Courseiva
← 200-301
Full test
mediummulti selectObjective-mapped

Exhibit

Relevant config:
interface GigabitEthernet0/1.20
 encapsulation dot1Q 20
 ip address 10.20.20.1 255.255.255.0
!
ip dhcp excluded-address 10.20.20.1 10.20.20.254
ip dhcp pool USERS20
 network 10.20.20.0 255.255.255.0
 default-router 10.20.20.1

A router is configured as a DHCP server for VLAN 20. Clients on the VLAN can reach the default gateway, but they do not receive leases. Which two configuration issues on the router would directly prevent successful address assignment?

Question 1mediummulti select
Full question →

A router is configured as a DHCP server for VLAN 20. Clients on the VLAN can reach the default gateway, but they do not receive leases. Which two configuration issues on the router would directly prevent successful address assignment?

Full question →

Answer choices

Why each option matters

Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.

A

Best answer

The excluded-address range removes the entire usable subnet

Excluding 10.20.20.1 through 10.20.20.254 leaves nothing assignable for clients.

B

Distractor review

The DHCP pool is missing a dns-server statement

DNS information is optional for lease allocation.

C

Distractor review

The subinterface lacks an ip helper-address

The router itself is the DHCP server for that subnet, so helper is not required.

D

Best answer

There are no available addresses left in the defined pool

Because the entire usable range is excluded, the pool cannot hand out any lease.

Common exam trap

Common exam trap: answer the scenario, not the keyword

A common exam trap is to incorrectly assume that missing optional DHCP parameters, such as the dns-server statement, or the absence of an ip helper-address on the subinterface, will prevent clients from receiving leases. Candidates may also overlook the impact of the excluded-address command consuming the entire subnet range, mistakenly thinking the router’s DHCP service is functioning correctly because clients can ping the gateway. The real issue is that no IP addresses remain available to assign, which is a subtle but critical configuration error that directly causes DHCP lease failures.

Technical deep dive

How to think about this question

Dynamic Host Configuration Protocol (DHCP) is a network service that automatically assigns IP addresses and other network configuration parameters to client devices. When a router is configured as a DHCP server for a VLAN, it manages a pool of IP addresses that it can lease to clients on that VLAN. The router must have an active DHCP pool with available addresses and must not exclude all usable addresses from that pool. Clients rely on the router to respond to DHCP requests with valid IP address leases to communicate properly on the network. In Cisco routers, the DHCP pool configuration includes defining the network range and optionally excluding certain addresses from being assigned to clients. The excluded-address command prevents specific IPs from being leased, often used to reserve addresses for static assignments like default gateways or servers. If the excluded-address range covers the entire subnet, no addresses remain available for clients, causing DHCP lease failures. Additionally, if the DHCP pool runs out of available addresses, clients cannot obtain leases. The ip helper-address command is irrelevant when the router itself is the DHCP server for the VLAN, as it is only needed to forward DHCP requests across different subnets. A common exam trap is assuming that missing optional parameters like dns-server or the absence of ip helper-address will prevent DHCP leases. However, DNS information is optional, and ip helper-address is unnecessary when the DHCP server is local to the VLAN. The real cause of lease failures is often related to address exhaustion or misconfigured excluded-address ranges that leave no assignable IPs. In practical networks, careful planning of excluded addresses and pool sizes prevents DHCP outages and ensures clients receive valid leases promptly.

KKey Concepts to Remember

  • A Cisco router configured as a DHCP server assigns IP addresses from a defined pool to clients within the same VLAN subnet.
  • The excluded-address command removes specific IP addresses from the DHCP pool, preventing those addresses from being leased to clients.
  • If the excluded-address range covers the entire usable subnet, the DHCP server has no addresses left to assign, causing lease failures.
  • The DHCP pool must contain available addresses; if all addresses are leased or excluded, new clients cannot obtain IP leases.
  • The ip helper-address command is only required when forwarding DHCP requests between different subnets, not when the router is the local DHCP server.
  • DNS server information in the DHCP pool is optional and does not affect the ability to assign IP addresses to clients.
  • Clients can reach the default gateway but still fail to receive DHCP leases if the DHCP pool is empty or fully excluded.
  • Proper DHCP configuration requires balancing excluded addresses and pool size to ensure sufficient assignable IPs for all clients.

TExam Day Tips

  • Watch for words such as best, first, most likely and least administrative effort.
  • Review why wrong options are wrong, not only why the correct option is correct.

Related practice questions

Related 200-301 practice-question pages

Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.

CCNA subnetting practice questions

Practise IPv4 subnetting, CIDR, masks, host ranges and subnet selection.

CCNA OSPF practice questions

Practise OSPF neighbours, router IDs, metrics, areas and routing-table interpretation.

CCNA VLAN practice questions

Practise VLANs, access ports, trunks, allowed VLANs and switching scenarios.

CCNA STP practice questions

Practise spanning tree, root bridge election, port roles and STP troubleshooting.

CCNA EtherChannel practice questions

Practise LACP, PAgP, port-channel behaviour and bundle requirements.

CCNA ACL practice questions

Practise standard and extended ACLs, permit/deny logic and traffic filtering.

CCNA NAT practice questions

Practise static NAT, dynamic NAT, PAT and inside/outside address translation.

CCNA DHCP practice questions

Practise DHCP scopes, relay, leases and troubleshooting.

CCNA show ip route practice questions

Practise routing-table output, longest-prefix match, AD and route selection.

CCNA show interfaces trunk practice questions

Practise trunk verification and VLAN forwarding across switches.

CCNA wireless security practice questions

Practise WLAN security, authentication and wireless architecture concepts.

CCNA IPv6 practice questions

Practise IPv6 addressing, routes, neighbour discovery and common IPv6 exam traps.

More questions from this exam

Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.

Question 1

A router learns the same prefix from both OSPF and EIGRP. Which route is installed by default?

Question 2

A router shows this output: R1#show ip ospf neighbor Neighbor ID Pri State Dead Time Address Interface 10.1.1.2 1 FULL/DR 00:00:34 192.168.12.2 GigabitEthernet0/0 10.1.1.3 1 2WAY/DROTHER 00:00:39 192.168.12.3 GigabitEthernet0/0 Which statement is correct?

Question 3

What is the OSPF metric called?

Question 4

A non-root switch has two uplinks toward the root bridge. One path has a lower total STP cost than the other. What role will the lower-cost uplink have?

Question 5

A router interface applies this ACL inbound: 10 deny tcp any any eq 80 20 permit ip any any A user reports that web browsing to a server by IP address fails, but ping works. Which statement best explains the behavior?

Question 6

A router learns route 198.51.100.0/24 from OSPF with AD 110 and also has a static route to the same prefix configured with AD 150. Which route is installed?

FAQ

Questions learners often ask

What does this 200-301 question test?

A Cisco router configured as a DHCP server assigns IP addresses from a defined pool to clients within the same VLAN subnet.

What is the correct answer to this question?

The correct answer is: The excluded-address range removes the entire usable subnet — The router can serve DHCP locally without an ip helper-address. The real problem is that the excluded-address range consumes every usable host address, leaving the pool with no assignable leases.

What should I do if I get this 200-301 question wrong?

Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.

Discussion

Loading comments…

Sign in to join the discussion.