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DHCP Troubleshooting Scenarios

Practise 300-410 DHCP questions covering DORA flow, scopes, excluded addresses, default gateway options, helper addresses, and troubleshooting clients that receive APIPA or cannot get an IP address.

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scenario questions

300-410

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Scenario guide

How to approach dhcp troubleshooting scenarios

DHCP questions cover server configuration, relay agents (ip helper-address), DHCP snooping, and the four-step DORA handshake. Common exam scenarios: a host isn't getting an IP, a relay agent isn't forwarding requests, or a rogue DHCP server is handing out wrong addresses.

Quick answer

DHCP questions usually test address assignment, scopes, relay agents, excluded addresses and why a client cannot obtain an IP address.

DHCP discovery, offer, request and acknowledgement flow.

DHCP scopes, excluded addresses and default gateway options.

DHCP relay using helper addresses.

Troubleshooting clients that receive APIPA or no address.

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Practice set

Practice scenarios

Question 1mediummultiple choice

Read the full DHCP explanation →

A network engineer runs the following debug command to troubleshoot a DHCPv4 issue on router R1:

R1# debug ip dhcp server events

Output: DHCPD: DHCPDISCOVER received from 0050.7966.6800 on interface GigabitEthernet0/0 DHCPD: Sending DHCPOFFER to 0050.7966.6800 via GigabitEthernet0/0 DHCPD: DHCPREQUEST received from 0050.7966.6800 DHCPD: No binding found for client 0050.7966.6800 DHCPD: Adding binding for client 0050.7966.6800 DHCPD: Sending DHCPACK to 0050.7966.6800 via GigabitEthernet0/0 DHCPD: DHCPINFORM received from 0050.7966.6800 DHCPD: Sending DHCPACK to 0050.7966.6800 via GigabitEthernet0/0

What does this output indicate?

A
The DHCP server failed to create a binding for the client.
Why wrong: The output shows 'Adding binding' and 'Sending DHCPACK', indicating successful binding creation.
B
The DHCP server successfully assigned an IP address to the client, and the client sent a DHCPINFORM to request additional parameters.
The sequence shows a successful DORA process (DISCOVER, OFFER, REQUEST, ACK) followed by an INFORM, which is used to get additional options like DNS servers.
C
The DHCP client is using a relay agent because the DISCOVER was received on a different interface.
Why wrong: The DISCOVER was received on GigabitEthernet0/0, which is the same interface the OFFER and ACK are sent on; no relay is indicated.
D
The DHCP server rejected the DHCPREQUEST because no binding was found.
Why wrong: The server created a new binding and sent an ACK; the 'No binding found' message is normal for a new client.

Full breakdown with real-world context →

Question 2hardmultiple choice

Read the full DHCP explanation →

A network engineer is troubleshooting a DHCPv6 prefix delegation issue on router R1 and runs the following command:

R1# debug ipv6 dhcp detail

Output: IPv6 DHCP: Received SOLICIT message from FE80::21A:2BFF:FE3C:4D01 on GigabitEthernet0/0 IPv6 DHCP: Using interface pool DHCP_POOL IPv6 DHCP: Sending ADVERTISE message to FE80::21A:2BFF:FE3C:4D01 IPv6 DHCP: Received REQUEST message from FE80::21A:2BFF:FE3C:4D01 IPv6 DHCP: Client requests prefix 2001:DB8:1::/48 IPv6 DHCP: Prefix 2001:DB8:1::/48 not available in pool DHCP_POOL IPv6 DHCP: Sending REPLY message with Status Code NoPrefixAvail

What does this output indicate?

A
The DHCPv6 client successfully received the prefix 2001:DB8:1::/48.
Why wrong: The server sent a REPLY with NoPrefixAvail, meaning the prefix was not assigned.
B
The DHCPv6 server has a pool configured but the requested prefix is not in that pool or is already allocated.
The server used pool DHCP_POOL but the prefix 2001:DB8:1::/48 is not available, likely because it is not included in the pool or is already assigned to another client.
C
The DHCPv6 client is using a relay agent because the SOLICIT was received on a different interface.
Why wrong: The SOLICIT was received directly on GigabitEthernet0/0; no relay is indicated.
D
The DHCPv6 server is configured with a stateless configuration because it sent an ADVERTISE without a prefix.
Why wrong: The ADVERTISE was sent, but the server later indicated the prefix was not available; this is stateful DHCPv6 for prefix delegation.

