[[Category:OPS235]][[Category:OPS235 Labs]] ==Overview== * In this lab, you will learn the basics of networking by using your Virtual Machines and your f17host machine.  * In addition, you will learn to associate network services with port numbers, and learn how to backup files by date/time.

* # Configure a virtual network for Virtual Machines* # Use the Fedora GUI program to configure network interfaces with static IP configuration and host name resolution* # Use the <code>find</code> command to locate the configuration files modified by the GUI network configuration program# To examine some of the Linux's TCP/IP configuration files in the <code>/etc/</code> directory# To configure a Fedora host with static network configuration without a GUI tool# To configure the linux firewall <code>iptables</code> to allow/disallow/forward different types of network traffic using simple rules   ==Required Materials (Bring to All Labs)== * Fedora 17 LIVE CD* Fedora 17 x86_64 Installation DVD* SATA Hard Disk (in removable disk tray)* USB Memory Stick* Lab Logbook ==Prerequisites== * Completion and Instructor "Sign-off" of Lab 5: [[OPS235 Lab 5]]  ==Linux Command Online Reference==Each Link below displays online manpages for each command (via [http://linuxmanpages.com/ http://linuxmanpages.com]):

{|width="100%" cellpadding="5" width="50%"|'''Networking Utilities:'''|'''Additional Utilities:'''||- valign="top"|* To examine some of the Linux's TCP[http:/IP configuration files in the <code>/etclinuxmanpages.com/<man8/code> directoryifconfig.8.php ifconfig]* To configure a Fedora host with static [http://fedoramobile.org/Members/MrHappy/system-config-network configuration without a GUI toolsystem-config-network]*[http://linuxmanpages.com/man8/route.8.php route]*[http://linuxmanpages.com/man8/ping.8.php ping]*[http://linuxmanpages.com/man8/arp.8.php arp]* To use and interpret the <code>[http://linuxmanpages.com/man8/netstat<.8.php netstat]*[http:/code> command to troubleshoot and monitor network services/linuxmanpages.com/man8/iptables.8.php iptables]|*[http://www.linuxcertif.com/man/1/systemctl/ systemctl] *[http://linuxmanpages.com/man1/find.1.php find]*[http://linuxmanpages.com/man1/tail.1.php tail]*[http://linuxmanpages.com/man1/cp.1.php cp]|}

== Reference Resources on the web==Additional links to tutorials and HOWTOs:* [http://en.wikipedia.org/wiki/Virtual_network Virtual Network - Definition]* [http://linuxmanpageswww.reallylinux.com/ man pagesdocs/networkingadmin.shtml Important Linux Networking Commands] for find, ifconfig, ping, netstat, NetworkManager, nslookup, iptables, arp(Also refer to lab 6 notes)* Online reading material for week 8[http://www.yolinux.com/TUTORIALS/LinuxTutorialNetworking.html Linux Network Configuration]* [[IPTables]] Reference* Lab6 Notes: [http://zenit.senecac.on.ca/wiki/index.php/OPS235_Lab_6#Investigation_8:_How_do_I_view_and_configure_the_IPTABLES_firewall.3F_--_Basic_Function.2FConfiguration IPTABLES Firewall]

Currently you should have the following network configuration:<br /><br />[[Image:network-config1.png]]* '''Fedora host ''' has 1 active network interface (probably <code>eth0'''em1'''</code>)that receives IP configuration from the School's DHCP server.* '''Fedora host ''' has 1 active network interface (<code>'''virbr0'''</code>) that has a static default configuration of '''192.168.122.1/255.255.255.0'''* '''Fedora1 VM ''' has 1 active interface (<code>'''eth0'''</code>) that receives a dynamic configuration from your Fedora Host* '''Fedora2 VM ''' has 1 active interface (<code>'''eth0'''</code>) that receives a dynamic configuration from your Fedora Host* '''Fedora3 VM ''' has 1 active interface (<code>'''eth0'''</code>) that receives a dynamic configuration from your Fedora Host 

{{Admon/important | Update your systems | It is advisable to perform a <code>yum update</code> on your Fedora host and all 3 VM's.}}{{Admon/important | Live disc installations and system-config-network | The '''fedora1 ''' VM was installed from Live CD. It is missing the GUI Network Configuration tool we will be using. Use the command <code>yum install system-config-network</code> to install it.}}

