DHCP
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Dynamic Host Configuration Protocol (DHCP) is used to automatically assign IP addresses, subnet masks, default gateways and other network configuration options to clients on a network. DHCP reduces network configuration workload. It uses a four step packet exchange process during the initial IP address lease and will attempt renewal at 50% and 87.5% of the lease time. DHCP servers must be authorized in Active Directory to lease addresses. Scopes are configured to define address ranges for clients, reservations assign specific addresses by MAC address, and relays allow a single DHCP server to service multiple subnets.
DHCP
- 2. 2 Objectives • Outline the benefits of using DHCP • Describe the DHCP lease and renewal process • Install and authorize the DHCP service • Configure DHCP scopes • Create DHCP reservations for client computers • Configure DHCP options • Understand and describe the purpose of a DHCP relay • Install and configure a DHCP relay
- 3. 3 DHCP Overview • Used to automatically deliver IP addressing • Reduces the amount of time you spend configuring computers on your network • Used by default unless you specify otherwise • The ipconfig /all command will indicate whether the configuration came from a DHCP server computer
- 6. 6 Leasing an IP Address • An IP address is leased during the boot process • The overall process is composed of four broadcast packets: • DHCPDISCOVER • DHCPOFFER • DHCPREQUEST • DHCPACK
- 7. 7 Leasing an IP Address (continued) • Any DHCP server that receives the DHCPDISCOVER packet responds with a DHCPOFFER packet • The DHCP client responds to the DHCPOFFER packet it receives with a DHCPREQUEST packet • A DHCPACK packet indicates confirmation that the client can use the lease • Once DHCPACK is received, the client can start using the IP address and options in the lease
- 8. 8 Leasing an IP Address (continued)
- 9. 9 Renewing an IP Address • The IP address can either be permanent or timed • A permanent address is never reused for another client • Timed leases expire after a certain amount of time • Windows clients attempt to renew their lease after 50% of the lease time has expired • A DHCP server may either honor or reject a renew request
- 10. 10 Renewing an IP Address (continued)
- 11. 11 Installing and Authorizing the DHCP Service • A DHCP service must be authorized after installation
- 12. 12 Installing the DHCP Service • DHCP is a standard service • It is included in Windows Server 2003 • It is not installed as part of a default installation
- 13. 13 Installing the DHCP Service (continued)
- 14. 14 Activity 4-1: Installing DHCP • Objective: Install DHCP on Windows Server 2003 • Make sure your network connection is statically configured • Install the service using the Add/Remove Windows Components utility
- 15. 15 Authorizing the DHCP Service • Unauthorized DHCP servers can hand out bad information • DHCP will not start unless authorized • If Active Directory is used, authorization takes place in Active Directory • DHCP servers are automatically authorized under certain conditions
- 16. 16 Authorizing the DHCP Service (continued)
- 17. 17 Authorizing the DHCP Service (continued)
- 18. 18 Activity 4-2: Starting an Authorized DHCP Server • Objective: View the results of starting a DHCP server that does not participate in an Active Directory domain • Check to make sure the service is running • Check out any relevant events using the System Log
- 19. 19 Activity 4-3: Installing the Active Directory Service • Objective: Install the Active Directory service on your computer and participate in an Active Directory domain • Use the dcpromo utility • Select “domain controller for a new domain” • Select “domain in a new forest” • Continue through the resulting dialogs
- 20. 20 Activity 4-4: Starting an Unauthorized DHCP Server • Objective: View the results of starting an unauthorized DHCP server • View the System Log to see the result of starting an unauthorized DHCP server
- 21. 21 Activity 4-5: Authorizing a DHCP Server • Objective: Authorize a DHCP server in Active Directory • Go to the DHCP snap-in and choose the activate option
- 22. 22 Configuring DHCP Scopes • Scope defines a range of IP addresses • Each scope is configured with: • Description • Starting IP address • Ending IP address • Subnet mask • Exclusions • Lease duration • Two strategies exist for defining the starting and ending IP addresses • Allow all and exempt the few static addresses • Use only the addresses not already in use
