CCNA DHCP Questions — Page 2 of 2

MCQmedium

A PC in VLAN 30 must obtain an address from a DHCP server in VLAN 99. Which feature is required on the Layer 3 interface for VLAN 30?

A.Port security

B.DHCP snooping

C.DHCP relay

D.Dynamic ARP inspection

AnswerC

Correct. DHCP relay is what allows a client to reach a server on another subnet.

Why this answer

DHCP Discover messages are broadcasts and do not cross Layer 3 boundaries on their own. DHCP relay, commonly configured with ip helper-address, forwards the requests to a server on another subnet.

Exam trap

A frequent exam trap is selecting DHCP snooping or port security as the solution for inter-VLAN DHCP communication. DHCP snooping is often misunderstood as a relay mechanism, but it only validates DHCP messages to prevent unauthorized servers and does not forward broadcasts between VLANs. Similarly, port security controls MAC address access on switchports but does not affect DHCP message forwarding.

Candidates may also confuse Dynamic ARP Inspection with DHCP relay, but DAI only inspects ARP traffic for security purposes. The key mistake is overlooking that DHCP broadcasts are Layer 2 broadcasts and require DHCP relay on the Layer 3 interface to reach servers in other VLANs.

Why the other options are wrong

Port security restricts MAC addresses on switchports to enhance security but does not forward DHCP broadcasts or enable clients in one VLAN to reach DHCP servers in another VLAN. It does not facilitate inter-VLAN DHCP communication.

DHCP snooping is a security feature that validates DHCP messages to prevent rogue DHCP servers but does not relay DHCP requests between VLANs. It cannot replace DHCP relay functionality needed for inter-VLAN DHCP address assignment.

Dynamic ARP Inspection inspects ARP traffic to prevent ARP spoofing attacks but does not forward DHCP messages or enable DHCP communication between VLANs. It is unrelated to DHCP relay or inter-VLAN DHCP address assignment.

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PBQhard

You are connected to R1 (a router acting as DHCP server) via the console. Configure R1 to provide DHCP addresses for VLAN 10 (192.168.10.0/24) on the switch SW1, which is connected via R1's G0/0. Exclude the first 10 addresses (192.168.10.1-10) and the last address (192.168.10.254). Set the default gateway to 192.168.10.1 and DNS server to 203.0.113.10. On SW1, enable DHCP snooping globally and for VLAN 10, configure G0/1 as trusted toward R1, and ensure the ip helper-address on the switch's VLAN 10 SVI points to R1's G0/0 IP. The current config has a wrong helper-address and an oversized excluded range; identify and fix all issues.

Network Topology

Hints

•Check the excluded-address range on R1 — it might be too broad.
•Verify the helper-address on SW1's VLAN 10 SVI — it should be the DHCP server's interface IP, not a different subnet.
•DHCP snooping requires the uplink to the DHCP server to be configured as trusted.

A.On R1: ip dhcp excluded-address 192.168.10.1 192.168.10.10 and ip dhcp excluded-address 192.168.10.254; ip dhcp pool VLAN10: network 192.168.10.0 255.255.255.0, default-router 192.168.10.1, dns-server 203.0.113.10. On SW1: ip dhcp snooping, ip dhcp snooping vlan 10, interface G0/1: ip dhcp snooping trust, interface Vlan10: ip helper-address 10.0.0.1.

B.On R1: ip dhcp excluded-address 192.168.10.1 192.168.10.10; ip dhcp pool VLAN10: network 192.168.10.0 255.255.255.0, default-router 192.168.10.1, dns-server 203.0.113.10. On SW1: ip dhcp snooping, ip dhcp snooping vlan 10, interface G0/1: ip dhcp snooping trust, interface Vlan10: ip helper-address 192.168.10.1.

C.On R1: ip dhcp excluded-address 192.168.10.1 192.168.10.10; ip dhcp pool VLAN10: network 192.168.10.0 255.255.255.0, default-router 192.168.10.1, dns-server 203.0.113.10. On SW1: ip dhcp snooping, ip dhcp snooping vlan 10, interface Vlan10: ip helper-address 10.0.0.1.

