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* [https://prezi.com/akyqt4h40oel/iptables-packet-filtering/ Week 3 Notes] Recommended to review and understand prior to performing this lab.
Refer Let's set a '''default policy''' to the following [httpsdisable all inbound traffic://prezi.com/akyqt4h40oel/iptables-packet-filtering/ OPS335 NOTES] if you need to review how to use the iptables command. You can also perform a Netsearch for additional examples (such as deleting iptables rules for a chain).
Let# Issue an 's set a default 'iptables command''to set the default policy''' to '''disable all inbound traffic.# Issue an ''iptables command'':to list rules to verify you correctly disabled all inbound traffic.
# Issue an The remaining iptables rules will relate to that same '''inbound'iptables command'' to set the policy to disable all inbound traffic.# Issue an iptables command to list rules to verify you correctly disabled all inbound traffic.chain:
The remaining tasks will relate to that same '''inbound''' traffic chain: <ol><li value="3">Issue the command '''iptables -L INPUT''', and note the rules associated for ssh in your lab logbook.</li><li>Issue an ''iptables command'' to delete the default ssh rule, and issue another iptables command to verify.</li><li>Issue an ''iptables command'' to insert an iptables rule to ACCEPT SSH connections at the SSH rule '''beginning''' of the chain (refer to your lab logbook for details) .</li><li>Verify that you inserted that rule at the beginning top of the INPUT chain. Verify that did what you thought it did, and then issue an iptable rule to delete that rule at the top of the chain (i.e. by number), and verify that it that rule was deleted.</li><li>Issue an ''iptables command'' to append the SSH rule to the end of the chain, verify, delete that same rule, and verify.</li><li>Issue an ''iptables command'' to delete the related,established rule. Test your network connectivity between your hosts and vms. What happened?</li><li>Issue an ''iptables command'Shut down your VMs''' to and '''restorereboot your host machine''' (i.e. not flush) What happens to the iptables rules you created for your host machine? Note in your OPS335 lab logbook how to save and restore your firewall iptables rules, and what the difference of '''restoring iptables rules''' as opposed to its default settings'''flushing iptables rules'''.</li></ol>
# Make a backup of the original default rules: <source lang='bash'>cp /etc/sysconfig/iptables /etc/sysconfig/iptables.original</source>
'''Depending You may choose to:* Submit screenshots of your work on your professor Blackboard, in which case you will either be asked don't need to come to submit the lab in class, or online. Follow * Or come to the appropriate set of instructions belowlab, show me your work, and talk to me about it.I want to hear what you'''ve learned and answer any questions you have.
===Online Submission===Follow You'll get the instructions for lab 2a on moodlesame grade regardless of how you choose to submit your work.
===In Class Submission===[[Image:lab1_signoff.png|thumb|right|300px|Students should be prepared with '''all required commands (system information) displayed in a terminal (or multiple terminals) prior to calling the instructor for signoff'''.]]'''Arrange evidence (command output) for each Expected results of these items on your screen, then ask your instructor to review them and sign off on the this lab's completionare:'''
→Creating Customized Chains
In this lab, you will learn how to use '''iptables''' to build a simple '''Linux firewall''' on your servers.
iptables is a <u>very complex</u> topic. Fortunately, you are not required to become an ''"iptables expert"'', but by the end of the course, you should be able to use iptables to properly secure your servers.
You were exposed to iptables in your OPS235 course. You should refer to [http://zenit.senecac.on.ca/wiki/index.php/Lab_6_Warnings_/_Debrief#Investigation_2:_Networking_Tweaks OPS235] or [https://prezi.com/akyqt4h40oel/iptables-packet-filtering/ OPS335] notes or find and use documentation to learn how to complete these tasks. You can also ask your professor or lab assistant during the lab for help when using iptables. Some basic iptables commands are provided in this lab for reference, but it is also essential that you know how to obtain help (man pages and online) in order to become self-reliant.
