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OPS235 Lab 6

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LAB PREPARATION
=LAB PREPARATION=
[[Image:my-network.png|thumb|right|350px|Setting up networks is an essential operation for a system administrator. Maintaining network connectivity and securing the network are also essential operations. In this lab, we will '''configure a Virtual Private Network private virtual network using static IP addresses''' (eg. wired workstation connections). We will learn how to setup a DHCP network (eg. for notebook, table and smartphones) in lab 8.]]
===Purpose / Objectives of Lab 6===
In this lab, you will learn the basics of networking by using your '''Virtual Machines'''. You will first set up a '''virtual private network (VPN)''' among those machines. In addition, you will learn to set up '''network names''' (to associate with server's IP Addresses), '''associate network services with port numbers''' for troubleshooting purposes, and use shell scripts with arrays to store network configuration data, and setup '''firewall policies''' via the '''iptables''' command.
<u>Main Objectives</u>
# Configure a private (virtual) network for your '''VMs''' and your '''c7host''' machine
# Configure network interfaces for your Virtual Machines using both '''graphical''' and '''command-line''' utilities.
# Use '''local hostname resolution''' to resolve simple server names with their corresponding IP Addresses
# Use common networking utilities to associate network services with port numbers for troubleshooting purposes
# Use '''shell scripts with arrays''' to store network configuration data
# Gain initial exposure to the '''iptables''' command used to configure and maintain a firewall for protection and troubleshooting
# Configure '''iptables''' to '''allow/disallow/forward''' different types of network traffic
|style="padding-left:20px;" | Networking Utilities<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://www.serverlab.ca/tutorials/linux/administration-linux/configure-centos-6-network-settings/ system-config-network]<br>
[http://man7.org/linux/man-pages/man8/route.8.html route]<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>
[http://man7.org/linux/man-pages/man8/netstat.8.html netstat]|style="padding-left:20px;" | Networking Configuration Files<br>[httphttps://zenitwww.senecaccentos.onorg/docs/5/html/Deployment_Guide-en-US/s1-networkscripts-interfaces.cahtml Interface Configuration]<br>[https:/wiki/indexlinux.die.phpnet/IPTables iptablesman/5/resolv.conf resolv.conf]<br>
|style="padding-left:20px;" |Additional Utilities<br>
[http://man7.org/linux/man-pages/man1/find.1.html find]<br>
|}
=INVESTIGATION 1: CONFIGURING A VIRTUAL PRIVATE NETWORK (VPN)=
For the remainder of this course, we will focus on networking involving our VMs. This lab will focus on setting up a virtual private network ('''VPN'''), connecting our VMs and c7host machine to the VPNnetwork, and configuring our VPN private network to make more convenient to use, troubleshoot and protect. '''Lab 7''' will focus on configuring SSH and making access to the VPN private network more secure. Finally, '''lab 8''' will focus on configuring mobile (as well as wired devices) via DHCP to automatically assign an IP address.
There are several reasons for creating '''VPNs'''virtual networks. The main reason is to '''safely connect servers together''' (i.e. to safely limit but allow the sharing of information among computer network users). This allows for a secure connection of computers yet controlling access to and monitoring (protecting) access to permitted users (discussed later in '''lab7''').
If we are going to setup a private network, there are a number of steps to perform: First, '''define a new private network in the Virtual Manager application'''; and second, '''configure each of our VMs to connect to this new private network'''. In Part 1, we will be perform the first operation. In part 2, we will be performing the second operation for all VMS (graphical and command-line).
Before configuring our network, we want to '''turn off dynamic network configuration for our Virtual Machines''' by turning off the '''"default"''' virtual network. We will then define our virtual private network.
:'''Perform the following steps:'''
# In the '''Connection Details''' dialog box, select the '''Virtual Networks''' tab
# Click to <u>de-select</u> the '''Autostart (on boot)''' check-box options and click the '''Apply''' button.
# Stop the default network configuration by clicking on the '''stop''' button at the bottom left-side of the dialog box.
# Click the '''add''' button (the button resembles a "plus sign") to add a new network configuration.
# Type the network name called: '''network1''', and then click the '''Forward''' button.
<li value="1">Let's start with our '''centos1 VM'''. Double-click on your '''centos1''' VM, but instead of running the VM, click on the '''view''' menu, and select: '''Details'''<br />(Note: the Virtual Machine window will appear - do not start virtual machine)</li>
<li>In the '''left pane''' of the Virtual Machine window, select '''NIC:''' and note that this NIC is on the "default" virtual network</li>
<li>Change it to '''Virtual Network network1: NAT''' (i.e. the VPN network that you just created) and click the '''Apply''' button.</li>
</ol>
</li>
[[Image:new_network_dialog.png|right|thumb|300px|Although the private network has been setup via the '''Virtual Machine Manager''', each virtual machine requires to change its own network setting individually (either '''graphically''' or by '''command line''').]]
 
