DHCP and Relay Agents Overview

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Questions and Answers

What happens if a DHCPACK is not received within a specified time frame?

The client broadcasts another DHCPREQUEST. (correct)
The client terminates the request without further action.
The client waits indefinitely for the acknowledgment.
The client switches to a static IP configuration.

Why might a DHCP relay agent be necessary in a network?

To manage local device configurations.
Because routers do not propagate broadcast messages. (correct)
To convert IPv4 addresses to IPv6 addresses.
To optimize traffic between clients on the same subnet.

What is the function of the DHCPACK message in the DHCP process?

To request a DHCP lease from the server.
To reject a lease request from the client.
To notify clients of lease expiration.
To verify lease information and confirm assignment to the client. (correct)

How can Router A be configured to handle DHCP requests in a more robust way?

Configure multiple DHCP servers for redundancy. (C) Signup and view all the answers

What might indicate that a DHCP lease duration is insufficient for a network client?

Frequent DHCPREQUEST broadcasts from the client. (B) Signup and view all the answers

What is the result of a DHCP client being on a different subnet than its DHCP server?

The client may fail to acquire an IP address. (B) Signup and view all the answers

What type of message does a DHCP client send to directly communicate with the DHCP server for lease renewal?

DHCPREQUEST (B) Signup and view all the answers

Which of the following is NOT typically returned by a DHCP server in its ACK message?

Hardware address of the client (D) Signup and view all the answers

In the DHCP communication process, which encapsulation order is correct from the DHCP server to the client?

DHCP > UDP > IP > Ethernet (D) Signup and view all the answers

What does DHCP provide in addition to the allocated IP address?

Name and IP address of DNS server (A) Signup and view all the answers

What does the lease duration in a DHCP configuration determine?

How often the client must renew its IP address (D) Signup and view all the answers

During a DHCP transaction, which message type does a client initially send to locate a DHCP server?

DHCPDISCOVER (D) Signup and view all the answers

Which component is essential for a DHCP server to function correctly in a network?

Built-in router with DHCP functionality (B) Signup and view all the answers

Which of the following statements about DHCP broadcast messages is true?

They are broadcasted to all devices on the local area network. (A) Signup and view all the answers

What is the main purpose of a DHCP server in a network?

To dynamically assign IP addresses to devices. (C) Signup and view all the answers

Which of the following accurately describes the lease period for an IP address assigned by a DHCP server?

Lease durations can vary but are typically from 24 hours to a week. (C) Signup and view all the answers

How does a DHCP client request an IP address from a DHCP server?

Through a broadcast message to discover available servers. (B) Signup and view all the answers

What type of protocol is DHCP classified as?

Application layer protocol. (B) Signup and view all the answers

Which device can be configured to provide DHCP services in a small organization?

Routers can be configured as DHCP servers. (D) Signup and view all the answers

When a DHCP lease expires, what must the client do?

Request another IP address from the DHCP server. (B) Signup and view all the answers

What message does a DHCP server send back to the client after receiving a DHCP discover message?

DHCP offer. (A) Signup and view all the answers

Which of the following statements about DHCP server configuration is true?

Leases and address pools can be configured by the administrator. (C) Signup and view all the answers

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Study Notes

DHCP Overview

Dynamic Host Configuration Protocol (DHCP) assigns IP addresses dynamically, allowing devices to communicate over a network.
DHCP eliminates the need for manual static IP address assignment.

DHCP Message Process

DHCP messages are encapsulated in UDP, which is then encapsulated in IP and Ethernet frames.
A broadcast Ethernet frame is sent to reach the DHCP server on the local area network (LAN).
The destination address for the Ethernet frame is FFFFFFFFFFFF (broadcast address).

DHCP Client Operations

The DHCP server formulates a DHCP ACK message that includes the client's assigned IP address, the first-hop router address, and DNS server information.
The DHCP reply is eventually de-encapsulated back at the client, providing necessary IP configuration details.

Additional DHCP Information

Besides IP addresses, DHCP can provide:
- First-hop router address
- DNS server name and IP address
- Network mask for distinguishing network/host portions of the address.

Lease Renewal Process

Clients initiate a renewal process before lease expiration by sending a DHCPREQUEST message to the original DHCP server.
Leases typically last between 24 hours to several days, after which clients must request a new address.

DHCP Server Functionality

DHCP servers manage IP address assignments and simplify network administration.
They can operate in various environments, including small home networks using routers as DHCP servers.
Configuration allows leases to timeout allowing for efficient IP address management.

Client-Server Interaction

When a client connects, it broadcasts a "DHCP discover" message to find available DHCP servers.
The server responds with a "DHCP offer," followed by the client sending a DHCPREQUEST for the offered address.
The server acknowledges this with a "DHCPACK," confirming the assignment.

DHCP Relay Agent

In larger networks, clients may be on different subnets than DHCP servers and cannot use broadcast messages across subnets.
A DHCP relay agent forwards messages between clients and servers across different IP networks.
Routers can be configured with helper addresses to forward DHCP requests as unicast to the appropriate servers, supporting multiple DHCP servers for redundancy.

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