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NET0183 Networks and Communications

Laboratory 5DHCP revealed(4 pages)

Part A (basic questions)
Write your answers to the following basic questions about DHCP and have them checked by the laboratory supervisor. Consult DHCP FAQ to obtain answers.

Who created DHCP?
When does a client start trying to renew its lease?
How long should a lease be to maximise the number of addresses free for distribution?
How long should a lease be to allow time for a DHCP server to be fixed?
How long should a lease be to allow for a weekend-long server outage?

Part B (wired and wirelessIP configurations)
Boot up a wired laboratory computer and boot up your wireless laptop computer and record the following details using ipconfig/all at the Windows command prompt. Which details are the same? Which details are different? Have the table checked by your laboratory supervisor.

Wired / Wireless / Same S
Different D
Host Name
IP Address
Subnet Mask
Default Gateway
DHCP Server(s)
DNS Server(s)
length of lease

The laboratory supervisor will discuss with students the reasons for any similarities/differences.

Part C (private or public IP addresses)

Are the IP addresses listed in Part B private or public? Write your answers in the box below and have it checked by your laboratory supervisor.

Part D (releasing wired and wireless IP configurations)
Use ipconfig/release at the Windows command prompt on the machines used in Part B. Then use ipconfig/all and record the following details. Which details are the same? Which details are different? Have the table checked by your laboratory supervisor.

Wired / Wireless / Same S
Different D
Host Name
IP Address
Subnet Mask
Default Gateway
DHCP Server(s)
DNS Server(s)
length of lease

Part E (broadcast address 255.255.255.255)
Does the IP broadcast address (255.255.255.255) of the zero network (0.0.0.0) reach all nodes on the Internet? Circle one answer and have your answer checked by the laboratory supervisor. Consult Broadcast address to obtain an answer.
YESNO

Part F (repeated release & renew)
What IP addressesare allocated if you release (ipconfig /release) and renew (ipconfig /renew) repeatedly? Complete the table below and have the table checked by your laboratory supervisor.

Wired / Wireless
1st release & renew
2nd release & renew
3rd release & renew
4th release & renew
5th release & renew
Same S
Different D

The laboratory supervisor will discuss with students the reasons for any similarities/differences.

Part G (Wireshark trace)
On your wireless laptop machine, perform an ipconfig /release. Then start up a Wireshark capture. Perform the sequence: ipconfig /renew thenipconfig /releasethena finalipconfig /renew.

Use the display filter bootp(not dhcp) to examine DHCP messages. Answer the following questions and have your answers checked by the laboratory supervisor.


Question / Answer
1. Is DHCP an application layer protocol?
2. Is DHCP sent over TCP or UDP?
3. When a client/host issues a Discover message what are the source and destination IP addresses used?
4. When a client/host issues a Request message what are the source and destination IP addresses used?
5. When a client/host issues a Discover message what are the source and destination port numbersused?
6. When a DHCP server issues an Offer message what are the source and destination port numbersused?
7. What is the value of the TRANSACTION IDENTIFIER in the first four (Discover/Offer/Request/ACK) messages?
8. What is the value of the TRANSACTION IDENTIFIER in the second four (Discover/Offer/Request/ACK) messages?
9. What BOOT FILE NAME is used in the first Offer?
10. What BOOT FILE NAME is used in the second Offer?
11. What option number is used for IP Address Lease Time?
12. What option number is used for DHCP Message Type?

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