== Lab Investigations Configuring a Network Using Virtual Machines ==

{{Admon/note | Note! Use the f17host | Complete the following steps on your fedora host'''f17host''' computer system.}}

# On the fedora host your '''f17host''' machine start Virtual Machine Manager# In the Virtual Machine Manager dialog box, Select '''Edit'''-> '''Connection Details'''.# In the '''Hosts ''' Details dialog box, select the '''Virtual Networks ''' tab# Disable the default configuration from starting at boot by '''deselecting the ''' '''"Autostart On Boot" ''' (on boot) checkbox.# Stop the default network configuration by clicking on the '''stop ''' button at the bottom left-side of the windowdialog box.# Click on the '''add ''' button (the button resembles a "plus sign") to add a new network configuration.# Give your new network a name (i.e. '''network1''')

#*'''192.168.235.0/24'''# Disable DHCP by '''deselecting ''' the check box.# Enable Network Forwarding by Selecting "'''Forwarding to physical network"'''# The destination should be "'''Any physical device" ''' and the mode should be "'''NAT"'''# Proceed with changes, and select '''Finish'''.# Before proceeding, check the "<u>default</u>" network connection (in the Virtual Networks section) to verify "'''Autostart On Boot" ''' is disabled, and that you have created the "'''network1" ''' configuration. You might be required to click Apply when the default '''Autostart''' option is deselected. If you have any problems launching your VMs, then it is recommend to reboot your main system.# '''Close''' the Virtual Manager, '''reboot''' your f16host, '''log-back into your f16host computer''', and '''restart''' the Virtual Machine Manager.{{Admon/note | Note! Repeat these steps for each VM | Complete the following steps on <u>each</u> of your VMsvirtual machines.}}# <ol> <li value="15">Now we need to add our new virtual network "'''network1" ''' to the 3 VM's##<ol type="a" style="margin-left:2cm"> <li value="1">Select the '''fedora1 ''' VM and edit the VM details'''Virtual Machine Details'''<br />(Note: the Virtual Machine window will appear - do not start virtual machine)</li>## <li>Under View select '''Details'''</li>## <li>In the '''left pane ''' of the Virtual Machine window, select the '''NIC :''' and note that this NIC is on the "default" virtual network</li>## <li>Click on the '''Remove ''' buttonat the bottom right-side of the dialog box.</li>## <li>Click on "'''Add Hardware" ''' on the bottom left-side of the dialog box and add a new network</li>## <li>For the host device , locate and select "'''Virtual Network network1" ''' : NAT</li> <li>Click finish to exit the Virtual Machine Details dialog box.</li></ol> </li># <li value="16">Repeat these steps '''a - g''' for '''fedora2 ''' and '''fedora3 ''' VM's.</li># </ol> '''Answer the Investigation 1 question observations / questions in your lab log book.'''

{{Admon/note | Note! Use fedora2 | Complete this investigation on your fedora2 VM.}}# Start '''fedora2 ''' VM and login# On your '''fedora host''' run <code>ifconfig</code> and make note of the IP address assigned to the <code>virbr1</code> interface. This will be your default gateway for your Vm's.[[Image:new_network_dialog.png|thumb|350px]]# Make certain to return to your fedora2 VM.# To configure a new interface on fedora2 go to System'''Applications'''->Administration'''Other'''->'''Network Connections'''.# Make certain there are no '''"Wired"''' connections (even if you have to click on the connection name and click the '''Delete''' button.# Create a new wired connection, with the "Connection Name" at the top to read '''eth1'''# Click on the '''Add''' button, and select the '''IPv4 Settings''' tab.# Change the method from "NewAutomatic (DHCP)" buttonto '''"Manual"'''.# Select Ethernet Device and choose In the network card named <code>eth1</code>'''Addresses section''', click '''"Add"'''.# Statically Manually set the IP configurationto:#: IP Address '''192.168.235.12'''#: Subnet Mask '''255.255.255.0'''#: Default Gateway '''192.168.235.1 ''' (The IP address of <code>virbr1</code> on your fedora host.)# Click on the '''DNS tab ''' field and add '''192.168.235.1 ''' as the primary DNS server.# Select ForwardClick '''Save''' to Finish, and then select Apply exit the Network Connections dialog box.# Your network connection may connect (view the Network Manager applet in the gnome panel at the top of the screen). If there is no connection after a few minutes, you should be able to right-click on the applet and click "eth1" to connect.# You should be able to use the systemctl command to Finishrestart your network.#'''Restart your network ''' on fedora2by issuing the commands:#*<code>systemctl stop NetworkManager. service</code>#*<code>systemctl start NetworkManager.service NetworkManager restart</code>

