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OPS235 Lab 7

3,162 bytes added, 17:52, 25 November 2020
Part 1: Confirming sshd service is Running on VMs.
[[Image:firewall.png|thumb|right|180px|Protecting a computer network from unauthorized access is one of the many day-to-day operations for a Linux system administrator and/or security specialist]]
Setting up a computer network is very important, but the Linux system administrator must also perform networking maintenance which includes '''trouble-shooting''', '''repairing network connection issues''' and '''maintaining network security'''. System administrators need to '''protect or "harden" their computer networks from "penetration" from unauthorized computer users'''. Hardening a computer system can range from running an '''IDS''' (Intrusion Detection System) to monitoring and flagging suspicious activity to implementing security policies which could range from running firewalls to setting locked screen savers on workstations.
Setting up a computer network is very important, but there are many other operations that occur on a daily basis that can include '''trouble-shooting''', '''repairing network connection issues''' as well as '''maintaining network security'''. System administrators need to '''protect or "harden" their computer networks from "penetration" from unauthorized computer users'''. Hardening a computer system can range from running an '''IDS''' (Intrusion Detection System) to monitoring and flagging suspicious activity to implementing screen savers on workstations. In this lab, you will learn how to install and configure the SSH service on a VM to allow users to securely access and share data between authorized personnel. In addition, you will learn various methods of running and configuring an ssh server which include: using '''Public Key Authentication''', setting up an '''SSH tunnel''' in order to securely run graphical applications safely among computers in the network, and '''disabling root login''', and '''changing the default ssh communication port''' to mislead potential penetration testers (also known as "pen-testers" or "hackers")into a Linux machine. You will also learn how to setup set up a firewall using the '''iptables''' command in order to control the flow of packets throughout your computer server.
<u>Main Objectives</u>
# Use To use the '''ssh''' and '''scp''' to access and copy data among Linux servers in a secure manner
# Set up, configure, and start the Secure Shell Service ('''sshd''')
#* To refuse root login from remote Linux servers or limit users that are permitted to ssh into Linux servers# Generate Public and Private keys to ensure secure connections between Linux servers# Use ssh to '''tunnel X Xwindow applications'''# To customize '''sshd''' to create a more private, secure systemLearn about the Linux firewall (via iptables):# Gain initial exposure to the * Use '''iptables''' command used to configure and maintain a firewall for protection and troubleshooting# * Configure '''iptables''' to set a default policy and add exceptions to the default policy
[http://man7.org/linux/man-pages/man8/netstat.8.html netstat]<br>
[http://man7.org/linux/man-pages/man8/ifconfig.8.html ifconfig]<br>
[http://man7.org/linux/man-pages/man8/ip.8.html ip]<br>
[http://man7.org/linux/man-pages/man8/ping.8.html ping]<br>
[http://man7.org/linux/man-pages/man8/arp.8.html arp]<br>
|style="padding-left:20px;"|Additional Utilities<br>
[http://man7.org/linux/man-pages/man7/hostname.7.html hostname]<br>
[http://linux.die.net/man/8/restorecon restorecon]<br><br>Managing Services<br>[http://linuxwww.diedsm.netfordham.edu/cgi-bin/man/8/chkconfig chkconfig-cgi.pl?topic=systemctl systemctl]<br><br>
Configuration Files<br>
[httphttps://linuxwww.aboutfreebsd.comorg/librarycgi/cmd/blcmdl5_ssh_configman.htm cgi?query=ssh_config&sektion=5 ssh_config]<br>[httphttps://linuxwww.aboutfreebsd.com/od/commandsorg/lcgi/blcmdl5_sshdconman.htm cgi?sshd_config(5) sshd_config]<br>
|style="padding-left:20px;"|SSH Reference<br>
[http://support.suso.com/supki/SSH_Tutorial_for_Linux A good ssh tutorial]<br>
=INVESTIGATION 1: INSTALLING AND MAINTAINING AN SSH SERVER=
So far, you have learned to use the '''ssh''' utility to establish a secure connection to a remote server in order to perform Linux administration tasks, administer the server. For these common operations, you You have issued the ''ssh'' command, which is actually the '''client''' application for ssh. In order to connect to a remote server (like your VMs, Matrix, etc) they need it needs to be running run the '''SSH service ''' (i.e. the '''ssh daemon''').
