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| − | =LAB PREPARATION=
| + | #REDIRECT [[OPS235]] |
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| − | ==Purpose / Objectives of Lab 6==
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| − | [[Image:network.png|thumb|right|150px|Setting up networks is an essential operation for a system administrator. Maintaining network connectivity and securing the network are also essential operations for a system administrator.]]
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| − | In this lab, you will learn the basics of networking by using your '''Virtual Machines''' and your '''centos1''' machine. You will first set up a virtual private network 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 setup '''firewall policies''' via the '''iptables''' command.
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| − | <u>Main Objectives</u>
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| − | # Configure a private (virtual) network for your '''VMs''' and your '''centos1''' machine
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| − | # Configure network interfaces for your Virtual Machines using both '''graphical''' and '''command-line''' utilities.
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| − | # Use '''local hostname resolution''' to resolve simple server names with their corresponding IP Addresses
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| − | # Backup more recent files (eg. '''incremental backup''') using the '''find''' command and a '''date/time-stamp''' file
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| − | # Use common networking utilities to associate network services with port numbers for troubleshooting purposes
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| − | # Gain initial exposure to the '''iptables''' command used to configure and maintain a firewall for protection and troubleshooting
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| − | # Configure '''iptables''' to '''allow/disallow/forward''' different types of network traffic
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| − | ==Minimum Required Materials==
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| − | {|cellpadding="15" width="40%"
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| − | |- valign="top"
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| − | |width="10%" | [[Image:harddrive.png|thumb|left|85px|<b>Removable Hard Disk Pack</b> (SATA)]]
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| − | |width="10%" |[[Image:ubs-key.png|thumb|left|85px|<b>USB key</b><br>(for backups)]]
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| − | |width="10%" |[[Image:log-book.png|thumb|left|70px|<b>Lab6 Log Book</b>]]
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| − | |}
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| − | ==My Toolkit (CLI Reference)==
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| − | {|width="100%" cellpadding="5" width="50%"
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| − | |'''Networking Utilities:'''
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| − | |'''Additional Utilities:'''
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| − | |- valign="top"
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| − | *[http://man7.org/linux/man-pages/man8/ifconfig.8.html ifconfig]
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| − | *[http://www.serverlab.ca/tutorials/linux/administration-linux/configure-centos-6-network-settings/ system-config-network]
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| − | *[http://man7.org/linux/man-pages/man8/route.8.html route]
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| − | *[http://man7.org/linux/man-pages/man8/ping.8.html ping]
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| − | *[http://man7.org/linux/man-pages/man8/arp.8.html arp]
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| − | *[http://man7.org/linux/man-pages/man8/netstat.8.html netstat]
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| − | * [[IPTables]] Reference
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| − | *[http://man7.org/linux/man-pages/man1/find.1.html find]
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| − | *[http://man7.org/linux/man-pages/man1/tail.1.html tail]
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| − | *[http://man7.org/linux/man-pages/man1/cp.1.html cp]
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| − | |}
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| − | =INVESTIGATION 1: CONFIGURING A VIRTUAL PRIVATE NETWORK=
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| − | For the remainder of this course, we will focus on networking involving our VMs and our centos1 machine. This lab will focus on setting up a virtual private network ('''VPN'''), connecting our VMs and centos1 machine to the VPN, and configuring our VPN to make more convenient to use, troubleshoot and protect. '''Lab 7''' will focus more on configuring SSH and making access to the VPN more secure. Finally, '''lab 8''' will focus on configuring the network for fixed workstations, mobile devices, or both at the same time.
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| − | There are several reasons for creating '''VPNs'''. The main reason is to '''safely connect servers together''' (i.e. to safely limit but allow share 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 in more depth in lab7).
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| − | ==Part 1: Configuring a Private Network (Via Virtual Machine Manager) ==
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| − | [[Image:network-config-centos.png|thumb|600px|right|This diagram shows the current network configuration of your '''centos1''' machine in relation to your '''Virtual Machines'''. In this section, you will be learning to change the default network settings for both your '''centos1''' machine and '''VMs''' to belong to a '''virtual network''' using fixed IP Addresses. ]]
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| − | If we are going to setup a private network, we must do 2 major operations: 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 parts 2, 3, and 4, we will be performing the second operation for all VMS (graphical and command-line).