# To verify that fedora2 has the correct default gateway configured, enter the command : <code>route -n</code># Verify the network by using : <code>ping 192.168.235.1</code># Record '''Answer the answer to Investigation 2 observations / questions in your logbooklab log book.'''

{{Admon/note | Note! Use fedora1 | Complete this investigation on your fedora1 VM.}} {{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.<br />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<br /><br />When the system is required to be fully restored, then the '''full backup''' is recovered, followed by each .<br />In this investigation, you will learn how to perform an '''incremental backup''' using the <code>find</code> utility|}} # Start '''fedora1 ''' VM and login

# Run the network configuration tool and enter the following static configuration in the same way that you configured '''fedora2'''.#* IP Address: '''192.168.235.11'''#* Subnetmask: '''255.255.255.0'''#* Default Gateway: '''192.168.235.1'''#* DNS Server: '''192.168.235.1'''# Save and quit and restart exit the network configuration tool.# Restart the NetworkManagerservice.# Verify the configuration by pinging fedora host ('''192.168.235.1''') and fedora2 ('''192.168.235.12''')

{{Admon/note | Creating an Incremental Backup |We will now be using the <code>find</code> command to::*Locate the configuration files (contained in the <code>/etc</code> directory) that were modified by the GUI network configuration program:*Copy those configuration files to a "specified" directory for backup purposes Previously, you created a file called <code>/tmp/timestamp</code> that just contains the current date and time prior to running the network configuration toool for fedora2.. Any files that were modified by the GUI network configuration program should have a timestamp later (or newer) than the "timestamp" file you created. All the Linux TCP/IP configuration files are stored under the '''/etc''' directory or its sub-directories. The <code>find</code> command (using the correct options) can be used to only list those files that have been recently created since the timestamp date contained in the <code>/tmp/timestamp</code> file.|}} <ol> <li value="8">Run the following Linux command: <ul> <li><code>find /etc -newer /tmp/timestamp &gt; /root/netcfg.lst</code></li> </ul> </li> <li>View the <code>/root/netcfg.lst</code> file. What does it contain?</li> <li>Create a new directory called: <code>/tmp/lab6</code></li> <li>Issue the following commands: <ul> <li><code>mkdir -p /tmp/lab6</code></li> <li><code>find /etc -newer /tmp/timestamp -exec cp {} /tmp/lab6 \;</code></li> </ul> </li> <li>View the contents of the <code>/tmp/lab6</code> directory. What does it contain?</li></ol> {{Admon/tip | Tip | Just for interest, it is relatively simple to automate your backups. You just create a Bash Shell script file using the <code>find</code> command above, give the shell script executable permissions, and use the <code>crontab</code> command to schedule when this script is to be run. If you want to learn more about shell scripting, you can take or refer to the course called '''OPS435''' .}} '''Answer the Investigation 3 observations / questions in your lab log book.''' === Investigation 4: How do I configure the network without a GUI tool?. ==={{Admon/note | Note! Use fedora3 | Complete this investigation on your fedora3 VM.}}# Start '''fedora3 ''' VM and login as root# Use the command <code>ifconfig</code> to list active interfaces, you should see one with a name of <code>eth1eth0</code> or a similar name.# To configure your card with a static address use the following command:#* <code>ifconfig eth1 eth0 192.168.235.13 netmask 255.255.255.0</code>

#* Copy that file to <code>ifcfg-eth1eth<b>N</b></code> or whatever name matches where <b>N</b> relates to your current eth interfacenumber (we will use <b>eth1</b> as an example).

