Experiment $1$ on DHCP

In order to observe DHCP in action, you will perform the following six steps and

capture the DHCP messages exchanged as a result of executing these steps.

Below is the step$-$by$-$step procedure to down a wireless interface, start collecting packets using

Wireshark, bring up the interface, stop capturing packets, and analyze DHCP IP address

assignment using Wireshark commands:

Step$-$by$-$Step Procedure:

$1.$ Disable Wireless Interface:

$$ Open a terminal on your Unix machine.

$$ Disable the wireless interface using the following command:

sudo ifconfig down

$($Replace with the name of your wireless

interface $($e$.$g$.,$ wlan$0))$

$2.$ Start Wireshark Capture:

$$ Open Wireshark on your Unix machine.

$$ Start capturing packets on the disabled wireless interface:

$$ Go to Capture $>$ Options.

$$ Select the interface corresponding to the wireless interface.

$$ Configure capture filters to capture DHCP packets only if desired.

$$ Start the capture.

$3.$ Enable Wireless Interface:

$$ After starting the capture, re$-$enable the wireless interface using the following command:

sudo ifconfig up

$($Replace with the name of your wireless interface.$)$

$4.$ Continue Capturing Packets:

$$ Let Wireshark continue capturing packets for a desired duration, during which DHCP

packets will be captured as well.

$5.$ Stop Wireshark Capture:

$$ After capturing packets for the desired duration, stop the Wireshark capture:

$$ Go to Capture $>$ Stop.

$6.$ Save Captured Packets:

$$ Save the captured packets to a file for analysis:

$$ Go to File $>$ Save As$.$

$$ Choose a location and filename as to save the

capture file.

Answer the following questions from the captured packet trace:

$1.$ Are DHCP messages sent over UDP or TCP$?$

$2.$ Draw a timing datagram illustrating the sequence of the first four$-$packet

Discover$/$Offer$/$Request$/$ACK DHCP exchange between the client and server. For each packet,

indicate the source and destination port numbers.

$3.$ What is the link$-$layer $($e$.$g$.,$ Ethernet$)$ address of your host?

$4.$ What values in the DHCP discover message differentiate this message from the DHCP

request message?

$5.$ What is the value of the Transaction$-$ID in each of the first four $($Discover$/$Offer$/$Request$/$ACK$)$

DHCP messages? What are the values of the Transaction$-$ID in the second set $($Request$/$ACK$)$

set of DHCP messages? What is the purpose of the Transaction$-$ID field?

$6.$ For each of the four DHCP messages $($Discover$/$Offer$/$Request$/$ACK DHCP$),$ indicate the

source and destination IP addresses that are carried in the encapsulating IP datagram.

$7.$ What is the IP address of your DHCP server?

$8.$ What IP address is the DHCP server offering to your host in the DHCP Offer message?

Indicate which DHCP message contains the offered DHCP address.

$9.$ Explain the purpose of the lease time. How long is the lease time in your experiment?

$10.$ Were any ARP packets sent or received during the DHCP packet$-$exchange period? If so$,$

explain the purpose of those ARP packets.Experiment $1$ on DHCP

In order to observe DHCP in action, you will perform the following six steps and

capture the DHCP messages exchanged as a result of executing these steps.

Below is the step$-$by$-$step procedure to down a wireless interface, start collecting packets using

Wireshark, bring up the interface, stop capturing packets, and analyze DHCP IP address

assignment using Wireshark commands:

Step$-$by$-$Step Procedure:

$1.$ Disable Wireless Interface:

$$ Open a terminal on your Unix machine.

$$ Disable the wireless interface using the following command:

sudo ifconfig down

$($Replace with the name of your wireless

interface $($e$.$g$.,$ wlan$0))$

$2.$ Start Wireshark Capture:

$$ Open Wireshark on your Unix machine.

$$ Start capturing packets on the disabled wireless interface:

$$ Go to Capture $>$ Options.

$$ Select the interface corresponding to the wireless interface.

$$ Configure capture filters to capture DHCP packets only if desired.

$$ Start the capture.

$3.$ Enable Wireless Interface:

$$ After starting the capture, re$-$enable the wireless interface using the following command:

sudo ifconfig up

$($Replace with the name of your wireless interface.$)$

$4.$ Continue Capturing Packets:

$$ Let Wireshark continue capturing packets for a desired duration, during which DHCP

packets will be captured as well.

$5.$ Stop Wireshark Capture:

$$ After capturing packets for the desired duration, stop the Wireshark capture:

$$ Go to Capture $>$ Stop.

$6.$ Save Captured Packets:

$$ Save the captured packets to a file for analysis:

$$ Go to File $>$ Save As$.$

$$ Choose a location and filename as to save the

capture file.

Answer the following questions from the captured packet trace:

$1.$ Are DHCP messages sent over UDP or TCP$?$

$2.$ Draw a timing datagram illustrating the sequence of the first four$-$packet

Discover$/$Offer$/$Request$/$ACK DHCP exchange between the cl