File transfer protocols (FTP and TFTP). Installing and configuring FileZilla FTP Server. Search servers. Specialized programs for downloading files. http clients

The FTP protocol has been used for a long time and at first glance is extremely simple. However, this simplicity is apparent and many begin to experience problems with establishing an FTP connection, especially when the server or client is behind a firewall or NAT. Therefore, today we will talk about the features of the work FTP protocol in various modes.

The FTP protocol is the oldest network protocol (created in 1971), but nevertheless is widely used to this day. An important feature of the protocol is that it uses several connections: one for control commands, the rest for data. Moreover, several connections for data transfer can be opened, in each of which files can be transferred in both directions. It is with this feature that a number of problems are associated.

Depending on the method of establishing a data connection, active and passive modes are distinguished FTP work. IN active mode the server itself establishes a data connection to the client, in a passive case it’s the other way around. Let's look at these modes in more detail.

Active mode

In most cases for normal operation For an FTP server behind NAT, it will be enough to forward 21 ports for the control session, 20 for the active mode (if used), as well as specify and forward a range of dynamic ports for data transfer.

Another important point, if you are forwarding ports for several FTP servers, then on each of them you should specify its own range of dynamic ports and forward to the same port numbers on the external interface. Why? Because the port number is transmitted by the server in the control command and does not know anything about forwarding, if the port number transmitted by the server does not match the port number on the external interface, then the client will not be able to establish a connection. While the control port and the active mode port can be forwarded to any external ports.

We hope that this article will help you better understand the mechanism of the FTP protocol and consciously approach the configuration and diagnostic process.

One of the oldest network protocols- this is FTP. What is it intended for, what is its role in the network “communication” of computers, how it works this protocol and whether it is worth using it - you will find the answers to all these questions in the article below.

What is the essence of FTP technology?

The modern FTP protocol is used somewhat differently than before. It was originally developed to work with large volumes of data. That’s why not only the FTP protocol was invented, but also the FTP archive. Now the latter has become a global repository for many files located on servers around the world. The archive is formed from a large number of FTP servers and there are special search engines, which allow you to search data by host, such as Napalm or FileSearch.

Not every part of the FTP archive can fit outsider through a search engine. There is a server with different levels access. Many people know FTP as the protocol that is needed to upload a website to hosting, that is, which is necessary for confidential use. For exactly the same purposes, an FTP archive is used for commercial organizations that store some kind of secret information in them.

But there are also many public FTP archives, which are similar to file sharing services. It is for such archives that special search engines have been created - so that users can immediately find files, and not articles from long description programs or games, instead of the applications themselves.

What is the purpose of the FTP protocol

The FTP protocol is intended for data transfer between the client and the server. It’s called “data transfer protocol”. Since it has been used for a very long time, FTP has become one of the Internet standards. The protocol was first used back in 1971. During its existence it has changed a lot. Some functions were removed, and the emphasis was placed on the fact that FTP is well suited for exchanging data between remote computers. Over time it was made more convenient for ordinary users. After all, you can log into an FTP server either using a special program or using standard services operating systems. For example, you can even connect to an FTP server using standard conductor Windows.

In addition, FTP is designed to distribute access rights between server users. Various users servers have their own set of rights. For example, some can only read data, while others can move, rename, edit and upload files to the host. Since creating an FTP server is as easy as using it, many users use this protocol to create remote access to your computers.

Some people confuse FTP and TCP. Although these concepts cannot be compared. FTP is a protocol and TCP is the channel over which it operates. And this channel is established between the server device and the client device. “Device”, not a computer, because FTP can also be used on smartphones using special programs, not only on a PC.

Please note that FTP is a good protocol to use on remote computer, if you need to upload some data there, or vice versa - download it.

But for transmission confidential information This protocol is not suitable at all. That is why the developers of the Yandex Disk service refused to use FTP as the main protocol and chose WebDAV instead. FTP is an open protocol that does not encrypt data. And even if you set up password authentication for clients on the server, the data they enter during authorization will be transferred to the host in clear text. That is, if they are intercepted, attackers will be able to penetrate the server.

How the FTP protocol works

In general, the operating model of the FTP protocol is very simple, so you should not have any problems while using it. The most common model is when the user uses an interpreter program. Using it, you can execute all commands in a convenient interface, so you don’t have to know them and enter them into the terminal. You issue commands to the interpreter, and it transmits them to the server via a control connection. The control connection operates in the TELNET protocol. Thus, by establishing contact with the server interpreter, the user is authorized on the host and is able to use more commands.

The behavior of the server and client, as well as the data transfer process, depends on the set of commands transmitted over the control connection. In addition, using commands you can control file system client and server.

