What is the name of the protocol that allows a client to send a broadcast message with its MAC address and receive an IP address in reply?

Question

Prepp Team · Accepted Answer

Understanding RARP: Resolving MAC to IP Addresses

The question asks about a network protocol that allows a client machine to start with only its physical address (MAC address) and request its logical address (IP address) by sending a broadcast message. Let's examine the given options to identify the correct protocol.

Analyzing the Network Protocols

ARP (Address Resolution Protocol): ARP is used to find the MAC address associated with a known IP address. A device knows the IP address of another device on the local network and needs to find its MAC address to send data directly. This is the reverse of what the question describes.
DNS (Domain Name System): DNS is primarily used to translate human-readable domain names (like www.example.com) into IP addresses. It does not involve using a MAC address to get an IP address directly on the local network.
RARP (Reverse Address Resolution Protocol): RARP is designed for diskless workstations or devices that do not have their IP address configured persistently. These devices know their MAC address and need to obtain an IP address from a server. They broadcast a RARP request containing their MAC address. A RARP server on the network hears this broadcast, looks up the corresponding IP address for that MAC address in its configuration, and replies to the requesting device with its IP address. This process perfectly matches the scenario described in the question.
ICMP (Internet Control Message Protocol): ICMP is a network layer protocol used for sending control and error messages, such as reporting if a destination is unreachable or requesting echo replies (like in the ping command). It is not used for obtaining an IP address based on a MAC address.

Based on the functions of these protocols, RARP is the specific protocol that enables a client to broadcast its MAC address to receive an IP address in reply. This was particularly useful for older systems that lacked local storage for configuration information.

Comparison of Protocols

Protocol	Function	Input Known	Output Received
ARP	Address Resolution	IP Address	MAC Address
RARP	Reverse Address Resolution	MAC Address	IP Address
DNS	Name Resolution	Domain Name	IP Address
ICMP	Control and Error Messaging	Various (e.g., IP, request type)	Control/Error Messages

The question specifically describes a client broadcasting its MAC address to obtain an IP address. This is the core function of the Reverse Address Resolution Protocol (RARP).

Conclusion

The protocol that allows a client to send a broadcast message with its MAC address and receive an IP address in reply is RARP.

Revision Table: Key Network Protocols

Protocol	Layer (OSI/TCP/IP)	Primary Use Case
RARP	Network (TCP/IP) / Data Link (OSI) - debated, often considered part of network layer's address resolution functions	Obtaining IP address from MAC address
ARP	Network (TCP/IP) / Data Link (OSI) - similar to RARP	Obtaining MAC address from IP address
DNS	Application (TCP/IP) / Application (OSI)	Translating domain names to IP addresses
ICMP	Network (TCP/IP) / Network (OSI)	Sending control and error messages

Additional Information: Modern Alternatives to RARP

While RARP served its purpose, it has largely been replaced by more flexible protocols in modern networks. Protocols like DHCP (Dynamic Host Configuration Protocol) are now commonly used for assigning IP addresses to clients. DHCP is more versatile than RARP as it can provide additional configuration information like the subnet mask, default gateway, and DNS server addresses, in addition to the IP address. DHCP can also assign IP addresses dynamically from a pool, whereas RARP typically required a static mapping between MAC and IP addresses on the RARP server.