Linux TCP Wrappers tutorial -Find If Program Is Compiled With TCPWrappers

What is TCP Wrappers ?

An important part of maintaining another level of security on Linux server is TCP Wrappers; you can restrict access to your system by remote hosts by using list of hosts are kept in the, TCP wrappers is host based networking access control list, it used to filter network access to internet.
 /etc/hosts.allow and /etc/hosts.deny files.

TCP Wrappers stand guard between an incoming request and the requested service.

Configuration Files 

When a client connects to a “ tcp wrapped” service, the access control list /etc/hosts.allow and /etc/hosts.deny are examined. The server will then either choose to accept or drop the connection, depending on the control list configuration. Policies can be specified for individual services and are usually configured in terms of the clients IP-Address.Both files have same basic syntax to allow or deny clients list

Permissions in /etc/hosts.allow

Denials in /etc/hosts.deny

Now the Question is which file will be checked first and the answer is /etc/hosts.allow

If the same client or IP  is listed in both hosts.deny & hosts.allow , in this case  hosts.allow takes precedence, and access will be permitted.

How do I Find Out Whether daemon Is Compiled with TCP Wrappers or Not?

To determine if TCP Wrappers supports that daemon

 $ ldd /daemon path | grep libwrap.so

If this command shows any output, then the daemon probably supports TCP Wrappers.

[root@tecgeeks ~]# whereis vsftpd

Sample Output:

vsftpd: /usr/sbin/vsftpd /etc/vsftpd /usr/share/man/man8/vsftpd.8.gz

Next, run the ldd command as follows to find out whether vsftpd daemon supports TCP Wrappers or not:

[root@tecgeeks ~]# ldd /usr/sbin/vsftpd | grep libwrap.so

Sample Output:

libwrap.so.0 => /lib/libwrap.so.0 (0x00db1000)



The ldd command is used to check  if libwrap.so is a dependency or not.

Syntax (format) Of Host Access or deny

Both /etc/hosts.allow and /etc/hosts.deny use the following format:

daemon name: client IP / client node name

Examples:

sshd: tecgeeks.com or 192.168.198.129

vsftpd: ALL EXCEPT: TecGeeks.com



In above example entry is on hosts.deny for denying ftp access to all client except 192.168.198.129.
Linux TCP Wrappers tutorial -Find If Program Is Compiled With TCPWrappers Linux TCP Wrappers tutorial -Find If Program Is Compiled With TCPWrappers Reviewed by Unknown on July 22, 2016 Rating: 5

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