DHCP server use when there is an IP address conflict?

[praveen_jayawardhana]

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.

pls i don't have idea Gratuitous ARP ? if someone can pls explain full theory 

thanks 

[M02@rt37 · Accepted solution]

Hello @praveen_jayawardhana,

ARP is a networking protocol used to resolve or map IP addresses to their corresponding MAC addresses on a local network. When a device wants to communicate with another device on the same network, it needs to know the MAC address of the destination device. It uses ARP to find the MAC address associated with the IP address it wants to reach.

Gratuitous ARP is a special type of ARP message that serves a different purpose than regular ARP. In Gratuitous ARP, a device sends an ARP announcement without being prompted by any specific ARP request. It is called gratuitous because the ARP announcement is not required or solicited by other devices on the network.

The main purposes of Gratuitous ARP are:

--IP Address Conflict Detection:
When a device comes online or joins a network, it typically sends a Gratuitous ARP message to announce its presence and inform other devices about its IP-MAC mapping. If another device already has the same IP address in its ARP cache, it will detect the IP address conflict and take appropriate action to resolve it.

--Updating ARP Caches:
Gratuitous ARP messages help in quickly updating the ARP caches of other devices on the network. When a device's MAC address changes for a specific IP address (due to hardware replacement or other reasons), it can send a Gratuitous ARP message to notify other devices of this change. This ensures that other devices update their ARP caches and use the correct MAC address when communicating with the device.

--Network Redundancy and High Availability:
In scenarios where network redundancy and high availability are important, devices or routers may use Gratuitous ARP to announce their presence or the availability of specific IP addresses. This can help in load balancing or failover scenarios, where devices can quickly detect changes in the network topology.

=> Basic sequence of events

-A device comes online.
-It constructs a Gratuitous ARP packet, which includes its own IP address as both the source and target IP address in the ARP packet.
-The device then sends the Gratuitous ARP packet as a broadcast on the local network.
-Other devices on the network receive the Gratuitous ARP packet.
-If another device already has the same IP address in its ARP cache, it will detect the IP address conflict.
-Devices that receive the Gratuitous ARP packet will update their ARP caches with the new IP-MAC mapping or refresh the existing mapping.

=> Security recommandation

Network admin can use Dynamic ARP inspection, called DAI, to prevent the ARP poisoning/spoofing attacks. DAI is a security feature that validates Address Resolution Protocol packets in a network by determining the validity of an ARP packet based on valid IP-to-MAC address bindings stored in the trusted DHCP snooping binding database.

Gratuitous ARP help in preventing IP address conflicts and ensure that ARP caches remain up-to-date, contributing to the overall efficiency of network communication. However, if not handled properly or exploited maliciously, it can become a security concern.