{{Admon/important |firewalld|In this course, we will be using ''iptables'', '''<u>not</u>''' ''firewalld''. Although firewalld can present information in the familiar iptables format, learning both would be too advanced at this point of learning Linux network administration.<br>In the first labs [httphttps://zenitwiki.senecaccdot.onsenecacollege.ca/wiki/index.php/OPS335_Installation_Lab#Using_iptables OPS335_Weekly_Schedule Prep for Labs], you should have disabled and stopped the firewalld service: .<br><br>You can also check the status of the firewalld service by issuing the [http://zenit.senecac.on.ca/wiki/index.php/Init_vs_systemd#systemd_Command_Usage systemctl] command. You can also check if the firewalld service is running by issuing '''iptables -L''' and noting a high volume of unexpected output (i.e. "a strange result").
}}
=== Online Resources===
* [https://en.wikipedia.org/wiki/Iptables#Overview Overview] A excellent concise overview of iptables (ignore diagram).
* [https://wiki.centos.org/HowTos/Network/IPTables CentOS Wiki] Listing of basic commands (not all required to know).
'''There are some important things to be aware of in terms of this diagram:'''
:*There are '''<u>two sets</u> ''' of IPtables rules (chains) that apply:''' '''OUTPUT/INPUT on the client''' and '''INPUT/OUTPUT on the server'''.<br>It is important to think about trafic from the perspective from the client as well as the server.
:* '''Outbound traffic is rarely blocked <u>unless</u> there is a security policy to <u>prevent</u> some kind of traffic'''.<br>Even in that case, that security policy is usually performed on a router.
:* '''Inbound traffic is of two distinct types'''. Our diagram shows:
::# '''New incoming <u>connections</u>''' (what you normally think of as '''<u>inbound traffic</u>'''): the web server receives a '''new incoming connection'''.::# '''Incoming <u>data</u> that client receives as a response from the server''': the web page that the server sent back in the diagram above.
::::The analogy would be like making a '''telephone call''':<ul><li>A '''NEW''' packet is like the phone ringing</li><li>An '''ESTABLISHED''' packet is the connection and the packet says "hello", along with any further communication.</li><li>A '''RELATED''' packet would be the same person calling on a second line. (eg. a second connection that is made because of something that happened in the first, like an ftp transfer).</li></ul>
::::We normally don't want to do anything special for the response. It is safe to assume that '''a connection that was allowed to be established should be allowed to receive a response'''. This is accomplished with the following '''INPUT chain rule''' that should be there by default on your machines:<br>
::# For the ''request'', the '''source port (sport) for the example in the above diagram is 40112''' and the '''destination port (dport) is 80'''
::# For the ''response'', the '''source port (sport) is 80''' and the '''destination port (dport) is 40112'''
::# Since the '''RELATED,ESTABLISHED''' rule already exists, we are only concerned about <u>'''controlling'''</u> the '''incoming traffic on the server''', which in our example, the '''chain is: INPUT''', the '''protocol is: tcp''', and the '''destination is: port 80'''.
:* '''Basically, most other services work in a similar way as discussed above'''.
:''The more you practice and get comfortable with iptables, the quicker you will be able to isolate and fix connection issues.''
:We don't expect you to become firewall experts, but there are some basics that you need to become familiar for this and future labs:
:* What is a '''chain'''?
:* '''Which chain''' applies to which traffic?
:* What's the '''default action''' for a chain and when that applies?
:* Understanding the differences between '''setting policies''', '''adding rules''', and '''inserting rules'''.
:* What In what '''order are the rules are executed in'''?
:* '''Reading and/or creating a rule''' for a specific service. That includes a basic understanding of:
:** '''Protocols'''
:** '''Ports'''
:** '''Protocols'''Source/Destination IPADDR:** HWADDR (MAC Address):** Network Interface name
:The best way to learn that is to <u>'''practice'''</u>.
=== Confirming Existing Network Connections ===
Before proceeding with iptables, we should first verify that your '''host machine''' and '''vmsVMs''' can connect with each other. We can also take the opportunity to record some observations which could be used for future labs.<br><br>
'''Perform the Following Steps:'''
# Find Determine the ''MAC address'' of the virtual network device on your '''host machine''' and the ''IP address'' assigned to it. Record this information in your lab log book.
# Launch all three of your '''VMs'''.
# For each '''VM''':
#* Login as root.
#* Find the MAC address of the '''Network Interface''' and the '''IP address ''' assigned to it. Record this information on your lab log book.
