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Q5(c) · DHCP dynamic allocation

2024-02-06 · 2022-23

Actual paper; 100 marks attempted. Current-syllabus alignment is stated per question.

Q5(c). Explain the working of DHCP protocol highlighting dynamic IP address allocation. [5 marks]

Answer

Definition. Dynamic Host Configuration Protocol (DHCP) provides IP configuration parameters to clients and can lease reusable addresses for limited periods.

Simple meaning. DORA = Discover, Offer, Request, Acknowledge.

Swipe across the diagram to read its labels ↔
DHCP initial allocation: DORA
Diagram: DHCP initial allocation: DORA. Labels: DHCP initial allocation: DORA | DHCP initial allocation: DORA | Client | Server | DISCOVER | OFFER | REQUEST | ACK | Client asks → server offers → client chooses → server confirms.
DHCP: automatic configuration through DORA

Understand it step by step

  1. Discover: a new client looks for DHCP servers. With no configured IPv4 address, it commonly starts from 0.0.0.0 and uses broadcast discovery.
  2. Offer: a server offers an address and configuration, such as subnet mask, lease information and other options.
  3. Request: the client indicates the selected offer and requested address. In initial allocation this also informs other servers of its choice.
  4. Acknowledge: the selected server confirms the lease/configuration. The client can then use the address after the required checks.
  5. DHCPv4 uses UDP server port 67 and client port 68. A DHCP relay can carry requests between a client subnet and a server elsewhere; ordinary routers do not simply forward local broadcasts by default.
  1. DHCPDISCOVER: client searches for a server.
  2. DHCPOFFER: server proposes an address/configuration.
  3. DHCPREQUEST: client requests the chosen allocation.
  4. DHCPACK: server confirms the lease.

DHCP reduces manual configuration and supports controlled address reuse through leases.

Yaad rakho: Discover–Offer–Request–ACK; pehle D, phir O, phir R, phir A.