Chapter 3

1. Chapter 3 Configuring and Managing the DHCP Server Role

2. DHCP overview • RARP – one of the first ways to assign addresses • BOOTP – Another legacy way to assign addresses. Still had manual aspects to it. • DHCP – Based heavily off of BOOTP, but it is all dynamic. • Centralized administration • Dynamic host configuration • Seamless • Flexibility and scalability

3. How DHCP works • Functions on the Application layer of OSI • Uses UDP broadcast messages • DHCP message Types • DHCPDISCOVER – sent by clients via broadcast to locate a DHCP Server. • DHCPOFFER – Sent by DHCP server to client in response to DHCPDISCOVER along with offered configuration parameters. • DHCPREQUEST - Sent by client to signal acceptance of offered address and parameters.

4. DHCP Messages contd. • DHCPDECLINE - Sent by client informing the server the offered IP address has been declined. • DHCPACK – Sent by server to confirm IP address. • DHCPNACK – Sent by server to deny the clients DHCPREQUEST. • DHCPRELEASE – sent by client relinquishing IP address and canceling the remaining lease. • DHCPINFORM – sent from client to ask for additional configuration parameters.

5. Putting the Messages to Work.

6. Putting the Messages to Work • The client will perform the initial process in the following situations: • The very first time the client boots • After releasing its IP address • After receiving a DHCPNACK message • Other situations, such as renewing, the process will be different. Refer to Page 40-41 of the reading.

7. Using the DHCP Relay Agent • Because DHCP uses broadcast messages you can not use DHCP across multiple subnets. • To pass DHCP messages through the router it must be RFC 1542 compliant. • If the router is not RFC 1542 compliant you can install the DHCP relay agent. • The relay agent will forward messages to the DHCP server.

8. Authorizing a DHCP Server • You must authorize a DHCP server in Active Directory before you can issue leases to clients. • In a workgroup environment this does not need to be done. • To authorize go into the DHCP console and choose to authorize.

9. Configuring DHCP Scopes • Scope – the addresses that able to be assigned • 192.168.1.1/24 through 192.168.1.254/24 is and example • Exclusion range – used to define addresses within the scope that will NOT be given out to clients. • Available Address Pool – after all ranges and exclusion are defined the remaining addresses are referred to this.

10. Configuring a DHCP Reservation • A reservation allows you to specify a specific address for a host. • Ensures the host will always have that address, sort of like assigning a static address • The host’s MAC address is used to make the reservation

11. Configuring DHCP Options • Options are additional client-configuration parameters • 4 types • Server options – apply to all clients of the DHCP server • Scope options – apply to all clients within a scope • Class options – provide DHCP parameters to DHCP clients based on type • Client options – apply to individual clients. Client options override all other options

12. Managing the DHCP Database • Backup and Restore • Reconciliation – verifies DHCP database against registry values. After restore. • Compacting the database –optimizes database and reclaims unused space. • Removing the database

13. You Learned • DHCP is a simple, standard protocol that makes TCP/IP network configuration much easier for the administrator by dynamically assigning IP addresses and providing additional configuration information to DHCP clients automatically. • Additional configuration information is provided in the form of options and can be associated with reserved IPs to a vendor or user class, to a scope, or to an entire DHCP server. Lesson 3

14. You Learned (cont.) • Because DHCP is a key component in your organization, you must manage and monitor it. • DHCP management consists of backing up and restoring the database as well as reconciling, compacting, and, in some cases, removing the database. Lesson 3