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New page: <h2>NAD710 - Introduction to Networks - Using Linux</h2> =Objectives= # Use the ifconfig and/or ip command(s) to display/assign IP paramenters to a network device # Use the ifconfig comma...
<h2>NAD710 - Introduction to Networks - Using Linux</h2>
=Objectives=
# Use the ifconfig and/or ip command(s) to display/assign IP paramenters to a network device
# Use the ifconfig command to disable/enable ARP on a network interface
# Use the arp command to display the system ARP cache
# Use the arp command to add manual entries to the system ARP cache
# Use the tcpdump command to capture and display network packets
=Background Information=
On a TCP/IP Ethernet network, every application [http://en.wikipedia.org/wiki/Data_packet data packet] contains 3 pairs of numbers: source and destination physical addresses (or [http://en.wikipedia.org/wiki/MAC_Address MAC addresses] ), source and destination [http://en.wikipedia.org/wiki/IP_Address IP addresses], and source and destination [http://en.wikipedia.org/wiki/TCP_Port ports]. The first two pairs of numbers are the main focuse of this lab.
==Software Requirements==
Linux Distributions:
* Fedora Core 8/9
RPM Packages:
* ethtool
* iproute
* net-tools
* tcpdump
==Hardware requirements==
Two Linux Machines on a Ethernet LAN
Lab with the proper hardware and software: T2107 in TEL building.
=Procedure=
You need two Linux systems connected to a LAN. Make sure that each system has only ONE network interface card. Label one system as Host-A and the other system as Host-B.
* Boot up both system to Fedora Core 8 or 9.
* Login to Host-A and Host-B under a regular user account. Don't login as "root".
* On Host-A, open up two terminal windows, set the title on one terminal windows to "T" and the other to "C". "T" for tcpdump window and "C" for command window.
* Do the same on Host-B as on Host-A.
* Switch to user "root" on all four terminal windows.
* Use the command "ifconfig" to find out the name (eth<font color="blue">xx</font>), IP address, broadcast address, netmask and the MAC address of the network device on Host-A and Host-B. Keep this information for later use.
* Use the command "ip addr" on Host-A and Host-B and keep the output for later use.
* Use the "ping" command to check the network connection between Host-A and Host-B. Ask for help if Host-A can not talk to Host-B.
* Commands in the following steps may contain the variable <font color="red">x</font>. If you are doing this lab using your own LAN, you can pick any value between 1 and 254 for <font color="red">x</font>. If you are working in the LUX lab, make sure you are not using the same <font color="red">x</font> value as any other students in the Lab.
* On terminal window "C" on Host-A, set the IP address for the network device to 172.16.<font color="red">x</font>.1, netmask to 255.255.255.0, and set the broadcast address to the appropriate value.
* On terminal window "C" on Host-B, set the IP address for the network device to 172.16.<font color="red">x</font>.2, netmask to 255.255.255.0, and set the broadcast address to the appropriate value.
* Use the "ifconfig" or "ip addr" on Host-A and Host-B to verify the newly assigned addresses. Make changes if necessary. Ask for help if you have any troubles.
* Use the "ping" command to verify the network connection between Host-A and Host-B for the new addresses. Go on to the next step only after a positive result.
* On terminal window "C" on Host-A, enter the following commands and keep the outputs for later use:
arp -n
ifconfig eth<font color="blue">xx</font> down
arp -n
ifconfig eth<font color="blue">xx</font> up
arp -n
* Do the same on Host-B.
* On terminal window "T" on Host-A, enter the following command and keep the output for later use:
tcpdump -n arp host 172.16.<font color="red">x</font>.1
* On terminal window "T" on Host-B, enter the following command and keep the output for later use:
tcpdump -n arp host 172.16.<font color="red">x</font>.2
* On terminal window "C" on Host-A, enter the following "ping" command and watch the outputs on terminal "T" on Host-A and Host-B.
* Do the same on Host-B.
* On terminal window "C" on Host-A, enter the command "arp -n", record the MAC address of Host-B and label it as MAC-B.
* On terminal window "C" on Host-B, enter the command "arp -n", record the MAC address of Host-A and label it as MAC-A.
* On terminal window "C" on Host-B only, enter the following commands and compare the outputs of the first and last "ifconfig" command and spot the difference(s).
ifconfig eth<font color="blue">xx</font>
ifconfig eth<font color="blue">xx</font> down
ifconfig eth<font color="blue">xx</font> -arp
ifconfig eth<font color="blue">xx</font> up
ifconfig eth<font color="blue">xx</font>
* On terminal window "T" on Host-B, terminate the "tcpdump" and retype the last tcpdump command.