D.On R1: ip dhcp excluded-address 192.168.10.1 192.168.10.254; ip dhcp pool VLAN10: network 192.168.10.0 255.255.255.0, default-router 192.168.10.1, dns-server 203.0.113.10. On SW1: ip dhcp snooping, ip dhcp snooping vlan 10, interface G0/1: ip dhcp snooping trust, interface Vlan10: ip helper-address 10.0.0.1.

AnswerA

solution

! R1
no ip dhcp excluded-address 192.168.10.1 192.168.10.254
ip dhcp excluded-address 192.168.10.1 192.168.10.10
ip dhcp excluded-address 192.168.10.254

! SW1
interface Vlan10
no ip helper-address 192.168.20.1
ip helper-address 10.0.0.1
exit
interface GigabitEthernet0/1
ip dhcp snooping trust

Why this answer

The DHCP server R1 had an excluded range that covered the entire subnet (192.168.10.1 through 192.168.10.254), preventing any addresses from being assigned. This was corrected by first removing that oversized exclusion, then setting the excluded range to 192.168.10.1 192.168.10.10 and adding 192.168.10.254 as a separate excluded address. On SW1, the ip helper-address pointed to 192.168.20.1 (wrong), which should be R1's G0/0 IP 10.0.0.1.

Also, DHCP snooping was enabled globally and for VLAN 10, but G0/1 (link to R1) was not trusted; it was set to trusted. These changes allow DHCP requests from VLAN 10 to be relayed to R1 and trusted from the correct interface. Option A is technically incomplete because it fails to include the removal of the original oversized exclusion.

Exam trap

A common trap is to add new exclusions without removing the old ones; Cisco IOS does not overwrite exclusions—it appends. You must explicitly remove the original oversized range or no addresses will be leased.

Why the other options are wrong

This option omits the `ip dhcp snooping trust` on G0/1 and uses the wrong helper-address (192.168.10.1, which is the default gateway, not R1's interface IP 10.0.0.1).

This option omits both the `ip dhcp snooping trust` on G0/1 and does not include the separate exclusion for 192.168.10.254.

This option leaves the oversized excluded range (192.168.10.1 to 192.168.10.254) intact, which blocks all address assignments, and uses the wrong helper-address (10.0.0.1 but on SW1's VLAN 10 SVI it is missing the trust on G0/1).

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MCQhard

Clients can join the Guest SSID and authenticate successfully, but they never receive an IP address. The DHCP scope for the guest network exists on the server. Based on the exhibit, what is the most likely cause?

A.The AP trunk is not allowing VLAN 300.

B.The DHCP server must use TCP instead of UDP.

C.The SSID name must match the DHCP pool name.

D.The AP should be configured as an access port for VLAN 1.

AnswerA

That prevents guest client traffic from reaching the proper VLAN.

Why this answer

The Guest SSID is mapped to VLAN 300, but the switch trunk toward the AP allows only VLANs 10,20,30. Client traffic for the guest WLAN never reaches the correct VLAN upstream, so DHCP requests for that WLAN fail. Authentication can still succeed depending on how the WLAN is designed.

Exam trap

A common exam trap is to incorrectly assume that DHCP issues stem from the DHCP server configuration or protocol errors, such as believing DHCP must use TCP instead of UDP. Another tempting mistake is thinking the SSID name must match the DHCP pool name, which is false because DHCP scopes are based on VLAN subnets, not SSID naming. Additionally, some candidates mistakenly configure the access point port as an access port on VLAN 1, which prevents multiple VLANs from passing and breaks guest VLAN connectivity.

These traps distract from the core issue of VLAN trunk misconfiguration preventing DHCP traffic.

Why the other options are wrong

Incorrect. DHCP uses UDP, not TCP. Changing the protocol to TCP is not valid and would cause DHCP to fail entirely, which is not the issue here since clients authenticate successfully.

Incorrect. DHCP scopes are tied to VLAN subnets, not SSID names. The SSID name does not need to match the DHCP pool name for clients to receive IP addresses.

Incorrect. Configuring the AP port as an access port on VLAN 1 restricts traffic to a single VLAN. Since multiple SSIDs typically map to different VLANs, the port must be a trunk to carry all VLANs, including VLAN 300 for the guest SSID.

