This document provides an overview and lessons for configuring and troubleshooting DHCP. It covers DHCP server roles, configuring scopes and options, managing the DHCP database, monitoring DHCP, and security configuration. A lab scenario tasks the user with implementing a fault-tolerant DHCP configuration across multiple offices to support network requirements.

1. Module 2
Configuring and
Troubleshooting DHCP

2. Module Overview
• Overview of the DHCP Server Role
• Configuring DHCP Scopes
• Configuring DHCP Options
• Managing a DHCP Database
• Monitoring and Troubleshooting DHCP
• Configuring DHCP Security

3. Lesson 1: Overview of the DHCP Server Role
• Benefits of Using DHCP
• New DHCP Features in Windows Server 2008/R2
• How DHCP Allocates IP Addresses
• How DHCP Lease Generation Works
• How DHCP Lease Renewal Works
• DHCP Server Authorization
• Demonstration: How to add the DHCP Server Role

4. Benefits of Using DHCP
DHCP reduces the complexity and amount of administrative
work by using automatic TCP/IP configuration
Manual TCP/IP Configuration
• IP addresses are entered
manually
• IP address could be entered
incorrectly
• Communication and network
issues can result
• Frequent computer moves
increase administrative effort
Automatic TCP/IP Configuration
• IP addresses are supplied
automatically
• Correct configuration
information is ensured
• Client configuration is updated
automatically
• A common source of network
problems is eliminated

5. New DHCP Features in Windows Server 2008
New DHCP features include:
• Windows Server 2008 Support for DHCPv6
• Support for advanced network security
configuration using NAP
• DHCP on Server Core
These new features were added with Windows Server 2008

6. How DHCP Allocates IP Addresses
DHCP Server
DHCP
Database
IP Address1: Leased to DHCP Client1
IP Address2: Leased to DHCP Client2
IP Address3: Available to be leased
DHCP Client2:
IP configuration
from DHCP server
Non-DHCP Client:
Static IP
configuration
DHCP Client1:
IP configuration
from DHCP server
Lease Renewal
Lease Generation

7. How DHCP Lease Generation Works
DHCP client broadcasts a DHCPDISCOVER
packet1
DHCP servers broadcast a DHCPOFFER packet2
DHCP client broadcasts a DHCPREQUEST packet3
DHCP Server1 broadcasts a DHCPACK packet4
DHCP
Client
DHCP
Server1
DHCP
Server2
DHCP client broadcasts a DHCPDISCOVER
packet1
DHCP servers broadcast a DHCPOFFER packet2
DHCP client broadcasts a DHCPREQUEST packet3
DHCP Server1 broadcasts a DHCPACK packet4
DHCP
Client
DHCP
Server1
DHCP
Server2

8. How DHCP Lease Renewal Works
DHCP Client sends a DHCPREQUEST packet1
DHCP Server1 sends a DHCPACK packet2
If the client fails to renew its lease, after 50% of the
lease duration has expired, then the DHCP lease renewal
process will begin again after 87.5% of the lease
duration has expired
If the client fails to renew it’s lease, after 87.5% of the
lease has expired, then the DHCP lease generation
process starts over again with a DHCP client
broadcasting a DHCPDISCOVER
DHCP Client
DHCP
Server1
DHCP
Server2
50% of lease
duration has
expired
87.5% of
lease
duration has
expired
100% of
lease
duration has
expired
DHCP Client
DHCP
Server1
DHCP
Server2
DHCP client sends a DHCPREQUEST packet1
DHCP Server1 sends a DHCPACK packet2
50% of lease
duration has
expired

9. DHCP Server Authorization
DHCP Server2 checks with the
domain controller to obtain a list of
authorized DHCP servers
If DHCP Server2 does not find its IP
address on the list, the service does
not start and support DHCP clients
DHCP client receives IP address
from authorized DHCP Server1
DHCP Server1 checks with the
domain controller to obtain a list
of authorized DHCP servers
If DHCP Server1 finds its IP
address on the list, the service
starts and supports DHCP clients
Domain
Controller
Active
Directory
DHCP Client
Unauthorized
Does not service
DHCP requests
Authorized
Services DHCP
requests
DHCP Server1
DHCP Server2
DHCP authorization is the process of registering the DHCP Server
service in the Active Directory domain to support DHCP clients

10. Demonstration: How to Add the DHCP Server Role
This demonstration shows how to:
• Install and authorize the DHCP server role

