When a DHCP server is configured which two IP addresses should never be assignable to hosts?

This is an Updated commonly asked CCNA exam question (2021).
You might see a different IP address and configuration. Just try and figure out what the question actually needs you to do.

Note: This DHCP question is used for demonstration only, you may come across different IP addresses, frame relay configuration, and Port allocation in the real CCNA exam. But it all works the same way if you could just grasp the technique.

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Question 1
Refer to the exhibit. Which rule does the DHCP server use when there is an IP address conflict?

A. The address is removed from the pool until the conflict is resolved.
B. The address remains in the pool until the conflict is resolved.
C. Only the IP detected by Gratuitous ARP is removed from the pool.
D. Only the IP detected by Ping is removed from the pool.
E. The IP will be shown, even after the conflict is resolved.

      Answer: A

Question 2
How does a DHCP server dynamically assign an IP address to a host?

A. Addresses are allocated after a negotiation between the server and the host to determine the length of the agreement.
B. Addresses are assigned for a fixed period of time. At the end of the period, a new quest for an address must be made, and another address is then assigned.
C. Addresses are leased to the host. A host will usually keep the same address by periodically contacting the DHCP server to renew the lease.
D. Addresses are permanently assigned so that the host uses the same address at all times.

Answer: C
Explanation
When a DHCP server dynamically allocates addresses to a client, the client leases its IP address for a certain period of time and must renew the lease to continue using it.
The lease renewal process begins when the client reaches what is known as the renewal time value, or T1 value, of its lease. When a client reaches this point or state, The client generates and transmits unicast DHCPREQUEST messages to the server that holds the lease.
When the server receives the message, it responds with either a DHCPACK message, which renews the lease and restarts the lease time clock, or a DHCPNACK message, which terminates the lease and forces the client to begin the address assignment process again from the beginning.

Question 3
When a DHCP server is configured, which two IP addresses should never be assignable to hosts? (Choose two)
A. network or subnetwork IP address
B. broadcast address on the network
C. IP address leased to the LAN
D. IP address used by the interfaces
E. manually assigned an address to the clients
F. designated IP address to the DHCP server

Answer: A B
Explanation
If a DHCP server was given a /24 subnet to use for host IPs eg. 192.168.1.0/24 it would not be allowed to assign the Network address of 192.168.1.0 or the Broadcast address of 192.168.1.255. It would only assign IPs in the range of 192.168.1.1 to 192.168.1.254. You will receive an error message when trying to assign these to hosts.

Question 4
Which two tasks does the Dynamic Host Configuration Protocol perform? (Choose two)
A. Set the IP gateway to be used by the network.
B. Perform host discovery using DHCPDISCOVER message.
C. Configure IP address parameters from DHCP server to a host.
D. Provide an easy management of layer 3 devices.
E. Monitor IP performance using the DHCP server.
F. Assign and renew IP address from the default pool.

Answer: C F

Question 5
Which statement is correct regarding the operation of DHCP?

A. A DHCP client uses a ping to detect address conflicts.
B. A DHCP server uses a gratuitous ARP to detect DHCP clients.
C. A DHCP client uses a gratuitous ARP to detect a DHCP server.
D. If an address conflict is detected, the address is removed from the pool and an administrator must resolve the conflict.
E. If an address conflict is detected, the address is removed from the pool for an amount of time configurable by the administrator.
F. If an address conflict is detected, the address is removed from the pool and will not be reused until the server is rebooted.

Answer: D
Explanation
An address conflict occurs when two hosts use the same IP address. During address assignment, DHCP checks for conflicts using ping and gratuitous ARP. If a conflict is detected, the address is removed from the pool. The address will not be assigned until the administrator resolves the conflict.
(Reference: https://www.cisco.com/en/US/docs/ios/12_1/iproute/configuration/guide/1cddhcp.html)

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