When a client and server are not on the same physical network, which device is used to forward requests and replies between client and server for…

A DHCP relay agent is a host or, more commonly, a router feature that forwards DHCP

packets between clients and servers when they are not on the same physical subnet.

The initial client request, a DHCPDISCOVER message, is a layer 2 broadcast, which

routers do not forward by default. The relay agent, located on the client's subnet,

intercepts this broadcast and forwards it as a unicast packet to a pre-configured DHCP

server on a different subnet. This mechanism is essential for centralized DHCP

management in a routed network environment.

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B. DHCP server: The DHCP server is the entity that receives the forwarded

request and provides an IP address configuration; it does not perform the

forwarding function between different networks.

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C. DHCPDISCOVER: This is the name of the broadcast message a DHCP client

sends to locate a DHCP server. It is a type of packet, not a network device.

•

D. DHCPOFFER: This is the name of the message a DHCP server sends in

response to a DHCPDISCOVER message, offering an IP address to the client. It

is a type of packet, not a network device.

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1. Internet Engineering Task Force (IETF) RFC 2131: "Dynamic Host

Configuration Protocol". Section 4.1, "DHCP relay agents," explicitly states:

"DHCP relay agents are used to forward requests and replies between clients

and servers when they are not on the same physical subnet."

o URL: https://datatracker.ietf.org/doc/html/rfc2131#section-4.1

o Reference: Section 4.1, Paragraph 1.

2. Cisco IOS XE Software Documentation: "Configuring the Cisco IOS XE DHCP

Relay Agent". The document states, "A DHCP relay agent is a Layer 3 device

that forwards DHCP packets between clients and servers... If you do not have a

DHCP relay agent, hosts on a subnet that does not have a DHCP server will not

be able to get IP addresses."

o URL: https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipaddrdhcp/configuration/xe-16-12/dhcp-xe-16-12-book/dhcp-relay-agent.html

o Reference: "Information About the DHCP Relay Agent" section.

3. Microsoft Learn Documentation: "What is DHCP Relay Agent?". The

documentation explains, "The DHCP Relay Agent is a component that can be

used to relay DHCP messages between DHCP clients and DHCP servers on

different IP networks."

o URL: https://learn.microsoft.com/en-us/windows-server/remote/remoteaccess/ras/dhcp/what-is-dhcp-relay-agent

o Reference: Introduction paragraph.

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