Question

Difficulty: MediumDHCP Server, Client, and Relay Agent Operation and Configuration

A newly connected host workstation requires an IPv4 address assignment. Place the steps of the standard DHCP address allocation and validation sequence in the correct chronological order from beginning to end.

  1. 1The host broadcasts a DHCPDISCOVER message using 0.0.0.00.0.0.0 as the source IP address to locate available DHCP servers.
  2. 2A DHCP server transmits a DHCPOFFER message providing an available IPv4 address, subnet mask, default gateway, and lease duration.
  3. 3The host broadcasts a DHCPREQUEST message specifying the chosen server's offer to accept the lease and release other potential offers.
  4. 4The DHCP server returns a DHCPACK message committing the lease parameters to the IP address binding table.
  5. 5The host issues a Gratuitous ARP request on the local segment for the offered IPv4 address to ensure no IP address conflict exists.

Answer

The correct sequence is: 1) Host broadcasts DHCPDISCOVER, 2) Server transmits DHCPOFFER, 3) Host broadcasts DHCPREQUEST, 4) Server returns DHCPACK, 5) Host issues Gratuitous ARP for duplicate IP detection.
The DHCP lease process follows the classic DORA sequence (Discover, Offer, Request, Acknowledge). First, the client broadcasts a DHCPDISCOVER message. The server responds with a DHCPOFFER message containing network configuration details. Next, the client broadcasts a DHCPREQUEST message to accept the offer. The server completes the sequence by sending a DHCPACK message. Finally, before binding the address to its logical interface, the host broadcasts a Gratuitous ARP to perform duplicate address detection on the local link segment.

Step-by-Step Solution

1
Initiate discovery
The host sends a DHCPDISCOVER broadcast to search for reachable DHCP servers.
The client has no configured IP address and must discover servers on the local subnet.
2
Server offer
The DHCP server responds with a DHCPOFFER message proposing IP parameters.
The server selects an available address from its pool for the client.
3
Client request
The client broadcasts a DHCPREQUEST accepting the offer.
Broadcasting the request notifies the selected server of acceptance while letting other servers release any reserved addresses.
4
Server acknowledgment
The server responds with a unicast DHCPACK confirming the lease.
DHCPACK completes the 4-step DORA process and confirms configuration parameters.
5
Conflict detection
The client transmits a Gratuitous ARP request for the leased IP address.
Checking the local link via ARP ensures no other host is actively using the assigned IP address.

Key Concept

DHCP DORA Process and Duplicate Address Detection (DAD)
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