#**GATEWAY=192.168.235.1#**DNS1=192.168.235.1#**DEVICE="eth1 " <-- '''<-- or the interface name you YOU have'''#**BOOTPROTOIPADDR=none"192.168.235.13"#**NETMASK="255.255.255.0"#**TYPEGATEWAY=Ethernet"192.168.235.1"#**HWADDR="52:54:00:3f:5c:fa " <-- '''<--use the HWADDR for your YOUR interface'''#**IPADDRDNS1="192.168.235.131" '''#**IPV6INITBOOTPROTO=no"static"#**ONBOOT="yes"#**USERCTLNM_CONTROLLED="yes"#**IPV6INIT="no"# Save the file and then restart the network connection by issuing the commands: <code>ifdown eth1</code> and then <code>NetworkManagerifup eth1</code> service<br /><br ><b>NOTE: </b>If there are errors, check that the hardware address in the config file matches the hardware address of the device its configuring<br /><br />

# '''Answer the Investigation question 4 observations / questions in your logbooklab log book.'''

{{Admon/note | Note! Use each machine | Complete this investigation on all of your VM's and the Fedora host.}}

{{Admon/note | Please take 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 '''fedoraproject.org''' to the computer friendly 32bit numeric addresses used by the IP protocol. On smaller ad-hoc networks we can use the <code>/etc/hosts</code> on each system to resolve names to addresses.}}

192.168.235.1 f13hostf17host

{{Admon/note | Note! Use your Fedora Host | Complete this investigation on your Fedora host.}}

{{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 addresses addresse'''s to communicate over an internetwork, 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 on our local network.<br /><br />Being able to determine remote MAC address information is useful from troubleshooting networking programs to using '''WOL''' (Wake up on Lan) to automatically boot remote workstations via the network. In this investigation, you will learn how to obtain MAC address information for various network cards.}}

# '''Answer the investigation question Investigation 6 observations / questions in your logbooklab log book.''' 

{{Admon/note | Note! Use All Machines | Complete this investigation on all of your VM's and the Fedora host.}} {{Admon/note | Network Ports | When our Fedora 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 <code>netstat</code> command.}}

{{Admon# On your fedora host execute the command: <code>netstat -at</note | Please take note! | When our Fedora system provides any services on code># This command will list all active TCP ports. Note the state of your ports.# TCP is a connection oriented protocol that uses a network, those services are accessible through handshaking mechanism to establish a port numberconnection. All network services Those ports that show a state of LISTEN are configured waiting for connection requests to be accessed on a particular service. For example you should see the <code>ssh</code> service in a LISTEN state as it is waiting for connections.# From one of your VM's login to your host using <code>ssh</code># On the fedora host rerun the command and in addition to the LISTEN port numberit should list a 2nd entry with a state of ESTABLISHED. This shows that there is a current connection to your ssh server. By examining which ports are active # Exit your ssh connection from the VM and rerun the command on our system we can know what services the fedora host. Instead of ESTABLISHED it should now show a state of CLOSE_WAIT. Indicating that the TCP connection is being closed.# On your fedora host try the command <code>netstat -atn</code>. How is this output different?# Without the <code>-n</code> option <code>netstat</code> attempts to resolve IP addresses to host names (using /etc/hosts) and points of attackport numbers to service names (using /etc/services) # Examine the <code>/etc/services</code> file and find which ports are available on our system. The ability to examine this information is important used for troubleshooting network the services : <code>ssh, ftp, http</code># Now execute the command <code>netstat -au</code> What is the difference between <code>-at</code> and securing our systems. One great tool for this <code>-au</code>?# When examining UDP ports why is there no state?# Using the <code>netstat</code> commandman page and experimentation make sure you understand how the following options work.}}#* -at#* -au#* -atp#* -aup#* -atn#* -aun#* -autnp

* On your fedora host execute '''Answer the command <code>netstat -at<Investigation 7 observations /code>* This command will list all active TCP ports. Note the state of questions in your portslab log book.* 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 <code>ssh</code> service in a LISTEN state as it is waiting for connections.* From one of your VM's login to your host using <code>ssh</code>* On the fedora 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.* Exit your ssh connection from the VM and rerun the command on the fedora host. Instead of ESTABLISHED it should now show a state of CLOSE_WAIT. Indicating that the TCP connection is being closed.* On your fedora host try the command <code>netstat -atn</code>. How is this output different?* 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)* Examine the <code>/etc/services</code> file and find which ports are used for the services <code>ssh ftp http</code>* Now execute the command <code>netstat -au</code> What is the difference between <code>-at</code> and <code>-au</code>?* When examining UDP ports why is there no state?''

