Quiz: DHCP & IP Address Management

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4 questions

L0 (1 questions)

1. What are the four steps of the DHCP process (DORA) and what transport protocol does it use?

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DORA uses UDP:
1. Discover — client broadcasts asking for an IP (src 0.0.0.0:68, dst 255.255.255.255:67).
2. Offer — server offers an IP.
3. Request — client broadcasts acceptance (broadcast so other servers retract their offers).
4. Acknowledge — server confirms the lease with IP, gateway, DNS, and lease duration.

L1 (1 questions)

1. How does a DHCP relay agent work, and why is it necessary?

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DHCP uses broadcast, which does not cross routers. A relay agent on the router receives the broadcast Discover, sets the giaddr field to its own IP on that subnet, and forwards it as unicast to the DHCP server. The server uses giaddr to determine which scope/pool to allocate from and sends the reply back through the relay. On Cisco, this is configured with 'ip helper-address'.

L2 (1 questions)

1. What are the T1 and T2 lease renewal timers and why does a client not wait for lease expiry?

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T1 is at 50% of lease time — the client sends a unicast RENEW to the original server. T2 is at 87.5% — the client broadcasts a REBIND to any server (in case the original is down). This ensures continuous connectivity. Waiting until expiry would mean losing the IP and having to restart DORA, causing a network outage for the client.

L3 (1 questions)

1. Compare split-scope and active failover for DHCP redundancy, including the tradeoff of each approach.

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Split scope: divide the pool between two servers (e.g., 60/40). No communication needed between servers. Tradeoff: if one server fails, its portion of the pool is unavailable until it returns. Active failover (ISC DHCP/Kea): both servers share state and can serve the full pool. Tradeoff: requires configuration of failover peering (ports, MCLT, load balance), more complex setup, and if peer communication fails, behavior depends on the MCLT timer.