=== Part 2: Configuring Network For centos1 VM===
# When finished, check your settings, and then click the '''Apply''' button.
# Open a terminal and issue the '''ifconfig''' command to confirm the IP ADDRESS settings change.
# Verify that '''centos1'''VM is now connected to the VPN private network by issuing the following command from your '''c7host''' machine:<br><b><code><span style="color:#3366CC;font-size:1.2em;">ping 192.168.235.11</span></code></b>
[[Image:network-scripts.png|thumb|right|250px|Although you can use the '''ifconfig''' command to temporarily create a static IP address connection to a network, you need to add the network settings in the '''/etc/sysconfig/network-scripts''' directory to automatically connect to the network upon Linux system boot-up.]]
 
=== Part 3: Configuring VM Network Setup via Command Line ('''centos3''' and '''centos2''') ===
# Configure your '''centos3''' VM (in the '''View''' -> '''Details''' menu of Virtual Machine Manager) to configure the NIC interface to '''network1''', click '''Apply''', and switch your centos3 VM view from ''details'' to '''console'''.
# Start your '''centos3''' VM, login, and su to '''root'''.
# Use the command called: '''ifconfig''' to list active interfaces, you should see one with a name of '''eth0''' or a similar name.<br><br>NOTE: If the '''ifconfig''' command is NOT available in your centos3 vm, issue the command:<br>'''yum install net-tools'''<br><br>
# To configure your card with a static address use the following command:
#:<b><code><span style="color:#3366CC;font-size:1.2em;">ifconfig eth0 192.168.235.13 netmask 255.255.255.0</span></code></b>
# List the contents of this directory. You should see 2 different types of files, network config scripts and network configuration files.
# Look for the configuration file for your original interface, it should be named '''ifcfg-eth0'''
# Edit the new file for you your interface and give it the following settings (or create a brand new file, might be easier than editing the old one):
#::DEVICE=eth0
#::IPADDR=192.168.235.13
#::NM_CONTROLLED=yes
#::IPV6INIT=no
# {|width="50%" cellspacing="0" |- valign="top" |{{Admon/important|Keep consistent with Quotation or no Quotation|You have the option to either place quotation marks around the values, or no to use quotation at all. Regardless of the method you chose, KEEP CONSISTENT. For example, if beginning value with a double-quote, end value with a double-quote. If beginning value without a double-quote, do not end with any quotation. }}|}<ol><li value="15">Save the file and then restart the network connection by issuing the commands:<br><b><code><span style="color:#3366CC;font-size:1.2em;">ifdown eth0</span></code></b> and <b><code><span style="color:#3366CC;font-size:1.2em;">ifup eth0</span></code></b></li># <li>Verify your configuration as you did before.</li># <li>Restart the '''centos3''' VM.</li># <li>Use the '''ifconfig''' and '''ping''' commands to verify your network connection to other VMs.</li># <li>Login and attempt to '''ssh''' to your matrix account to verify the settings.<br><br>We need to also configure your centos2 VM for a persistent network connection as well:<br><br></li># <li>Configure the centos2 VM (in the '''View''' -> '''Details''' menu of Virtual Machine Manager) to configure the NIC interface to '''network1''', click '''Apply''', and switch your centos2 VM view from details to '''console'''.</li># <li>Start your '''centos2''' VM, login, and su to '''root'''.</li># <li>Issue the command: <b><code><span style="color:#3366CC;font-size:1.2em;">ip address</span></code></b> and write down the '''MAC address''' for your eth0 network interface.</li># <li>Edit the '''/etc/sysconfig/network-scripts/ifcfg-eth0''' file using the IPADDR: '''192.168.235.12''' , and the same '''NETMASK''', '''GATEWAY''', '''DNS1''' and '''MAC address''' information for you centos2 VM (i.e. recorded in the previous steppreviously).</li># <li>Save changes, re-issue the '''ifdown''' and '''ifup''' commands, and then issue the '''ip address''' and '''ping''' commands to verify that you can connect to other VMs on your network.</li></ol>
'''Answer INVESTIGATION 1 observations / questions in your lab log book.'''
 
