or both.

How to View TCP Connections on Your Machine

Regardless of your OS, you can always get to the netstat command line tool, although the specific parameters you use will depend on your OS. In Windows, start with a command prompt and type:

This will output a table of all current TCP connections on the system. Unfortunately, you can't do all that much besides looking at it.

There's another option, though, and that's to type:

This outputs a lot more data that's much more useful. This includes all the parameters.

What's a Good Tool for Viewing TCP Information?

If you're working on a Windows machine, TCPView.exe is strongly recommended. A Microsoft property now, it was originally developed by Mark Russinovich. There's also a command line version of the tool called TCPVcon that's also free.

What's great about TCPView is its graphical interface. And the interface is more than just a netstat query on steroids, there's a lot of context and information in its interface.

Running TCPView, you may discover that you have quite a lot more running on your system in terms of remote connections than you might have otherwise been aware. That's one of the reasons TCPView is an excellent way to diagnose rogue processes. It could be a trojan horse, some sort of backdoor administrative application that phones home. You can easily identify those tools, by taking a look.

Don't be surprised if you see many applications running with processes going like Outlook, Chrome, or Dropbox. If you right-click one of these items that's listed, you'll get a specific ID of the image or the executable program that's running. You can also end the process — terminate it from there — by right-clicking and pressing "close application". You can right-click a process and do a WHOIS lookup. There's a lot of good things to do in TCPView and you should play around with it.

The bottom line with TCPView is that by using it you can see that for each process that you have running on your system, you can see at a glance if it's TCP or UDP. And you can see the local and remote port. You'll see that UDP doesn't have remote ports, that's because UDP is a connectionless protocol  and doesn't require an end-to-end circuit like TCP does. Which is why TCP tells us on this interface where we're connected, both locally and to a remote system.

Wrapping Up

TCP is an important concept for any network professional to understand. It's one of the tools that has made our modern digital age possible. All this information about understanding TCP/IP lends itself to learning much more about IT professions. If you're looking for more detail, check out our CompTIA A+ training .

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The Most Popular TCP and UDP Port Numbers

Some ports can be used for anything, while others have long-established purposes

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The Transmission Control Protocol (TCP)  uses a set of communication channels called ports  to manage system messaging among several different applications running on the same physical device. Unlike the physical ports on computers like USB ports or  Ethernet ports , TCP ports are virtual—programmable entries numbered between 0 and 65535.

Most TCP ports are general-purpose channels that can be called into service as needed but otherwise sit idle. Some lower-numbered ports, however, are dedicated to specific applications. While many TCP ports belong to applications that no longer exist, certain ones are very popular.

Jason Gillikin

TCP does not actually use port 0 for network communication, but this port is well-known to network programmers. TCP socket programs use port 0 by convention to request an available port be chosen and allocated by the operating system. This saves a programmer from having to pick ("hardcode") a port number that might not work well for the situation.

TCP Ports 20 and 21

FTP servers use TCP port 21  to manage their side of FTP sessions. The server listens for FTP commands arriving at this port and responds accordingly. In active mode FTP, the server additionally uses port 20 to initiate data transfers back to the FTP client.

TCP Port 22

 Simon Steinberger/Pixabay

Secure Shell uses port 22. SSH servers listen on this port for incoming login requests from remote clients. Due to the nature of this usage, port 22 of any public server frequently gets probed by network hackers and has been the subject of much scrutiny in the network security community. Some security advocates recommend that administrators relocate their SSH installation to a different port to help avoid these attacks, while others argue this is only a marginally helpful workaround.

TCP Port 23

Port 23 governs telnet , a text-based system for logging into remote systems. Although modern remote-access approaches rely on Secure Shell on port 22, port 23 remains reserved for the older and less-secure telnet application.

TCP Ports 25, 110, and 143

 Joli Ballew

Email relies on several standard ports. Port 25 governs the Simple Mail Transfer Protocol — the tool by which an email on your computer makes its way to a mail server, and then from that server to the larger internet for routing and delivery.