# Change to your '''host machine''', open a terminal window, and perform the following connectivity tests for each vm:<br><br>
<source lang="bash">
ping -c 1 [ip-of-vm]
ssh [ip-of-vm]
'''Perform the Following Steps:'''
# Leave your VMs running for this section (which seems counter-intuitive).
# On your '''host machine''', stop the '''libvirtd''' service (refer to [http://zenit.senecac.on.ca/wiki/index.php/Init_vs_systemd#systemd_Command_Usage systemctl] command), and '''restart ''' the '''iptables''' service.
# Run '''iptables -L -v''' but redirect the output to a text file called '''before.txt''' (you will be using this file later).
#You should notice the virtual machine manager no longer contains the lists your vms(i.e. vm1, vm2, or vm3).
#Close and then restart the virtual machine manager. What Happens?<br /> What are the states of your VMs? Record your observations in your lab logbook.
#Close the virtual machine manager application window again.
# '''Restart ''' the '''libvirtd''' service.
#Now, restart the virtual machine manager ('''note:''' it should indicate that the virtual machine manager connecting - be patient and wait until you are prompted you to enter the root password). What happens? What is the status of your VMs?
#What does this mean when you lose your vm connections (including the disruption of the libvirtd service)? <br>Record your observations in your lab logbook.
# Re-issue '''iptables -L -v''' commands making certain to redirect output to a second file ('''after.txt'''). This should provide a listing of the new state of your firewall settings.
# You now should have two text files representing the <u>before</u> and <u>after</u> states of your firewall. Compare differences between these two files using the '''diff''' command<br>(You should have used this tool in '''ULI101''').
#You can use these tools to compare any two text files, they often come in handy. Note in your lab logbook the iptables rules that were added automatically by the '''libvirtd''' service.
#Are there any differences between those 2 files? What does this mean if your VMs get disconnected in terms of the firewall rules?
{{Admon/tip|Graphically Compare File Differences|You can also install a graphical tool that makes it much easier to see differences: '''kompare before.txt after.txt<br><br>NOTE: Make certain to run the command as a regular user (not i.e. NOT root!).}}
=== Practice Setting Firewall Rules on Host Machine===
We will run some iptables commands on your '''host machine''' to practice and get a basic understanding of how to set rules. We will NOT be saving the iptables rules in this section, so you don't have to worry about "messing-up" your host machine - you can simply reboot your host machine to load the default iptables rules.
'''Record steps, commands, and your observations in INVESTIGATION 1 in your OPS335 lab log-book'''
<tr> <td>'''Always back-up the default iptables settings'''</td><td>When you install iptables in CentOS it already has some rules predefined.<br />Make a copy of the file that creates these rules (including the ones that allow communication with your other machines). This way you can always restore them to have a functional machine even if you completely mess up your rules.</td></tr>
<tr> <td>'''Place your iptables commands (i.e. Rules) within a bash Bash shell script'''</td><td>If you need to reset iptables, then you can run a shell script to quickly re-apply rules to save time.</td></tr>
<tr> <td>'''Don't Panic if disconnected from a VM'''</td><td> Some of the traffic between your host and VirtManager goes through IPtables.<br> When you mess with IPtables rules on the host, you might end up losing the console connection to the virtual machines.<br>'''Don't worry, the virtual machines are still running and you can still use them once you re-establish your connection'''.</td></tr>
'''Perform the following steps for your <u>host </u> machine:'''
# '''Stop libvirtd''' and '''restart iptables''' so that you have only the minimal default rules.
# Make a backup of the original default rules: <source>cp /etc/sysconfig/iptables /etc/sysconfig/iptables.original</source># Use the '''ifconfig ''' or '''ip address ''' command to determine the IP ADDRESS of your external facing address [ens33] (i.e. IP address beginning with '''10192.x168.x40.x'''if you are using an SSD).# Find Open a partner to terminal on the Windows machine and '''ping''' your external facing IP addressof your Linux host (ens33). Was your partner it successful? (it should have worked)
# Change the '''default policy''' on the '''INPUT''' and '''FORWARD''' chains in the filter table to '''DROP'''.
# Remove the rules from the '''INPUT''' and '''FORWARD''' chains (if any) that are '''rejecting''' all traffic (we are now better protected by the ''default policy'').<br><br>We will now create a new chain in order to create rules just relating to the '''ssh''' service:<br><br>
#* '''Note:''' Use '''--jump''' or '''-j''' (<u>not</u> -g or --goto) to move to a target.