In this section, you will learn how to install and configure an SSH server on and restart the ssh service for an existing VM. You will also learn how to configure , restart, and use SSH in order to create secure connections between your Linux machines (host as well as VMs).
:'''Perform the following steps:'''
# Launch your '''c7host machine ''' and ALL of your '''centos1''' and '''centos3''' VMs.
# Switch to your '''c7host''' VM.
# Create a file in your current directory of your c7host machine with some text in it called: '''myfile.txt'''# Issue Ensure you've successfully connected to the VPN required for Matrix (https://inside.senecacollege.ca/its/services/vpn/studentvpn.html). Then issue the following command (using your Matrix login id):<br><b><code><span style="color:#3366CC;font-size:1.2em;">scp &nbsp; myfile.txt &nbsp; yourmatrixid@matrix.senecac.on.ca:/home/yourmatrixid</span></code></b> and enter <br>(followed by your Matrix password. )<br>What did this command do?# Issue the following single command (arguments are separated by a space - use your Matrix login id):<br><b><code><span style="color:#3366CC;font-size:1.2em;">ssh &nbsp; myfile.txt yourmatrixid@matrix.senecac.on.ca &nbsp; ls /home/yourmatrixid/myfile.txt</span></code></b><br>(followed by your Matrix password)<br>What did this command do? <br>Issue the following Linux command:<br><b><code><span style="color:#3366CC;font-size:1.2em;">ssh &nbsp; yourmatrixid@matrix.senecac.on.ca &nbsp; cat /home/yourmatrixid/myfile.txt</span></code></b><br>How does it do these commands differ from using issuing the ssh command without the ls or cat command? How is this useful?<br><br>The client ssh application contains the utlities: '''ssh''', '''scp''' and '''sftp''' (learned in ULI101) to connect to remote Linux servers in order to issue commands or transfer files between Linux servers. You can install the SSH service on your Linux server, although this has already been performed upon installation. We will now confirm that the ssh service is running on all of your VMs.<br><br>
# OpenSSH should have been installed by default. Let's confirm this by issuing the command:<br /> <b><code><span style="color:#3366CC;font-size:1.2em;">rpm -qa | grep ssh</span></code></b>
# You should see a number of packages installed including <b>openssh-clients</b> and <b>openssh-server</b>
# <b><code><span style="color:#3366CC;font-size:1.2em;">The '''openssh-server</span></code></b> ''' package installs a service called '''sshd'''. Confirm # Login as '''root''' and confirm that this service is running by issuing the command:<br /><b><code><span style="color:#3366CC;font-size:1.2em;">systemctl status sshd</span></code></b><ol><li value="910">Now that you know the service is running, investigate what '''port number''' and '''protocol''' sshd uses by issuing the command:<br /><b><code><span style="color:#3366CC;font-size:1.2em;">netstat -atunp | grep sshdmore</span></code></b><br>What protocol and port is the sshd process using? What is the state of the port? Why would you think that UDP ports don't have a state?</li>
<li>Reissue the <b><code><span style="color:#3366CC;font-size:1.2em;">netstat</span></code></b> command without the '''-n''' option. What is the difference?</li>
<li>You can refer to the '''/etc/services''' file in order to determine a port number for a service. Issue the following command to confirm that port 22 is associated with ssh:<br><b><code><span style="color:#3366CC;font-size:1.2em;">grep ssh /etc/services</span></code></b>
<li>Make sure the '''sshd''' service is running on '''all 3 of your VM's'''</li>
<li>Remember that you can view the '''/etc/services''' file in case you need to reference a service with a corresponding port number.</li>
</ol>
 
===Part 2: SSH Server Security Configuration===
Any time that you configure your computer to allow logins from the network you are leaving yourself '''vulnerable to potential unauthorized access''' by so called "penetration testers or even hackers". Running the sshd service is a fairly common practice but '''care must be taken to make things more difficult for those hackers individuals that attempt to use "'''brute force" attacks ''' to gain access to your system. Hackers use their knowledge of your system and many can use '''password guesses guessing programs''' help to gain access'''. They know which port is likely open to attack (TCP:22), the administrative account name (root), all they need to do is to "guess" the password.<br><br> Making your root password (and all other accounts!) both quite complex but easy to remember is not hard.