On the receiving end, port 110 governs Post Office Protocol, version 3, and port 143 is dedicated to Internet Mail Access Protocol. POP3 and IMAP control the flow of emails from your provider's server to your inbox.

The secure versions of SMTP and IMAP vary depending on configuration, but ports 465 and 587 are common.

UDP Ports 67 and 68

Panumas Nikhomkhai/​Pexels

Dynamic Host Configuration Protocol  servers use UDP port 67 to listen for requests while DHCP clients communicate on UDP port 68.

TCP Ports 80 and 443

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Arguably the single most famous port on the Internet, TCP port 80 is the default that HyperText Transfer Protocol  Web servers listen on for Web browser requests. 

Port 443 is the default for secure HTTP.

UDP Port 88

 Anthony/Pexels

The Xbox network gaming service uses several different port numbers including UDP port 88.

UDP Ports 161 and 162

 Brett Sayles/Pexels

By default, the Simple Network Management Protocol uses UDP port 161 for sending and receiving requests on the network being managed. It uses UDP port 162 as the default for receiving SNMP traps from managed devices.

TCP Port 194

 Pixabay/Pexels

Although tools like smartphone messaging apps and services like Slack and Microsoft Teams have cut into the use of Internet Relay Chat, IRC still proves popular with people around the globe. By default, IRC uses port 194.

Ports Above 1023

TCP and UDP port numbers between 1024 and 49151 are called registered ports . The Internet Assigned Numbers Authority maintains a listing of services using these ports in order to minimize conflicting uses.

Unlike ports with lower numbers, developers of new TCP/UDP services can select a specific number to register with IANA rather than having a number assigned to them. Using registered ports also avoids the additional security restrictions that operating systems place on ports with lower numbers.

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Service Name and Transport Protocol Port Number Registry

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Port 21 vs. Port 22

What's the difference.

Port 21 and Port 22 are both commonly used network ports, but they serve different purposes. Port 21 is used for FTP (File Transfer Protocol) connections, allowing users to transfer files between a client and a server. On the other hand, Port 22 is used for SSH (Secure Shell) connections, providing a secure way to access and manage remote servers. While both ports are essential for network communication, Port 22 offers an added layer of security with encryption and authentication mechanisms, making it a preferred choice for secure data transfer and remote access.

Further Detail

Introduction.

Port numbers are used to identify specific processes or services running on a computer network. Two commonly used ports are Port 21 and Port 22. Port 21 is typically used for FTP (File Transfer Protocol) while Port 22 is used for SSH (Secure Shell) connections. In this article, we will compare the attributes of these two ports to understand their differences and similarities.

Port 21 is the default port for FTP, a protocol used for transferring files between a client and a server on a computer network. FTP is commonly used for website maintenance, file sharing, and data backup. Port 21 operates on the TCP (Transmission Control Protocol) and is considered an insecure protocol because it transmits data in plain text, making it vulnerable to eavesdropping attacks. Despite its security risks, Port 21 remains widely used for FTP connections due to its simplicity and ease of use.

One of the main advantages of using Port 21 for FTP connections is its compatibility with a wide range of FTP clients and servers. Many FTP software applications are configured to use Port 21 by default, making it easy for users to establish connections without having to modify port settings. Additionally, Port 21 allows for both active and passive FTP modes, giving users flexibility in how they transfer files between the client and server.

However, one of the drawbacks of using Port 21 is its lack of encryption, which poses a security risk when transmitting sensitive data over the network. Without encryption, data transferred over Port 21 can be intercepted and read by malicious actors, compromising the confidentiality of the information being transmitted. To address this issue, users can opt to use secure FTP protocols like FTPS (FTP over SSL) or SFTP (SSH File Transfer Protocol) that encrypt data transmissions over Port 21.

Port 22 is the default port for SSH, a secure network protocol used for remote access, file transfer, and command execution on a computer network. SSH provides a secure way to communicate with a server by encrypting data transmissions, making it resistant to eavesdropping and man-in-the-middle attacks. Port 22 operates on the TCP and is widely regarded as a secure protocol for establishing secure connections between clients and servers.

