Keyinator Keyinator

Some examples of SNAT, DNAT with iptables with comments

mainly used in start-up script

How to test 'safely'

When we play with iptables aka firewall we might end up in situation, where we execute rule, which has unforseen impact - lock yourself out. Recovering from this situation is necessity.

How to:

Enable reboot via SMS.

Test all commands in shell first before putting them into Start-up script. This way the command will be wiped out, when unit is rebooted.

masquarade all outgoing packets to be WLAN0 IP

syn-flood protection

Limit the number of incoming TCP connections.

iptables -N syn_flood
iptables -A INPUT -p tcp --syn -j syn_flood
iptables -A syn_flood -m limit --limit 1/s --limit-burst 3 -j RETURN
iptables -A syn_flood -j DROP

--limit 1/s: Maximum average matching rate in seconds

Markdown Text 101

Want to inject some flavor into your everyday text chat? You're in luck! Discord uses Markdown, a simple plain text formatting system that'll help you make your sentences stand out. Here's how to do it! Just add a few characters before & after your desired text to change your text! I'll show you some examples...

What this guide covers:

Text Formatting
Organizational Text Formatting
- Headers
Subtext

The netfilter hooks in the kernel and where they hook in the packet flow

The figure below calls out

The netfilter hooks
The order of table traversal

Learning `discord.py`

This guide assumes your version of discord.py is updated to at least v1.0 or greater.
You can check your version with pip show discord.py.

Show Contents

Required Knowledge
Essential References
Creating a Discord Bot Account

	// Just before switching jobs:
	// Add one of these.
	// Preferably into the same commit where you do a large merge.
	//
	// This started as a tweet with a joke of "C++ pro-tip: #define private public",
	// and then it quickly escalated into more and more evil suggestions.
	// I've tried to capture interesting suggestions here.
	//
	// Contributors: @r2d2rigo, @joeldevahl, @msinilo, @_Humus_,
	// @YuriyODonnell, @rygorous, @cmuratori, @mike_acton, @grumpygiant,

	##TCP FLAGS##

	Unskilled Attackers Pester Real Security Folks
	==============================================
	TCPDUMP FLAGS
	Unskilled = URG = (Not Displayed in Flag Field, Displayed elsewhere)
	Attackers = ACK = (Not Displayed in Flag Field, Displayed elsewhere)
	Pester = PSH = [P] (Push Data)
	Real = RST = [R] (Reset Connection)
	Security = SYN = [S] (Start Connection)

	### 1: Drop invalid packets ###
	/sbin/iptables -t mangle -A PREROUTING -m conntrack --ctstate INVALID -j DROP

	### 2: Drop TCP packets that are new and are not SYN ###
	/sbin/iptables -t mangle -A PREROUTING -p tcp ! --syn -m conntrack --ctstate NEW -j DROP

	### 3: Drop SYN packets with suspicious MSS value ###
	/sbin/iptables -t mangle -A PREROUTING -p tcp -m conntrack --ctstate NEW -m tcpmss ! --mss 536:65535 -j DROP

	### 4: Block packets with bogus TCP flags ###

	Detecting and Mitigating DDOS Attacks

	#List all Finish (FIN) packets
	machine1 : sudo /usr/sbin/tcpdump -Nnn -i any -s0 'tcp[13] & 1 != 0'


	#List all SYN and SYN-ACK packets
	machine1 : sudo /usr/sbin/tcpdump -Nnn -i any -s0 'tcp[13] & 2 != 0'