The Linux system administrator can also '''configure the SSH server ''' in order to make the SSH server more secure'''less vulnerable to attacks. Examples include not permitting root login, and change changing the default port number for the sshservice.
:'''Perform the following steps:'''
# For this section, you will still be using your '''c7host''' and '''centos1''' VMs.# <br><br>The next change you can make is to prevent the root account from logging in to sshd altogether.<br><br>
# Change to your '''centos1''' VM and open a terminal.
# Edit the file '''/etc/ssh/sshd_config''' and look for the option <b><code><span style="color:#3366CC;font-size:1.2em;">PermitRootLogin</span></code></b>. <u>'''<br>Un-comment the option'''</u> (or add the option if it does not appear) and change the option value to <b><code><span style="color:#3366CC;font-size:1.2em;">no</span></code></b>.<br><br>'''NOTE:''' Now any hacking attempt also has to guess an account name as well as the password. <br>If you need to ssh with root access, ssh as a regular user and use '''su -''' to become root.<br><br># Even better, it is possible to restrict access to just specific users that require it:<br>Edit the file '''/etc/ssh/sshd_config''' and '''add ''' a new option of <b><code><span style="color:#3366CC;font-size:1.2em;">AllowUsers accountyourAccountName</span></code></b> using '''(where "yourAccountName" is your''' login account regular user accountname for accountyour centos1 VM)<br>
# In order for these changes to take affect, you need to restart the sshd daemon. Issue the following command to restart the '''sshd''' service:<br /><b><code><span style="color:#3366CC;font-size:1.2em;">systemctl restart sshd</span></code></b>
# Try SSHing from your '''c7host''' VM to your '''centos1''' VM as '''root'''. Where you successful? Now try # Try SSHing from your c7host VM to your centos1 VM as a your regular user accountname. Did it work?# Create another regular user that was permitted called: '''other'''# Set the password for the newly-created called '''other'''# Try SSHing from your c7host VM to connect via your centos1 VM for the account called '''other'''. Why didn't it work?# Edit the file '''/etc/ssh/sshd_config''' to add the account '''other''' for the '''AllowUsers''' option (use a space to separate usernames instead of a comma).# Restart the sshservice.# Try SSHing from your c7host VM to your centos1 VM for the account called '''other'''. Did it workthis time? What would happen for # Issue the following command to make a backup copy of your sshd_config file to your original regular user's home directory:<br><b><code><span style="color:#3366CC;font-size:1.2em;">cp /etc/ssh/sshd_config /home/regularuserid/sshd_config.bk</span></code></b># Issue the following command to allow same group and other user accounts that were not permitted?group members to view the file contents:<br><b><code><span style="color:#3366CC;font-size:1.2em;">chmod og+r /home/regularuserid/sshd_config.bk</span></code></b><ol><li value="816">Finally, as a system administrator, you should periodically monitor your system logs for unauthorized login attempts.</li>
<li>On CentOS systems the log file that is used is '''/var/log/secure''' </li>
<li>It also logs all uses of the '''su''' and '''sudo''' commands.</li>
<li>Inspect the log to see what kind of information is logged.</li>
</ol>
 
'''Answer INVESTIGATION 1 observations / questions in your lab log book.'''