{{Admon/important | Note! Non-Persistent Changes to your Host System | We will complete Complete this lab on the your host machinesystem (f16host).

It should be noted that all of the commands that we do here with iptables will not be persistentunless you have your configuration. That means if you re-boot, the default iptables configuration will be loaded.}}

target prot opt source # Execute the command <code>iptables -L</code> and check 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:#* <code>iptables -A OUTPUT -j LOG</code># The above rule tells <code>iptables</code> to log packets and relevant information to <code>/var/log/messages</code>. # This entry in the OUTPUT policy will therefore log all packets being sent out of the machine.# 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.#* <code>tail /var/log/messages</code># 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 /><br /><blockquote><code>Mar 3 09:21:03 koala-laptop kernel: [90775.407304] IN= OUT=wlan0 SRC=192.168.1.107 DST=66.249.90.104 LEN=1470 TOS=0x00 PREC=0x00 TTL=64 ID=19752 DF PROTO=TCP SPT=45431 DPT=80 WINDOW=108 RES=0x00 ACK PSH URGP=0</code></blockquote># 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 destinationport 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?# Using the commands we already know, change the default policies on all of your chains to ACCEPT. # Open a browser and confirm that you can access the world wide web.# Enter the command:#* <code>iptables -I OUTPUT -p tcp -s0/0 -d 0/0 --dport 80 -j DROP</code># Try to access the Web. If you have done everything right, you should not have been successful.# After you have completed the test execute the following command:#* <code>iptables -F</code>{{Admon/note| Interpreting iptables commands |Here is the command you just used:

target prot opt 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 destinationaddress, and a deistination port of 80. Any packet that matches will be dropped.

target prot opt source destinationThe '''-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</precode>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).

{{Admon/note | | Each chain has a default policy. In my example here the default policy is ACCEPT. This means that if data The '''-p tcp''' switch tells iptables to only match TCP packets are checked and there is no rule that matches that packet in the chain the data will be allowed to pass to it's destination. ConverselyAlternately, if the policy is protocol could be set to DROP then the packet will be dropped if there is no matchudp, icmp, or all.

See The '''-s0/0''' switch specifies the MAN page for <code>iptables<source IP address. 0/code> 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. for detailed information on switches and optionsYou can change this value if you want to the IP address that has been specifically assigned to your PC.}}

* Set 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 default policy for WWW, we will never know the INPUT chain specific IP address of web server that is trying to DROP:** <code>iptables -P INPUT DROP</code>be accessed.

{{Admon/note| |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>-P-sport</code> switch stands for POLICY. This tells <code>iptables</code> that we are changing the policy for the INPUT chain. The policy is to be changed to DROP.

Note that <code>iptables</code> commands (as well as all other Linux commands) '''-j''' means jump to a particular target – Basic targets are case sensitiveACCEPT, DROP, REJECT, and LOG. Check your syntax carefullyThe available targets depend on which table contains the chain.}}

* Now try on your own '''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 change the default policies for source host. '''ACCEPT''' causes the OUPUT and FORWARD chains packet to be processed. '''LOG''' causes an entry to DROP* Write 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 commands chain - so you executed can log a packet with one rule, and then use a later rule in your lab book.* Can we mix these policies? Try to set the FORWARD chain policy to DROP, REJECT, or ACCEPTit. Did it work?

}}{{Admon/note|0/0 Addresses|Source and destination addresses of 0/0 will match all addresses. Therefore, they '''Testing policiesdon't do anything''' and can be removed:

