Tag Archives: iptables

Iptables and Connection Limits

Create connection limits for any users using a very basic script in the firewall area as shown below   iptables -I FORWARD -p tcp –syn -m iprange –src-range -m connlimit –connlimit-above 60 -j DROP iptables -I FORWARD -p tcp –syn -m iprange –src-range -m connlimit –connlimit-above 60 -j DROP iptables -I FORWARD -m

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Prevent DOS with iptables | Shadows of epiphany

Prevent DOS with iptables | Shadows of epiphany.

Prevent DOS with iptables

After a recent conversation on the Ubuntu Forums I wanted to post an example of using iptables.

Of course there are several types of DOS attacks , in this post I will demonstrating the use if iptables to limit the traffic on port 80.

The goal is to keep your web server “responsive” to legitimate traffic, but to throttle back on excessive (potential DOS) traffic.

In this demonstration iptables is configured :

  1. The default policy is ACCEPT (to prevent lockout in the event of flushing the rules with iptables -F).
  2. “Legitimate” traffic is then allowed. In this example I am allowing traffic only on port 80.
  3. All other traffic is then blocked at the end of the INPUT chain (the final rule in the INPUT chain is to DROP all traffic).


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IP Tables Primer

IP Tables Primer.

image unavailable

Note:The above “IPTables Flow chart” was originally published here,

is licensed under the GNU FDL, and is used with permission.

Table of Contents

  1. Overview
  2. Basic Networking Concepts
  3. Anatomy of iptables
  4. Using iptables for Filtering
    • Options
    • Rules
    • Saving your configuration
    • Additional Tips
  5. NAT – Network Allocation Table
  6. References


The man who wears robes made from rags off the dust heap, who is gaunt, with his sinews standing out all over his body, alone meditating in the forest – that is what I call a brahmin.

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