 
=INVESTIGATION 2: ADDITIONAL METHODS TO SECURE YOUR SSH SERVER =
|- valign="top"
|{{Admon/note |Storing Fingerprints | When a user connects to a host using ssh, the host sends a fingerprint or digital signature to the client to establish its identity. The first time a connection is established the identity must be stored for subsequent connections. The fingerprints are stored separately for each user in a file called <code>~/.ssh/known_hosts</code> . <br /><br />From now on when you connect to that host the client will compare the received fingerprint against the list of known hosts before connecting. If the fingerprint does not match it could indicate somebody had setup a system to impersonate the computer you wish to connect to and you would receive a message like this.}}
|}
=== Part 1: Generating Private and Public Keys (Public Key Infrastructure) ===
As a system administrator, you have the ability to generate or create '''public''' and '''private''' keys to ensure safe and secure ssh connections. This will require a user to prove who they say they are in order to access a Linux server via SSH (i.e. Authentication'''authentication'''). The system administer can generate these keys for the first time, or if the system administrator suspects that a hacker has compromised or trying to penetrate the server, they can remove the existing keys and generate new keys. 
A common type of attack, '''Arp Poisoning (Man in the Middle Attack)''', can be used to <u>redirect</u> packets to a third party while maintaining the illusion that the connection is secure. Therefore, understanding about the generation and management of public/private keys are important to the security of servers.
 
:'''Perform the following steps:'''
# Switch to your '''centos3''' VM.<br><br>
:We can use the '''netstat''' utility as a trouble-shooting / confirmation tool to view the SSH service and determine which STATE the SSH service is performing: <br> '''LISTENING''', '''ESTABLISHED''', '''CLOSED''' , or '''WAITING''' <br><br>
<ol><li value="2">Run the '''netstat -atunp''' command (pipe to "grep sshd") to check the state of a possible ''ssh connection''. What is the state (i.e. LISTENING or ESTABLISHED)?</li>
<li>While in your '''centos3''' VM, issue the following command to connect to the '''your same VM ''' via ssh: <b><code><span style="color:#3366CC;font-size:1.2em;">ssh ops235@centos3</span></code></b></li>
<li>Enter yes at the prompt, and enter your OPS235 password.<br>The output should appear similar as what is shown below:<br><br>
:<span style="font-family:courier">The authenticity of host 'centos3 (192.168.235.13)' can't be established.</span><br>
:<span style="font-family:courier">Warning: Permanently added 'centos3' (RSA) to the list of known hosts.</span><br><br></li>
<li>Issue the following command to confirm that you connected to your centos3 VM: <b><code><span style="color:#3366CC;font-size:1.2em;">hostname</span></code></b></li></ol>[[Image:spoof.png|thumb|right|485px|If you receive a message like the one displayed above, you should investigate why it is happening as it could indicate a '''serious security issue''', or it could just mean that something on '''the host has changed'''(i.e. the OS was <u>reinstalled</u>)]]<ol><li value="7">Re-run that same '''netstat pipeline command'''. Any change to the connection status?</li>
<li>Log-out of your ssh connection by typing <b><code><span style="color:#3366CC;font-size:1.2em;">exit</span></code></b>.
<li>Run that same '''netstat''' command again. Wait a few minutes and then check again. Record your observations.</li>
[[Image:spoof.png|thumb|right|485px|If you ever receive a message like the one displayed above, you should investigate why it is happening as it could indicate a '''serious security issue''', or it could just mean that something on '''the host has changed'''(i.e. the OS was <u>reinstalled</u>)]]
So far, we have learned to establish an ssh connection to another host using a password to establish your identity. But '''passwords are not the only or even the best way of authenticating your identit'''y. We can also use '''Public/Private key encryption'''.
