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Computer Networking Basics

When a device obtains an IP address with DHCP, what is the correct order of messages?

  1. ARequest → Offer → Discover → Ack
  2. BDiscover → Offer → Request → Ack
  3. COffer → Discover → Ack → Request
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Answer: B. Discover → Offer → Request → Ack

A device with no address yet does not know where the DHCP server is either, so it first broadcasts a Discover. A server proposes an address and other settings in an Offer, the device states which server's offer it accepts in a Request, and the server confirms with an Ack. From the initials this is called DORA. Besides the IP address, the device receives the subnet mask, the default gateway, the DNS server addresses and more. Addresses are lent for a limited time (the lease), and the device asks for renewal before it expires. To use a DHCP server beyond a router, a DHCP relay is configured on the router.

  • A. Unless the device first sends a Discover looking for a server, the server does not know the device exists.
  • B. Correct. Discover, Offer, Request, Ack, known as DORA.
  • C. A server's Offer is sent in answer to the device's Discover.
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