=INVESTIGATION 2: MANAGING YOUR NEWLY-CREATED NETWORK=
Connecting a Creating private network is networks are an important task, but a system administrator also needs to manage the network to make it '''convenient to use''', make it '''safer from unauthorized access''', and '''troubleshoot''' network connectivity problems.
This investigation will expose you to useful "tweaks" and utilities to help accomplish this task. '''Lab 7''' requires that you understand these concepts and have a good general understanding how to use these troubleshooting utilities (like '''netstat''' and '''iptables''').
{| width="40%" align="right" cellpadding="10"
|{{Admon/note | Hosts files vs. the Domain Name System | On large public networks like the Internet or even large private networks we use a network service called [http://en.wikipedia.org/wiki/Domain_Name_System Domain Name System (DNS)] to resolve the human friendly hostnames like '''centos.org''' to the numeric addresses used by the IP protocol. On smaller networks we can use the <code>/etc/hosts</code> on each system to resolve names to addresses.}}
|}
=== Part 1: Using /etc/host hosts File for Local Hostname Resolution ===
After setting up a private network, it can be hard to try to remember IP addresses. In this section, we will setup your network to associate easy-to-remember server names with IP ADDRESSES.
#Verify that you can now ping any VM by their hostname instead of the IPADDR.
 
 
=== Part 2: Network Connectivity &amp; Network Service Troubleshooting Utilities===
{| width="40%" align="right" cellpadding="10"
|- valign="top"
|
<table cellspacing="0" cellpadding="5" style="border-top: thin solid black;margin-left:60px;">
<caption>'''Common Network Troubleshooting Tools'''</caption>
<tr valign="top>
 
<td style="border-bottom: thin solid black;font-weight:bold;background-color:#ffffff;">Purpose</td>
<td style="border-bottom: thin solid black;font-weight:bold;background-color:#ffffff;padding-left:100px;">Command(s)</td>
 
</tr>
<tr valign="top">
<td style="border-bottom: thin solid black;">Network Connectivity</td>
<td style="border-bottom: thin solid black;padding-left:100px;"><b><code><span style="color:#3366CC;font-size:1.2em;">ping</span></code></b><br><b><code><span style="color:#3366CC;font-size:1.2em;">arp</span></code></b><br><b><code><span style="color:#3366CC;font-size:1.2em;">ifconfig</span></code></b></td>
</tr>
<tr valign="top">
<td style="border-bottom: thin solid black;">Network Service Status</td>
<td style="border-bottom: thin solid black;padding-left:100px;"><b><code><span style="color:#3366CC;font-size:1.2em;">netstat'''</span></code></b></td>
</tr>
 
</table>
|}
 
 
Troubleshooting network problems is an extremely important and frequent task for a Linux/Unix system administrator. Since network services (such as file-server, print-servers, web-servers, and email-servers) depend on network connectivity, as Linux/Unix sysadmin must be able to quickly and effectively pin-point sources of network problems in order to resolve them.
 
Network service problems may not be entirely related to a "broken" network connection, but a service that is not running or not running correctly. The following table lists the most common listing of utilities to assist with detection of network connectivity or network service problems to help correct the problem.
 