<li value="10">Switch to your '''centos2''' VM.</li>
<li>Confirm you are in your centos2 VM by entering the command: <b><code><span style="color:#3366CC;font-size:1.2em;">hostname</span></code></b></li>
<li>Make <u>certain</u> that you are in your centos centos2 VM and that you are NOT logged in as root!a '''regular user''' (i.e. NOT root!) (you have been warned!)</li>
<li>To generate a keypair (public/private keys), issue the following command: <b><code><span style="color:#3366CC;font-size:1.2em;">ssh-keygen</span></code></b></li>
<livalue="14">After generating the keys it prompts you for the location to save the keys. The default is '''~/.ssh''' Your private key will be saved as <b>id_rsa</b> and your public key will be saved as '''id_rsa.pub'''. Press ENTER to accept the default, .</li><li>You will then enter be prompted for a '''pass-phrase used '''. The pass-phrase must be entered in order to establish use your identityprivate key. Pass-phrases are more secure than passwords and should be lengthy, hard to guess and reeasy to remember. For example one pass-enter phrase that meets this criteria might be ''"seneca students like to dance at 4:00am"''. Avoid famous phrases such as ''"to be or not to be"'' as they are easy to guess. It is possible to leave the pass-phrase blank but this is dangerous. It means that if a hacker were able to get into your account they could then use your private key to verifyaccess other systems you use.<br><br>The output should appear similar as what is shown below:</li></ol>
<pre style="font-family:monospace;background-color:white;border-style:none;padding-left:50px;">
</pre>
<ol><li value="15"> After generating the keys it prompts you for the location to save the keys. The default is '''~/.ssh''' Your private key will be saved as <b>id_rsa</b> and your public key will be saved as '''id_rsa.pub'''</li><li>You will then be prompted for a pass-phrase. The pass-phrase must be entered in order to use your private key. Pass-phrases are more secure than passwords and should be lengthy, hard to guess and easy to remember. For example one pass-phrase that meets this criteria might be "seneca students like fish at 4:00am". Avoid famous phrases such as "to be or not to be" as they are easy to guess. It is possible to leave the pass-phrase blank but this is dangerous. It means that if a hacker were able to get into your account they could then use your private key to access other systems you use.<br><br></li><li16>Now issue the command <b><code><span style="color:#3366CC;font-size:1.2em;">ssh-copy-id -i ~/.ssh/id_rsa.pub ops235@centos3</span></code></b></li>
<li>When prompted for password, enter OPS235's root password</li>
<li>Try using ssh to now log into your '''centos3''' VM <u>from</u> your '''centos2''' VM. What happens? Were you required to use your pass-phrase?</li>
# Exit the '''gedit''' application.
# In which VM was the file saved? What does that tell you about the use of tunneling for this section?
# Run the graphical program remotely by issuing only one Linux command:<br> <b><code><span style="color:#3366CC;font-size:1.2em;">ssh -X -C yourUserID@centos1 &nbsp; gedit</span></code></b> (Note: ignore warning messages).# Exit the gedit application.# Experiment with running other GUI applications through (in the /bin directory with applications starting with the letter "x" via '''ssh'''(for example: xev or xchat).
'''Answer INVESTIGATION 2 observations / questions in your lab log book.'''
 
=INVESTIGATION 3: MANAGING FIREWALLS FOR PROTECTION &amp; TROUBLESHOOTING =
==== Linux Firewall (iptables) Concepts====
Since Linux servers can be connected to the Internet, it is very important to run a '''firewall ''' to control what comes packets might come into the computer system, what goes packets might go out of the computer system, and what may packets might be forwarded to another computer. A We are currently using the utility called '''iptables''' can be used to set the firewall rules on a Linux server.
=== Part 1: Listing &amp; Clearing Existing iptables Rules ===
Let's get some practice using the iptables command as we introduce concepts such as listing CHAIN rules, and clearing the CHAIN rules:  
:'''Perform the following steps:'''
# For the remainder of this section, use your '''c7host''' machine.
# Issue the following command to list the existing iptables policy rules: <b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.2em;">iptables -L</span></code></b>.
