It would appear that once the DHCP Offer message is received, that the client may have all of the information it needs to proceed. However, the client may have received OFFERS from multiple DHCP servers and so a second phase is needed, with two more mandatory messages - the client-to-server DHCP Request message, and the server-to- client DHCP ACK message is needed. But at least the client knows there is at least one DHCP server out there! Let's take a look at the DHCP Request message, remembering that although we've already seen a Discover message in our trace, that is not always the case when a DHCP request message is sent. Locate the IP datagram containing the first DHCP Request message in your trace, and answer the following questions. 10. What is the UDP source port number in the IP datagram containing the first DHCP Request message in your trace? What is the UDP destination port number being used? 11. What is the source IP address in the IP datagram containing this Request message? Is there anything special about this address? Explain. 12. What is the destination IP address used in the datagram containing this Request message. Is there anything special about this address? Explain. 13. What is the value in the transaction ID field of this DHCP Request message? Does it match the transaction IDs of the earlier Discover and Offer messages? 14. Now inspect the options field in the DHCP Discover message and take a close look at the "Parameter Request List". The DHCP RFC notes that *The client can inform the server which configuration parameters the client is interested in by including the 'parameter request list' option. The data portion of this option explicitly lists the options requested by tag number." What differences do you see between the entries in the 'parameter request list option in this Request message and the same list option in the earlier Discover message? Locate the IP datagram containing the first DHCP ACK message in your trace, and answer the following questions. 15. What is the source IP address in the IP datagram containing this ACK message? Is there anything special about this address? Explain. 16. What is the destination IP address used in the datagram containing this ACK message. Is there anything special about this address? Explain. 17. What is the name of the field in the DHCP ACK message (as indicated in the Wireshark window) that contains the assigned client IP address? 18. For how long a time (the so-called "lease time") has the DHPC server assigned this IP address to the client? 19. What is the IP address (returned by the DHCP server to the DHCP client in this DHCP ACK message) of the first-hop router on the default path from the client to the rest of the Internet?
It would appear that once the DHCP Offer message is received, that the client may have all of the information it needs to proceed. However, the client may have received OFFERS from multiple DHCP servers and so a second phase is needed, with two more mandatory messages - the client-to-server DHCP Request message, and the server-to- client DHCP ACK message is needed. But at least the client knows there is at least one DHCP server out there! Let's take a look at the DHCP Request message, remembering that although we've already seen a Discover message in our trace, that is not always the case when a DHCP request message is sent.
Locate the IP datagram containing the first DHCP Request message in your trace, and answer the following questions.
10. What is the UDP source port number in the IP datagram containing the first DHCP Request message in your trace? What is the UDP destination port number being used?
11. What is the source IP address in the IP datagram containing this Request message? Is there anything special about this address? Explain. 12. What is the destination IP address used in the datagram containing this Request
message. Is there anything special about this address? Explain. 13. What is the value in the transaction ID field of this DHCP Request message?
Does it match the transaction IDs of the earlier Discover and Offer messages?
14. Now inspect the options field in the DHCP Discover message and take a close look at the "Parameter Request List". The DHCP RFC notes that
*The client can inform the server which configuration parameters the client is interested in by including the 'parameter request list' option. The data portion of this option explicitly lists the options requested by tag number."
What differences do you see between the entries in the 'parameter request list option in this Request message and the same list option in the earlier Discover message?
Locate the IP datagram containing the first DHCP ACK message in your trace, and answer the following questions.
15. What is the source IP address in the IP datagram containing this ACK message? Is there anything special about this address? Explain.
16. What is the destination IP address used in the datagram containing this ACK message. Is there anything special about this address? Explain. 17. What is the name of the field in the DHCP ACK message (as indicated in the
Wireshark window) that contains the assigned client IP address? 18. For how long a time (the so-called "lease time") has the DHPC server assigned this IP address to the client?
19. What is the IP address (returned by the DHCP server to the DHCP client in this DHCP ACK message) of the first-hop router on the default path from the client to the rest of the Internet?
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