DHCPv4/DHCPv6 Services Practice Questions

Answers and explanations appear when you work through the set above.

1. What is the standard message order a DHCPv4 client and server exchange when the client is acquiring a brand-new lease?

   • Discover, Offer, Request, Acknowledge
   • Request, Discover, Offer, Acknowledge
   • Solicit, Advertise, Request, Reply
   • Hello, Init, Exchange, Full

2. A DHCPv4 relay agent is forwarding client requests to the correct server, but the server keeps assigning addresses from the wrong subnet's pool. Which field in the relayed packet determines how the server maps the request to a subnet?

   • The giaddr (gateway/relay address) field set by the relay agent
   • The BGP router ID of the relay
   • The OSPF DR priority on the client VLAN
   • The VRF route distinguisher

3. Which two UDP ports are fundamental to standard DHCPv4 client and server communication?

   • UDP 546 and 547
   • UDP 67 and 68
   • UDP 161 and 162
   • UDP 500 and 4500

4. A router is configured with ip helper-address on a VLAN interface. Why might it relay TFTP broadcasts as well as DHCP, and how can an engineer stop only the TFTP relay behavior?

   • ip helper-address only ever forwards DHCP traffic regardless of configuration
   • TFTP UDP 69 is in the default forwarded-service list; no ip forward-protocol udp tftp can remove it while DHCP relay remains enabled
   • The router needs a second helper-address for TFTP specifically pointed at the DHCP server
   • TFTP cannot be relayed by any Cisco IOS feature

5. IPv6 hosts on a segment build their own global addresses using SLAAC, but administrators also want those hosts to learn DNS server addresses from a DHCPv6 server without leasing an IPv6 address from it. Which operating mode does this describe?

   • Stateful DHCPv6
   • Stateless DHCPv6
   • DHCPv4 relay in dual-stack mode
   • SLAAC with privacy extensions disabled

6. Which router advertisement flag tells IPv6 hosts using SLAAC to also contact a DHCPv6 server for additional configuration data such as DNS, without requesting an address from it?

   • The Managed Address Configuration (M) flag
   • The Other Configuration (O) flag
   • The Router Lifetime field
   • The Hop Limit field

7. In an environment where DHCPv6 is expected to fully assign IPv6 addresses to clients rather than letting them self-generate addresses via SLAAC, which Router Advertisement flag must be set?

   • The Other Configuration (O) flag only
   • The Managed Address Configuration (M) flag
   • The Router Preference field set to High
   • The Current Hop Limit field

8. Which message sequence best matches typical stateful DHCPv6 address acquisition (the IPv6 analog of DORA)?

   • Discover, Offer, Request, Acknowledge
   • Solicit, Advertise, Request, Reply
   • Open, Update, Keepalive, Notification
   • Hello, DBD, LSR, LSU

9. An IPv6 client on a routed VLAN never receives a DHCPv6 Advertise even though the DHCPv6 server on another subnet is healthy. The router interface facing the client has no DHCPv6 relay configuration. What is the fix?

   • Configure `ipv6 dhcp relay destination <server-address>` on the client-facing interface
   • Configure `ip helper-address` on the interface
   • Enable OSPFv3 on the interface
   • Add a static route toward the DHCPv6 server

10. DHCPv6 clients on a segment send Solicit messages to which well-known destination?

    • The unicast address of the DHCPv6 server
    • The All_DHCP_Relay_Agents_and_Servers multicast address, FF02::1:2
    • The All Nodes multicast address, FF02::1
    • The default gateway's link-local address

11. A workstation on an access VLAN unexpectedly receives an IP address, gateway, and DNS servers from an unauthorized machine that a user connected to the network, rather than from the corporate DHCPv4 server. Which control best addresses this at the switch layer?

    • DHCP snooping with the rogue port left untrusted
    • uRPF strict mode on the access port
    • SNMPv3 privacy encryption
    • An extended ACL applied to the DHCP server's own interface

12. After enabling DHCP snooping on a switch, legitimate clients on an access port stop getting addresses, and the snooping binding table shows no entries for that port. What is a likely misconfiguration?