# Were there already iptables policy rules that already existed by default?
# Before we proceed, we need to understand various methods to list iptables rules:<br><br>'''Listing iptables Rules:'''<br><table width="100%" cellpadding="10" cellspacing="0" border="1"><tr><td width="30%">'''iptables -L'''</td><td>List all iptables rules (eg. INPUT, OUTPUT. FORWARD, and any customized chains (if any)</td></tr><tr><td>'''iptables -L -v'''</td><td>Verbosely List all iptables rules including information such as total size of packets affected by rules</td></tr><tr><td>'''iptables -L CHAIN-NAME'''</td><td>List all iptables rules for that particular chain-name for less clutter (eg. INPUT or OUTPUT, etc)</td></tr></table><br>
# Issue the following Linux command: <b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.2em;">iptables -L INPUT</span></code></b><br>What do you notice is different with this command compared to the previous iptables command?
# Issue the iptables command separately to display the rules for the '''OUTPUT''' chain and for the '''FORWARD''' chain.
# Issue the following command: <b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.2em;">iptables -L -v </span></code></b><br>What do you notice about this command as opposed to the first iptables command you issued? <br>What sort of additional information does this command provide regarding affected packets?<br><br>
# Sometimes it may be useful to completely clear the rules for all or a particular chain. Note the options that can be used to clear (or flush) the iptables rules,<br><br>'''Clearing (Flushing) iptables Rules:'''<br><table width="100%" cellpadding="10" cellspacing="0" border="1"><tr><td width="30%">'''iptables -F'''</td><td>Clears the rules for ALL of the chains</td></tr><tr><td>'''iptables -F CHAIN-NAME'''</td><td>Clears the rules for only the specified CHAIN-NAME (eg. INPUT or OUTPUT)</td></tr></table><br>
# Issue the following command to reset the iptables rules for the INPUT chain: <b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.2em;">iptables -F INPUT</span></code></b>
# Issue the '''iptables -L INPUT''' command to verify that the iptables rules for the INPUT chain have been cleared.
# Now, issue the command: <b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.2em;">iptables -F</span></code></b><br>and then issue the command: <b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.2em;">iptables -L</span></code></b> . <br>What do you notice?
=== Part 2: Setting a Default Policy / Setting Policy Exceptions (iptables) ===
Usually when setting policy rules with iptables, a general "overall" policy is set (default policy chain). A good way to think about setting policies is to have a '''"safety -net "''' to take some sort of action to prevent un-handled packets from passing through the firewall by mistake.After the default policy is set-up, then specific exceptions to the default policy can be added to control specific network traffic.
An example would be to set a default policy for incoming network traffic (INPUT chain) to DROP everything, and then set an exception certain exceptions (like ssh connections). Note the following table below for policy setting examples.<br><br>
:'''Perform the following steps:'''