- 24. 24 Configuring DHCP Scopes (continued) • Exclusions are used to prevent some IP addresses from being handed out dynamically • Lease duration defines how long client computers are allowed to use an IP address • Default lease duration is eight days • A scope must be activated before the DHCP service can begin using it
- 25. 25 Activity 4-6: Creating a Scope • Objective: Create a scope to distribute IP addresses to client computers • Manually enter the IP configuration settings as directed by the text • Create a new scope using the configuration settings provided
- 26. 26 Activity 4-7: Activating and Testing a Scope • Objective: Activate a DHCP scope, and then test it with a partner • One person will activate the scope created in the previous activity • Another person will try to obtain an automatic IP address from the server
- 27. 27 Creating DHCP Reservations • Reservations are used to hand out a specific IP address to a particular client • Useful when delivering IP addresses to devices that would normally use static addresses • Can also be beneficial when firewalls are in place • Reservations are created based on MAC addresses
- 29. 29 Activity 4-12: Creating and Testing a Reservation • Objective: Create a DHCP reservation, and test it with a client • Configure the server to reserve an IP address for a client machine • Test to see if the client machine picks up the reserved address
- 30. 30 Configuring DHCP Options • DHCP can hand out a variety of other IP configuration options • It is common that all workstations within an entire organization use the same DNS servers • DNS is often configured at the server level
- 33. 33 Activity 4-13: Setting Server Options • Objective: Set the DNS server option for a DHCP server • Check 006 DNS servers option • Add the IP address x.0.0.250
- 34. 34 Activity 4-14: Setting Scope Options • Objective: Set the default gateway in the scope options • Use the DHCP snap-in to complete this activity
- 35. 35 Activity 4-15: Testing Server & Scope Options • Objective: Activate a DHCP scope, and then test it with a partner to ensure that scope options are handed out • Activate a DHCP scope • Configure a client to access the server • Check the default gateway and DNS settings to find out whether or not the configurations entered in previous activities were done correctly
- 36. 36 Configuring a DHCP Relay • DHCP packets cannot travel across a router • A relay agent is necessary in order to have a single DHCP server handle all leases • Relay agents receive broadcast DHCP packets and forward them as unicast packets to a DHCP server • The DHCP relay cannot be installed on the same server as the DHCP service
- 37. 37 Configuring a DHCP Relay (continued)
- 38. 38 Configuring a DHCP Relay (continued)
- 39. 39 Activity 4-16: Configuring a DHCP Relay • Objective: Uninstall the DHCP service from your computer and configure it as a DHCP relay • Uninstall the DHCP service • Configure the computer as a relay by using the Routing and Remote Access tool provided in Windows
- 40. 40 Summary • DHCP dynamically assigns IP address information to clients on a network • The DHCP lease process is composed of four packets: • DHCPDISCOVER • DHCPOFFER • DHCPREQUEST • DHCPACK • A DHCP client attempts to renew its lease at 50%, 87.5%, and 100% of the lease time • The commands ipconfig /release and ipconfig /renew can be used to release and renew DHCP leases
- 41. 41 Summary (continued) • If the Active Directory service is present on your network, each DHCP server must be authorized in Active Directory to lease addresses to clients • A scope defines a range of IP addresses that are leased to clients • A superscope combines two scopes into a single logical unit to service network segments with two subnets
- 42. 42 Summary (continued) • An exclusion in a scope can stop a DHCP server from handing out specific addresses • A reservation allows you to give a specific workstation a defined IP address by tying the DHCP lease to the MAC address of the client • Vendor and user classes can be used to configure some client computers with different options, depending on the class to which they belong • A DHCP relay agent is required on each network that requires IP configuration from a DHCP server across a router