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| − | # Perform this section in your '''centos1''' machine.<br><br>'''NOTE:''' 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. Follow the steps in order to perform these operations. <br><br>
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| − | # Make certain that <u>'''ALL'''</u> virtual machines are powered off.
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| − | # In the Virtual Machine Manager dialog box, Select '''Edit'''-> '''Connection Details'''.
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| − | # In the '''centos1 Connection Details''' dialog box, select the '''Virtual Networks''' tab
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| − | # Disable the default configuration from starting at boot by '''<u>deselecting</u>''' '''Autostart (on boot)''' check-box and click the '''Apply''' button.
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| − | # Then Stop the default network configuration by clicking on the '''stop''' button at the bottom left-side of the dialog box.
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| − | # Click the '''add''' button (the button resembles a "plus sign") to add a new network configuration.
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| − | # Give your new network a name (i.e. '''network1''') then click the '''Forward''' button.
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| − | # In the next screen, enter in the new network IP address space:
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| − | #:'''192.168.235.0/24'''
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| − | # Disable DHCP4 by '''deselecting''' the check box and click the '''Forward''' button twice (accepting the defaults).
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| − | # Enable Network Forwarding by Selecting '''Forwarding to physical network''', the destination should be '''Any physical device''' and the mode should be '''NAT'''
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| − | # Proceed with changes, and click '''Finish'''.
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| − | <ol>
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| − | <li value="13">We will now reconfigure each of our VMs to use our new virtual network '''network1'''
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| − | <ol type="a">
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| − | <li value="1">Let's start with our '''centos2 VM'''. Double-click on your '''centos2''' 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>
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| − | <li>In the '''left pane''' of the Virtual Machine window, select '''NIC:''' and note that this NIC is on the "default" virtual network</li>
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| − | <li>Change it to '''Virtual Network network1: NAT''' (i.e. the VPN that you just created) and click the '''Apply''' button.</li>
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| − | </ol>
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| − | </li>
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| − | <li>Repeat the same steps for your '''<u>centos3</u>''' and '''<u>centos4</u>''' VMs!</li>
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| − | </li>
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| − | </ol>
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| − | '''Answer Part 1 observations / questions in your lab log book.'''
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| − | == Part 2: Configuring VM Network Setup Graphically ('''system-config-network''')==
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| − | For Parts 2 and 3 of this investigation, we will be using a graphical tool to connect our '''centos2''' and '''centos3''' VMs to our private network.
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| − | [[Image:new_network_dialog.png|right|thumb|250px|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''').]]
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| − | # On your '''centos1''' machine, run <b>ifconfig</b> and make note of the IP address assigned to the '''virbr1''' (i.e. "Virtual Bridge) interface. This will be the default gateway and DNS server for your VMs.
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| − | # Start your '''centos2''' VM and login.
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| − | # Within your centos2 VM, click '''Applications''' menu, then select '''System Tools''', and then '''Settings'''.
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| − | # In the ''Settings'' Dialog Box, click on the '''Network''' icon.
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| − | # For the '''Wired''' connection, click the '''settings''' button (The <u>icon</u> appears as a <u>gear</u> located at the bottom right-hand corner of the dialog box).
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| − | # Select the '''IPv4''' tab. Change Address from ''Automatic (DHCP)'' to '''Manual'''.
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| − | # Edit the existing wired connection, using the information displayed below:
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| − | # In the '''IPv4 Settings''' tab change the method from "Automatic (DHCP)" to '''"Manual"'''.
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| − | # In the Addresses section, enter the following information:
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| − | #: IP Address: '''192.168.235.11'''
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| − | #: Subnet Mask: '''255.255.255.0'''
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| − | #: Default Gateway: The IP address of '''virbr1''' on your centos host.
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| − | # Click on the '''DNS''' field and add The IP address (''virbr1''' on your centos host) as the primary DNS server.
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| − | # When finished, check your settings, and then click the '''Apply''' button.
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| − | # Open a terminal and issue the '''ifconfig''' command to confirm the IP ADDRESS settings change.
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| − | # Verify that '''centos2'''VM is now connected to the VPN by issuing the following command from your '''centos1''' machine:<br><b><code><span style="color:#3366CC;font-size:1.2em;">ping 192.168.235.11</span></code></b>
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| − | '''Answer Part 2 observations / questions in your lab log book.'''