 
:'''Perform the following steps:'''
 
#Switch to your '''c7host''' machine.
#Issue the '''ping''' command to test connectivity to your '''centos1''', '''centos2''', and '''centos3''' VMs.
#Examine the contents of the ARP cache by using the command: <b><code><span style="color:#3366CC;font-size:1.2em;">arp</span></code></b> What is the purpose of ARP?
#Check the contents of the cache again by using the command: <b><code><span style="color:#3366CC;font-size:1.2em;">arp -n</span></code></b> What was the difference in output?
#Issue the following command: <b><code><span style="color:#3366CC;font-size:1.2em;">netstat -at</span></code></b> This command will list all active TCP ports. Note the state of your ports.
 
'''TCP''' is a connection oriented protocol that uses a handshaking mechanism to establish a connection. Those ports that show a state of LISTEN are waiting for connection requests to a particular service. For example you should see the ssh service in a LISTEN state as it is waiting for connections.
 
<ol><li value="6">From one of your VM's login to your host using the '''ssh''' command.</li>
<li>On your c7host VM rerun the <b><code><span style="color:#3366CC;font-size:1.2em;">netstat -at</span></code></b> command and in addition to the '''LISTEN''' port it should list a 2nd entry with a state of ESTABLISHED. This shows that there is a current connection to your ssh server.</li>
<li>Exit your ssh connection from the VM and rerun the command on the CentOS host. Instead of '''ESTABLISHED''' it should now show a state of '''CLOSE_WAIT'''. Indicating that the TCP connection is being closed.</li>
<li>On your c7host VM, try the command: <b><code><span style="color:#3366CC;font-size:1.2em;">netstat -atn</span></code></b> How is this output different?
Without the -n option netstat attempts to resolve IP addresses to host names (using /etc/hosts) and port numbers to service names (using /etc/services)</li>
<li>Examine the '''/etc/services''' file and find which ports are used for the services: ssh, sftp, http</li>
<li>Now execute the command netstat -au What is the difference between the options: -at and -au? When examining UDP ports why is there no state?</li>
</ol>
 
 
 
===Part 3: Using Arrays to Collect VM Network Information===
{|width="40%" align="right" cellpadding="10"
|- valign="top"
</li></ul>'''<u>Working with Temporary Files</u>'''<br><br><ul><li>When creating temporary files, it is important NOT to store on a user's account (to avoid overwriting their existing files). Instead, temporary files can be created in the '''/tmp''' directory.<br><br></li><li>The $$ variable can be used as the filename extension which assigns the current PID of the shell script running to make the filename unique, and allow easy removal at the end of the shell script by deleting ALL files in the /tmp directory with the extension: .$$<br><br></li><li>Example:<br><br>''ls -lR &gt; /tmp/temp-file.$$''<br>''grep secret /tmp/temp-file.$$''<br>''rm /tmp.$$''<br></li></ul> }}
|}
===Part 2: Using Arrays to Collect VM Network Information===
 
