Understanding & Managing FTP Server
What is FTP?
FTP protocol (File Transfer Protocol) is, as its name indicates a protocol for transferring files. The implementation of FTP dates from 1971 when a file transfer system between MIT machines (Massachusetts Institute of Technology) was developed. Many RFC have since made improvements to the basic protocol, but the greatest innovations date from July 1973. FTP, the File Transfer Protocol, is one of the original network applications developed with the TCP/IP protocol suite. It follows the standard model for network services, as FTP requires a client and a server , FTP set out to solve the need to publish documents and software so that people could get them easily from other computer systems. On the FTP server, files were organized in a directory structure; users could connect to the server over the network ,and download files from (and possibly upload files to) the server.
The role of FTP protocol:
FTP protocol defines the way in which data must be transferred over a TCP/IP network.
The aim of FTP protocol is to:
allow file sharing between remote machines allow independence between client and server machine system files
enable efficient data transfer
The FTP model:
FTP protocol falls within a client-server model, i.e. one machine sends orders (the client) and the other awaits requests to carry out actions (the server).During an FTP connection, two transmission channels are open:
A channel for commands (control channel)
A channel for data
So, both the client and server have two processes allowing these two types of information to be managed:
DTP (Data Transfer Process) is the process in charge of establishing the connection and managing the data channel. The server side DTP is called SERVER-DTP, the client side DTP is called USER-DTP.
PI (Protocol Interpreter) interprets the protocol allowing the DTP to be controlled using commands received over the control channel. It is different on the client and the server:
The SERVER-PI is responsible for listening to the commands coming from a USER-PI over the control channel on a data port, establishing the connection for the control channel, receiving FTP commands from the USER-PI over this, responding to them and running the SERVER-DTP.
The USER-PI is responsible for establishing the connection with the FTP server, sending FTP commands, receiving responses from the SERVER-PI and controlling the USER-DTP if needed. When an FTP client is connected to a FTP server, the USER-PI initiates the connection to the server according to the Telnet protocol. The client sends FTP commands to the server, the server interprets
them, runs its DTP, then sends a standard response. Once the connection is established, the server-PI gives the port on which data will be sent to the Client DTP. The client DTP then listens on the specified port for data coming from the server. It is important to note that since the control and data ports are
separate channels, it is possible to send commands from one machine and receive data on another. So, for example it is possible to transfer data between FTP servers by passing through a client to send control instructions and by transferring information between two server processes connected on the
right port. In this configuration, the protocol imposes that the control channels remain open throughout the data transfer. So a server can stop a transmission if the control channel is broken during transmission.
What is vsftpd?
The Very Secure FTP Server (vsFTPd) is the only FTP server software included in the Red Hat Linux distribution , vsFTPd is becoming the FTP server of choice for sites that need to support thousands of concurrent downloads. It was also designed to secure your systems against most common attacks.
Configuration Files
/etc/vsftpd/vsftpd.conf : Main Configuration File /etc/vsftpd/ftpusers : Contains Users list to deny permanently
/etc/vsftpd/user_list : Contains Users list to allow or deny
FTP uses TCP ports 20 (for ftp data) & 21 (ftp program).
Installing FTP service:
root@vijay~]# yum install vsftpd
root@vijay~]# vim /etc/vsftpd/vsftpd.conf
(if you want to deny all user from login) at the end of file write down the following line.
userlist_deny=NO
and add the name of user to whom you want to grant permission for login in user_list
Starting vsftpd service:
root@vijay~]#service vsftpd start;chkconfig vsftpd on
Client Side Commands For Connecting to FTP Server
root@vijay~]#ftp 0 (for local login)
root@vijay~]#ftp x.x.x.x (for remote login)
For Installing Packages from FTP server
root@vijay~]#rpm -ivh ftp://x.x.x.x/pub/Server/package.rpm
Limiting maximum connections
VSFTPD allows unlimited connection from the same client IP address. You can easily force
vsftpd ftp server to use limited number of connection. There is a special directive called
max_per_ip.
root@vijay~]# vim /etc/vsftpd/vsftpd.conf
max_per_ip=3max_clients=2 ----- max simultaneous connections
Allowing “anonymous” upload to FTP
STEP – 1:
root@vijay~]# vi /etc/vsftpd/vsftpd.conf
anon_upload_enable=YESchown_uploads=YES
chown_username=daemon
anon_umask=077
STEP -2: Create a directory under –
root@vijay~]#mkdir /var/ftp/incoming
root@vijay~]#chmod 770 /var/ftp/incoming
root@vijay~]#chown root:ftp /var/ftp/incoming
root@vijay~]#setfacl -m u:vijay:rwx /var/ftp/incoming
root@vijay~]#setsebool -P allow_ftpd_full_access
root@vijay~]#service vsftpd restart
root@vijay~]# ftp 192.168.0.15
Connected to 192.168.0.14 (192.168.0.14).220 (vsFTPd 2.2.2)
Name (192.168.0.14:root): vijay
331 Please specify the password.
Password:
230 Login successful.
Remote system type is UNIX.
Using binary mode to transfer files.
ftp> cd /var/ftp/pub
250 Directory successfully changed.
ftp> ls
227 Entering Passive Mode (192,168,0,14,67,118).
150 Here comes the directory listing.
-rw-r--r-- 10 0 0 Aug 02 04:35 h1
-rw-r--r-- 10 0 0 Aug 02 04:35 h2
-rw-r--r-- 10 0 0 Aug 02 04:35 h3-rw------- 12 50 0 Aug 02 04:40 popo
drwx------
2 14
50
4096 Aug 02 04:52 raj
226 Directory send OK.
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