One of the key advantages of using Port 22 for SSH connections is its strong encryption capabilities, which ensure that data transmitted over the network is protected from unauthorized access. SSH uses cryptographic algorithms to encrypt data, authenticate users, and establish secure connections, making it a preferred choice for secure remote access and file transfer operations. Additionally, Port 22 supports key-based authentication, which enhances security by eliminating the need for passwords.

Another benefit of using Port 22 for SSH connections is its versatility in supporting various protocols and applications. SSH can be used for secure file transfers (SFTP), secure copy (SCP), secure tunneling, and remote command execution, making it a versatile tool for managing and securing network communications. Port 22 also allows for secure remote access to servers and devices, enabling administrators to manage systems securely from remote locations.

When comparing Port 21 and Port 22, it is evident that they serve different purposes and have distinct attributes. Port 21 is primarily used for FTP connections, which are insecure by default and lack encryption, while Port 22 is used for SSH connections, which are secure and encrypted by default. Port 21 is suitable for transferring non-sensitive files and data over the network, while Port 22 is ideal for secure remote access, file transfers, and command execution.

• Port 21 is insecure and transmits data in plain text, making it vulnerable to eavesdropping attacks.
• Port 22 is secure and encrypts data transmissions, ensuring the confidentiality and integrity of the information being transmitted.
• Port 21 is widely used for FTP connections due to its simplicity and ease of use.
• Port 22 is preferred for secure remote access, file transfers, and command execution on a computer network.
• Port 21 lacks encryption, posing a security risk when transmitting sensitive data over the network.
• Port 22 uses strong encryption algorithms to protect data transmissions and authenticate users securely.

In conclusion, Port 21 and Port 22 have distinct attributes that make them suitable for different purposes in a computer network. Port 21 is commonly used for FTP connections, while Port 22 is preferred for SSH connections. Understanding the differences between these two ports can help users make informed decisions when choosing the appropriate protocol for their specific networking needs.

Comparisons may contain inaccurate information about people, places, or facts. Please report any issues.

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IP Address vs. Port Number: What‘s the Difference and How Do They Work Together?

• May 26, 2024
• by Tom Wells

Imagine you‘re throwing a party and inviting friends to your house. They‘ll need two key pieces of information to show up at the right place: your street address to locate your house, and some identifier like your apartment number so they know to ring the right doorbell. In the world of computer networking, IP addresses and port numbers serve similar roles in enabling communication between devices.

But what exactly are IP addresses and port numbers, and how do they differ? Are port numbers actually part of IP addresses? In this guide, we‘ll demystify these fundamental concepts and explain their vital roles in connecting devices and applications over the internet. Whether you‘re a network administrator, developer, or just curious how the web works, understanding IP addresses and ports is key to troubleshooting connectivity issues and securing your online communications.

What is an IP Address?

An Internet Protocol (IP) address is a numeric label assigned to every device connected to a computer network. Just like a street address identifies a particular building, an IP address uniquely identifies a specific device like a computer, smartphone, or server on the internet or a local network. When a device communicates with another, it uses the IP address to specify where to send the data packets.

IP addresses come in two flavors: IPv4 and IPv6. IPv4 addresses are 32-bit numbers usually expressed as four decimal numbers ranging from 0 to 255, separated by dots. For example, 192.168.1.1 is a valid IPv4 address you might see for a home router. However, due to the explosive growth of internet-connected devices, the world is running out of available IPv4 addresses.

To solve this problem, IPv6 was developed using 128-bit hexadecimal addresses, providing a much larger pool of unique identifiers. An example IPv6 address looks like this: 2001:0db8:85a3:0000:0000:8a2e:0370:7334. While most networks still use IPv4, the transition to IPv6 is accelerating to accommodate the expanding internet.

Another important distinction is between public and private IP addresses. A public IP address is assigned by your Internet Service Provider (ISP) and is globally unique, allowing your device to communicate directly over the internet. A private IP address is used within a local network and is not publicly routable. Multiple devices can share the same public IP address using a technique called Network Address Translation (NAT).