We finish shell scripting by using arrays by reading and storing networking information for each VM (centos1, centos2, and centos3) to be stored in a report in your c7host machine. We will use the ssh command in order to grab the network information (one VM at a time), and store the network setup into an Associative array in our c7host machine.
&#35;<br>
&#35; Purpose: Creates system info report<br>
&#35;<br>&#35; USAGE: ./network-info.bash [full pathname to ifcfg-eth0 file-pathname]<br>
<br>
if [ $USER != "root" ] # only runs if logged in as root<br>
if [ $# -ne 1 ]<br>
then<br>
&nbsp;echo "You need to provide a the full pathname to ifcfg-eth0 file-pathname" >&2<br>&nbsp;echo "USAGE: $0 [full pathname to ifcfg-eth0 file-path-name]" >&2<br>
&nbsp;exit 0<br>
fi
+<br>
<br>
for((x=0; x<$index; x++))<br>
do<br>
&nbsp;echo "&lt;tr&gt;&lt;td&gt;${network[$x]}&lt;/td&gt;&lt;/tr&gt;" &gt;&gt; /root/network-info.html<br>
</code>
<br><br>
<ol><li value="7">Give this shell script execute permissions and run this shell script.</li><li>You will need to determine the full pathname of the '''ifcfg-en0ens33''' file in the /etc/sysconfig/network-scripts directory to use as an argument for this shell script.</li><li>Run the shell script. What do you notice from the report that the shell script generated?</li><li>The the Then use wget command to download another variation of the network-info.bash shell script using the awk command to separate the variables and values into separate columns:<br><b><code><span style="color:#3366CC;font-size:1.2em;">httphttps://cs.senecacict.onsenecacollege.ca/~murray.saulops235/labs/network-info-2.bash</span></code></b><br></li></ol>  {| width="40%" align="right" cellpadding="10"|- valign="top"|<table cellspacing="0" cellpadding="5" style="border-top: thin solid black;margin-left:60px;"> <caption>'''Common Network Troubleshooting Tools'''</caption> <tr valign="top>  <td style="border-bottom: thin solid black;font-weight:bold;background-color:#ffffff;">Purpose</td> <td style="border-bottom: thin solid black;font-weight:bold;background-color:#ffffff;padding-left:100px;">Command(s)</td>  </tr> <tr valign="top"> <td style="border-bottom: thin solid black;">Network Connectivity</td> <td style="border-bottom: thin solid black;padding-left:100px;"><b><code><span style="color:#3366CC;font-size:1.2em;">ping</span></code></b><br><b><code><span style="color:#3366CC;font-size:1.2em;">arp</span></code></b><br><b><code><span style="color:#3366CC;font-size:1.2em;">ifconfig</span></code></b></td> </tr><tr valign="top"> <td style="border-bottom: thin solid black;">Network Service Status</td> <td style="border-bottom: thin solid black;padding-left:100px;"><b><code><span style="color:#3366CC;font-size:1.2em;">netstat'''</span></code></b></td> </tr>  <tr valign="top"> <td style="border-bottom: thin solid black;">Firewall Status</td> <td style="border-bottom: thin solid black;padding-left:100px;"><b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.2em;">iptables</span></code></b></td> </tr></table>|}=== Part 3: Network Connectivity &amp; Network Service Troubleshooting Utilities=== Troubleshooting network problems is an extremely important and frequent task for a Linux/Unix system administrator. Since network services (such as file-server, print-servers, web-servers, and email-servers) depend on network connectivity, as Linux/Unix sysadmin must be able to quickly and effectively pin-point sources of network problems in order to resolve them. Network service problems may not be entirely related to a "broken" network connection, but a service that is not running or not running correctly. The following table lists the most common listing of utilities to assist with detection of network connectivity or network service problems to help correct the problem.
:'''Perform the following steps:'''
#Switch to your '''c7host''' machine.
#Issue the '''ping''' command to test connectivity to your '''centos1''', '''centos2''', and '''centos3''' VMs.
#Examine the contents of the ARP cache by using the command: <b><code><span style="color:#3366CC;font-size:1.2em;">arp</span></code></b>arp What is the purpose of ARP?
#Check the contents of the cache again by using the command: <b><code><span style="color:#3366CC;font-size:1.2em;">arp -n</span></code></b> What was the difference in output?
#Issue the following command: <b><code><span style="color:#3366CC;font-size:1.2em;">netstat -at</span></code></b> This command will list all active TCP ports. Note the state of your ports.
 
'''TCP''' is a connection oriented protocol that uses a handshaking mechanism to establish a connection. Those ports that show a state of LISTEN are waiting for connection requests to a particular service. For example you should see the ssh service in a LISTEN state as it is waiting for connections.
 
