Commands using iptables

this alternative shows the differences as they occur so that they are made plain

Rather then editing the /etc/sysconfig/iptables file, or during a kickstart doing some awk/sed magic, easily add a rule in the correct place within iptables

This command will open tcp port 3000 in your machine

If you changed the default policy on any chain other than filter table chain's, this won't be enough.

To save all rules so that they are not lost in case of a server reboot:

/etc/init.d/iptables save

Thanks to http://www.cyberciti.biz/faq/how-do-i-block-an-ip-on-my-linux-server/

Should run with sudo

Ddos syn attack

Takes IP from web logs and pipes to iptables, use grep to white list IPs.. use if a particular file is getting requested by many different addresses.

Sure, its already down pipe and you bandwidth may suffer but that isnt the concern. This one liner saved me from all the traffic hitting the server a second time, reconfigure your system so your system will work like blog-post-1.php or the similar so legitimate users can continue working while the botnet kills itself.

Clear iptables rules safely

a simple command in order to make iptables rules permanent, run @ sudo!

Destination IPs will become invisible to source IPs!

Safe for whitespaces in names.

show your current iptable rules from every available iptable table

I was previously unaware of the -v switch. As a result I never got specifics about which interfaces the allowed or dropped applied to. Thought I'd share the wealth...

FYI, -n prevents DNS resolving of IPs.

Retrieve top ip threats from http://isc.sans.org/sources.html and add them into iptables output chain.

Stuck behind a restrictive firewall at work, but really jonesing to putty home to your linux box for some colossal cave? Goodness knows I was...but the firewall at work blocked all outbound connections except for ports 80 and 443. (Those were wide open for outbound connections.) So now I putty over port 443 and have my linux box redirect it to port 22 (the SSH port) before it routes it internally. So, my specific command would be:

Note that I use -A to append this command to the end of the chain. You could replace that with -I to insert it at the beginning (or at a specific rulenum).

My linux box is running slackware, with a kernel from circa 2001. Hopefully the mechanics of iptables haven't changed since then. The command is untested under any other distros or less outdated kernels.

Of course, the command should be easy enough to adapt to whatever service on your linux box you're trying to reach by changing the numbers (and possibly changing tcp to udp, or whatever). Between putty and psftp, however, I'm good to go for hours of time-killing.

Removes an iptables rule created by fail2ban. This example shows how to remove a rule for an IP from the fail2ban-SSH chain. Can be used for any service monitored by fail2ban.

For more on fail2ban, see http://www.fail2ban.org/wiki/index.php/Main_Page

This turns your iptables packet filter to a "Allow any from any to any" filter, so you can rule out any filtering issues when you have a problem to enable a connection from or to your host.

To re-enable it, run /etc/init.d/iptables restart

This is just one method of checking to see if an IP is blocked via IP tables or CSF. Simple and to the point. Replace xx.xx.xx.xx with the IP you wish to check.