Full breakdown with real-world context →

Question 3hardmultiple choice

Read the full DHCP explanation →

What is the default DHCPv4 client lease time on a Cisco IOS-XE router configured as a DHCP client?

A
3600 seconds (1 hour)
Why wrong: This is not the default; 3600 seconds is a common server-assigned lease time, not the IOS client default.
B
43200 seconds (12 hours)
Why wrong: This is a possible server-assigned value but not the IOS default client lease time.
C
86400 seconds (1 day)
Cisco IOS-XE DHCP client requests a lease time of 86400 seconds by default.
D
1800 seconds (30 minutes)
Why wrong: This is too short; the IOS default is 86400 seconds.

Full breakdown with real-world context →

Question 4easymultiple choice

Read the full DHCP explanation →

A network engineer runs the following command to verify DHCPv4 server bindings on router R1:

R1# show ip dhcp binding

Output: Bindings from all pools not associated with VRF:

IP address       Client-ID/              Lease expiration        Type

Hardware address/ User name

192.168.1.10     0050.7966.6800           Mar 01 2025 12:00 PM   Automatic
 192.168.1.11     0063.6973.636f.2d30      Mar 01 2025 01:00 PM   Automatic
 192.168.1.12     0100.1a.2b.3c.4d.5e     Mar 01 2025 02:00 PM   Automatic

What does this output indicate?

A
The DHCP server has three static bindings configured.
Why wrong: The type is 'Automatic', indicating dynamic assignments, not static.
B
The DHCP server has dynamically assigned three IP addresses to clients.
Each entry shows an IP address, client identifier, lease expiration, and type 'Automatic', confirming dynamic assignments.
C
The DHCP server is out of IP addresses because all bindings are in use.
Why wrong: The output only shows three bindings; it does not indicate whether the pool is exhausted.
D
The DHCP server is using relay agents because the client IDs are long hexadecimal strings.
Why wrong: Client IDs can include MAC addresses or relay-agent IDs, but this does not necessarily indicate relay agents are in use.

Full breakdown with real-world context →

Question 5mediummultiple choice

Read the full DHCP explanation →

A network engineer runs the following command to troubleshoot DHCPv6 address assignment on router R1:

R1# show ipv6 dhcp binding

Output: Client: FE80::21A:2BFF:FE3C:4D01 DUID: 0003000121A2B3C4D5E6

Username: unassigned

VRF: default IA NA: IA ID 0x00040001, T1 302400, T2 483840 Address: 2001:DB8:1::100 Preferred lifetime 604800, valid lifetime 2592000 Expires at Mar 01 2025 12:00 PM (2592000 seconds) IA PD: IA ID 0x00040002, T1 302400, T2 483840 Prefix: 2001:DB8:1::/48 Preferred lifetime 604800, valid lifetime 2592000 Expires at Mar 01 2025 12:00 PM (2592000 seconds)

What does this output indicate?

A
The DHCPv6 server has assigned only an IPv6 address to the client.
Why wrong: The output shows both an IA NA (address) and an IA PD (prefix delegation).
B
The DHCPv6 server has assigned both an IPv6 address and a prefix delegation to the client.
The IA NA section shows an address assignment, and the IA PD section shows a prefix delegation, both with lifetimes.
C
The DHCPv6 client is using stateless autoconfiguration (SLAAC) because no address is shown.
Why wrong: An address is shown under IA NA, indicating stateful DHCPv6.
D
The DHCPv6 server has a pool with only one prefix available.
Why wrong: The output only shows one binding; it does not indicate the size of the pool.

Full breakdown with real-world context →

Question 6mediummultiple choice

Read the full DHCP explanation →

A network engineer runs the following command to verify DHCPv4 server statistics on router R1:

R1# show ip dhcp server statistics

Output: Memory usage: 12345 Address pools: 2 Database agents: 0 Automatic bindings: 150 Manual bindings: 5 Expired bindings: 10 Malformed messages: 0

Message Received

BOOTREQUEST    0

DHCPDISCOVER 200 DHCPREQUEST 180 DHCPDECLINE 2 DHCPRELEASE 5 DHCPINFORM 10

What does this output indicate?