<ol><li value="6">From one of your VM's login to your host using the '''ssh''' command.</li>
<li>On your c7host VM rerun the <b><code><span style="color:#3366CC;font-size:1.2em;">netstat -at</span></code></b> command and in addition to the '''LISTEN''' port it should list a 2nd entry with a state of ESTABLISHED. This shows that there is a current connection to your ssh server.</li>
<li>Exit your ssh connection from the VM and rerun the command on the CentOS host. Instead of '''ESTABLISHED''' it should now show a state of '''CLOSE_WAIT'''. Indicating that the TCP connection is being closed.</li>
<li>On your c7host VM, try the command: <b><code><span style="color:#3366CC;font-size:1.2em;">netstat -atn</span></code></b> How is this output different?
Without the -n option netstat attempts to resolve IP addresses to host names (using /etc/hosts) and port numbers to service names (using /etc/services)</li>
<li>Examine the '''/etc/services''' file and find which ports are used for the services: ssh, sftp, http</li>
<li>Now execute the command netstat -au What is the difference between the options: -at and -au? When examining UDP ports why is there no state?</li>
</ol>
 
 
{| width="40%" align="right" cellpadding="10"
|- valign="top"
|
[[Image:chains.png|thumb|600px|right|When using iptables packets must pass-through "a chain of policy rules" in order to handle packets. If a packet matches a rule, then an action is taken (some examples include: '''ACCEPT''', '''DROP''', '''REJECT''', or '''LOG'''); otherwise, the packet will be directed to the default policy chain. ]]
|}
==== Using Firewalls in Linux (iptables)====
 
Since Linux servers can be connected to the Internet, it is very important to run a firewall to control what comes into the computer system, what goes out of the computer system, and what may be forwarded to another computer. A utility called '''iptables''' can be used to set the firewall rules on a Linux server.
 
Basically, there is a list ('''chain''') of policy rules that <u>'''packets'''</u> must pass-through in order to handle packets. If a packet matches a rule, then an action is taken (some examples include: '''ACCEPT''', '''DROP''', '''REJECT''', or '''LOG'''). If the packet passes through the chain of rules without a match, then the packet is directed to the default policy chain (for example: ''ACCEPT'', ''REJECT'', or ''DROP'').
 
You can create your own '''customized chains''' (which you will learn in the OPS335 course) but to keep thing simple, we only deal with 3 '''common predefined chains''':
 
:*'''INPUT''': Packets coming into current Linux server
:*'''OUTPUT''': Packets leaving current Linux server
:*'''FORWARD''': Packets being routed between Linux servers
 
 
:'''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?
# Issue the following command to reset the iptables policy rules: <b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.2em;">iptables -F</span></code></b>.
# Issue the '''iptables -L''' command to verify that the iptables rules have been reset.
 
 
==== Setting Default Policy and Policy Exceptions with iptables ====
 
Usually when setting policy rules with iptables, a general "overall" policy is set (default policy chain), and then set policy rules in other chains which act as exceptions to the default policy. A general policy would apply to ALL types of packets (tcp, udp, icmp) and all communication port numbers (80, 22, etc).
 
The option <b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.5em;">-P</span></code></b> is used with the iptables command to set a default policy chain.
 
'''Examples:'''
 
<table width="100%" cellpadding="10" cellspacing="0" border="1">
<tr>
<td width="30%">'''iptables -P INPUT DROP'''</td><td>Set default policy to drop all incoming connections for ALL protocols, ALL communication ports, ALL IP addresses</td>
</tr><tr>
<td>'''iptables -P OUTPUT DROP'''</td><td>Set default policy to drop all outgoing connections for ALL protocols, ALL communication ports, ALL IP addresses</td>
</tr>
</table>
 
 
After the overall default policy is set, then you can create policy rules that are "exceptions" to the default policy rules. The <b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.5em;">-j</span></code></b> option is used to redirect (jump) packets to actions (ACCEPT, REJECT, DROP, LOG) if the packet match that policy rule. The option <b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.5em;">-p</span></code></b> will indicate the protocol used (eg. tcp, upd, icmp). The options <b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.5em;">--dport</span></code></b> or <b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.5em;">--sport</span></code></b> indicate the "destination communication port" or "source communication port" respectively. You can view the file '''/etc/services''' to determine the communication port number for the appropriate network service. The option <b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.5em;">-A</span></code></b> is used to append the policy rule to the <u>bottom</u> of the chain. The option <b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.5em;">-I</span></code></b> is used to insert a policy rule before an existing policy line number (if used with no number, will insert at the <u>top</u> of the chain)
 