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PBQhard

You are connected to R1 via the console. R1 is the DHCP server for the 192.168.50.0/24 LAN. Configure DHCP on R1 to assign addresses from 192.168.50.10 to 192.168.50.200, with default gateway 192.168.50.1 and DNS server 8.8.8.8. Also, configure R1 to act as a DHCP relay agent for the 10.0.0.0/30 link to reach a remote DHCP server at 203.0.113.10. Then, troubleshoot and fix a misconfiguration that causes clients on VLAN 50 to not receive IP addresses.

Network Topology

Hints

•Check the excluded-address range — it may be too large.
•A helper-address on the same subnet as the DHCP server is not needed.
•The relay agent must be configured on the interface that receives the client broadcasts.

A.[CORRECT] The DHCP pool is misconfigured: the excluded-address range covers most of the pool (192.168.50.1 through 192.168.50.200), but leaves 192.168.50.201-254 assignable, violating the requirement. The correct configuration should exclude 192.168.50.1-9 (gateway) and 192.168.50.201-254 (upper end). The 'ip helper-address' on GigabitEthernet0/0 is unnecessary because R1 itself is the DHCP server for that subnet; it should be removed. The relay agent configuration is missing on the interface facing the remote DHCP server—'ip helper-address 203.0.113.10' should be added to GigabitEthernet0/1.

B.The DHCP pool is misconfigured: the excluded-address range should be 192.168.50.1 192.168.50.9, but the helper-address on GigabitEthernet0/0 is correct because it forwards DHCP requests to the remote server. The relay agent configuration is missing on GigabitEthernet0/1.

C.The DHCP pool is correctly configured with excluded-address 192.168.50.1 192.168.50.9. The issue is that the 'ip helper-address' on GigabitEthernet0/1 is missing; it should be added to forward requests to the remote server. Additionally, the 'ip helper-address' on GigabitEthernet0/0 is correct because it forwards requests from VLAN 50 to the remote server.

D.The DHCP pool is misconfigured: the excluded-address range should be 192.168.50.1 192.168.50.9. The 'ip helper-address' on GigabitEthernet0/0 should be removed. The relay agent configuration is correct because 'ip helper-address 203.0.113.10' is already configured on GigabitEthernet0/1.

AnswerA

solution

! R1
no ip dhcp excluded-address 192.168.50.1 192.168.50.200
ip dhcp excluded-address 192.168.50.1 192.168.50.9
interface GigabitEthernet0/0
no ip helper-address 203.0.113.10
exit
interface GigabitEthernet0/1
ip helper-address 203.0.113.10
exit

Why this answer

The DHCP pool is misconfigured: the excluded-address range of 192.168.50.1 through 192.168.50.200 covers most of the pool, but leaves addresses 192.168.50.201 to 192.168.50.254 assignable, which violates the requirement to assign addresses only from 192.168.50.10 to 192.168.50.200. To meet the requirement, you must exclude both the lower range (192.168.50.1 to 192.168.50.9, reserving the gateway) and the upper range (192.168.50.201 to 192.168.50.254). Additionally, the 'ip helper-address' on GigabitEthernet0/0 is unnecessary because R1 itself is the DHCP server for that subnet; it should be removed.

The relay agent configuration is missing on the interface facing the remote DHCP server—'ip helper-address 203.0.113.10' should be added to GigabitEthernet0/1 so that broadcasts from the 10.0.0.0/30 subnet are forwarded.

Exam trap

A single 'ip dhcp excluded-address' range does not limit the DHCP pool to only the desired contiguous range; you must explicitly exclude all addresses you do not want assigned, even those at the upper end. Ensure you create multiple excluded-address ranges when the pool is not contiguous.

Why the other options are wrong

The specific factual error is that a helper-address should not be configured on an interface where the router itself is the DHCP server for that subnet.

The specific factual error is that the helper-address on the LAN interface is not needed and would cause issues, and the excluded-address range is actually correct in this option, but the question's misconfiguration is the excluded-address being too broad.

