Name: _________________________________________________

Operating System _________________________________

System used for lab _____________________________________

Overview

This lab contains instructions for both LINUX and Windows. Windows provides fewer options for the user, but to do the things we want to do, it is simpler. The Windows instructions are provided in case you use your own machine with Wireshark. Malone lab Windows machines do not have Wireshark installed.

We will trace three functions:

1. Renewing our DHCP - this will request a DHCP address. This might be used if we had lost our connection.
2. Release our lease.
3. Renew (obtain) our connection.

Lab steps

When you start Wireshark, it is helpful to filter unwanted traffic. We could use a filter of "udp" since DHCP uses UDP packets, but this can get unwanted packets. The best capture filter to use is:

src port 67 or src port 68

These are the ports used for DHCP.

1. Start Wireshark

2. Renew our DHCP lease:
   • Windows: At a Windows command line: "ipconfig /renew".
   • LINUX: sudo dhclient

3. Stop Wireshark

   • 1. What DHCP command is sent? ________________________

   • 2. What is the IP address this command is sent to? __________________

   • 3. What DHCP reply is received? _______________________

   • 4. Look inside the DHCP reply. What do you see?

     _______________________________________

   • 5. Confirm your IP address with the command:
     • Windows ipconfig
     • LINUX ifconfig

     IP Address: ____ . _____ . ______ . _______

4. Start Wireshark

5. Release our lease
   • Windows: At a Windows command line: "ipconfig /release".
   • LINUX: sudo dhclient -r

6. Stop Wireshark

   • 5. What DHCP command is sent? ________________________

   • 6. What is the IP address this command is sent to? __________________

   • 7. What DHCP reply is received? _______________________

   • 8. Confirm your IP address is no longer there with the command.
     • Windows ipconfig
     • LINUX ifconfig

7. Start Wireshark

8. Ask DHCP to obtain an IP address
   • Windows: At a Windows command line: "ipconfig /renew".
   • LINUX: sudo dhclient

9. Stop Wireshark

   • 8. What DHCP command sequence is sent? ________________________

   • 9. What is the IP address the first command is sent to? __________________

   • 10. To what IP address is the DHCP Offer sent to? ______________________

   • 11. What is the IP address the DHCP Request is sent to? _____________

   • 12. Compare the results of the two DHCP replies. What do you see?

   • 13. Since UDP is connectionless, what field to you see that the DHCP client can use to connect the replies (Offer and Ack) to the request (Discover or Request).

     ____________________________________________________________

   • 14. Looking at the sequence, which UDP port number is used for the DHCP server? __________
     and for the DHCP client? __________

     _______________________________________

     _______________________________________

   • 15. Confirm your IP address with the command:
     • Windows ipconfig
     • LINUX ifconfig

     IP Address: ____ . _____ . ______ . _______

To hand in

This handout with answers.