A
The DHCP server has 150 active automatic bindings and 5 manual bindings.
The output shows 'Automatic bindings: 150' and 'Manual bindings: 5', indicating the number of active leases.
B
The DHCP server has received 200 DHCPREQUEST messages.
Why wrong: The output shows 180 DHCPREQUEST messages received, not 200.
C
The DHCP server has 10 malformed messages, indicating a configuration issue.
Why wrong: Malformed messages are 0, so no malformed messages were received.
D
The DHCP server has 2 database agents configured.
Why wrong: Database agents are 0, meaning no external database is used for lease storage.

Full breakdown with real-world context →

Question 7mediummultiple choice

Read the full DHCP explanation →

A network engineer runs the following command to troubleshoot DHCPv6 relay on router R1:

R1# debug ipv6 dhcp relay

Output: IPv6 DHCP relay: Received SOLICIT message from FE80::1 on GigabitEthernet0/0 IPv6 DHCP relay: Forwarding SOLICIT to server 2001:DB8:2::1 via GigabitEthernet0/1 IPv6 DHCP relay: Received ADVERTISE message from server 2001:DB8:2::1 via GigabitEthernet0/1 IPv6 DHCP relay: Forwarding ADVERTISE to client FE80::1 via GigabitEthernet0/0 IPv6 DHCP relay: Received REQUEST message from FE80::1 on GigabitEthernet0/0 IPv6 DHCP relay: Forwarding REQUEST to server 2001:DB8:2::1 via GigabitEthernet0/1 IPv6 DHCP relay: Received REPLY message from server 2001:DB8:2::1 via GigabitEthernet0/1 IPv6 DHCP relay: Forwarding REPLY to client FE80::1 via GigabitEthernet0/0

What does this output indicate?

A
The DHCPv6 relay agent is not functioning because messages are not being forwarded.
Why wrong: The output clearly shows messages being forwarded in both directions.
B
The DHCPv6 relay agent is successfully forwarding messages between the client and server.
The relay receives client messages, forwards them to the server, and forwards server responses back to the client.
C
The DHCPv6 server is unreachable because no REPLY is received.
Why wrong: A REPLY is received and forwarded to the client.
D
The DHCPv6 client is using a global unicast address as its link-local address.
Why wrong: The client uses FE80::1, which is a link-local address.

Full breakdown with real-world context →

Question 8easymultiple choice

Read the full DHCP explanation →

A network engineer runs the following command to verify DHCPv4 pool configuration on router R1:

R1# show ip dhcp pool DHCP_POOL

Output: Pool DHCP_POOL : Utilization mark (high/low) : 100 / 0 Subnet size (first/next) : 0 / 0 Total addresses : 254 Leased addresses : 100 Pending event : none 1 subnet is currently in the pool : Current index IP address range Leased addresses

192.168.1.1          192.168.1.1 - 192.168.1.254         100

What does this output indicate?

A
The DHCP pool has 254 addresses available, and 100 are currently leased.
Total addresses is 254, leased addresses is 100, so 154 are available.
B
The DHCP pool is exhausted because 100 addresses are leased.
Why wrong: 100 out of 254 are leased, so the pool is not exhausted.
C
The DHCP server is using a database agent to store leases.
Why wrong: No database agent information is shown in this output.
D
The DHCP pool has a utilization mark of 100%, meaning it is full.
Why wrong: The utilization mark is a threshold for logging, not current utilization.

Full breakdown with real-world context →

Question 9hardmultiple choice

Read the full DHCP explanation →

What is the default DHCPv4 server lease time on a Cisco IOS-XE router configured as a DHCP server?

A
3600 seconds (1 hour)
Why wrong: This is not the default; the default is 86400 seconds.
B
43200 seconds (12 hours)
Why wrong: This is a common configured value but not the IOS default.
C
86400 seconds (1 day)
The default lease time for Cisco IOS-XE DHCP server is 86400 seconds.
D
604800 seconds (7 days)
Why wrong: This is too long; the default is 86400 seconds.

Full breakdown with real-world context →

Question 10mediummultiple choice

Read the full DHCP explanation →

A network engineer runs the following command to verify DHCPv6 pool configuration on router R1:

R1# show ipv6 dhcp pool

Output: Pool DHCPv6_POOL : Prefix number: 1 Prefix: 2001:DB8:1::/48 Preferred lifetime 604800, valid lifetime 2592000 Expires at Mar 01 2025 12:00 PM (2592000 seconds) DNS server: 2001:DB8::1 Domain name: example.com Active clients: 5

What does this output indicate?

