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→INVESTIGATION 2: IPTABLES TROUBLESHOOTING CHECKLIST
<table border="1" cellspacing="0" cellpadding="5" >
<tr><th>Step</th><td>'''Procedure'''</td><td>'''Explanation'''</td></tr>
<tr> <th>1</th><td>'''Test Network Connectivity'''</td><td>You can use the [httphttps://zenitwiki.senecaccdot.onsenecacollege.ca/wiki/index.php/OPS335_Lab_1#Linux_Network_Connection_Configuration_Troubleshooting steps in lab 1] as a guide, but keep in mind the firewall may be blocking pings and DNS requests.</td></tr>
<tr> <th>2</th><td>'''Verify Service is Running & listening on the correct interfaces'''</td><td>You should learn to read the output of '''ss -atnp''' and '''ss -aunp''' to complement the '''systemctl status''' command.</td></tr>
<tr> <th>3</th><td>'''List your iptables Rules & Perform a "Walk-Thru"'''</td><td>For many decades, when troubleshooting programs that don't run properly, programmers will resort to reading their "source-code" line-by-line and pretend they are the computer to perform the operation. The programmer "walks-through" the code to force them to think like a computer in order to spot and fix subtle problems.<br><br>Therefore, you can follow a packet's path as you understand it should follow. Keep in mind [http://zenit.senecac.on.ca/wiki/index.php/OPS335_Lab_2#How_Firewalls_.28iptables.29_Relate_to_the_Labs_in_this_Course the diagram from the lecture last week]. What chain applies first on which machine? What's the first rule that matches the packet? What happens if no rules match the packet?<br><br>Don't forget that even if you're tracing the path of outgoing traffic - the INPUT chain on your machine still applies (for the response that comes back to your request).</td></tr>