The specific factual error is that the helper-address on the interface facing the remote server is not configured, so DHCP broadcasts from the 10.0.0.0/30 subnet will not be forwarded.

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MCQmedium

Users on VLAN 20 are not receiving IPv4 addresses from the centralized DHCP server at 10.50.0.10. Users in other VLANs are working normally. Based on the exhibit, which change should fix the issue for VLAN 20 clients?

A.Change the helper address on interface Vlan20 to 10.50.0.10.

B.Convert the VLAN 20 user ports to trunk mode.

C.Configure a default gateway on the user PCs manually.

D.Disable DHCP snooping on VLAN 20.

AnswerA

That points DHCP relay to the actual DHCP server.

Why this answer

The SVI for VLAN 20 is forwarding DHCP requests to the wrong helper address. DHCP relay depends on the Layer 3 interface for that VLAN sending client broadcasts to the correct server. Trunks, access ports, and the DHCP pool name on the server are not the first issue shown here.

DHCP snooping can filter DHCP server replies on untrusted ports, but since other VLANs are working and no trust misconfiguration is indicated, the root cause is the incorrect ip helper-address on Vlan20.

Exam trap

A frequent exam trap is assuming that user ports must be trunks or that disabling DHCP snooping will fix DHCP address assignment issues. In reality, user ports should remain in access mode to maintain VLAN membership, and DHCP snooping is unrelated to this specific forwarding problem because the exhibit shows a misconfigured helper address while other VLANs function normally. Another common mistake is thinking that manually configuring a default gateway on clients solves DHCP problems, but DHCP discovery requires proper relay configuration on the Layer 3 interface.

Misconfiguring or omitting the ip helper-address on the VLAN interface causes DHCP requests to fail, which is the core issue here.

Why the other options are wrong

Disabling DHCP snooping is unnecessary because the other VLANs work, and the scenario does not indicate a trust misconfiguration; the real problem is the incorrect helper address on Vlan20.

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MCQhard

What is the strongest explanation for why hosts in VLAN 40 are receiving addresses from the wrong DHCP scope?

A.The relay path is sending requests to the wrong DHCP scope or server target.

B.The VLAN 40 SVI must be changed to a trunk port.

C.DHCP can provide only one scope in the entire network.

D.The clients must use static addresses before DHCP relay can work.

AnswerA

This is correct because the clients are receiving addresses, but from the wrong network scope.

Why this answer

Option A is correct because the DHCP relay agent (typically configured on the VLAN 40 SVI with the 'ip helper-address' command) is forwarding client broadcast requests to a DHCP server that either has no scope for VLAN 40 or has a scope configured for a different subnet. This causes the server to assign an address from the wrong scope, as the relay agent does not filter by scope—it simply forwards the packet to the configured server IP.

Exam trap

Cisco often tests the misconception that DHCP can only serve one scope per network, when in fact the issue is typically a misconfigured relay path or server scope mapping, not a protocol limitation.

Why the other options are wrong

This option is wrong because an SVI (Switched Virtual Interface) for a VLAN cannot be configured as a trunk port; it must be an access port. VLANs are typically assigned to access ports, and changing the SVI to a trunk would not resolve DHCP scope issues.

This option is incorrect because DHCP can support multiple scopes across different VLANs, allowing for distinct address ranges for each VLAN. Thus, having multiple scopes is not a limitation of DHCP itself.

This option is incorrect because DHCP relay does not require clients to use static addresses; it is designed to facilitate dynamic IP address assignment. Static addresses would not affect the relay process or the DHCP server's ability to assign addresses from the correct scope.

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MCQhard

After configuring DHCP snooping on VLAN 10 to prevent rogue DHCP servers, all clients in the VLAN stop receiving DHCP offers from the legitimate DHCP server that is connected to port Gi0/1. The administrator verifies the DHCP server is operational and reachable. What should the technician do next?

A.Enable Dynamic ARP Inspection on VLAN 10.

B.Configure interface Gi0/1 as a DHCP snooping trusted port.

C.Add an ip helper-address on the VLAN 10 SVI pointing to the DHCP server.

D.Reconfigure the DHCP server scope to include DHCP Option 82.

