CyberCertPrepNetwork FundamentalsDNS & DHCPEASYFree question
What are the DORA steps in the DHCP lease acquisition process, and what transport protocol and ports are used?
- A.DORA: Discover (UDP 67→68), Offer (UDP 68→67), Request (UDP 67→68), Acknowledge (UDP 67→68)
- B.DORA: DNS (UDP 53), OSPF (IP protocol 89), Routing (TCP 179), ARP
- C.DORA uses TCP for reliability: Discover (TCP 68), Offer (TCP 67), Request (TCP 68), ACK (TCP 67)
- D.DORA: Discover (UDP broadcast, client port 68 → server port 67), Offer (UDP, server 67 → client 68), Request (UDP broadcast, client 68 → server 67), Acknowledge (UDP, server 67 → client 68). All use UDP; Discover and Request are broadcasts (255.255.255.255); Offer and ACK are directed broadcasts or unicast
Why D is correct
DHCP DORA (RFC 2131): Discover: Client broadcasts (src: 0.0.0.0:68, dst: 255.255.255.255:67) - 'I need an IP.' Offer: Server responds (src: server-IP:67, dst: 255.255.255.255:68 or directed broadcast) - 'Here is an offered IP, gateway, DNS, lease time.' Request: Client broadcasts (src: 0.0.0.0:68, dst: 255.255.255.255:67) - 'I accept the offered IP from this server' (broadcast informs other DHCP servers their offers are rejected). Acknowledge: Server sends ACK (src: server-IP:67, dst: broadcast or client-IP:68) - 'IP is confirmed, here are your final parameters.' Ports: UDP 67 = server, UDP 68 = client.
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