    • The port facing the real DHCP server was left untrusted, so its Offer/Ack replies are being dropped
    • The client-facing port has too high a DHCP snooping rate limit
    • The VLAN has DTP enabled
    • The client is using a static IP address

13. A network needs to support both DHCPv4 relay for legacy clients and DHCPv6 relay for dual-stack clients on the same VLAN interface. What is true about configuring both?

    • Only one relay type can be active on a single interface, so DHCPv4 and DHCPv6 clients must be on separate VLANs
    • ip helper-address (IPv4) and ipv6 dhcp relay destination (IPv6) are independent, separately configured features that can coexist on the same interface
    • Configuring ip helper-address automatically enables DHCPv6 relay as well
    • DHCPv6 relay requires disabling SLAAC on the interface

14. A branch office has two VLANs served from a single central DHCPv4 server, each needing addresses from a different scope. Which relay configuration detail ensures the server can tell the VLANs apart when both broadcasts arrive relayed from the same router?

    • The relaying router must use a distinct giaddr per VLAN, which naturally happens since each VLAN interface has its own IP address used as the relay source
    • The DHCP server must be configured with matching VLAN tags in its scope definitions
    • Both VLANs must share the same subnet to avoid confusing the server
    • The relay must use NAT to translate all requests to one shared source address

15. DHCPv4 clients on a subnet are getting addresses, but none of them receive the intended default gateway or DNS server options even though the scope defines them. Where should the troubleshooting focus?

    • The DHCP pool's option configuration (default-router and dns-server statements) on the server
    • The OSPF passive-interface configuration
    • The switch spanning-tree topology
    • The relay agent's ip helper-address value

16. Which statement correctly compares SLAAC to stateful DHCPv6 for IPv6 address assignment?

    • SLAAC lets a host derive its own address from advertised prefixes and its interface identifier, with no per-client lease state kept on a server, while stateful DHCPv6 has a server track and assign specific addresses
    • SLAAC and stateful DHCPv6 both require a central server to track leases identically
    • SLAAC is only usable for link-local addresses, never global addresses
    • Stateful DHCPv6 cannot coexist with SLAAC on the same link under any circumstance

17. A DHCPv4 scope is exhausted and new clients fail to get leases, while `show ip dhcp conflict` reports no conflicts and existing clients still renew successfully. What is the most likely explanation?

    • The pool's address range is too small for the current number of active leases, and the lease time may need shortening or the range widened
    • The relay agent's giaddr is incorrect
    • DHCP snooping is blocking new client requests
    • The DHCPv6 server needs to be restarted

18. Two DHCPv4 servers on the same switched broadcast domain answer client Discover messages from overlapping scopes. Which switch-side control most directly blocks replies from the unauthorized server?

    • DHCP snooping trust boundaries, so only the authorized server's uplink port is trusted to relay Offer/Ack messages
    • Increasing the DHCP lease time on the authorized server
    • Enabling uRPF loose mode on the client VLAN
    • Adding a static ARP entry for the authorized server

19. A router configured as a DHCPv6 relay agent is forwarding Solicit messages, but the central DHCPv6 server allocates addresses from the wrong pool for one particular VLAN. What field, analogous to IPv4's giaddr, should be checked in the relayed message?

    • The link-address field set by the relay agent in the Relay-Forward message
    • The transaction ID
    • The client's DUID
    • The IAID

20. Which command verifies the currently active DHCPv4 address bindings and their remaining lease time directly on a Cisco IOS router acting as the DHCP server?

    • show ip dhcp binding
    • show ip dhcp conflict
    • show ip dhcp relay
    • show ip dhcp pool summary

21. A router is both an OSPFv3-enabled IPv6 gateway and a DHCPv6 relay agent for its attached VLAN. Clients report they get a link-local default route via Router Advertisements but never receive a DHCPv6-assigned global address, even though M is set correctly on the RA. What should be checked?

    • That ipv6 dhcp relay destination on the VLAN interface points at a reachable DHCPv6 server and that the server has a matching pool for that prefix
    • That OSPFv3 is using the correct area type
    • That the client's DUID matches the router's DUID
    • That IPv6 unicast routing is disabled on the router