AnswerB

DHCP snooping blocks DHCP server messages on untrusted ports. Since the legitimate server is on Gi0/1, trusting the port allows the switch to forward DHCP offers from that port, resolving the issue.

Why this answer

By default, DHCP snooping marks all ports as untrusted, which blocks DHCP server replies (including offers) from those ports. Since the legitimate server is connected to Gi0/1, the port must be explicitly trusted to allow DHCP offers through. This step directly addresses the Layer 2 access control mechanism.

Exam trap

The most common mistake is to enable Dynamic ARP Inspection on VLAN 10, assuming it is required for DHCP snooping to work, but DAI only uses the DHCP snooping binding table and does not control DHCP traffic.

Why the other options are wrong

Misunderstanding that DAI controls DHCP traffic rather than ARP packets.

Assuming DHCP snooping introduces routing changes or that the server is on a different subnet.

Confusing DHCP snooping with DHCP relay agent functionality and option 82 insertion.

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MCQmedium

A DHCP server is located on a different VLAN from the clients. Which feature is required so the clients can still receive addresses?

A.DHCP snooping

B.DHCP relay

C.Port security

D.NAT overload

AnswerB

Correct. DHCP relay enables cross-VLAN DHCP service.

Why this answer

DHCP relay forwards client broadcasts to a remote server as unicast, typically using ip helper-address on the Layer 3 interface.

Exam trap

A common exam trap is selecting DHCP snooping as the solution for clients on different VLANs to receive DHCP addresses. DHCP snooping is a security mechanism that filters DHCP messages to prevent rogue servers but does not forward DHCP broadcasts across VLANs. Another tempting but incorrect choice is port security, which controls MAC address access on switch ports but does not affect DHCP broadcast forwarding.

NAT overload is unrelated to DHCP address assignment and only translates IP addresses for outbound traffic. The key misunderstanding is confusing DHCP relay’s role in forwarding broadcasts with security or address translation features.

Why the other options are wrong

DHCP snooping is a security feature that prevents unauthorized DHCP servers by filtering DHCP messages. It does not forward DHCP broadcasts across VLANs, so it cannot enable clients on different VLANs to receive addresses.

Port security restricts the number and identity of MAC addresses on switch ports to enhance security. It does not affect DHCP broadcast forwarding or enable clients to receive addresses from servers on different VLANs.

NAT overload translates multiple private IP addresses to a single public IP address for outbound traffic. It does not address the issue of forwarding DHCP broadcasts between VLANs or enable DHCP clients to obtain addresses from remote servers.

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Multi-Selectmedium

Which TWO commands would a network engineer use to verify that a Windows client has received an IP address from a DHCP server and can resolve a domain name to an IP address?

Select 2 answers

A.ping 8.8.8.8

B.ipconfig /all

C.tracert www.courseiva.com

D.nslookup www.courseiva.com

E.arp -a

AnswersB, D

This command displays full TCP/IP configuration, including the DHCP server, lease obtained/expires, and the assigned IP address, confirming DHCP operation.

Why this answer

Option B is correct because `ipconfig /all` displays the full TCP/IP configuration for all adapters, including whether the IP address was obtained from a DHCP server (the DHCP Enabled and DHCP Server fields). Option D is correct because `nslookup www.courseiva.com` queries the configured DNS server to resolve the domain name to an IP address, confirming DNS resolution works.

Exam trap

Cisco often tests the distinction between connectivity verification (ping) and configuration verification (ipconfig /all, nslookup), leading candidates to mistakenly select ping or tracert as tools for confirming DHCP and DNS functionality.

Why the other options are wrong

It checks network reachability, not DHCP or DNS.

It shows the path taken, not DHCP or DNS status.

It shows Layer 2 address mappings, not DHCP or DNS.

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PBQhard

You are connected to R1. Configure R1 as a DHCP server for the 192.168.100.0/24 subnet, reserving the first 10 addresses and the address 192.168.100.254 for static assignments, with default gateway 192.168.100.1 and DNS server 8.8.8.8. Then, on the same router, enable DHCP relay for the 10.1.1.0/24 subnet by configuring the helper address pointing to the DHCP server at 192.168.100.1. Finally, verify that the DHCP pool is correctly configured and that the helper address is set.

