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Microsoft Windows 2000 Network Infrastructure Administration

• Chapter 10

• Implementing Dynamic Host Configuration Protocol (DHCP)

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Introducing and Installing DHCP

• Lesson 1 Topics

• TCP/IP configuration issues• Functionality of DHCP

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Introducing and Installing DHCP

• Lesson Objectives

• To describe the differences between manual and automatic configuration of TCP/IP

• To identify TCP/IP configuration parameters that can be assigned by a DHCP server

• To describe IP lease requests and offers• To install DHCP in Windows 2000

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DHCP and BOOTP

• DHCP is an extension of Boot Protocol (BOOTP).

• BOOTP enables diskless clients to start up and automatically configure TCP/IP

• Allows diskless clients to configure TCP/IP automatically.

• Centralizes and manages the allocation of TCP/IP.

• Automatically assigns addresses.

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How a DHCP Client Interacts with a DHCP Server

Client

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Configuring TCP/IP Manually

• Administrative overhead

• Bad or duplicate IP addresses

• Moving between subnets

• Difficult to trace to the cource

• Typing the IP address, subnet mask, or default gateway can lead to problems.

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Configuring TCP/IP Using DHCP

• Centralized management

• Automatic supply of address information to clients

• Supplies all of the necessary configuration information to all of the DHCP clients.

• Easier to troubleshoot

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TCP/IP Configuration Parameters Assigned by DHCP

• IP address for network adapter

• Subnet masks

• Default gateways

• Additional parameters such as IP address for DNS or WINS servers a client may use

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Phases Process of DHCP

• Most DHCP messages are sent by broadcast

• Routers must support forwarding DHCP broadcasts

• DHCP Phases

• IP lease discover• IP lease offer• IP lease request• IP lease acknowledgment

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Four Phases of DHCP Client Configuration

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IP Lease Discover and Offer

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IP lease Discover

The client initializes a limited version of TCP/IP and broadcasts a request for the location of a DHCP sever and IP addressing

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IP lease offer

• All DHCP severs that have valid IP addressing information available send and offer to the client.

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IP lease request

• The client selects the IP addressing information from the first offer it receives and broadcasts a message requesting to lease the IP addressing information in the offer.

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IP lease acknowledgment

• The DHCP sever that made the offer responds to the message, and all other DHCP servers withdraw their offers. The addressing information is assigned to the client and an acknowledgment is sent. The client finishes initializing and binding the TCP/IP protocol.

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IP Lease Offer

• All DHCP severs that receive the request and have a valid configuration for client broadcast an offer with the following information:

• The client’s hardware address (MAC)• An offered IP address• Subnet mask• Length of the lease• A server identifier ( DHCP server IP address)

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Sending a DHCPOFFER Message

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When No DHCP Servers Online

• Client waits 1 second.

• Client rebroadcasts at 9, 13, 16 seconds and then at random intervals.

• Client retries every 5 minutes.

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Automatic Private IP Addressing (APIPA)

• Client attempts request.

• Autoconfiguration of a Class B address.

• Clients tests for conflicts for 10 addresses.

• Client rechecks for a DHCP server every 5 minutes.

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IP Lease Request

• Client broadcasts DHCPREQUEST message and includes the server identifier (IP Address) of the server whose offer was accepted.

• Other DHCP servers retract offers so their IP addresses are available for the next lease request.

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DHCPACK

• DHCP server sends DHCPACK that contains a valid lease for and IP address and possibly other configuration information.

• Client is bound DHCP client.

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DHCPNACK

An unsuccessful acknowledgment DHCPNACK is broadcast if the client is trying to lease its previous IP address and IP address is no longer available.

• The IP address is no longer available.

• The client has been moved to a different subnet.

• The client returns to the process of requesting an IP lease.

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Before Installing DHCP

• Hardware and storage requirements

• Which computers to configure immediately

• Which computers to configure manually

• DHCP options and values to be predefined

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Options that Determine Configuration

• Default gateway

• Domain Name System (DNS) server

• NetBIOS over TCP/IP name resolution

• Windows Internet Name Service (WINS) server

• NetBIOS scope ID

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Report Displayed for Ipconfig /all

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Ipconfig Command-Line Switches

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DHCP Relay Agent

• Relays messages between clients and servers on subnets

• One DHCP server per subnet when routed• Relay agent to support clients on multiple

subnets

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Configuring DHCP

• Lesson 2 Topic

• Configuring DHCP on Windows 2000–based server

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Configuring DHCP

• Lesson Objectives

• To identify the benefits of using DHCP on a network

• To configure a DHCP server and clients

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Setting a Client to Obtain an IP Address from a DHCP Server

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How DHCP Servers Provide Optional Data

• Default gateways that connect network segments

• IP addresses for DNS servers

• IP addresses for WINS servers

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Installing DHCP

• Install Microsoft DHCP Server service.

• Authorize the DHCP server.

• Configure a scope or pool of addresses.

• Configure global and client scope.

• The DHCP server can be configured to always assign the same IP address to the same DHCP client

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Authorizing a DHCP Server• Windows 2000 servers are verified.

• DHCP servers are authorized.

• First server in Active Directory• Installed as domain controller or member server—not

stand-alone• Authorization process depends on server role.

• Domain controller• Member server• If you deploy Active Directory, all computers

operating as DHCP servers must be either domain controller or domain member server before they can authorized in the directory service and provide DHCP service to clients.

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DHCP Scope

Scope is a pool of valid IP addresses available for lease to DHCP lients.

