Follow Techotopia on Twitter

On-line Guides
All Guides
eBook Store
iOS / Android
Linux for Beginners
Office Productivity
Linux Installation
Linux Security
Linux Utilities
Linux Virtualization
Linux Kernel
System/Network Admin
Programming
Scripting Languages
Development Tools
Web Development
GUI Toolkits/Desktop
Databases
Mail Systems
openSolaris
Eclipse Documentation
Techotopia.com
Virtuatopia.com

How To Guides
Virtualization
General System Admin
Linux Security
Linux Filesystems
Web Servers
Graphics & Desktop
PC Hardware
Windows
Problem Solutions
Privacy Policy

  




 

 

7.6. iptables and Connection Tracking

iptables includes a module that allows administrators to inspect and restrict connections to services available on an internal network using a method called connection tracking. Connection tracking stores connections in a table, which allows administrators to allow or deny access based on the following connection states:

  • NEW — A packet requesting a new connection, such as an HTTP request.

  • ESTABLISHED — A packet that is part of an existing connection.

  • RELATED — A packet that is requesting a new connection but is part of an existing connection, such as passive FTP connections where the connection port is 20, but the transfer port can be any unused port 1024 or higher.

  • INVALID — A packet that is not part of any connections in the connection tracking table.

You can use the stateful functionality of iptables connection tracking with any network protocol, even if the protocol itself is stateless (such as UDP). The following example shows a rule that uses connection tracking to forward only the packets that are associated with an established connection:

iptables -A FORWARD -m state --state ESTABLISHED,RELATED -j ALLOW

 
 
  Published under the terms of the GNU General Public License Design by Interspire