Hardening SSH:

Overview:

0. Intention
1. Description
2. Commands
3. Connection States
4. Persistence
5. Examples
6. Additional Options
7. Closing Thoughts
8. Additional Resources & Recommended Reading

0) Introduction & Intention

This write-up is intended to be a simple walkthrough for linux netfilter, and will be written more like a cheatsheet than a tutorial. It'll cover a basic explanation of netfilter terminology, using basic iptables commands for configuring netfilter, some example rules, and a few additional capabilities.

1) $$$$Description

Explanation of netfilter,and iptables vs ip6tables

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what are chains

actions

default policies

basic structure of a command

2) $$$$$IPTables Commands

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3) $$$$$Connection States

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4) $$$$$$Making Rulesets Persistent

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5) $$$$$$$Example Rulesets

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6) $$$$$$Additional Options

Brute-Force Protection

Ban by Geolocation

Fail2Ban

7) $$$$$$Closing Thoughts

This cheatsheet should hopefully give you a solid understanding of what the linux netfilter is, and how to use the iptables command for basic configuration. It is important to always keep in mind that your needs and your environment will determine which, if any, of these recommendations work for you. You should always keep your threat model in mind when implementing configuration changes, and never blindly follow advice on the internet. Remember: Trust, but verify! Do you think I missed something? Did a step not work? Could this simply be the most bestest article you've ever seen on the interwebz? Feel free to stop by the channel and let us know what you think. You can send your flames or flattery for this article to PrettyKittie via IRC or email.

8) $$$$$$$Additional Resources & Recommended Reading

• The #NetFilter IRC channel on Freenode
• Additional NetFilter links and tutorials
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