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| − | == Part 3: Backing up Only Recent File Changes ==
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| − | This part is a repeat of part2, except we will be demonstrating how to use the '''find''' command to backup recent changes to files. In this case, we will save date/time stamp information in a file, configure to connect '''centos3''' to the network, run the '''find''' command, and prove that the incremental backup worked (showing the files created as a result of the configuration of centos2 to the VPN).
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| − | {| width="40%" align="right" cellpadding="10"
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| − | |- valign="top"
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| − | |{{Admon/note | Backing up Files |One very important aspect of system admin is performing backups. There are many methods for backing up the data on a a computer system. The following is an example of a common backup system used in Business Unix/Linux systems:<br /><br />'''Full Backup''': Backup all specified files (eg. configuration, data files, etc)<br>'''Incremental Backup''': Backup of only files that have changed since last (full) backup.|}}
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| − | |}
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| − | # Keep your '''centos2''' VM running (you will need it running later in this lab).
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| − | # Start the '''centos3''' VM and login
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| − | # Before we configure centos3 network configuration, we should create a timestamp file that can be used to see which files have changed as a result of using the GUI tool. Issue the following command:
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| − | #: <b><code><span style="color:#3366CC;font-size:1.2em;">date > /tmp/timestamp</span></code></b>
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| − | # Run the network configuration tool and enter the following static configuration in the same way that you configured '''centos2'''.
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| − | #* IP Address: '''192.168.235.12'''
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| − | #* Subnetmask: '''255.255.255.0'''
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| − | #* Default Gateway: '''192.168.235.1'''
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| − | #* DNS Server: '''192.168.235.1'''
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| − | # Save and exit the network configuration tool.
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| − | # You may have to restart the network using the correct command.
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| − | # Verify the configuration by pinging the VMs and centos1 using their IP addresses.
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| − | # We will now create an '''Incremental Backup'''. Run the following Linux command as root:
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| − | #: <b><code><span style="color:#3366CC;font-size:1.2em;">find /etc -newer /tmp/timestamp > /root/netcfg.lst</span></code></b>
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| − | #View the '''/root/netcfg.lst''' file. What does it contain?</li>
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| − | #Create a new directory called: '''/tmp/lab6'''
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| − | {| width="40%" align="right" cellpadding="10"
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| − | |- valign="top"
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| − | |{{Admon/tip | Tip | You can create a Bash Shell script file using the ''find'' command above, give the shell script executable permissions, and use the ''crontab'' command to schedule running this script on a periodic basis.}}
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| − | |}
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| − | <ol>
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| − | <li value="11">Issue the following commands:
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| − | <dl>
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| − | <dd><b><code><span style="color:#3366CC;font-size:1.2em;">find /etc -newer /tmp/timestamp -exec cp {} /tmp/lab6 \;</span></code></b>
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| − | </dl>
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| − | </li>
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| − | <li>View the contents of the '''/tmp/lab6''' directory. What does it contain?</li>
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| − | </ol>
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| − | '''Answer Part 3 observations / questions in your lab log book.'''
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| − | == Part 4: Configuring VM Network Setup via Command Line ('''centos4''') ==
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| − | Our centos4 VM is a '''text-based only''' system, thus we cannot use a graphical tool to configure centos4 to connect to our private network. Therefore we will learn how to perform this task by using command-line tools.
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| − | # Leave your '''centos2''' and '''centos3''' VM running, but start your '''centos4''' VM, login, and su to '''root'''.
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| − | # Use the command '''ifconfig''' to list active interfaces, you should see one with a name of '''eth0''' or a similar name.
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| − | # To configure your card with a static address use the following command:
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| − | #:<b><code><span style="color:#3366CC;font-size:1.2em;">ifconfig eth0 192.168.235.13 netmask 255.255.255.0</span></code></b>
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| − | # To configure a default gateway for that interface enter the command:
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| − | #: <b><code><span style="color:#3366CC;font-size:1.2em;">route add default gw 192.168.235.1</span></code></b>
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| − | # To configure a DNS server for this VM, edit the file '''/etc/resolv.conf'''. Change the nameserver line to read:
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| − | #: <b>nameserver 192.168.235.1</b>
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| − | # Save your editing session.
