DHCP Relay Configuration

Questions and Answers

What is the purpose of the IP helper feature on the router?

To forward DHCP requests to a remote DHCP server

What is the destination port used by the UDP header in the DHCPDISCOVER message?

What is the primary purpose of using DHCP relay in a network?

To provide DHCP services to clients on a different network than the DHCP server

What is the reason why the DHCP packets are unicast in this scenario?

Because the router is acting as a DHCP relay agent Signup and view all the answers

Why might a router not be used as a DHCP server in a network?

Because it does not support DHCP services Signup and view all the answers

What is the source port used by the client in the DHCPDISCOVER message?

68 Signup and view all the answers

What command can be used to determine the network connected to a router interface?

show ip route Signup and view all the answers

What is the purpose of identifying the network connected to a router interface in the context of DHCP relay?

To determine the network that needs DHCP services Signup and view all the answers

What is the purpose of the DHCP relay agent?

To forward DHCP requests to a remote DHCP server Signup and view all the answers

What happens to the DHCP offer packet after it is received by the router?

It is forwarded to the client Signup and view all the answers

What information is needed to configure a DHCP pool for the 10.2.0 network?

The network address and range of host addresses Signup and view all the answers

What is the number of packets involved in the traditional DHCP process?

4 Signup and view all the answers

What is the range of host addresses that might be used for the 10.2.0 network?

.150 through .160 Signup and view all the answers

Where would the DHCP pool be configured in the context of DHCP relay?

On the DHCP server at headquarters site Signup and view all the answers

What is the role of the router in the DHCP process when it is configured as an IP helper?

It forwards DHCP requests to a remote DHCP server Signup and view all the answers

What is the IP address of the DHCP server in the scenario?

1.1.1.1 Signup and view all the answers

What is the purpose of IP helper or UDP forwarding on the default gateway interface?

To forward DHCP requests to the DHCP server Signup and view all the answers

What is the IP address of the DHCP server in this scenario?

1.1.1.1 Signup and view all the answers

What is the default gateway of the DHCP pool?

10.2.0.2 Signup and view all the answers

What is the command used to set up the IP helper feature on the Cisco router?

ip helper-address Signup and view all the answers

What is the purpose of the DISCOVER message in DHCP?

To request an IP address from the DHCP server Signup and view all the answers

Why is IP helper necessary in this scenario?

Because the DHCP server is on a different subnet than the client Signup and view all the answers

What is the result of enabling IP helper on the default gateway interface?

The DHCP server will respond to DHCP requests from the remote subnet Signup and view all the answers

What is the IP address of the client after it receives an IP address from the DHCP server?

10.2.0.150 Signup and view all the answers

What is the purpose of capturing the traffic on the router?

To verify that the IP helper is forwarding DHCP requests Signup and view all the answers

Why is the IP address of the DHCP server necessary to configure on the router?

So the router can forward DHCP requests to the DHCP server Signup and view all the answers

Study Notes

DHCP Relay

A DHCP relay is used when a DHCP server is not directly connected to the network where clients need DHCP services.
It allows clients to receive IP addresses from a DHCP server located on a different network segment.

Identifying the Network

To set up a DHCP relay, you need to identify the network that needs DHCP services.
You can do this by checking the routing table on the router connected to the network.

Configuring the DHCP Pool

The DHCP pool needs to be configured on the DHCP server to support the identified network.
The pool should include a range of addresses that can be assigned to clients on the network.
For example, if the network is 10.2.0.0, the pool could include addresses from 10.2.0.150 to 10.2.0.160.

DHCP Server Configuration

The DHCP server should be configured with a default gateway and DNS server addresses.
For example, the default gateway could be 10.2.0.2 and the DNS server could be 8.8.8.8.

DHCP Relay Agent

The DHCP relay agent is set up on the router interface connected to the network that needs DHCP services.
It listens for DHCP requests from clients and forwards them to the DHCP server as unicast packets.
The relay agent sources the packets from its own interface IP address.

IP Helper

IP Helper is a feature that allows the router to forward DHCP requests to the DHCP server.
It is also known as UDP forwarding.
To configure IP Helper, you need to enable it on the router interface and specify the IP address of the DHCP server.

DHCP Request and Response

When a client sends a DHCPDISCOVER message, it is broadcast on the local network.
The DHCP relay agent forwards the message to the DHCP server as a unicast packet.
The DHCP server responds with a DHCPOFFER message, which is forwarded back to the client by the relay agent.
The client then sends a DHCPREQUEST message, which is forwarded to the DHCP server, and the server responds with a DHCPACK message.

Capturing DHCP Traffic

You can capture DHCP traffic on the router to see the forwarded DHCP packets.
The traffic is unicast, even though the original DHCP request was broadcast on the local network.

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Description

Learn how to configure DHCP relay to provide DHCP services to clients on a different network segment when a DHCP server is not directly connected. This scenario is demonstrated on Site 2 of a network.