# Make certain you are in your '''c7host''' machine.
# Issue the following Linux command: <b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.2em;">iptables -P INPUT DROP</span></code></b>
# Issue the '''iptables -L''' command verify . Can you see the INPUT policy has been to DROP all incoming connections?# Although you have set (look for a default policy to DROP all incoming connections, there is a problem: now, you cannot browse the Policy section, NOT INPUT)Internet. You can confirm that by opening a SEPARATE web-browser and perform a Net-search.<br><br>After the overall default policy is setIn order to fix that problem, then you can create policy rules that are "exceptions" make an exception to the default policy rulesallow incoming web-based traffic (via port 80). These Those iptables commands to create exceptions are more complex since you need to determine: <ul><li>'''Where each rules appears in the chain'''? (order can be important)</li><li>'''Which protocol(s)''' are affected (eg. tcp, udp, icmp)</li><li>'''What source or destination IP Addresses''' are affected?</li><li>'''What port numbers''' are affected?</li><li>'''What action to take''' if all of the above conditions are met? (eg. ACCEPT, REJECT, DROP, or LOG)</li></ul><br><br>'''iptables Command Structure (for setting exceptions):<br>(NOTE: If element in column is not specified in the iptables command, then rule relates to ALL elements)'''<br><table width="100%" cellpadding="10" cellspacing="0" border="1"><tr valign="top><td>Place Rule in Chain</td><td>Chain Name</td><td>Specify Protocol</td><td>Source/Destination IPADDR</td><td>Port Number</td><td>Action<br> -&gt;</td><td>Target</td></tr><tr valign="top"><td>'''-A''' (add / Append to bottom of chain)<br>'''-I''' (insert at top of chain)<br>'''-i I CHAIN-NAME 5''' (insert before line 5) </td><td>'''INPUT'''<br>'''OUTPUT'''<br>'''FORWARD'''<br>'''CHAIN-NAME'''</td><td>'''-p tcp''' (tcp packets)<br>'''-p udp''' (datagram packets)<br>'''-p tcp,udp,icmp''' (combined)<br><br>(refer to '''/etc/protocols''' )</td><td>'''-s IPADDR''' (originating IPADDR)<br>'''-d IPADDR''' (destination IPADDR)</td><td>'''<span style="font-family:courier">--</span>sport 22''' (originating port 22 - SSH)<br>'''<span style="font-family:courier">--</span>sport dport 80''' (originating destined port 80 - http)<br><br>(refer to '''/etc/services''')</td><td>'''-j''' </td><td>'''ACCEPT'''<br>'''REJECT'''<br>'''DROP'''<br>'''LOG'''</td></tr></table><br># Issue the following Linux commands to ensure the loopback interface is not affected by these rules. The computer should be able to communicate with itself with any state and protocol:<br><b><code><span style="pointer-events: none;cursor: default;color:# Make certain you are in your '''c7host''' machine3366CC;font-size:1.2em;">iptables -A INPUT -i lo -p all -j ACCEPT</span></code><br><code><span style="pointer-events: none;cursor: default;color:# Determine the '''external facing address''' of your c7host machine (ip address should start with 103366CC;font-size:1. 2em;">iptables -A INPUT -m state -- otherwisestate RELATED, type ip address in webESTABLISHED -browser)# Have a lab neighbour try to ping that external facing address. Were they successful?j ACCEPT</span></code></b># Issue the following iptables policy Linux command to ADD an exception to the INPUT chain to DROP all allow web-based incoming connectionstraffic (ie. port 80):<br><b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.2em;">iptables -P A INPUT DROP-p tcp --dport 80 -j ACCEPT</span></code></b># Have Issue an iptables command to confirm that their is an exception rule to handle incoming tcp packets over port 80.# Use your neighbour try other web-browser to ping confirm that you can now browse the Internet. If you cannot, contact your lab assistant or professor for help.# Determine the '''external facing address''' of your c7host machine.<br>('''Tip:''' in a web-browser, enter the term: '''"ip address"'''. The external facing IP Addressshould start with '''"10."'''). What happened? Why# Provide your external facing address, and provide another lab-mate to ping that external facing address. Were they successful?# Have your neighbour obtain the lab-mate determine THEIR external facing address and obtain that IP Address on THEIR c7host machine.# Issue the following iptables command to ADD ping allow an exception for pings from your neighbour's IPAddresslab-mate:<br><b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.2em;">iptables -A INPUT -p icmp -s {neighbour's exeternal external facing address} -j ACCEPT</span></code></b><br>Is # Have your neighbour able to ping YOUR repeat pinging your external facing IP Address. What happened? Why?