11. Lesson 2: Configuring DHCP Scopes
• What Are DHCP Scopes?
• What Are Superscopes and Multicast Scopes?
• Demonstration: How To Configure DHCP Scopes
• What Is a DHCP Reservation?
• DHCP Sizing and Availability

12. What Are DHCP Scopes?
A scope is a range of IP addresses that are available
to be leased
Scope Properties
• Scope name
• Exclusion range
• Lease duration
• Network IP
address range
• Network ID
• Subnet mask
LAN A LAN B
DHCP Server
Scope BScope A

13. What Are Superscopes and Multicast Scopes?
LAN A LAN B
DHCP Server
Scope A and Scope B
LAN A LAN B
DHCP Server
Scope BScope A

14. Demonstration: How To Configure DHCP Scopes
This demonstration shows how to:
• Create an IPv4 scope

15. What Is a DHCP Reservation?
A reservation is a specific IP address, within a scope, that
is reserved permanently for lease to a specific DHCP client
Subnet A Subnet B
Workstation 1
DHCP Server
Workstation 2
File and Print
Server
IP Address1: Leased to Workstation 1
IP Address2: Leased to Workstation 2
IP Address3: Reserved for File and
Print Server

16. DHCP Sizing and Availability
DHCP
Clients
DHCP
Server1
192.168.0.1
DHCP
Server2
192.168.1.1
DHCP
Clients
DHCP Server1 has 80% of addresses as follows:
•Scope range: 192.168.0.2-192.168.0.254
•Excluded addresses: 192.168.0.200-192.168.0.254
DHCP Server2 has 20% of addresses as follows:
•Scope range: 192.168.0.2-192.168.0.254
•Excluded addresses: 192.168.0.2-192.168.0199

17. Lesson 3: Configuring DHCP Options
• What Are DHCP Options?
• What Are DHCP Class-Level Options?
• How DHCP Options Are Applied
• Demonstration: How to Configure DHCP Options

18. What Are DHCP Options?
• WINS Servers
Common scope options are:
DHCP options are values for common configuration data
that applies to the server, scopes, reservations, and
class options
• DNS Servers
• DNS Name
• WINS Servers
• Default Gateway

19. What Are DHCP Class-Level Options?
DHCP class-level options are scope options that apply to a
specific type of device
DHCP class-level
option
Description
Vendor-class
Configured by vendors such as
Microsoft, HP, and Sun
User-class Set and viewed by the user

20. How DHCP Options Are Applied
DHCP options can be applied at various levels:
• Server
• Scope
• Reserved client
• Class

21. Demonstration: How to Configure DHCP Options
This demonstration shows how to:
• Configure scope options
• Configure server options
• Create a user class for options
• Enable scope and configure client computer user class

22. Lesson 4: Managing a DHCP Database
• Overview of DHCP Management Scenarios
• DHCP Server Configuration Options
• What Is a DHCP Database?
• How a DHCP Database Is Backed Up and Restored
• How a DHCP Database Is Reconciled
• Moving a DHCP Database
• Demonstration: How to Manage a DHCP Database

23. Overview of DHCP Management Scenarios
Scenarios for managing DHCP:
The DHCP service needs to be managed to respond to
network changes
• Managing DHCP database growth
• Protecting the DHCP database
• Ensuring DHCP database consistency
• Adding clients
• Adding new network service servers
• Adding new subnets

24. DHCP Server Configuration Options

25. What Is a DHCP Database?
• Windows Server 2003 stores the DHCP database in the
%Systemroot%System32Dhcp folder
• The DHCP database files include:
• Dhcp.mdb
• Dhcp.tmp
• J50.log and J50*.log
• Res*.log
• J50.chk
The DHCP database is a dynamic database that contains
configuration information
• The DHCP database contains DHCP configuration data such as:
• Scopes
• Address leases
• Reservations

26. How a DHCP Database Is Backed Up and Restored
DHCP
Server
DHCP
DHCP
Offline
Storage
The DHCP service automatically backs up the DHCP
database to the backup directory on the local drive
If the original database is unable to load, the DHCP
service automatically restores from the backup
directory on the local drive
The administrator moves a copy of the backed up
DHCP database to an offline storage location
In the event that the server hardware fails, the
administrator can restore only from the offline
storage location
Back up Restore
Back up
Restore

27. How a DHCP Database Is Reconciled
Example
Registry DHCP Database After Reconciliation
Client has IP address
192.168.1.34
IP address 192.168.1.34
is available
Lease entry is created in
DHCP Database
DHCP Server
DHCP
Database
Registry Summary IP
address lease
information
Detailed IP
address lease
information
Compares and
reconciles
inconsistencies in
the DHCP Database