A different channel than the control channel is used to transmit data. But the latter initiates the data connection call. The operating principle of a data connection is different from the operating principle of a control channel, because the server initiates the exchange of files and data. Although this connection can be used in both directions: both for receiving and transmitting data.

And here's what it's all about general algorithm works for any FTP protocol on the server:

The server is always in some state of waiting on the user's side. The client can connect to the server at any time, because the control channel keeps port 21 open. This is where all control commands go. Port 21 is the default, but can be changed. Then the user will have to enter the port number manually, otherwise he will not be able to access the control channel.
After connecting through the control channel port, the client-side program can issue commands to the server interpreter. These commands determine both changes within the server file system, as well as the method of data transfer, its content, volume, type of operating mode, and much more.
After all commands for data transfer are agreed upon, one of the connection participants goes into passive standby mode (server or client). It waits until it is given a port number to open it and receive or send data on it.
After the end of the data transfer process, the connection is closed, but the control channel still remains open. This allows the user to do everything again: give a command to the server and start transferring data again. There is no need to re-create the session. That's why FTP works using two types of connections.

Since this is the most common model of how the FTP protocol works, there are more complex cases. For example, when it is not the user who works with the server, but the server with the server. In this case, the client controls the transfer of data directly between servers, without intermediaries. And there are a lot of similar examples of server-client configurations. This is one of the advantages of the FTP protocol - flexibility of operation.

The main thing you need to understand about the FTP protocol is the interaction of connections and ports. Most errors when working using this protocol are due to the fact that one of the parties to the connection has not configured its port. There is a passive and active side of the protocol. The passive one must listen carefully and wait until the active one transmits the port number, which must be opened immediately. If the port is not open, data transfer will not begin.

Don't think that you have to manually wait for any commands from active participant connections - this is all done automatically. Problems appear when, for example, one or another port on your computer is already occupied or blocked for incoming/outgoing connections. It is at such moments that you will have to “roll up your sleeves” and manually configure your computer so that it can work correctly using FTP.

What commands does the FTP protocol use?

Most likely, you will not need them in your work, since you will use the user agent in the form of a program with user-friendly interface. One such program is FileZIlla. But anything can happen. Perhaps you only have Far Maneger at hand, where everything needs to be done through the terminal. In that case, you should get to know main teams for FTP.

To connect to the server, you will have to use the USER command. It is necessary to indicate the name of the user who wants to open a session with the server. After you enter your user ID in the USER command, you need to enter a login password. To do this use special team- PASS.

One of the most popular features that allows you to “travel” around the server is CWD. The command is needed so that you can move between server directories. To use the command, enter CWD and the path of the directory you want to go to.

If in some case you need to reinitialize, that is, omit all data and settings of the current connection, then use the REIN command. While it is being used, data transmission does not stop and the transmission parameters remain the same as they were before the REIN command. Or you can do it in an even more radical way - close the control connection using the QUIT command. It also does not interrupt data transfer, and only after the download is completed is the session completely interrupted.

In order to register a port in active mode, that is, assign it to a passive participant, you need to use the PORT command. The problem is that this command is very difficult to write - you will need to specify 32 bits of the server IP and 16 bits of the port number, which is completely inconvenient. Therefore, it is better to find a way to use a simplified client to work via the FTP protocol, so as not to burden yourself too much. In such a client, changing the port number is a piece of cake. Just go to the settings, find the desired item and enter another number instead of the current one.

You will use the RETR and STOR commands to transfer data from and to the server. The first command is needed to send the selected file to the client device, and the second to the server. And to rename a file, you need to use two consecutive commands. First write RNFR with the old file name, and then RNTO with the new file name. You will also need the DELE command, which is needed to delete data from the file system, more precisely the file that is currently selected.

Other commands are used to remove directories. To remove the selected directory, you will need the RMD command. And to create new folder, use the MKD string. Also, users often need the function of viewing files that are in a directory. To do this, use the LIST or NLST command.

What are the analogues of FTP?

At the transfer protocol FTP data there are its direct “heirs”, that is, protocols that are formed from FTP. These are two protocols: TFTP and SFTP. The first protocol is not the most popular, because it is very limited in terms of commands. It is much less suitable for managing the server's file system than FTP. You won't even be able to view a list of directory files using it. TFTP is needed only to transfer the simplest 8-bit information, no more. And in this protocol there are only 5 commands that are needed for reading, writing, requesting a data packet and other simple operations.

And here SFTP protocol much more successful than TFTP and in some cases - than FTP. The fact is that this is a secure FTP protocol. It is a combination of an encrypted SSH connection and the FTP data transfer protocol. In addition, SFTP has many unnecessary functions excluded are those that were introduced into FTP a long time ago, but are not used by anyone. That's why SFTP is safer than FTP, and at the same time more modest in in a good way this word. It is recommended to choose SFTP in cases where you are working with some confidential data. Then, even if hackers intercept the data sent over the control connection, it will still be encrypted and will not bring any value to the hackers.