# Have your neighbour try to SSH into YOUR c7host. Were they Successful?
# Issue an iptables rule (in a similar way as with the following previous iptables command:<br><b><code><span style="pointer-events: none;cursor: default;color:) to allow an exception for incoming ssh traffic (eg. port #3366CC;font-size:1.2em;">iptables -A INPUT -p tcp -s {22) from your neighbour's exeternal external facing IP address} --sport 22 -j ACCEPT</span></code></b><br>.# Have your neighbour try to SSH into YOUR c7host(at least to get a password prompt). Were they Successful? If so, why?# Issue the following iptables command to add a rule at bottom of OUTPUT chain to DROP http (port 80 connections). Try to think of the command yourself.# Open another web-browser. Can you connect to a webpage?# Issue iptables rule to '''flush''' the OUTPUT chain. Does your web-browser now work?
# Shutdown all VMs and restart your c7host Linux machine.
# List the iptables rules for the INPUT chain. What happened to your iptables rules for the INPUT chain?
# Proceed to the next part to learn how to learn how to make your iptables rules persistent.
 
=== Part 3: Making iptables Policies Persistent ===
# Flush all of your iptables rules by issuing the following command: <b><code><span style="color:#3366CC;font-size:1.2em;">iptables -F</span></code></b>
# Set the default INPUT policy to ACCEPT by issuing the following command: <b><code><span style="color:#3366CC;font-size:1.2em;">iptables -P INPUT ACCEPT</span></code></b>
# Verify there are no iptables rules by issuing the command: <b><code><span style="color:#3366CC;font-size:1.2em;">iptables -L</span></code></b>
# Make a backup of the file '''/etc/sysconfig/iptables''' by issuing the command:<br><b><code><span style="color:#3366CC;font-size:1.2em;">cp /etc/sysconfig/iptables-save > /etc/sysconfig/iptables.bk</span></code></b>
#To make the iptables rules '''persistent''' (i.e. keeps rules when system restarts), you issue the command: <br><b><code><span style="color:#3366CC;font-size:1.2em;">iptables-save > /etc/sysconfig/iptables</span></code></b>
# Verify that the file '''/etc/sysconfig/iptables''' exists.
= LAB 7 SIGN-OFF (SHOW INSTRUCTOR) =
===Exclusively for Summer 2020 term, submissions are accepted only online!===
Follow the submission instructions for lab 7 on Blackboard.
{{Admon/important|Time for a new backup!|If you have successfully completed this lab, make a new backup of your virtual machines as well as your host machine.}}
# Switch to your '''c7host''' VM and '''su -''' into root.
# Change to the '''/root/bin''' directory.
# Issue the Linux command: <b><code><span style="color:#3366CC;font-size:1.2em;">wget httphttps://matrixict.senecac.onsenecacollege.ca/~murray.saulops235/ops235labs/lab7-check.bash</span></code></b>
# Give the '''lab7-check.bash''' file execute permissions (for the file owner).
# Run the shell script and if any warnings, make fixes and re-run shell script until you receive "congratulations" message.
#Arrange proof of the following on the screen:<br><blockquote><span style="color:green;font-size:1.5em;">&#x2713;</span> '''centos2''' VM:<blockquote><ul><li>have logged into centos3 VM using '''public key authentication''' (with a pass-phrase)</li></ul></blockquote><span style="color:green;font-size:1.5em;">&#x2713;</span> '''c7host''' Machine:<blockquote><ul><li>have tunneled Xwindows application from '''centos1''' via ssh</li><li>Run the '''lab7-check.bash''' script in front of your instructor (must have all <b><code><span style="color:#66cc00;border:thin solid black;font-size:1.2em;">&nbsp;OK&nbsp;</span></code></b> messages)</li></ul></blockquote><span style="color:green;font-size:1.5em;">&#x2713;</span> '''Lab7''' log-book filled out.
 
= Practice For Quizzes, Tests, Midterm &amp; Final Exam =
[[Category:OPS235]]
[[Category:OPS235 Labs]]
[[Category:CentOSS 7]]
[[Category:SSD2]]
[[Category:Digital Classroom]]
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