So how do devices get their IP addresses? For home networks, your router automatically assigns private IP addresses to connected devices using Dynamic Host Configuration Protocol (DHCP). These addresses can change over time, especially if you reboot your router. Public IP addresses are assigned by your ISP, and can be dynamic (changing periodically) or static (remaining constant).

What is a Port Number?

If an IP address is like your street address, a port number is like your apartment number – it identifies a specific application or service running on a device. Ports are virtual communication endpoints that allow multiple networking processes to share the same IP address without conflicting.

Technically speaking, a port is an unsigned 16-bit integer, meaning it can range from 0 to 65535. Ports 0-1023 are called well-known ports and are reserved for common protocols like HTTP (port 80), FTP (port 21), and SSH (port 22). Ports 1024-49151 are registered ports assigned by the Internet Assigned Numbers Authority (IANA) for specific applications. Dynamic ports 49152-65535 can be used by any application.

To understand how ports enable multiplexing network traffic, consider a web server hosting multiple websites. Each site runs on the same physical server with a single IP address, but are differentiated by port numbers. The default port for unencrypted HTTP traffic is 80, while secured HTTPS uses port 443. So when your browser requests a webpage, it specifies both the IP address and the port to connect to the appropriate website.

Here are some common default port numbers and their associated applications:

Keep in mind that these are conventions but not requirements – applications can use custom port numbers as needed. When running a server application, you often need to specify which port to listen on for incoming connections.

How IP Addresses and Ports Work Together

Now that we‘ve defined IP addresses and port numbers individually, let‘s explore their relationship. The key idea is that IP addresses specify a device, while port numbers specify an application or service running on that device. Together they enable the delivery of data to the right place.

Imagine you‘re configuring a Minecraft server on your computer to play with friends over the internet. By default, the server software listens for incoming connections on port 25565. To connect, players need to enter your public IP address (which identifies your router on the internet) and the port number (which identifies the Minecraft server software on your computer). The combination of IP address and port number, called a socket, uniquely identifies the connection endpoint.

We can break down the components of a connection like this:

Here, 192.168.1.100 is the IP address (of the Minecraft server) and 25565 is the port number. The colon separates the two parts to form a socket address. It‘s important to understand that the port number is not actually part of the IP address itself, even though they are often written together. Multiple connections to different ports on the same device will all use the same IP address.

This diagram illustrates how ports enable communication between a client and server:

The client connects from its own ephemeral port (43210) to the server‘s well-known port 80, used for HTTP traffic. The server sends back the requested webpage to the client‘s IP address and port. The combination of source and destination IP addresses and ports enables two-way communication.

Ports and Network Security

While ports are essential for enabling network applications, they can also introduce security risks when not properly managed. Every open port on a public network is a potential attack surface for hackers to exploit. Port scanning tools like Nmap can quickly identify which ports are accepting connections, giving attackers clues about which applications are running and whether they have known vulnerabilities.

To mitigate these risks, network administrators should follow best practices like:

• Closing unnecessary ports and disabling unused services
• Placing servers behind firewalls to restrict traffic to only required ports
• Requiring strong authentication and access controls for administrative ports
• Regularly patching software and updating applications to fix security flaws
• Using encryption like SSL/TLS for sensitive data transmission
• Monitoring open ports for suspicious activity or brute-force attacks

Using NAT and port forwarding can also enhance security by masking the original source IP and port of traffic. With NAT, multiple devices with private IPs can share a single public IP, with the router translating the ports to keep connections distinct. Port forwarding maps an external port to an internal IP and port, allowing incoming traffic to reach a specific device. However, port forwarding can also expose internal services if not secured properly.

Some examples of how ports impact security:

• Many ISPs block port 25 (used for SMTP) to curb the spread of spam and malware from compromised machines.
• SSH (port 22) is frequently scanned and attacked with default or weak credentials. Key-based authentication and IP restrictions are recommended.
• Opening ports for P2P applications like BitTorrent can expose your IP address and system information to other peers, potentially leading to attacks.
• Checking for open ports is a common way to identify command and control servers for botnets.