And it’s better to use the FTP protocol in normal client programs, and not in the terminal. After all, this way you will significantly speed up the work on the data transfer protocol and gain access to its more sophisticated functions.

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This technology is one of the most popular for downloading and uploading data from/to remote servers, dispersed throughout the world.

Ftp systems are used to create websites. All information relating to the Internet resource is stored on ftp server. When a developer needs to make some adjustments to the site, he goes to the server, downloads the file that needs to be corrected, and then uploads it back. And that's it, the change took effect. It's fast and convenient.

What does an FTP server look like?

The visual presentation depends on the system through which you are logging in. Eat special programs type FileZilla, it displays data in the form familiar to everyone Total Commander.

Many hosting sites have their own management system, which also looks like a familiar set of folders and files.

FTP server features

Let's take a closer look at the technical aspects and tell you what an ftp server is and how it works.

The main function of FTP is to transfer files.

In addition to uploading and downloading information, various commands, with which you can manage files and directories:

Authentication required.
Availability of a dedicated channel for each connection.
Supports 2 data transmission modes: text and binary (in binary system). The second option reduces time and traffic.
Use of multiple connections, at least two-channel. Through one, control commands are transmitted and processed responses are returned. With the help of others it is carried out file transfer based on a dedicated channel for each.

How to connect to an FTP server

To enter the server, you need to fill out an authorization form, in other words, pass authentication. After entering the login (user) and password (pass), this information is transferred to the system. If accepted, the client will receive an invitation and the work session will open.

There are login options without specifying registration data. In this case, the options available to the visitor will be limited.

There is another option to go to FTP server - anonymous access. By default, login occurs when you enter the login “anonymous”; the spelling may differ in the case of letters. However, the most common method is when they offer to log in using email address. This access option is used by many FTP hosts that send out software updates.

To connect, you can use a web browser or file managers like Total Commander, FileZilla. Through the browser, you will be able to view and download files, but you will not be able to make changes.

It is more convenient to work through FileZilla client program(can be downloaded in the public domain).

Create a new connection as follows:

In the “Host” field, enter the address of the ftp server.
Fill in the fields “User name”, “Password” and, if necessary, “Port”.

Where can I get the address? If you connect to a server hosted on a host, the site owner has all access; it was provided by the provider.

What else is FTP used for?

Website files are the most common use case, but that's not all that resides on FTP servers.

There you can store any working or personal information large volumes, as an option, photographs, videos.

Almost any information that is used daily by millions of people is posted on FTP storages. These are software, demo versions of programs, e-books, legislative acts, articles, films, music - everything that can be formatted in a file representation. Catalogs have been created on the Internet containing terabytes of useful or entertaining information. Typically available anonymously and does not require payment.

Disadvantages of FTP servers

Weak protection against hacking and attacks. Because of technical features It can damage not only servers, but also clients. Therefore, confidential information should not be stored on them.

There is no authentication of the source of the data transmission packet, which leads to vulnerability to DDoS attacks.

The FTP protocol is a type of data transfer protocol that is used for the purpose of copying and moving files on the Internet and within TCP networks. FTP is often used to download pages and documents. various types to hosting computers. The FTP protocol uses a client-server architecture and various connections within a network in order to transmit commands and information from client to server and vice versa. FTP users are allowed to authenticate using a login and password, or, if this form is allowed on the server, users can access anonymously.
In addition to the regular protocol, FTPS is also used, which is a special extension of standard FTP, which allows clients to access the server and use encrypted information transfer sessions. This approach is implemented by sending the "auth tls" authentication command, which allows the server to accept or reject connections that do not request TLS connections.

SFTP

SFTP is a standard for transferring information on the Internet, which is intended for moving and copying files using a highly reliable and secure SSH (Secure Shell) connection. This type of connection can provide access and secure transfer, which is carried out with encryption of both the login and password, and the content of the transmission itself, thereby protecting passwords and confidential information from open transmission on the network.
Unlike FTP, the SFTP protocol, despite similar functions, uses a different data transfer protocol, and therefore standard clients cannot communicate with SFTP servers.

Features of the FTP standard

This standard is one of the oldest network protocols, which was created 45 years ago and is widely used on the Internet today. One of the most important features The protocol advocates the use of several connections: one for the purpose of transmitting control commands, and others for direct file transfer. In this case, you can open several parallel connections, each of which can transmit data in both directions.
There are two modes of FTP operation, which differ in the way connections are established: passive and active. During the active mode, the server establishes a connection to transmit information to the user, and during the passive mode, vice versa.
This standard has been used for quite a long time and at first glance is extremely simple. But such simplicity can be quite deceptive, since a large number of users may experience problems while gaining access via this standard, especially if the server or user is using a firewall or NAT.