* Execute the command <code> iptables -L</code> and check that the policies on your INPUT and I OUTPUT chain are set to -p tcp -s0/0 -d 0/0 --dport 80 -j 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:** <code>iptables -A OUTPUT -j LOG</code>* The above rule tells <code>iptables</code> to log packets and relevant information to <code>/var/log/messages</code>. * This entry in the OUTPUT policy will therefore log all packets being sent out of the machine.* 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.** <code>tail /var/log/messages</code>* 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: <blockquote><code>Mar 3 09:21:03 koala-laptop kernel: [90775.407304] IN= OUT=wlan0 SRC=192.168.1.107 DST=66.249.90.104 LEN=1470 TOS=0x00 PREC=0x00 TTL=64 ID=19752 DF PROTO=TCP SPT=45431 DPT=80 WINDOW=108 RES=0x00 ACK PSH URGP=0</code></blockquote> * 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 equivalent 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?* Using the commands we already know, change the default policies on all of your chains to ACCEPT. * Open a browser and confirm that you can access the world wide web.* Enter the command:** <code>iptables -I OUTPUT -p tcp -s0/0 -d 0/0 --dport 80 -j DROP</code> {{Admon/note| |This command can be read like this, Insert a line into the iptables OUTPUT chain that will look at tcp information and DROP any packet with a source address from anywhere, to a destination address to anywhere if the destination port is 80. Let's break down the command to see how it works. 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. Most people simply write scripts to ensure this. The '''-p tcp''' switch tells iptables to filter data by looking at TCP information in the packets. For now, we simply want to filter data by source and destination TCP ports so we need this switch. 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. 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. The switch '''--dport 80''' tells iptables to look at the destination port in the packet and see if it is equal to 80 '''-j''' means jump to a particular condition – Basic conditions are ACCEPT, DROP and LOG. There are others and you also have the ability to create your own. '''DROP''' means drop the packet – do not let it leave the computer.

# 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.# After you have completed this task, flush the iptables again.# Make sure that your ssh server is running on the host machine and try to access it from a virtual machine of your choice. # 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.# Confirm that your rule works by testing from your VM''Additional Exercises'''s# Does iptables close the port? Check using <code>netstat</code># Now insert a rule on the fedora host that would ACCEPT connections from the fedora2 VM only.# Fully test your configuration.

* Using the information you have learned, try on your own to achieve the same goal as above (block www access to {{Admon/note | iptables Service |When your computer) by using the INPUT chain instead of the OUTPUT chain.* After you have completed this task, flush the iptables again.* Make sure that your ssh server is running on the host machine and try to access service starts or at boot time it from a virtual machine of your choice. * Once you have confirmed that ssh is running on the host machine, insert an iptables rule on the host machine to prevent access has to load the ssh server rules from all VM's on the virtual network.* Confirm that your rule works by testing from your VM's* Does iptables close the port? Check using file <code>netstat/etc/sysconfig/iptables</code>* Now insert a rule on the fedora host that would ACCEPT connections from the fedora2 VM only.* Fully test your configuration.}}

{{Admon<ol> <li value="9">'''Make a backup of the file <code>/etc/sysconfig/note | |When your iptables service starts or at boot time it has </code>'''</li> <li>Examine the file to load the see how rules from are added.</li> <li>Issue the file command: <code>iptables-save >/etc/sysconfig/iptables</code> to save the rules you added with the iptables command, above.}}</li>* Make a backup of <li>Verify that the file <code>/etc/sysconfig/iptables</code> was updated with your new rules.</li>* Examine <li>Restart your iptables service and test your configuration. </li> <li>Write a short bash script to add a rule allowing the file fedora1 and fedora3 VM's to connect to see how rules are added<code>ssh</code> on the fedora host.</li>* Enter in your 2 new rules created above.</ol>

{{Admon'''Answer the Investigation 8 observations /important | Carefull! | Remember mistakes questions in iptables can have a significant impact on your systemlab log book. Make sure you are '''appending the rules to the INPUT chain'''}} * Restart your iptables service and test your configuration. * Write a short bash script to append a rule allowing the fedora1 and fedora3 VM's to connect to <code>ssh</code> on the fedora host.* Answer the investigation in your logbook

 Now you should have the following network configuration:<br /><br />

 * '''Fedora host ''' has 1 active network interface (probably <code>eth0'''em1'''</code>)that receives IP configuration from the School's DHCP server.* '''Fedora host ''' has 1 active network interface (<code>'''virbr1'''</code>) that has a static default configuration of '''192.168.235.1/255.255.255.0'''* '''Fedora1 ''' VM has 1 active interface (<code>'''eth1'''</code>) that has a static configuration of '''192.168.235.11/255.255.255.0'''* '''Fedora2 ''' VM has 1 active interface (<code>'''eth1'''</code>) that has a static configuration of '''192.168.235.12/255.255.255.0'''* '''Fedora3 ''' VM has 1 active interface (<code>'''eth1'''</code>) that has a static configuration of '''192.168.235.13/255.255.255.0'''

 == Preparing for the Quizzes ==