* On terminal window "C" on Host-A, send two ping packets to Host-B and watch the outputs to Host-A and Host-B's terminal window "T"s. Record your observation for later use.
* On terminal window "C" on Host-A only, enter the following commands and record the output for later reference:
arp -s 172.16.<font color="red">x</font>.2 MAC-B (put Host-B's MAC here)
arp -n
* On terminal window "C" on Host-A, send two ping packets to Host-B and record your observation.
* On terminal window "C" on Host-B, enter the following commands and record the output:
arp -s 172.16.<font color="red">x</font>.1 MAC-A (put Host-A's MAC here)
arp -n
* On terminal window "C" on Host-A, send two ping packets to Host-B and record your observation.
* On terminal window "C" on Host-B, enter the following commands and record your observation:
ifconfig eth<font color="blue">xx</font> down
ifconfig eth<font color="blue">xx</font> arp
ifconfig eth<font color="blue">xx</font>
arp -n
* Make sure that the tcpdump command is still running on terminal window "T" on Host-B.
* Send two ping packets from Host-B to Host-A, wait for 30 seconds and send another two ping packets to Host-A. Compares the two sets of packets captured and record your observation.
=Exercise=
When Host-A pings Host-B the very first time, Host-A sends an ethernet broadcast to find out which network device owns the target IP address. The network device that has a matching IP address will response with its MAC address. Once the MAC address was found, Host-A will keep the MAC address and the corresponding IP address in its system ARP cache table for a short period (a few minutes) of time and then the information will be discarded. Use Host-A and Host-B to determine the life time of an ARP reply entry on your Linux system correct to the nearest minute.
=Questions=
Based on your observation of the outputs from the commands issued during the lab, prepare the answers for the following questions:
# What is the effect of the first "ifconfig ethxx down" command on the system's ARP cache?
# What command disable ARP on a network interface?
# How do you enable ARP on a network interface if it has been disabled?
# What is the consequence of disabling ARP on a network interface?
# How do you manually add an entry to the ARP cache?
# What would be the possible advantage of disabling ARP on a network interface?
# Describe the procedure you used in determining the life time of an ARP cache entry on a Linux system.
=Completing this Lab=
Login to blackboard (my.senecacollege.ca) and complete an online lab 2 quiz after you receive an notification from your instructor.
=Objectives=
# Use the ifconfig and/or ip command(s) to display/assign IP paramenters to a network device
# Use the ifconfig command to disable/enable ARP on a network interface
# Use the arp command to display the system ARP cache
# Use the arp command to add manual entries to the system ARP cache
# Use the tcpdump command to capture and display network packets
=Background Information=
On a TCP/IP Ethernet network, every application [http://en.wikipedia.org/wiki/Data_packet data packet] contains 3 pairs of numbers: source and destination physical addresses (or [http://en.wikipedia.org/wiki/MAC_Address MAC addresses] ), source and destination [http://en.wikipedia.org/wiki/IP_Address IP addresses], and source and destination [http://en.wikipedia.org/wiki/TCP_Port ports]. The first two pairs of numbers are the main focuse of this lab.
==Software Requirements==
Linux Distributions:
* Fedora Core 8/9
RPM Packages:
* ethtool
* iproute
* net-tools
* tcpdump
==Hardware requirements==
Two Linux Machines on a Ethernet LAN
Lab with the proper hardware and software: T2107 in TEL building.
=Procedure=
You need two Linux systems connected to a LAN. Make sure that each system has only ONE network interface card. Label one system as Host-A and the other system as Host-B.
* Boot up both system to Fedora Core 8 or 9.
* Login to Host-A and Host-B under a regular user account. Don't login as "root".
* On Host-A, open up two terminal windows, set the title on one terminal windows to "T" and the other to "C". "T" for tcpdump window and "C" for command window.
* Do the same on Host-B as on Host-A.
* Switch to user "root" on all four terminal windows.
* Use the command "ifconfig" to find out the name (eth<font color="blue">xx</font>), IP address, broadcast address, netmask and the MAC address of the network device on Host-A and Host-B. Keep this information for later use.
* Use the command "ip addr" on Host-A and Host-B and keep the output for later use.
* Use the "ping" command to check the network connection between Host-A and Host-B. Ask for help if Host-A can not talk to Host-B.
