DHCP Interview Questions and Answers

1.What is DHCP?
Dynamic Host Configuration Protocol: assigns IPs to the clients requested dynamically or automatically.

2.Describe the process of installing a DHCP server in an AD infrastructure ?
Open Windows Components Wizard. Under Components , scroll to and click Networking Services. Click Details . Under Subcomponents of Networking Services , click Dynamic Host Configuration Protocol (DHCP) and then click OK .

Click Next . If prompted, type the full path to the Windows Server 2003 distribution files, and then click Next. Required files are copied to your hard disk.

3.Process of DHCP (DORA)?
Discover: The Client discovers DHCP
Offers: The DHCP server offers a group of IPs to the clients to pick any
Request:The client selects an IP and request DHCP to confirm it
Acknowledgement: The DHCP server makes a confirmation by sending an DHCPPACK to the client.

4.How to authorize a DHCP server in Active Directory Open DHCP ?.
In the console tree, click DHCP
. On the Action menu, click Manage authorized servers.
. The Manage Authorized Servers dialog box appears. Click Authorize.
. When prompted, type the name or IP address of the DHCP server to be authorized, and then click OK.

5.What is a Scope?
Range of IP Addresses.

6.What is DHCPINFORM ? 
DHCPInform is a DHCP message used by DHCP clients to obtain DHCP options. While PPP remote access clients do not use DHCP to obtain IP addresses for the remote access connection, Windows 2000 and Windows 98 remote access clients use the DHCPInform message to obtain DNS server IP addresses, WINS server IP addresses, and a DNS domain name.

The DHCPInform message is sent after the IPCP negotiation is concluded. The DHCPInform message received by the remote access server is then forwarded to a DHCP server. The remote access server forwards DHCPInform messages only if it has been configured with the DHCP Relay Agent.

7.What is an IP Lease?
DHCP server clients an IP to the client for a period of 8 days. This offer is called IP Lease.

8.Describe the integration between DHCP and DNS? 
Traditionally, DNS and DHCP servers have been configured and managed one at a time. Similarly, changing authorization rights for a particular user on a group of devices has meant visiting each one and making configuration changes.

DHCP integration with DNS allows the aggregation of these tasks across devices, enabling a company’s network services to scale in step with the growth of network users, devices, and policies, while reducing administrative operations and costs. This integration provides practical operational efficiencies that lower total cost of ownership.

Creating a DHCP network automatically creates an associated DNS zone, for example, reducing the number of tasks required of network administrators. And integration of DNS and DHCP in the same database instance provides unmatched consistency between service and management views of IP address-centric network services data.

9.What is the default duration of a lease?
8 Days.

10.How  does  DHCP  and  BOOTP  handle  multiple  subnets?

For the situations where there is more than one LAN, each with its own subnet number, there are two ways. First of all, you can set up a seperate server on each subnet. Secondly, a feature of some routers known as “BOOTP forwarding” to forward DHCP or BOOTP requests to a server on another subnet and to forward the replies back to the client. The part of  such a router (or server acting as a router) that does this is called a “BOOTP forwarding agent”. Typically you have to enable it on the interface to the subnet to be served and have to configure it with the IP address of the DHCP or BOOTP server. On a Cisco router, the address is known as the “UDP Helper Address”.

11.What is authentication DHCP server?
Enabling AD Know the availability of DHCP server Useful when we have multiple DHCP Server and you want to you designate one particular DHCP server to be active. Then we should authorize.

12.What ports are used by DHCP and the DHCP clients ?
UDP Port 68 used for Requests.
UDP Port 67 used for server Replies.

13.What is IP Reservation?
Resolving a particular dynamic IP for a particularly system.

14.How can I prevent unauthorized laptops from using a network that uses DHCP for dynamic addressing?
This would have to be done using a mechanism other than DHCP. DHCP does not prevent other clients from using the addresses it is set to hand out nor can it distinguish between a computer’s permanent MAC address and one set by the computer’s user. DHCP can impose no restrictions on what IP address can use a particular port nor control the IP address used by any client.

15.What is exclusion?
Omitting assigning from the range selected IPs.

16.Can DHCP work with AppleTalk or IPX?
No, it is too tied to IP. Furthermore, they don’t need it since they have always had automated mechanisms for assigning their own network addresses.

17.What is a SUPER SCOPE?
Group of scopes is called as super scope.

18.Can DHCP support statically defined addresses?
Yes. At least there is nothing in the protocol to preclude this and one expects it to be a feature of any DHCP server.
This is really a server matter and the client should work either way. The RFC refers to this as manual allocation.

19.Purpose of DHCP Relay agent?
DHCP server is available on another N/W and you want another N/W to obtain IPs from the DHCP server. Then the DHCP, RA can forward the request from the clients to the DHCP server to obtain IPs for the clients it acts like a mediator between clients and DHCP.

20.When will the server to server protocol be defined?
The DHC WG of the IETF is actively investigating the issues in inter-server communication. The protocol should be defined “soon”.

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