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| − | # Confirm your settings work by doing the following (you might need to do the steps '''3''' and '''4''' a few times before it works; keep checking with the commands below and wait a bit before each attempt):
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| − | #: <b><code><span style="color:#3366CC;font-size:1.2em;">ifconfig</span></code></b>
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| − | #:<b><code><span style="color:#3366CC;font-size:1.2em;">route -n</span></code></b>
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| − | #: <b><code><span style="color:#3366CC;font-size:1.2em;">ping</span></code></b> (your other VM's and centos1)
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| − | #: <b><code><span style="color:#3366CC;font-size:1.2em;">ssh</span></code></b> ( to your Seneca's Matrix account to test your DNS)
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| − | # Restart the <code>centos4</code> VM, or just wait a few minutes.
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| − | # Login and test your configuration again. What happened?
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| − | # While we can configure network settings from the command line those settings are not persistent. To configure persistent network configurations we need to edit the configuration files.
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| − | # Change to the '''/etc/sysconfig/network-scripts''' directory<br>[[Image:new-network-config.png|thumb|300px|right|This diagram should show the newer network configuration of your '''centos1''' machine in relation to your '''Virtual Machines'''.]]
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| − | # List the contents of this directory. You should see 2 different types of files, network config scripts and network configuration files.
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| − | # Look for the configuration file for your original interface, it should be named '''ifcfg-eth0'''
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| − | # Edit the new file for you interface and give it the following settings (or create a brand new file, might be easier than editing the old one):
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| − | #::DEVICE="eth0"
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| − | #::IPADDR="192.168.235.13"
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| − | #::NETMASK="255.255.255.0"
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| − | #::GATEWAY="192.168.235.1"
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| − | #::HWADDR="52:54:00:3f:5c:fa" <-- '''DO NOT COPY THIS VALUE! Use MAC address for YOUR interface using:''' <code><span style="color:#3366CC;font-size:1.2em;">ifconfig eth0</span></code>
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| − | #::DNS1="192.168.235.1" '''
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| − | #::BOOTPROTO="static"
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| − | #::ONBOOT="yes"
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| − | #::NM_CONTROLLED="yes"
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| − | #::IPV6INIT="no"
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| − | # Save the file and then restart the network connection by issuing the commands: <b><code><span style="color:#3366CC;font-size:1.2em;">ifdown eth0</span></code></b> and then <b><code><span style="color:#3366CC;font-size:1.2em;">ifup eth0</span></code></b>
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| − | # Verify your configuration as you did before.
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| − | # Restart the '''centos4''' VM.
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| − | # Login and attempt to '''ssh''' to your matrix account to verify the settings.
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| − | '''Answer Part 4 observations / questions in your lab log book.'''
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| − | =INVESTIGATION 2: VIRTUAL NETWORKING ENVIRONMENT TWEAKS AND OTHER USEFUL UTILITIES=
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| − | Connecting a private network is an important task, but a system administrator also needs to "tweak" the network to make it '''convenient to use''', make it '''safer from unauthorized access''', and use troubleshooting utilities to help '''troubleshoot''' network connectivity problems as they occur. This investigation will expose you to some useful tricks and utilities to help accomplish this task.
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| − | '''NOTE:''' Lab 7 requires that you understand these concepts and have a good general understanding how to use these troubleshooting utilities (like '''netstat''' and '''iptables''').
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| − | == Part 1: Using Local Hostname Resolution ==
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| − | {| width="40%" align="right" cellpadding="10"
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| − | |- valign="top"
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| − | |{{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.}}
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| − | |}
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| − | 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.
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| − | # Complete this investigation on '''all of your VMs''' and the '''centos1''' machine.
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| − | # Use the <b><code><span style="color:#3366CC;font-size:1.2em;">hostname</span></code></b> and <b><code><span style="color:#3366CC;font-size:1.2em;">ifconfig</span></code></b> commands on your centos1 machine and all of your 3 VM's to gather the information needed to configure the '''/etc/hosts''' file on all of your Linux systems.