Future of Ports with QUIC

Looking ahead, the way we use ports for network communication is evolving with the development of new protocols. One exciting example is QUIC (Quick UDP Internet Connections), a transport protocol designed by Google to improve performance and security compared to TCP.

Unlike TCP, QUIC runs on top of UDP (User Datagram Protocol) to avoid head-of-line blocking and enable faster connection establishment. QUIC also has built-in encryption and authentication, providing security equivalent to TLS. Interestingly, QUIC uses UDP port 443, the same as HTTPS, to avoid issues with firewalls and middleboxes that might block unfamiliar protocols.

As QUIC gains adoption, it could change how we think about port numbers. Since QUIC handles connections at the application layer, the concept of server ports may become less relevant. However, clients will still use ephemeral ports to enable multiple simultaneous connections. It remains to be seen how QUIC will affect network operations and security compared to the current TCP/IP model.

We‘ve covered a lot of ground in this deep dive into IP addresses and port numbers. To recap, an IP address identifies a device on a network, while a port number identifies an application or service running on that device. Together they form a socket that enables communication between clients and servers. Securing open ports is crucial to preventing unauthorized access and attacks.

If you‘re a developer building networked applications, understanding ports is essential for enabling communication and avoiding conflicts. When debugging connectivity issues, checking IP addresses and ports is often the first step. By using tools like Netstat or Wireshark, you can inspect which ports are open and which processes are using them.

For system administrators and network engineers, auditing and monitoring open ports should be a regular security practice. Unnecessarily exposed services are a frequent vector for data breaches and malware. Following the principle of least privilege, you should restrict access to sensitive ports and segments using firewalls, VPNs, and other controls.

Hopefully this guide has demystified some of the jargon and technical details behind IP addresses and ports. While they may seem like arcane concepts, they‘re fundamental to how devices communicate and how the internet operates. By understanding their roles and relationships, you can better secure your systems and networks from ever-evolving cyber threats.

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Nest Wifi Pro Port Forwarding: Complete Setup Guide

Having a reliable and secure home network is essential. the nest wifi pro system is a powerhouse when it comes to seamless connectivity and robust network management. one crucial aspect of network configuration is port forwarding, which allows specific data packets to traverse through a network’s firewall and reach their intended destination.

Port forwarding plays a vital role in various applications such as online gaming, video streaming, remote access to devices, and hosting servers. Without proper port forwarding settings, some applications may not function correctly or be accessible from outside the local network.

Table of Contents

Understanding Port Forwarding

Port forwarding is a networking technique that redirects communication traffic from one IP address and port number combination to another. This process enables external devices to connect to specific services or applications hosted on devices within a private network. There are different types of ports used in port forwarding, including TCP (Transmission Control Protocol), UDP (User Datagram Protocol), and port ranges, each serving a distinct purpose in data transmission.

Configuring Port Forwarding on Nest Wifi Pro

Setting up port forwarding on the Nest Wifi Pro is a straightforward process through the Google Home app. By following these steps, users can easily establish port forwarding rules to facilitate smooth data flow to their desired devices:

You can find more information on Google Nest Wifi Pro 6E Reviews: What Users Are Saying

Specific Port Forwarding Examples

Here are some common port forwarding scenarios with their associated port numbers:

1. Port 25 (SMTP): Used for email servers.

2. Port 80 (HTTP): Essential for hosting web servers.

Check this blog on Nest Wifi Pro Range: How Far Can It Cover?

3. Port 443 (HTTPS): Enables secure communication for web servers.

4. Port 21 (FTP): Facilitates file transfer operations.

Troubleshooting Port Forwarding

When setting up port forwarding, encountering issues is not uncommon. To tackle these challenges, users can follow these troubleshooting steps:

– Verify the device’s IP address and port settings to ensure accuracy.

– Check for any firewall or antivirus software that may be blocking the port forwarding rules.

Check this blog on Nest Wifi Pro Firmware Update: How to Keep Your System Up-to-Date

Dive deeper into Google Nest Wifi vs Google Nest Wifi Pro: Which Is Better for Your Home?