Hints

•Check the default-router in the DHCP pool — it should be the gateway address, not an excluded address.
•The helper-address on G0/1 must point to the DHCP server interface IP, not to a reserved address.
•Examine the excluded-address list to understand which addresses are reserved.

A.The default-router is incorrectly set to 192.168.100.254 instead of 192.168.100.1, and the ip helper-address on G0/1 points to 192.168.100.254 instead of 192.168.100.1.

B.The default-router is correctly set to 192.168.100.1, but the ip helper-address on G0/1 points to 192.168.100.254 instead of 192.168.100.1.

C.The default-router is incorrectly set to 192.168.100.254 instead of 192.168.100.1, but the ip helper-address on G0/1 correctly points to 192.168.100.1.

D.Both the default-router and the ip helper-address are correctly configured as 192.168.100.1.

AnswerA

solution

! R1
configure terminal
ip dhcp pool POOL_100
default-router 192.168.100.1
exit
interface GigabitEthernet0/1
ip helper-address 192.168.100.1
end
copy running-config startup-config

Why this answer

The configuration has two critical errors. First, the default-router in the DHCP pool is incorrectly set to 192.168.100.254, which is an excluded address meant for static assignment, not the actual gateway (192.168.100.1). Second, the ip helper-address on G0/1 points to 192.168.100.254 (the wrong address) instead of the DHCP server's own interface IP 192.168.100.1.

To fix, change the default-router to 192.168.100.1 and update the helper-address to 192.168.100.1.

Exam trap

Be careful not to confuse the excluded addresses (reserved for static assignment) with the gateway address. Also, remember that when a router acts as both DHCP server and relay, the helper-address should point to the router's own interface IP on the server subnet, not to an excluded address.

Why the other options are wrong

The specific factual error is that the helper-address should be the DHCP server's IP, not an excluded address.

The specific factual error is that the default-router must be the gateway address, not an excluded address.

The specific factual error is that the question states the configuration uses 192.168.100.254 for both, so this option does not match the given scenario.

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Multi-Selectmedium

A branch router is acting as a DHCP server. Which two parameters can it provide directly to clients through DHCP?

Select 2 answers

A.Default gateway

B.DNS server address

C.OSPF area number

D.Switch port duplex setting

E.STP root bridge priority

AnswersA, B

This is usually supplied with the router option.

Why this answer

DHCP (Dynamic Host Configuration Protocol) is designed to automatically assign IP configuration parameters to clients. The default gateway (option 3) and DNS server address (option 6) are standard DHCP options defined in RFC 2132, which a router acting as a DHCP server can directly provide to clients to enable network connectivity and name resolution.

Exam trap

Cisco often tests the distinction between DHCP-provided parameters (Layer 3/4) and switch-specific or routing protocol parameters (Layer 2/3), leading candidates to mistakenly select options like OSPF area or STP priority that are not DHCP options.

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MCQhard

A user reports that their computer cannot access the network. The technician checks the computer's IP configuration and finds an APIPA address (169.254.x.x). The computer is connected to a switch port on VLAN 20. The DHCP server is located on VLAN 1. The technician then examines the router's interfaces using 'show ip interface brief' and sees that all interfaces shown are up/up. What should the technician do next?

A.Check the DHCP server logs to see if it is receiving Discover messages.

B.Verify that the ip helper-address command is configured on the router's VLAN 20 interface.

C.Attempt to ping the DHCP server's IP address from the host's APIPA address.

D.Restart the DHCP service on the server and recheck the host.

AnswerB

The router is the intervlan router, and the DHCP server is on a different subnet. For a DHCP Discover broadcast to cross VLANs, the router must have an IP helper-address pointing to the DHCP server's IP address on the VLAN 20 interface. Since all ports are up/up, the problem is almost certainly the missing relay. Checking this config directly addresses the most probable cause.

Why this answer

The APIPA address (169.254.x.x) indicates the host failed to obtain a DHCP lease. Since the DHCP server is on VLAN 1 and the host is on VLAN 20, a DHCP relay (ip helper-address) must be configured on the router's VLAN 20 interface to forward DHCP broadcast messages to the server. The 'show ip interface brief' shows all interfaces are up/up, so the next logical step is to verify the relay configuration.