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| − | # Edit the '''/etc/hosts''' file on <u>each</u> of the '''virtual machines and host machine'''. Add the following contents to the <u>bottom</u> of the '''/etc/hosts''' file:<br><br>
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| − | #::192.168.235.1 centos1
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| − | #::192.168.235.11 centos2
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| − | #::192.168.235.12 centos3
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| − | #::192.168.235.13 centos4<br><br>
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| − | #Confirm that each host can ping all three of the other hosts by name.
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| − | '''Answer Part 1 observations / questions in your lab log book.'''
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| − | == Part 2: Obtaining MAC (Hardware) addresses on Network Computers ==
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| − | {| width="40%" align="right" cellpadding="10"
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| − | |- valign="top"
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| − | |{{Admon/note | Obtaining Remote MAC Addresses| The term '''MAC''' address stands for '''Media Access Control''' address, which provides a unique ID to prevent confusion among computer systems within a network. While we use '''32bit IP addresse'''s to communicate over an internet, on the local ethernet network packets are delivered to a '''48bit hardware address''' (sometimes called a MAC address). The '''ARP''' protocol resolves 32bit IP addresses to 48bit MAC addresses by using a broadcast and caching the results. We can examine the ARP cache to get the MAC addresses of other computers to solve problems involving MAC addresses (such as '''Wake Up on Lan''').}}
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| − | |}
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| − | When our CentOS system provides any services on a network, those services are accessible through a port number. All network services are configured to be accessed on a particular port number. By examining which ports are active on our system we can know what services (and points of attack) are available on our system. The ability to examine this information is important for troubleshooting network services and securing our systems. One great tool for this is the '''netstat''' command.
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| − | # Perform this section on your '''centos1''' machine.
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| − | # On the centos host '''ping''' each of your VM's
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| − | # 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>
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| − | # 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>
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| − | # What was the difference in output? For what other command did the option '''-n''' have a similar effect?
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| − | # On your CentOS host execute the command: <b><code><span style="color:#3366CC;font-size:1.2em;">netstat -at</span></code></b>
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| − | # This command will list all active TCP ports. Note the state of your ports.
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| − | # 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.
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| − | # From one of your VM's login to your host using '''ssh'''
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| − | # On the CentOS host rerun the 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.
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| − | # 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.
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| − | # On your CentOS host try the command <b><code><span style="color:#3366CC;font-size:1.2em;">netstat -atn</span></code></b>. How is this output different?
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| − | # Without the <code>-n</code> option <code>netstat</code> attempts to resolve IP addresses to host names (using '''/etc/hosts''') and port numbers to service names (using '''/etc/services''')
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| − | # Examine the '''/etc/services''' file and find which ports are used for the services: '''ssh''', '''sftp''', '''http'''
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| − | # Now execute the command <b><code><span style="color:#3366CC;font-size:1.2em;">netstat -au</span></code></b> What is the difference between the options: '''-at''' and '''-au'''?
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| − | # When examining UDP ports why is there no state?
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| − | '''Answer Part 2 observations / questions in your lab log book.'''
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| − | == Part 3: Introduction to Firewalls: iptables ==
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| − | {| width="40%" align="right" cellpadding="10"
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| − | |- valign="top"
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| − | |{{Admon/note | | '''[http://en.wikipedia.org/wiki/Iptables Iptables] is the built-in firewall for LINUX'''consisting of a '''list of rules''' (or '''"tables of policies"'''). If data matches a specified <u>policy</u>, it must “jump” to an existing '''condition'''. Simple conditions include '''ACCEPT''', '''DROP''' and '''LOG''' but there are also more complex conditions that can be applied and there is even the option to create your own conditions.
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| − | When using iptables, the '''Filter''' table is important because it contains the following essential '''chains''':<br><br>
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| − | | |
| − | '''INPUT:'''<br>Data is checked against the INPUT chain to see if it is <u>allowed into</u> the PC.<br><br>
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| − | '''OUTPUT:'''<br>Data is checked against the OUTPUT chain to see if it is <u>allowed to go outside</u> of the PC.<br><br>
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| − | '''FORWARD:'''<br>PC is acting as a router it does not actually send or receive data, it <u>FORWARDS</u> data from one machine to another.
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| − | }}
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| − | |}
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| − | Since Linux servers may 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. Linux uses the command called '''iptables''' to set the firewall rules. Although graphical programs can be used to configure iptables, it is important for students of Linux Administration to learn how to use the iptables command for more complex and automated configuration via shell scripting.