'''Examples:'''
 
<table width="100%" cellpadding="10" cellspacing="0" border="1">
<tr>
<td width="40%">'''iptables -A INPUT -p tcp --sport 80 -j ACCEPT'''</td><td>Append policy to <u>'''bottom'''</u> of INPUT chain to accept all tcp packets from port 80</td>
</tr><tr>
<td>'''iptables -A OUTPUT -p tcp --dport 80 -j ACCEPT'''</td><td>Append policy to <u>'''bottom'''</u> of OUTPUT chain to accept all tcp packets to port 80</td>
</tr><tr>
<td>'''iptables -I INPUT -p tcp --sport 22 -j LOG'''</td><td>Insert policy at '''<u>top</u>''' of INPUT chain to log all tcp packets from port 22</td>
</tr><tr>
<td>'''iptables -I INPUT 3 -p tcp --dport 22 -j LOG'''</td><td>Insert policy <u>'''before line 3'''</u> of INPUT chain to log all tcp packets from port 22</td>
</tr>
</table>
 
 
You can also set exceptions to the default policy for specific IP Addresses by using the options <b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.5em;">-d IPADDR</span></code></b> or <b><code><span style="pointer-events: none;cursor: default;color:#3366CC;font-size:1.5em;">-s IPADDR</span></code></b>
 
 
<table width="100%" cellpadding="10" cellspacing="0" border="1">
<tr>
<td width="45%">'''iptables -A INPUT -p tcp -s 192.168.0.0/24 -sport 22 -j ACCEPT'''</td><td>Append policy to bottom of INPUT chain to ACCEPT tcp packets from IP Address 192.168.0.0 from communication port 22</td>
</tr><tr>
<td>'''iptables -A OUTPUT -p tcp -d 192.168.0.138/24 -dport 80 -j REJECT'''</td><td>Append policy to bottom of OUTPUT chain to REJECT tcp packets to IP Address 192.168.0.138 via communication port 80</td>
</tr>
</table>
 
 
:'''Perform the following steps:'''
 