28. Moving a DHCP Database
DHCP
Database
Old DHCP
Server
New DHCP
Server
DHCP
Database
Backup
Media

29. Demonstration: How To Manage a DHCP Database
This demonstration shows how to:
• Examine the backup interval
• Back up the DHCP database
• Reconcile the scope data

30. Lesson 5: Monitoring and Troubleshooting DHCP
• Overview of Monitoring DHCP
• Common DHCP Issues
• What Are DHCP Statistics?
• What Is a DHCP Audit Log File?
• Monitoring DHCP Server Performance
• Demonstration: How to Monitor DHCP

31. Overview of Monitoring DHCP
Why monitor DHCP?
• To observe the dynamic DHCP environment
• To determine DHCP server performance
• To facilitate planning for current and future needs
DHCP data includes:
• DHCP statistics
• DHCP events
• DHCP performance data

32. Common DHCP Issues
• Address conflicts
• Failure to obtain a DHCP address
• Address obtained from incorrect scope
• DHCP database suffered data corruption or loss
• DHCP server has exhausted its IP address pool

33. What Are DHCP Statistics?
DHCP statistics are collected at either the server level or
scope level
DHCP Server

34. What Is a DHCP Audit Log File?
A DHCP audit log is a log of service-related events

35. Monitoring DHCP Server Performance
• Create a DHCP performance baseline
• Check the standard counters for
server performance
• Review DHCP server counters for significant
changes in DHCP traffic
Performance
counters
What to look for after a
baseline is established
Packets
received/second
Monitor for sudden increases or decreases, which
could reflect network problems
Requests/second
Monitor for sudden increases or decreases, which
could reflect network problems
Active queue
length
Monitor for sudden and gradual increases, which
could reflect increased load or decreased server
capacity
Duplicates
dropped/second
Monitor for any activity that could indicate that
more than one request is being transmitted on
behalf of clients

36. Demonstration: How to Monitor DHCP
This demonstration shows how to:
• View server statistics
• View the log files
• Use Network Monitor to monitor DHCP

37. Lesson 6: Configuring DHCP Security
• Preventing an Unauthorized User from Obtaining a Lease
• Restricting Unauthorized, Non-Microsoft DHCP Servers
from Leasing IP Addresses
• Restricting DHCP Administration

38. Preventing an Unauthorized User from Obtaining
a Lease
To prevent an unauthorized user from obtaining
a lease:
• Ensure that unauthorized persons do not have
physical or wireless access to your network
• Enable audit logging for every DHCP server
on your network
• Regularly check and monitor audit log files
• Use 802.1X-enabled LAN switches or wireless
access points to access the network
• Configure NAP to validate users and security
policy compliance

39. Restricting Unauthorized, Non-Microsoft DHCP
Servers from Leasing IP Addresses
To eliminate an unauthorized DHCP server, you
must locate and disable it from communicating on
the network either physically or by disabling the
DHCP service

40. Restricting DHCP Administration
To restrict who can administer the DHCP service:
• Limit the members of the DHCP Administrators group
• Add users needing read-only access to the
DHCP Users group
Account Permissions
DHCP Administrators group
Can view and modify any data about the
DHCP server
DHCP Users group
Has read-only DHCP console access to
the server

41. Lab: Configuring and Troubleshooting the DHCP
Server Role
• Exercise 1: Selecting a Suitable DHCP Configuration
• Exercise 2: Implementing DHCP
• Exercise 3: Reconfiguring DHCP
• Exercise 4: Testing the Configuration
• Exercise 5: Troubleshooting DHCP Issues
Estimated time: 75 minutes
Logon information
Virtual machines
6421B-NYC-DC1
6421B-NYC-RTR
6421B-NYC-SVR2
6421B-NYC-CL2
User name ContosoAdministrator
Password Pa$$w0rd

42. Lab Scenario
Contoso is deploying DHCP to their branch offices. Fault
tolerance is important, and you are tasked with configuring
the DHCP services in the head office and branch offices to
support the requirements.

43. Lab Review
• In the lab, you configured the router with the DHCP Relay
agent. What does the agent do?
• In the lab, you configured a scope for the branch office
computers on each of two DHCP servers to provide for
fault tolerance. What would happen to clients that
renewed when both DHCP servers were unavailable?

44. Module Review and Takeaways
• Review Questions
• Tools