Features of active mode

During active mode, the client initiates a control connection to server port 21 by sending the “port” command, which specifies the address and port for transferring information. After receiving this command, the server starts a connection from its own port 20 to the specified user port.
The main disadvantage this method It is mandatory for the user to have a dedicated IP address on the Internet in order to work. Additionally, some problems may occur if the client is behind a firewall or NAT.

Passive Mode Features

In order to establish a passive connection, the user must send the special “pasv” command to the server. As a response to this command, the server sends information about the address and port with which the client should establish a connection. After receiving this data, the user connects to the server computer and transfers information.
Using passive mode Absolutely all connections are initiated by the client, and therefore there are no requirements for it. The user is allowed to use NAT and a firewall, and not use a dedicated IP address. Therefore, today the passive mode is used as the main type of access and file transfer via FTP on the Internet.

Settings if using a firewall

When using a firewall and active mode, users may experience access issues. If the firewall is configured to reject incoming connections not initiated internally, the server computer will not be able to establish a connection and begin transmitting information. And due to the fact that the port for information is of a dynamic type, some difficulties arise when setting up the firewall. The best option V in this case is to indicate the range of ports used, and organize a special allowing firewall rule for them.
When using passive mode with similar complexity risks colliding server computer.

In this case, you can use a similar solution - specify in the options a certain range of ports used and create a special rule for this range.

Configuration when using NAT For the correct functioning of FTP over NAT and successful file transfer, it is not enough to simply configure forwarding of working ports, since a server computer operating under NAT will transfer internal address
port, and the client simply will not be able to connect and transfer information. Some modern NAT implementations can monitor the control channel of an FTP connection and replace the internal address with an external one for normal data transfer. In addition, FTP servers have the ability to specify, which should appear in the control session.
Most often for normal transmission files via FTP protocol via NAT, forwarding port 21 is enough to implement a control session, as well as specifying and forwarding the range dynamic addresses used for the purpose of transmitting data on the Internet.

, including, what is it needed for FTP access, its protection capabilities and the current rating of FTP clients .

Using the FTP protocol, files and folders of files are transferred on the Internet. That is, the user can upload data to the server without using a browser. FTP on hosting is intended for uploading sites directly to the hosting itself.

Review of popular FTP and SSH clients for transferring files (data).

Let's first figure out what you need to know in order to upload a website to the hosting provider's server. First of all, this is the login, access password, and FTP server address. All these the data is usually sent in a letter from the hoster after ordering the service you have chosen.

To transfer data, it is recommended to use FTP clients, which make the user’s work much easier. While connecting a PC to a server with using FTP Data transmission is carried out via a TCP port (numbered from 1024 to 65535). In active mode, the port number is set by the user, in passive mode – by the hosting provider’s server. In most cases, hosters use passive mode.

How to secure FTP access? FTP hacks most often occur due to the fact that there are viruses on the computer of the user who uploads files via FTP. Such viruses steal logins and passwords and then gain access to your website. Therefore, if you use FTP upload be sure to take care of the absence of all kinds malware on PC, otherwise the consequences can be sad.

Good protection isusing SSH . The essence of this technology is as follows: SSH is essentially a key that the user and the server have. It allows you to encrypt information during transmission and decrypt it on the server. Therefore, while transferring data using these keys, it is impossible to hack and connect before the connection and your information is in complete safety. like some other hosters provide SSH access for their users.

There is another method to secure FTP access.Using the .ftpaccess file It is possible to block FTP access for any directory on the server with saved files. To create such a file, you need to do personal computer most regular file ftpaccess.txt, in it make a record of IP addresses that can access via FTP access. Then you need to rename it to .ftpaccess and upload it to a folder that will be blocked. That's all.

For convenient work with FTP use specialFTP client programs. Among the most relevant and widely used areFilezilla, SmartFTP, Far Manager, Total Commander, AceFTP and others. More details .

How to connect to hosting via FTP using FileZilla.

Process creating FTP accounts on hosting depends on the preinstalled control panel, but regardless of whether it is cPanel, ISP manager or Parallels Plesk, the process is very similar and simple even for someone new to hosting management. You need to find the FTP accounts or FTP access section and manually create an FTP user there with given name and password.

How to create new FTP Cpanel account. .

To set up FTP connection , you need to use the following parameters: FTP server (host) – Domain name site, technical address (if the domain is not directed to the hosting site) or server IP address, port – 21, username – FTP login, password – FTP password.

We hope our tips will help you in working with FTP. If you have any additional questions, please contact our 24/7 technical support. We will be happy to help you!