# Remain in your '''c7host''' VM for this section.
# Set the default policy for the INPUT chain to DROP by issuing the command:<br><b><code><span style="color:#3366CC;font-size:1.2em;">iptables -P INPUT DROP</span></code></b>
# Now try on your own to change the default policies for the OUTPUT chain to DROP
# Issue the commmand <b><code><span style="color:#3366CC;font-size:1.2em;">iptables -L</span></code></b> to verify that the policies on your INPUT and OUTPUT chain are set to DROP
# Open a browser and attempt to access the Internet. Were you successful?
# Using the commands you have learned so far, change the policies on the INPUT and OUTPUT chains to ACCEPT
# Open your browser and attempt to access the Internet again. Were you successful?
# Change the policies on all of the chains to DROP
#In the OUTPUT chain, add the following rule:<br><b><code><span style="color:#3366CC;font-size:1.2em;">iptables -A OUTPUT -j LOG</span></code></b>. The above rule tells '''iptables''' to log packets and relevant information to '''/var/log/messages'''.
#Try to access the Internet again. Because the policies have been set to DROP, you should be unsuccessful. However, every packet of data that your PC attempted to send out was logged.
# Let's have a look at the log file and analyze the data: <b><code><span style="font-family:courier;color:#3366CC;font-size:1.2em;">tail /var/log/messages</span></code></b><br><br>
::This command shows us the last 10 lines of the file. While there are many things being logged to this file, the last thing we did was try to access the Internet so we should be able to see the data we need. Look for a line that looks similar to the following:<br><code style="font-family:courier;font-size:1.2em;">Jun 24 12:41:26 c7host kernel: IN= OUT=lo SRC=127.0.0.1 DST=127.0.0.1 LEN=52 TOS=0x00 PREC=0x00 TTL=64 ID=16442 DF PROTO=TCP SPT=57151 DPT=5902 WINDOW=1024 RES=0x00 ACK URGP=0</code><br><br>Your IP, host names and date will be different, but the one thing that should be the same is the DPT=80 value. When your computer tried to send OUT a request to connect to the Internet using the WWW, the computer used a destination port of 80. This is the standard port for the WWW. Because we have set the default policy to DROP it drops these packets. The problem is we are dropping all packets. What if we just want to drop the WWW packets?<br><br>
<ol>
<li value="11">Using the commands we already know, change the default policies on all of your chains to ACCEPT.</li>
<li>Open a browser and confirm that you can access the world wide web.</li>
<li>Enter the command:<br><b><code><span style="color:#3366CC;font-size:1.2em;">iptables -I OUTPUT -p tcp -s0/0 -d 0/0 --dport 80 -j DROP</span></code></b></li>
<li>Try to access the Web. If you have done everything right, you should not have been successful.</li>
<li>After you have completed the test execute the following command:<br><b><code><span style="color:#3366CC;font-size:1.2em;">iptables -F</span></code></b><br></li>
<li>Using the information you have learned, try on your own to achieve the same goal as above (block www access to your computer) by using the INPUT chain instead of the OUTPUT chain.</li>
<li>After you have completed this task, flush the iptables again.</li>
<li>Make sure that your ssh server is running on the host machine and try to access it from a virtual machine of your choice.</li>
<li>Once you have confirmed that ssh is running on the host machine, insert an iptables rule on the host machine to prevent access to the ssh server from all VM's on the virtual network.</li>
<li>Confirm that your rule works by testing from your VM's</li>
<li>Does iptables close the port? Check using '''netstat'''</li>
<li>Now insert a rule on the CentOS host that would ACCEPT connections from the centos3 VM only.</li>
<li>Fully test your configuration.</li>
<li>Flush the iptables rules for INPUT, OUTPUT and FORWARD chains.</li></ol>
 
{{Admon/important|Make Certain iptables rules are Flushed Before Saving|In the next section, you will learn to keep your iptables rules persistent, so they remain even if the Linux system is rebooted. If you do NOT flush the iptables rules prior to the next section, your lab6-checking script will not generate all OKs, and you may experience problems in lab7.}}
==== Making iptables Policies Persistent ====
 
Any changes to your iptables policy rules will be lost when you restart your Linux server, unless you make your iptables rules persistent. Failure to perform the following steps after setting up your firewall rules can cause confusion and wasted time.
 
 
:'''Perform the following steps:'''
 
# 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>
# 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;">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.
# Restart your iptables service and test your configuration.
'''Answer INVESTIGATION 2 observations / questions in your lab log book.'''
 
= LAB 6 SIGN-OFF (SHOW INSTRUCTOR) =
# Switch to your '''c7host''' VM.
# 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/lab6-check.bash</span></code></b>
# Give the '''lab6-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>'''ssh''' from '''centos2''' to '''c7host''' VM.</li></ul></blockquote><span style="color:green;font-size:1.5em;">&#x2713;</span>'''c7host''' machine<blockquote><ul><li>A list of your '''iptables''' rules</li><li>Output from running the '''network-info.bash''' shell script</li><li>Run the '''lab6-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> '''Lab6''' log-book filled out.
= Practice For Quizzes, Tests, Midterm &amp; Final Exam =
# What is a port?
# What command will set your IP configuration to 192.168.55.22/255.255.255.0 ?
# What file contains the systems <code>iptables</code> rules?
# What is the difference between UDP and TCP?
# What port number is used for DHCP servers?
# What is the function of the file <code>/etc/services</code> ?
# What is the function of the file <code>/etc/hosts</code> ?
# What is the purpose of the file <code>/etc/sysconfig/network-scripts/ifcfg-eth0</code> ?
[[Category:OPS235]]
[[Category:OPS235 Labs]]
[[Category:CentOS 7]]
[[Category:SSD2]]

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