– If issues persist, consider resetting the Nest Wifi Pro router to its default settings.

Advanced Options

For users looking to optimize their networking experience, the Nest Wifi Pro offers advanced port forwarding options:

– Create multiple port forwarding rules for various services or applications.

– Utilize virtual servers to redirect traffic to specific devices within the network.

– Enable UPnP (Universal Plug and Play) for automatic port forwarding setup, ideal for devices that require dynamic port configurations.

mastering the art of port forwarding on the Nest Wifi Pro can significantly enhance network accessibility and performance. By understanding the fundamentals, configuring specific rules, troubleshooting common issues, and exploring advanced options, users can harness the full potential of their home network. Remember, while port forwarding offers numerous benefits, it’s crucial to prioritize security by implementing best practices and staying vigilant against potential threats. Start unleashing the true potential of your network with efficient port forwarding on the Nest Wifi Pro.

Frequently Asked Questions

What is port forwarding.

Port forwarding is a technique used to allow external devices to access specific services or applications on a private network by mapping a port number on your router to a specific IP address and port number on a local device.

Why is port forwarding important for Nest Wifi Pro?

Port forwarding is essential for enabling remote access to your Nest Wifi Pro network, such as accessing security cameras, online gaming, or running a personal website.

How do I set up port forwarding on Nest Wifi Pro?

To set up port forwarding on Nest Wifi Pro, you will need to access the Google Home app, navigate to the network settings, and configure port forwarding rules by specifying the external port, internal IP address, and internal port of the device you want to access remotely.

You can find more information on Google Nest Wifi Pro vs Eero Pro 6E: Which is Better for 2024?

Are there any security risks associated with port forwarding on Nest Wifi Pro?

Yes, port forwarding can potentially expose your devices to security vulnerabilities if not configured correctly. It is essential to only open necessary ports for trusted services and keep your devices updated with the latest security patches.

Can I test if port forwarding is working on Nest Wifi Pro?

Yes, you can use online port checking tools to test if port forwarding is correctly configured on Nest Wifi Pro. Simply input your public IP address and the specific port you want to test, and the tool will check if the port is open and accessible from the internet.

Related Post

Google nest wifi ⚠️ pro 6e review: features, pros, and cons.

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Nest Wifi Pro 2: Rumored Features and Release Date

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Cannot open Port 21

I tried adding an FTP service for my local server for external client to use for FTP. Input the external and internal port using port 21 and TCP protocol. Enabled it but when I checked on port checker, it is closed. However, I added HTTP service and input the external and internal port using port 80 using the same TCP protocol, checked the port on port checker and it is open. My ISP does not block port 21. What instruction did I miss? How do I enable and open port 21?

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FlightAware network traffic to port 44975. Legit?

I have PiAware running on an RPi. While trawling my syslog for an unrelated error, I came across a “UFW BLOCK” entry blocking traffic between IP 206.253.80.198 ( cagso.hou.flightaware.com ) and my instance from port 1200 to port 44975.

Here is the [edited] log entry:

What is port 44975 used for? Should I ‘ALLOW’ port 44975? Will it help FlightAware in any way - it does not seem to be affecting my feed.

Ta much Bagoong

This is reply traffic for an outbound TCP connection made from your Pi to a FA server’s port 1200, which is normal traffic.

44975 is the locally-allocated port number on the Pi’s side of the connection, and will change from connection to connection.

Normally your firewall should match this reply traffic against the established connection and allow it automatically.

Thanks a ton.

I just checked my logs. It would seem that this UFW BLOCK has only happened twice this week. I’m going to ignore it while I sort out the other problem which may actually have caused the BLOCK.

I’ll come back later if it irks me.

Again, thanks a ton!

If I had to guess, it would be that the Pi had just rebooted (the kernel message is timestamped 45s after reboot) and the traffic that got blocked was for a pre-reboot connection that was not cleanly torn down (i.e. the server side thinks it is still live). But the post-reboot firewall state doesn’t know about that connection at all and drops the traffic.