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| − | # For the remainder of this section, use your '''centos1''' machine.
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| − | # As root on the CentOS host enter the following commands at the prompt:
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| − | #: <b><code><span style="color:#3366CC;font-size:1.2em;">iptables -L</span></code></b>
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| − | #: <b><code><span style="color:#3366CC;font-size:1.2em;">iptables -F</span></code></b>
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| − | # What did those commands issued above do? Refer to the ''manpages'' for ''iptables'' if not certain.
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| − | # Set the default policy for the INPUT chain to DROP by issuing the command:
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| − | #: <b><code><span style="color:#3366CC;font-size:1.2em;">iptables -P INPUT DROP</span></code></b>
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| − | # Now try on your own to change the default policies for the OUTPUT and FORWARD chains to DROP
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| − | # Write the commands you executed in your lab book.
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| − | # Can we mix these policies? Try to set the FORWARD chain policy to ACCEPT. Did it work?
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| − | | |
| − | === Testing iptables Policies ===
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| − | # Execute the command <b><code><span style="color:#3366CC;font-size:1.2em;">iptables -L</span></code></b> and check that the policies on your INPUT and OUTPUT chain are set to DROP
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| − | # Open a browser and attempt to access the Internet. Were you successful?
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| − | # Using the commands you have learned so far, change the policies on the INPUT and OUTPUT chains to ACCEPT
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| − | # Open your browser and attempt to access the Internet again. Were you successful?
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| − | # Change the policies on all of the chains to DROP
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| − | {| width="40%" align="right"
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| − | |- valign="top"
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| − | |{{Admon/note| Interpreting iptables commands |Here is the command you issue in step #15:
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| − | iptables -I OUTPUT -p tcp -s0/0 -d 0/0 --dport 80 -j DROP
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| − | Which can be read like this: Insert a rule into the iptables OUTPUT chain that will match any tcp packet, with any a source address, any destination address, and a deistination port of 80. Any packet that matches will be dropped.
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| − | | |
| − | '''Let's break down the command to see how it works:'''
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| − | The '''-I''' switch tells iptables to INSERT this line into the OUTPUT policy. This means it will be the first line in the policy. If we used a -A switch it would have appended the line and it would be the last line of the policy. If you are writing complex iptables rules where multiple matches can occur, it is important that the lines go in the right order. If you follow the -I with a number, the new rule will be inserted at that location in the chain (for example, <code>-I 3 OUTPUT</code> will insert the rule into the 3rd position in the OUTPUT chain, moving the existing rules down as necessary (the old rule #3 will become the new rule #4, for example).
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| − | The '''-p tcp''' switch tells iptables to only match TCP packets. Alternately, the protocol could be set to udp, icmp, or all.
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| − | The '''-s0/0''' switch specifies the source IP address. 0/0 means a source address of “anywhere.” this has been put into the lab because your ip address will change because it is dynamically assigned. You can change this value if you want to the IP address that has been specifically assigned to your PC.
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| − | The '''-d0/0''' switch specifies the destination address. It makes sense that this address is set to “anywhere” because if we want to block all requests to the WWW, we will never know the specific IP address of web server that is trying to be accessed.
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| − | | |
| − | The switch '''--dport 80''' tells iptables to look at the destination port in the packet and see if it is equal to 80. Alternately, you can filter based on source addresses using the <code>--sport</code> switch.
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| − | '''-j''' means jump to a particular target – Basic targets are ACCEPT, DROP, REJECT, and LOG. The available targets depend on which table contains the chain.
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| − | '''DROP''' means drop the packet – make it disappear - and do not continue processing rules. '''REJECT''' is similar, but causes an error packet to be sent back to the source host. '''ACCEPT''' causes the packet to be processed. '''LOG''' causes an entry to be made in the system logs showing that the packet was processed. Note that the LOG target is the only one that does not stop rule-checking in the chain - so you can log a packet with one rule, and then use a later rule in the chain to DROP, REJECT, or ACCEPT it.