# Add a rule to your '''MYSSH''' chain to accept all traffic on your virtual interface from '''192.168.X.0/24''' (i.e. your internal network).
# Add a rule to the '''beginning of your MYSSH chain''' that allows traffic from the IP address of your main host (probably Windows or Mac) machine.
# Add a rule to the '''end of the MYSSH chain''' to drop all remaining '''ssh''' connections, but to log these denied packets with log level 'info' and log prefix "DENIED BY MYSSH" before doing so.
#Remove the rule in your '''INPUT''' chain that was allowing all '''ssh''' traffic.
# Make a new chain named '''MYICMP'''.
# Insert a rule to the '''beginning of the INPUT chain''' to send '''ICMP''' packets to your '''MYICMP''' chain.
# Find a partner and get the '''IP ADDRESS''' and '''MAC address''' of your Windows machine'''their''' '''external s internal facing interface''' (should be an internal address beginning with '''10192.x168.x40.x''') .
# Add a rule to your '''MYICMP''' chain that allows '''ICMP''' packets coming in from '''192.168.X.0/24''' (i.e. your internal network).
# Insert a rule to the '''beginning of your MYICMP chain''' that denies '''ICMP pings''' originating with MAC address of your partner's main host (probably Windows) machine.# Insert a rule to the '''beginning of your MYICMP chain''' that denies '''ICMP pings''' originating with IP address of your partner's main host (probably Windows) machine.
# Issue '''iptables -L -v''' to view your firewall rules for your newly-created chains.
# Have your partner attempt Attempt to connect to your machine using the external facing address to ensure your rules are working.<br />They should not be able to connect, and the counters in iptables should show that packets are being caught in your MYICMP and MYSSH chains.<br><br>'''NOTE:''' Your system logs (such as: '''/var/log/messages''' or in the case (using a customized chains) the command: '''journalctl --dmesg | grep MYSSH''' should also show their your failed attempts to '''ssh''' to you with your '''customized''' message.# When you are confident the rules are working, save them by running <source lang=(''bash'>iptables-save > /etc/sysconfig/iptables</source><br />Note ''' ''that this should not include the rules from the virtual network. They will always be added automatically when libvirtd starts.'') <source>iptables-save > /etc/sysconfig/iptables</source>
# Now start libvirtd again, and test that your firewall still allows the VMs to connect to the host and each other (ping and ssh). Do not continue until it works.
{{Admon/tipimportant |Time for Backup your VMs!|You MUST perform a new '''full backup!|Once have successfully completed this lab''' of ALL of your VMs whenever you complete your '''OPS335 labs''' or when working on your '''OPS335 assignments'''. You should be using the dump or rsync command, make a new and you should use the Bash shell script that you were adviced to create in order to backup all of your virtual machinesVMs.}}
'''Record steps, commands, and your observations in INVESTIGATION 2 in your OPS335 lab log-book'''
Upon completion of this lab, your host machine has a firewall protecting it from unexpected traffic. You should now have a basic understanding of the commands necessary to modify firewalls using iptables. You will be building on these rules for the rest of the course.
===Online Submission===
Follow the instructions for lab 2a on blackboard.
<!--
===Andrew's sections===
::<span style="color:green;font-size:1.5em;">✓</span>You can explain what the purpose is of the INPUT and OUTPUT iptables chains, and how traffic is evaluated against each rule.
::<span style="color:green;font-size:1.5em;">✓</span>Proof that the iptables rules work for your host.
::<span style="color:green;font-size:1.5em;">✓</span>Download and run https://ict.senecacollege.ca/~andrew.smith/ops335/labcheck2a.bash
::<span style="color:green;font-size:1.5em;">✓</span>Issue command: '''journalctl --dmesg | grep -i MYSSH''' to confirm that outside ssh connections logged.
::<span style="color:green;font-size:1.5em;">✓</span>Download the lab2 checking bash shell script by issuing the command:<br><br>'''wget http://matrix.senecac.on.ca/~peter.callaghan/files/OPS335/labcheck2a.bash'''<br><br>set execute permission and run the shell script in your c7host machine. ::*For '''Peter's classes''', follow his Online Submission instructions in Moodle.::*For '''Murray's classes''', run command (piping You know how to the '''more''' command) and show output to instructorread a diff file.-->
=EXPLORATION QUESTIONS=