That’s about right. I’ve had to reboot the Pi often due to a problem with fr24feed - keeps getting lost and then going ‘berserk’. Need to first do a power reboot, then when it comes back a software reboot. I don’t fully understand that problem yet - have to fill idle gaps with that research at the moment. Anyhow, that’s not your problem.

Thanks a ton!

(Before purging fr24feed, open file /etc/fr24feed.ini and note down fr24key . You will need it when re-installing it by last command below)

Also brows following post:

Thanks a ton, that’s sensible advice. I was going to rebuild the entire Pi, but perhaps purge/reinstall will work, and it’s a shorter route.

I’ll definitely take a gander at the link you sent.

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Protocole de transport TCP

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Présentation

1 - NORMALISATION

2 - CARACTÉRISTIQUES DU PROTOCOLE

• 2.2 - Numéros de port
• 2.4 - Acquittement : mécanisme de base
• 2.6 - Options

3 - TRANSPORT DE DONNÉES

4 - FIABILITÉ ET CONTRÔLE D’ERREURS : RETRANSMISSION DES DONNÉES

• 4.1 - Stratégie de retransmission

5 - CONTRÔLE DE CONGESTION : LES VERSIONS DE TCP

• 5.2 - Réaction face aux pertes
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• 5.4 - TCP Reno
• 5.5 - TCP NewReno : fast retransmit amélioré

| Réf : TE7570 v1

Auteur(s) : David ROS

Date de publication : 10 mai 2005

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Le protocole de transport TCP (Transmission Control Protocol) permet d’assurer des services de communication fiables entre des applications hébergées dans les équipements terminaux. Ceci n’est pas le cas du protocole IP (Internet Protocol) qui n’offre aucune garantie quant à la réception des paquets. C’est ce qui explique en partie le succès du protocole TCP, retenu comme protocole de transport dans bon nombre d’applications au sein de réseaux basés sur le protocole IP. L’article présente ses caractéristiques, la particularité des échanges et de la retransmission des données sous TCP. Pour terminer, il aborde le phénomène de congestion.

Lire cet article issu d'une ressource documentaire complète , actualisée et validée par des comités scientifiques.

David ROS : Maître de conférences à l’École nationale supérieure des télécommunications (ENST) de Bretagne

INTRODUCTION

Dans les réseaux IP, le protocole IP (Internet Protocol) offre un service à datagrammes ; autrement dit, il ne fournit aucune garantie quant à la réception correcte des paquets. En effet, ces paquets peuvent être perdus ou dupliqués, et ils peuvent aussi arriver dans un ordre différent de l’ordre d’émission. Or, de nombreuses applications ont besoin d’un transfert ordonné et fiable de leurs données. Le protocole de transport TCP (Transmission Control Protocol, ou protocole de contrôle de transmission) joue alors un rôle fondamental : celui d’assurer des services de communication fiables entre des applications hébergées dans les équipements terminaux. En suivant le principe dit « de bout en bout » (« end-to-end principle »), le réseau IP sous-jacent est vu comme une boîte noire, le soin de cacher ses imperfections aux applications étant laissé à TCP.

Depuis sa conception au début des années 1980, TCP s’est imposé comme le protocole de transport de choix pour de nombreuses applications. De plus, il est incontestablement le plus utilisé dans les réseaux basés sur le protocole IP, en termes de paquets et d’octets échangés.

Dans le modèle de référence en couches protocolaires de l’Internet, TCP se situe au niveau de la couche 4 (figure  1 ). Il est généralement mis en œuvre par le système d’exploitation, de sorte que celui-ci offre ces services de transport aux applications à travers une interface de programmation (API : Application Programming Interface), dont la plus populaire est celle connue sous le nom d’ API sockets [1].

TCP offre aux applications et aux protocoles qui l’utilisent un canal transparent, sans erreurs et bidirectionnel (en mode « full duplex ») qui transporte une séquence d’octets. C’est un protocole de point à point (il n’est pas adapté au « multicast ») et de bout en bout  : seules les deux extrémités participant à la communication, ou connexion , déroulent le protocole (figure  2 ).

