Web Hosting Tutorials

TCP wrappers

Posted on October 12th, 2006 by Admin.
Categories: Cpanel Hosting, Server Security, Linux.

Greetings,

TCP Wrapper is a host-based network ACL system, used to filter network access to Internet protocol services run on Unix-like Operating Systems such as Linux or BSD. It allows host or subnetwork IP addresses names and/or query replies, to be used as tokens on which to filter for access control purposes .
First “/etc/hosts.allow” is check, and if there is an entry in this file, no more checking it done. If are no matches in “/etc/hosts.allow”, the “/etc/hosts.deny” file is checked and if a match is found, that service is blocked for that host.

Example “/etc/hosts.deny” file:

sshd: 192.168.1.1

The above file blocks access to computer 192.168.1.1 . It’s also possible to run commands when someone from this computer tries to ssh in.

This example sends mail.
sshd: 192.168.1.1: spawn (echo -e “%d %h %H %u”| /bin/mail -s ‘hosts.deny entry’ root)

Of course, you can also run commands in the “/etc/hosts.allow” if you wanted mail sent for a successful login.

Cheers

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