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FTP experiment and overview

2022-07-26 05:26:00 【Blue moon Champions League King】

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Catalog

2. Build and configure FTP service

build FTP The server

3. Check the information

4. Set anonymous user access to FTP service ( Maximum authority )

One 、FTP

1. summary

FTP (File TransferProtocol, File transfer protocol ) Is a typical C/S Application layer protocol of architecture , The server software is required 、 The two parts of the client software jointly realize the file transfer function .FTP The connection between the client and the server is reliable , Connection oriented , It provides reliable guarantee for data transmission .TCP agreement :20,21 port

FTP It's a file transfer protocol , It supports two modes , One way is called Standard ( That is to say Active, Active way ), One is Passive( That is to say PASV, Passive way ).Standard Pattern FTP The client sends PORT Order to FTP server. Passive Pattern FTP The client sends PASV Order to FTP Server

(1)Standard Pattern

FTP The client first communicates with FTP Server Of TCP 21 Port establish connection , Send commands through this channel , When the client needs to receive data, it will send it on this channel PORT command .
PORT The command contains what port the client uses to receive data . When transmitting data , Server side through their own TCP 20 Port send data .FTP server A new connection must be established with the client to transmit data .

(2)Passive Pattern

When establishing control channels and Standard Similar model , When the client sends through this channel PASV When ordered ,FTP server Open a window located in 1024 and 15000 And notify the client of the request to transmit data on this port , then FTP server Data will be transmitted through this port , This is the time ETP server There is no need to establish a new connection with the client .

2. Build and configure FTP service

build FTP The server

1) Experimental environment

The server : CentOS 7 System ip: network address
client : Win10 System ip: network address
very secure ftlp

2) Software installation
linux In the system , yes vsftpd carry for ftp Service for ( No dependency packages , Directly yum install , It can also be installed on CD )

yum install -y vsftpd

3) The configuration file

/etc/ vsftpd/ vsftpd. conf ftp The main profile of the server
/etc/pam.d/vsftpd
/etc/vsftpd/ ftpusers No login user list , Default root Unable to land
/etc/vsftpd/user_ user name You can set that only users in this list can log in , If the same user at the same time Appear in the ftpusers and user_ user name Then the user is also forbidden to log in , Take the strictest Authority .
/var/ ftp ftp Root directory , Default login location
/var/ ftp/pub .

4) user
① Anonymous users : anonymous/ftp Default on , The password is empty.
② Local users : linux Users in the system ( You can log in directly without configuration, but there are security risks )
③ Virtual user : Customized virtual users ( Configuration is troublesome but relatively safe )

5) Opening service
systemctl start vsftpd

6) Anonymous users can download but not upload by default , Modify anonymous user permissions to upload

modify /etc/vsftpd/vsftpd.conf, Turn on anon _upload_ enable-YES
modify /var/ ftp/pub by 777 jurisdiction , Do not modify /var/ftp Otherwise, you cannot log in

7) allow root land .
modify /etc/vsftpd/ ftpusers, take root notes
modify /etc/vsftpd/vsftpd.conf, Add a row userlist_ _deny-NO
Restart the service .

8) Lock the user's home directory and do not switch at will
modify /etc/vsftpd/ vsftpd. conf
chroot_ local_ user-YES uncomment , Lock the home directory , But if the home directory has write permission ftp Will refuse to connect
allow writeable chroot-YES Add this line

(9) Restart the service
tepdump -i ens33 -nnX port 21
-nn: Directly to IP And portnumber Show , Instead of hostname and service name
-X : You can list hexadecimals (hex) as well as ASCII Contents of the package , It is very useful for monitoring the contents of packets

3. Check the information

yum info vsftpd

FTP (File Transfer Protocol: File transfer protocol ) effect : Internet The protocol used to transfer documents on .
VSFTP Full name (very secure FTP )
VSFTP Pattern : C/S Pattern
FTP The server defaults to TCP Agreed 20、21 Port to communicate with the client
20 Ports are used to establish data connections , And transfer file data
21 Ports are used to establish control connections , And transmit FTP Control command
FTP Data connection is divided into active mode and passive mode
Active mode : The server initiates the data connection actively
Passive mode : The server passively waits for data connections

Opening service , Turn off firewalls and enhanced security X
systemctl stop firewalld
setenforce 0
rpm -qa l grep vsftp

yum install -y vsftpd
cd /etc/ vsftpd/
cp vsftpd. conf vsftpd. conf .bak

4. Set anonymous user access to FTP service ( Maximum authority )

1) Modify the configuration file
vim /etc/vs ftpd/vsftpd. conf
anonymous_ enable-YES Enable anonymous user access . The default is on (FTP)
write_ enable=YES Open server write permissions ( To upload , Must be turned on ). The default is on

anon_ umask=022 Set the permission mask for anonymous users to upload data ( Unmask ).
anon_ upload_ enable-YES Allow anonymous users . Upload files . Default annotated , Need to uncomment
anon_ mkdir_ write_ enable=YES Allow anonymous users to create (. Upload ) Catalog . Default E notes , Need to uncomment
anon_ other_ write_enable=YEs Allow others to delete 、 rename 、 Covering and other operations . Need to add
chmod 777 /var/ftp/pub/ Access is anonymous ftp Under the root directory of pub Set the maximum permissions for subdirectories , In order to Users upload data

2) Opening service , Turn off firewalls and enhanced security

systemctl start vsftpd .
systemctl stop firewalld
setenforce 0

3) Anonymous access testing
stay windows The system opens the start menu , Input cmd Command opens the command prompt
establish ftp Connect
ftp network address
Anonymous access , The user is called ftp, The password is empty. , Just press enter to complete the login
ftp> pwd Anonymous access ftp The root month of is recorded as Linux Systematic /var/ftp/ Catalog
ftp> ls View current directory
ftp> cd pub Switch to pub Catalog
ftp> get file name Download the file to the current Windows Local directory
ftp> put file name Upload files to ftp Catalog
ftp> quit sign out

yum install -y vsftpd