• At least one scope for every DHCP server.

• Exclude static IP addresses from scope.

• Multiple scopes will centralize administration and to assign IP addresses specific to a subnet.

• One scope to a subnet.

• DHCP servers do not share scope information.

• IP addresses must be unique to scope.

• Determine starting and ending addresses.

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DHCP Scope Configuration Options

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Scope and IP Address Ranges for Server A and Server B

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Integrating DHCP with Naming Services

• Lesson 3 Topics

• Dynamic updates in DNS• Integrating DHCP with DNS

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Integrating DHCP with Naming Services

• Lesson Objectives

• To integrate DNS and DHCP• To describe how Dynamic DNS updates work• To identify how DHCP client updates are

typically handled

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Registering for DNS Updates

• Windows 2000 can register with a DNS server.

• Supports DNS Dynamic update protocol for automatic record updating.

• DHCP acts as registration proxy.

• An additional DHCP Option Code 81 enables return of fully qualified domain name (FQDN).

• DHCP and static DNS are not compatible.

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DHCP Clients and DNS

• DHCP servers provide default support for legacy DHCP clients in DNS zones.

• DHCP/DNS update interaction for Windows 2000.

• DHCP/DNS update interaction for pre-Windows 2000.

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A DHCP Client Interacting with the DNS Dynamic Update Protocol

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DHCP/DNS Interaction with Older Windows Clients

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Using DHCP with Active Directory

• Lesson 4 Topics

• Integration with Active Directory and DNS service

• Monitoring as statistical reporting for DHCP servers

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Using DHCP with Active Directory

• Lesson Objectives

• To describe how IP address and naming management is managed through DHCP and Active Directory integration

• To describe how DHCP servers are authorized

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Integrated IP Management

• Windows 2000 Sever naming and address services offer flexibility and interoperability with other address and naming systems

• Address assignment and naming services

• Support for legacy servers

• New with Windows 2000 Server is support for Dynamic DNS, Active Directory integration of DHCP and DNS, and DHCP rely agent

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Rogue Server Detection Feature

• Windows 2000 detects unauthorized DHCP servers.

• DHCP servers not authorized are not able to run the DHCP service.

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Troubleshooting DHCP

• Lesson 5 Topics

• Troubleshooting DHCP clients• Troubleshooting DHCP servers

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Troubleshooting DHCP

• Lesson Objectives

• To identify and solve DHCP client problems• To identify and solve DHCP server problems

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Preventing DHCP Problems

• Use 75/25 design rule.

• Use superscopes for multiple DHCP servers on each subnet. A superscope allows a DHCP server to provide leases from more than one scope to clients on a single physical network.

• Deactivate scopes only when removing a scope permanently.

• Use server-side conflict detection.

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Preventing DHCP Problems (con’t)

• Create reservations on all potential DHCP servers.

• DHCP is disk intensive; use optimal hardware. Consider RAID 0 or RAID 5 solutions when purchasing hardware for your server computer.

• Use audit log.

• Integrate DHCP with other services, such as DNS and WINS

• Use appropriate number of DHCP servers.

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Number of DHCP Servers

• Size of network

• Number of DHCP-enabled clients

• Transmission speed between network segments

• Speed of network links

• IP address class of the network

• Isolated or multiple DHCP servers

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Troubleshooting DHCP Clients

• Failed IP configuration

• Invalid IP address configuration

• Autoconfiguration problems (Microsoft has reserved IP addresses from 169.254.0.1 through 169.255.254 and uses this range to support APIPA

• Missing configuration details

• DHCP not providing IP addresses

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Failed IP Configuration

• Check for client problem.

• Check system event log and DHCP audit logs for clues.

• Use Ipconfig TCP/IP utility.

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Invalid IP Address

• Client does not have IP address, or client has IP address of 169.254.x.x.

• Client cannot contact DHCP server.

• Determine whether network hardware failure or DHCP server is unavailable.

• Verify that client has valid functioning network connection.

• Check hardware.

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Autoconfiguration Problems

• Windows could not find a DHCP server and provided APIPA IP address.

• In larger networks, consider disabling APIPA.

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Missing Configuration Details

• Client is missing DHCP options.

• Verify that options distribution is configured at server, scope, client, or class level.

• Check DHCP option settings.

• DHCP is configured with incorrect DHCP router option (Option Code 3).

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DHCP Servers Do Not Provide IP Addresses

• IP address of the DHCP server was changed.

• DHCP clients are located across router from subnet where DHCP server resides.

• Multiple DHCP servers exist on same local area network (LAN).

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Three Ways to Discover Problem

• Client configured to use an address not provided by the server.

• Server sends error message back to client.

• Server leases IP address, but client has network configuration-based problems.

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Relay Agent Not Working

• DHCP Relay Agent and DHCP server are on the same computer.

• Install DHCP server and DHCP Relay Agent on different computers.

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Console Reports Incorrect Lease Expirations

• Scope time and lease time should be identical.

• Reassign lease times or add reservations to the scope.

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No Address Leases for New Scope

• Configure DHCP server to use superscope with old and new scopes.

• Change primary IP address to that in new scope.

• Windows NT Server 3.51, change first IP address to address in new scope range.

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System Monitor

• All types of DHCP messages sent and received

• Average amount of processing time per message packet sent and received

• Number of message packets dropped from internal delays

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Moving DHCP Server Database

• May need to move DHCP database to another computer

• May need to reconcile database

• Can force lease updates by typing Ipconfig /renew