300-410 Question #64: Real Exam Question with Answer & Explanation

Question

Users were moved from the local DHCP server to the remote corporate DHCP server. After the move, none of the users were able to use the network. Which two issues will prevent this setup from working properly? (Choose two)

Options

• AAuto-QoS is blocking DHCP traffic.
• BThe DHCP server IP address configuration is missing locally
• C802.1X is blocking DHCP traffic
• DThe broadcast domain is too large for proper DHCP propagation
• EThe route to the new DHCP server is missing

Explanation

Users failing to obtain IP addresses from a remote DHCP server usually indicates that a local DHCP helper address is missing, preventing DHCP broadcasts from reaching the server, or that there is no route from the local network to the remote DHCP server.

Common mistakes.

• A. Auto-QoS prioritizes certain traffic and typically does not block essential services like DHCP completely, making it an unlikely cause for all users to fail getting IP addresses.
• C. 802.1X is a port-based authentication mechanism that usually operates after or alongside DHCP. While it can block network access, it's not the primary cause of DHCP traffic itself failing to reach the server for initial address acquisition.
• D. For a remote DHCP server, DHCP relies on unicast forwarding by a relay agent, not direct broadcast propagation across subnets, so the size of the local broadcast domain is not the direct cause of remote DHCP failure.

Concept tested. DHCP Relay Agent and Routing for Remote DHCP

Reference. https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipaddr_dhcp/configuration/15-mt/dhcp-15-mt-book/dhcp-relay.html

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