A
The DHCPv6 pool has 5 active clients and provides prefix delegation, DNS, and domain name.
The output shows a prefix for delegation, DNS server, domain name, and 5 active clients.
B
The DHCPv6 pool is used only for stateless address autoconfiguration (SLAAC).
Why wrong: The pool includes a prefix for delegation, which is used for stateful prefix delegation, not SLAAC.
C
The DHCPv6 pool has 5 clients with addresses from the prefix 2001:DB8:1::/48.
Why wrong: The prefix is for delegation, not for address assignment; the clients may have delegated prefixes.
D
The DHCPv6 pool has a preferred lifetime of 2592000 seconds.
Why wrong: The preferred lifetime is 604800 seconds; the valid lifetime is 2592000 seconds.

Full breakdown with real-world context →

Question 11easymultiple choice

Read the full DHCP explanation →

A network engineer runs the following command to verify DHCPv4 server conflict detection on router R1:

R1# show ip dhcp conflict

Output:

IP address       Detection method   Detection time        VRF
 192.168.1.50     Ping               Mar 01 2025 10:00 AM  default
 192.168.1.75     Gratuitous ARP     Mar 01 2025 11:00 AM  default

What does this output indicate?

A
The DHCP server has detected two IP address conflicts on the network.
Two IP addresses are listed with detection methods and times, indicating conflicts.
B
The DHCP server has successfully assigned IP addresses 192.168.1.50 and 192.168.1.75.
Why wrong: These addresses are in conflict, meaning they were not assigned due to detection of another device using them.
C
The DHCP server uses only ping to detect conflicts.
Why wrong: Both ping and gratuitous ARP are shown as detection methods.
D
The DHCP server has cleared all conflicts from the database.
Why wrong: The output shows two conflicts, so they have not been cleared.

Full breakdown with real-world context →

Question 12easymultiple choice

Read the full DHCP explanation →

Which DHCPv4 message type does a client send to request a specific IP address previously offered?

A
DHCPDISCOVER
Why wrong: DHCPDISCOVER is used to locate servers, not to request a specific address.
B
DHCPOFFER
Why wrong: DHCPOFFER is sent by the server to offer an address.
C
DHCPREQUEST
DHCPREQUEST is sent by the client to request the offered IP address.
D
DHCPACK
Why wrong: DHCPACK is sent by the server to acknowledge the request.

Full breakdown with real-world context →

Question 13hardmultiple choice

Read the full DHCP explanation →

What is the default DHCPv6 client DUID type on a Cisco IOS-XE router?

A
DUID-LLT (Link-Layer plus Time)
Why wrong: DUID-LLT is used by some implementations but not the default on Cisco IOS-XE.
B
DUID-EN (Enterprise Number)
Why wrong: DUID-EN is used for vendor-specific DUIDs, not the default.
C
DUID-LL (Link-Layer)
Cisco IOS-XE defaults to DUID-LL for DHCPv6 clients.
D
DUID-UUID (Universally Unique Identifier)
Why wrong: DUID-UUID is not a standard DUID type in RFC 8415.

Full breakdown with real-world context →

Question 14mediummultiple choice

Read the full DHCP explanation →

In DHCPv6, what is the purpose of the SOLICIT message?

A
To request a renewal of an existing lease
Why wrong: Renewal uses RENEW or REBIND messages.
B
To confirm a previously allocated prefix
Why wrong: Confirmation uses CONFIRM messages.
C
To discover available DHCPv6 servers
SOLICIT is the initial discovery message in DHCPv6.
D
To release an IP address
Why wrong: Release uses RELEASE messages.

Full breakdown with real-world context →

Question 15mediummultiple choice

Read the full DHCP explanation →

Which DHCPv4 option is used by a client to request a specific IP address in the DHCPREQUEST message?

A
Option 12 (Host Name)
Why wrong: Option 12 is for host name, not IP address request.
B
Option 50 (Requested IP Address)
Option 50 carries the requested IP address in DHCPREQUEST.
C
Option 54 (Server Identifier)
Why wrong: Option 54 identifies the server, not the requested IP.
D
Option 51 (IP Address Lease Time)
Why wrong: Option 51 specifies lease time, not the requested address.

Full breakdown with real-world context →

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