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How to understand the Raysync file transfer protocol, in view of this problem, this article introduces the corresponding analysis and answer in detail, hoping to help more partners who want to solve this problem to find a more simple and easy way.

File transfer Protocol (FTP) is defined in RFC 959 and was released in October 1985. File transfer Protocol (FTP) is designed to be a cross-platform, simple and easy to implement protocol. File transfer Protocol (FTP) has a long history of evolution and is one of the most important applications on the Internet, but today, it has been in decline. Some shortcomings of File transfer Protocol (FTP) are listed from various aspects.

1. Unreasonable data transmission mode

It is unreasonable to use ASCII mode to transfer data regardless of the contents of the file itself. File transfer Protocol (FTP) should have automatic detection function, of course, users can also customize it.

Although many Linux and Windows clients now support automatic transfer mode, generations of UNIX and Windows clients use ASCII transfer mode by default, which can even cause file corruption.

2. The design of working mode is unreasonable.

File transfer Protocol (FTP) can work in either active mode (PORT) or passive mode (PASV), which determines how data links are established.

In active mode, the client first sends the IP address and port number to the server, and then waits for the server to establish a TCP link. In passive mode, the client also establishes a link to the server first, but the server opens a port (between 1024 and 5000) and waits for the client to transmit data.

The most amazing thing about File transfer Protocol (FTP) is that the client listens on the server side!

3. Do not coordinate with the firewall

Before File transfer Protocol (FTP) was born in Network address Translation (NAT) and firewalls, there were no malicious attacks on the network at that time. Today, the IPv4 addresses of most end users are no longer routable because of the use of firewalls and a shortage of IPv4 addresses.

What does this mean for FTP? This means that if the FTP client IP address is not routable or is behind a firewall, data can only be transferred using passive transfer mode.

What if the server-side IP address is also non-routable or behind a firewall? FTP will not be able to transfer data!

Today, many firewalls are suitable for NAT environments, and special techniques (hacks) can be used to allow FTP to work properly behind the firewall. Of course, this requires the configuration of the firewall.

4. The password security policy is not perfect.

In the early days of the Internet, the File transfer Protocol (FTP) did not provide for password security. On the FTP client and server, data is transmitted in clear text, and anyone who has control over the routing on the communication path can sniff your password and data.

Of course, we can use SSL to encapsulate FTP, but FTP transmits data by establishing multiple links, so it is difficult for us to protect the security of data transmission even if we protect the security of passwords.

Since the release of File transfer Protocol (FTP), secure data transfer has also undergone considerable development. It is recommended to use SCP instead of FTP for file transfer.

5. FTP protocol is inefficient.

Retrieve a file from the FTP server that contains the cumbersome exchange handshake steps:

The client establishes a TCP Socket link to the control port of the FTP server and waits for the TCP handshake to complete

The client waits for the server to send a receipt.

The client sends a user name to the server and waits for a response

The client sends a password to the server and waits for a response

The client sends SYST commands to the server and waits for a response

The client sends TYPE I commands to the server and waits for a response

If the user needs to switch directories on the server side, the client still sends a command and waits for a response

In active mode, the client needs to send a PORT command to the server and then wait for a response (passive mode is the opposite of active mode)

Establish a data transfer link (requires a three-way handshake to establish a TCP Socket connection)

Transfer data through a link

The client waits for the server to send 2xx instructions from the control connection to ensure successful data transmission

The client sends a QUIT command and waits for the server to respond

In the same situation, let's look at the HTTP protocol:

The HTTP client establishes a TCP Socket connection to the HTTP server

The HTTP client sends GET commands to the HTTP server, including URL, HTTP protocol version, virtual hostname, and so on, and waits for a response

The response from the HTTP server contains all the data you want, done!

To transfer a file, FTP needs to go back and forth 10 times, while HTTP only needs 2! If you transfer multiple files, FTP can omit the step of sending a user name and password, while HTTP can use fixed sockets (Socket) to transfer files over the same TCP connection.

To sum up, although the File transfer Protocol (FTP) was once famous for a time, it is now out of date. It is neither insecure, nor friendly, nor inefficient, and is bound to be replaced.

This is the answer to the question on how to understand the Raysync file transfer protocol. I hope the above content can be of some help to you. If you still have a lot of doubts to be solved, you can follow the industry information channel to learn more about it.

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