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| − | }}
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| − | | |
| − | |}
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| − | <ol>
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| − | <li value="6"> 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></li>
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| − | <li>The above rule tells '''iptables''' to log packets and relevant information to '''/var/log/messages'''.</li>
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| − | <li>This entry in the OUTPUT policy will therefore log all packets being sent out of the machine.</li>
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| − | <li>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:<br><b><code><span style="color:#3366CC;font-size:1.2em;">tail /var/log/messages</span></code></b></li>
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| − | <li>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 /><blockquote><code>Jun 24 12:41:26 centos1 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></blockquote></li>
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| − | <li>Your IP, host names and date will be different, but the one thing that should be the same is the DPT=80 value.</li>
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| − | <li>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?</li>
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| − | <li>Using the commands we already know, change the default policies on all of your chains to ACCEPT.</li>
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| − | <li>Open a browser and confirm that you can access the world wide web.</li>
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| − | <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>
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| − | <li>Try to access the Web. If you have done everything right, you should not have been successful.</li>
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| − | <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>
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| − | <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>
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| − | <li>After you have completed this task, flush the iptables again.</li>
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| − | <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>
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| − | <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>
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| − | <li>Confirm that your rule works by testing from your VM's</li>
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| − | <li>Does iptables close the port? Check using '''netstat'''</li>
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| − | <li>Now insert a rule on the CentOS host that would ACCEPT connections from the centos3 VM only.</li>
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| − | <li>Fully test your configuration.</li>
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| − | </ol>
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| − | | |
| − | === Making iptables Policies Persistent ===
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| − | It should be noted that all of the commands that we do here with iptables will not be persistent unless you have your configuration. That means if you re-boot, the default iptables configuration will be loaded. When your iptables service starts or at boot time it has to load the rules from the file '''/etc/sysconfig/iptables-config'''.
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| − | The final section below teaches you to make your iptables settings permanent.
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| − | # 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>
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| − | #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>
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| − | # Verify that the file '''/etc/sysconfig/iptables''' exists.
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| − | # Restart your iptables service and test your configuration.
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| − | | |
| − | '''Answer the Part 3 observations / questions in your lab log book.'''
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| − | | |
| − | = LAB 6 SIGN-OFF (SHOW INSTRUCTOR) =
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| − | {{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.}}
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| − | | |
| − | ===Download and Run Lab6 Checking Script & Show Lab6 Work===
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| − | '''Perform the Following Steps:'''
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| − | # Issue the Linux command: <b><code><span style="color:#3366CC;font-size:1.2em;">wget http://matrix.senecac.on.ca/~murray.saul/ops235/lab5-check.bash</span></code></b>
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| − | # Give the '''lab6-check.bash''' file execute permissions (for the file owner).
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| − | # Run the shell script and if any warnings, make fixes and re-run shell script until you receive "congratulations" message.
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| − | #Arrange proof of the following on the screen:<br><blockquote><span style="color:green;font-size:1.5em;">✓</span> '''centos3''' VM:<blockquote><ul><li>Contents of '''/tmp/lab6''' directory.</li><li>'''ssh''' from centos3 to the CentOS host</li></ul></blockquote></li></li><li><span style="color:green;font-size:1.5em;">✓</span> '''<u>All</u> VMs''':<blockquote><ul><li>'''ifconfig''' information</li><li>Contents of '''/etc/hosts''' file</li></ul></blockquote><span style="color:green;font-size:1.5em;">✓</span>'''centos1''' machine<blockquote><ul><li>'''arp''' cache information</li><li>Contents of '''/etc/hosts''' file</li><li>Proof of backup</li><li>A list of your '''iptables''' rules</li></ul></blockquote><span style="color:green;font-size:1.5em;">✓</span> '''Lab6''' log-book filled out.
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| − | | |
| − | = Practice For Quizzes, Tests, Midterm & Final Exam =
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| − | | |
| − | # What is a port?
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| − | # What command will set your IP configuration to 192.168.55.22/255.255.255.0 ?
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| − | # What file contains the systems <code>iptables</code> rules?
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| − | # What is the difference between UDP and TCP?
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| − | # What port number is used for DHCP servers?
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| − | # What is the function of the file <code>/etc/services</code> ?
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| − | # What is the function of the file <code>/etc/hosts</code> ?
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| − | # What is the purpose of the file <code>/etc/sysconfig/network-scripts/ifcfg-eth0</code> ?
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| − | # What tool is used to show you a list of current TCP connections? | |
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| − | [[Category:OPS235]] | |