Lorsqu’une application fournit à TCP des données pour transmission, TCP peut découper ces données en blocs, afin d’adapter la taille des paquets résultants à la taille de l’unité maximale de transmission du réseau (MTU : Maximum Transfer Unit). Chacun de ces blocs, précédé d’un en-tête, forme l’unité de données (PDU : Protocol Data Unit) du protocole, nommée segment (figure  3 ).

Le service de transport offert par TCP est nommé parfois un « flot d’octets » (« byte-stream ») : de son point de vue, TCP transporte des octets sans aucune structure, car il peut découper les données applicatives en segments de façon arbitraire, indépendamment de leur sémantique ; la délimitation de ces octets relève exclusivement de l’application, pas de TCP.

La fiabilité est assurée grâce à un mécanisme d’acquittement (« acknowledgement »). À chaque octet émis correspond un numéro de séquence, et cette numérotation permet l’acquittement des données reçues.

TCP opère en mode connecté , autrement dit, avant de pouvoir envoyer des données, il faut établir une connexion à l’aide d’une procédure de signalisation.

Enfin, TCP met en œuvre des mécanismes de contrôle de flux et de contrôle de congestion afin d’éviter, dans la mesure du possible, l’engorgement du récepteur ainsi que la saturation chronique des équipements intermédiaires d’interconnexion.

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DOI (Digital Object Identifier)

https://doi.org/10.51257/a-v1-te7570

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Bibliographie.

(1) - WRIGHT (G.), STEVENS (W.R.) -   TCP/IP Illustrated, vol. 2 : The Implementation.  -  Addison-Wesley (1995).

(2) - POSTEL (J.) -   Transmission Control Protocol.  -  RFC 793, IETF (septembre 1981).

(3) - DUKE (M.), BRADEN (R.), EDDY (W.), BLANTON (E.) -   A Roadmap for TCP Specification Documents.  -  Internet Draft draft-ietf-tcpm-tcp-roadmap-00, work in progress (octobre 2004).

(4) - RAMAKRISHNAN (K.), FLOYD (S.), BLACK (D.) -   The Addition of Explicit Congestion Notification (ECN) to IP.  -  RFC 3168, IETF (septembre 2001).

(5) -   Ports Numbers.  -  http://www.iana.org/ assignments/port-numbers

(6) - STEVENS (W.R.) -   TCP/IP Illustrated, vol. 1 : The Protocols.  -  Addison-Wesley (1994).

DANS NOS BASES DOCUMENTAIRES

Routage dans les réseaux Internet.

Architecture en couches des protocoles : concepts de base.

Principaux protocoles de transmission de données.

Architecture TCP/IP.

IPv6, la nouvelle génération du protocole IP.

2.1 Internet Engineering Task Force (IETF)

2.2 Groupes de travail de l’IETF

• 2.3 Internet Research Task Force (IRTF)
• 2.4 Internet assigned numbers authority (IANA)

Thèses

GURTOV (A.) - Efficient data transport in wireless overlay networks. - Thèse de doctorat, université de Helsinki (2004).

NOUREDDINE (W.) - Improving the performance of TCP applications using network-assisted mechanisms. - Thèse de doctorat, université de Stanford (2002).

BARAKAT (C.) - Évaluation des performances du contrôle de congestion dans l’Internet. - Thèse de doctorat, université de Nice-Sophia-Antipolis (2001).

2 Organismes

http://www.ietf.org

Tous les documents issus des groupes de travail, ainsi que les Internet drafts (documents de travail), sont disponibles gratuitement sur le site de l’IETF.

http://www.ietf.org/html.charters/tcpm-charter.html

http://www.ietf.org/html.charters/tsvwg-charter.html

DANS LES RESSOURCES DOCUMENTAIRES

• TCP : performance et évolution du protocole
• TCP - Impact des caractéristiques des liaisons
• Nouvelles techniques de transport du multimédia : le protocole DCCP
• Techniques de supervision de la sécurité des réseaux IP

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• L'IIoT : l’Internet des objets pour le Manufacturing (9 Mars 2021)
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