FTP server

File Transfer Protocol

File Transfer Protocol is the one of the oldest network protocols to transfer which is used to transfer the the files with strong security

FTp server allows anonymous users to upload content and it will restrict the downloading of files by anonymous users

FTP user can download content from the FTP server that was uploaded by some other  FTP user

ActiveFTP

Your client connects to the FTP server by establishing an FTP control connection to port 21 of the server. Your commands such as 'ls' and 'get' are sent over this connection.
 Whenever the client requests data over the control connection, the server initiates data transfer connections back to the client. The source port of these data transfer connections is always port 20 on the server, and the destination port is a high port (greaterthan1024)on the client.

Thus the ls listing that you asked for comes back over the port 20 to high port connection, not the port 21 control connection.
FTP active mode therefore transfers data in a counter intuitive way to the TCP standard, as it selects port 20 as it's source port (not a random high port that's greater than 1024) and connects back to the client on a random high port that has been pre-negotiated on the port 21 control connection.
Active FTP may fail in cases where the client is protected from the Internet via many to one NAT .This is because the firewall will not know which of the many servers behind it should receive the return connection.

Passive FTP

Your client connects to the FTP server by establishing an FTP control connection to port 21 of the server. Your commands such as ls and get are sent over that connection.                                                                   

Whenever the client requests data over the control connection, the client initiates the data transfer connections to the server. The source port of these data transfer connections is always a high port on the client with a destination port of a high port on the server.
Passive FTP should be viewed as the server never making an active attempt to connect to the client for FTP data transfers. Because client always initiates the required connections, passive FTP works better for clients protected by a firewall.
As Windows defaults to active FTP, and Linux defaults to passive, you'll probably have to accommodate both forms when deciding upon a security policy for your FTP server

Regular FTP 

By default, the VSFTPD package allows regular Linux users to copy files to and from their home directories with an FTP client using their Linux usernames and passwords as their login credentials.

VSFTPD also has the option of allowing this type of access to only a group of Linux users, enabling you to restrict the addition of new files to your system to authorized personnel.

The disadvantage of regular FTP is that it isn't suitable for general download distribution of software as everyone either has to get a unique Linux user account or has to use a shared username and password. Anonymous FTP allows you to avoid this difficulty. 

Anonymous FTP 

Anonymous FTP is the choice of Web sites that need to exchange files with numerous unknown remote users. Common uses include downloading software updates . Anonymous FTP requires only a username of anonymous and your email address for the password. Once logged in to a VSFTPD server, you automatically have access to only the default anonymous FTP directory (/var/ftp in the case of VSFTPD) and all its subdirectories.

Configuration of FTP server

Service profile

Service:  vsftpd

Package: vsftpd

Port no:20 for download

              21 for upload

Configuration file: /etc/vsftpd/vsftpd.conf

/etc/vsftpd/ftpusers

/etc/vsftpd/user_list

/etc/pam.d/vsftpd

/etc/vsftpd/chroot_list

Script file: /etc/init.d/vsftpd

Daemons: vsftpd

Step:1

Install packages

[root@ftp~]#yum install vsftpd* -y

Step:2

Create the resources on the ftp server

Create user and assign to whom you want to allow logging through ftp `

[root@ftp~]#useradd raju

[root@ftp~]#passwd yyyyyy

Create or Copy files inside /var/ftp/pub

[root@ftp~]#cd /var/ftp/pub

[root@pub]#touch  file[1..10]

[root@pub]#ls  

Create a Upload folder for anonymous users and give full permissions for read/write

[root@ftp~]#mkdir /var/ftp/upload

[root@ftp~]#chmod 777  /var/ftp/upload

Step:3

Edit the main configuration

[root@ftp~]#vi /etc/vsftpd/vsftpd.conf

 anonymous_enable=YES

local_enable=YES

anon_upload_enable=YES

:wq!

[root@ftp~]#chkconfig vsftpd on

[root@ftp~]#service vsftpd restart