* Commands in the following steps may contain the variable <font color="red">x</font>. If you are doing this lab using your own LAN, you can pick any value between 1 and 254 for <font color="red">x</font>. If you are working in the LUX lab, make sure you are not using the same <font color="red">x</font> value as any other students in the Lab.
* On terminal window "C" on Host-A, set the IP address for the network device to 172.16.<font color="red">x</font>.1, netmask to 255.255.255.0, and set the broadcast address to the appropriate value.
* On terminal window "C" on Host-B, set the IP address for the network device to 172.16.<font color="red">x</font>.2, netmask to 255.255.255.0, and set the broadcast address to the appropriate value.
* Use the "ifconfig" or "ip addr" on Host-A and Host-B to verify the newly assigned addresses. Make changes if necessary. Ask for help if you have any troubles.
* Use the "ping" command to verify the network connection between Host-A and Host-B for the new addresses. Go on to the next step only after a positive result.
* On terminal window "C" on Host-A, enter the following commands and keep the outputs for later use:
arp -n
ifconfig eth<font color="blue">xx</font> down
arp -n
ifconfig eth<font color="blue">xx</font> up
arp -n
* Do the same on Host-B.
* On terminal window "T" on Host-A, enter the following command and keep the output for later use:
tcpdump -n arp host 172.16.<font color="red">x</font>.1
* On terminal window "T" on Host-B, enter the following command and keep the output for later use:
tcpdump -n arp host 172.16.<font color="red">x</font>.2
* On terminal window "C" on Host-A, enter the following "ping" command and watch the outputs on terminal "T" on Host-A and Host-B.
* Do the same on Host-B.
* On terminal window "C" on Host-A, enter the command "arp -n", record the MAC address of Host-B and label it as MAC-B.
* On terminal window "C" on Host-B, enter the command "arp -n", record the MAC address of Host-A and label it as MAC-A.
* On terminal window "C" on Host-B only, enter the following commands and compare the outputs of the first and last "ifconfig" command and spot the difference(s).
ifconfig eth<font color="blue">xx</font>
ifconfig eth<font color="blue">xx</font> down
ifconfig eth<font color="blue">xx</font> -arp
ifconfig eth<font color="blue">xx</font> up
ifconfig eth<font color="blue">xx</font>
* On terminal window "T" on Host-B, terminate the "tcpdump" and retype the last tcpdump command.
* On terminal window "C" on Host-A, send two ping packets to Host-B and watch the outputs to Host-A and Host-B's terminal window "T"s. Record your observation for later use.
* On terminal window "C" on Host-A only, enter the following commands and record the output for later reference:
arp -s 172.16.<font color="red">x</font>.2 MAC-B (put Host-B's MAC here)
arp -n
* On terminal window "C" on Host-A, send two ping packets to Host-B and record your observation.
* On terminal window "C" on Host-B, enter the following commands and record the output:
arp -s 172.16.<font color="red">x</font>.1 MAC-A (put Host-A's MAC here)
arp -n
* On terminal window "C" on Host-A, send two ping packets to Host-B and record your observation.
* On terminal window "C" on Host-B, enter the following commands and record your observation:
ifconfig eth<font color="blue">xx</font> down
ifconfig eth<font color="blue">xx</font> arp
ifconfig eth<font color="blue">xx</font>
arp -n
* Make sure that the tcpdump command is still running on terminal window "T" on Host-B.
* Send two ping packets from Host-B to Host-A, wait for 30 seconds and send another two ping packets to Host-A. Compares the two sets of packets captured and record your observation.
=Exercise=
When Host-A pings Host-B the very first time, Host-A sends an ethernet broadcast to find out which network device owns the target IP address. The network device that has a matching IP address will response with its MAC address. Once the MAC address was found, Host-A will keep the MAC address and the corresponding IP address in its system ARP cache table for a short period (a few minutes) of time and then the information will be discarded. Use Host-A and Host-B to determine the life time of an ARP reply entry on your Linux system correct to the nearest minute.
=Questions=
Based on your observation of the outputs from the commands issued during the lab, prepare the answers for the following questions:
# What is the effect of the first "ifconfig ethxx down" command on the system's ARP cache?
# What command disable ARP on a network interface?
# How do you enable ARP on a network interface if it has been disabled?
# What is the consequence of disabling ARP on a network interface?
# How do you manually add an entry to the ARP cache?
# What would be the possible advantage of disabling ARP on a network interface?
# Describe the procedure you used in determining the life time of an ARP cache entry on a Linux system.
=Completing this Lab=
Login to blackboard (my.senecacollege.ca) and complete an online lab 2 quiz after you receive an notification from your instructor.