Exam trap

Cisco often tests the concept that a DHCP relay (ip helper-address) is required when the DHCP server is on a different subnet, and candidates mistakenly focus on server-side issues or ping tests instead of the router configuration.

Why the other options are wrong

This action assumes the DHCP request has already reached the server; it bypasses verifying the network path that would deliver the broadcast to the server, which is the most likely missing piece.

Candidates might think that if the ping fails, the problem is network connectivity, but APIPA addresses are non-routable and the test itself is invalid in this context.

Many techs jump to rebooting a service when a simple configuration check would reveal the real problem. This violates the principle of least intrusive troubleshooting.

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MCQhard

A network administrator has configured a switch port to support a VoIP phone and a desktop PC. Users report that the desktop PC cannot obtain an IP address via DHCP, while the VoIP phone registers successfully. The switch port is up/up, and the desktop is connected to the phone's PC port. What is the most likely cause of the issue?

A.The switchport mode access should be changed to switchport mode trunk to allow both vlans.

B.The switchport access vlan should be changed to the data VLAN to match the subnet expected by the desktop.

C.The switchport voice vlan should be removed because the desktop cannot use it.

D.The spanning-tree portfast should be disabled to prevent DHCP delays.

AnswerB

With the phone's PC port forwarding the switch's access VLAN, correcting the access VLAN to the data VLAN ensures the desktop receives a DHCP offer from the data subnet.

Why this answer

The desktop PC obtains its IP address from the data VLAN, but the switch port's access VLAN is likely misconfigured to the voice VLAN. Changing the access VLAN to the correct data VLAN places the PC in the proper subnet and allows DHCP to function. Option A is unnecessary because a voice-access port does not need to be a trunk.

Option C would break the VoIP phone without fixing the PC's VLAN assignment. Option D is irrelevant; PortFast speeds up STP convergence and does not block DHCP.

Exam trap

Cisco often tests the misconception that the PC uses the voice VLAN or that the port must be a trunk, when in reality the phone handles the VLAN separation internally and the switch port remains an access port with a separate voice VLAN.

Why the other options are wrong

The current configuration uses access mode with voice vlan, which is correct for a phone+PC setup. Trunk mode is unnecessary and could break the phone's untagged traffic expectations.

The voice vlan is correctly configured for the phone; the problem is with the data vlan assignment for the desktop.

Portfast is beneficial for host ports; disabling it would worsen the issue by introducing STP convergence delays.

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Multi-Selectmedium

Which two statements accurately describe DHCP?

Select 2 answers

A.It can automatically provide an IP address to a client.

B.It can provide additional configuration such as default gateway and DNS server information.

C.It resolves hostnames into IP addresses.

D.It elects the designated router in OSPF.

E.It replaces the need for subnet masks.

AnswersA, B

This is correct because address assignment is a core DHCP function.

Why this answer

DHCP is used to provide IP configuration automatically to hosts. In practical terms, it can supply an IP address, subnet mask, default gateway, and often DNS server information. This reduces manual effort and helps standardize endpoint configuration across a network.

The wrong answers often confuse DHCP with DNS or routing. The two correct answers are the ones focused on automatic host configuration.

Exam trap

A common exam trap is confusing DHCP with DNS or routing protocol functions. Some candidates mistakenly believe DHCP resolves hostnames to IP addresses, but this is the role of DNS. Others incorrectly think DHCP participates in routing protocol processes such as OSPF designated router elections, which it does not.

Additionally, some may assume DHCP eliminates the need for subnet masks, but DHCP actually provides subnet mask information to clients. Recognizing that DHCP strictly handles IP address and related configuration assignment prevents these errors.

Why the other options are wrong

Incorrect. DHCP does not resolve hostnames to IP addresses; this is the responsibility of DNS, a separate IP service.

Incorrect. DHCP does not participate in routing protocol operations like OSPF designated router election, which is a function of OSPF itself.

Incorrect. DHCP supplies subnet masks to clients but does not replace the need for subnet masks; subnetting remains a fundamental network design concept.

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