1. 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 2

3. Overview of the DHCP Server Role
Benefits of Using DHCP
How DHCP Allocates IP Addresses
How DHCP Lease Generation Works
How DHCP Lease Renewal Works
DHCP Server Authorization

4. Benefits of Using DHCP
DHCP reduces the complexity and amount of administrative work by using automatic TCP/IP configuration
Manual TCP/IP Configuration
Automatic 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
IP addresses are supplied automatically
Correct configuration information is ensured
Client configuration is updated automatically
A common source of network problems is eliminated

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

6. How DHCP Lease Generation Works
DHCP client broadcasts a DHCPDISCOVER packet 1
DHCP servers broadcast a DHCPOFFER packet 2
DHCP client broadcasts a DHCPREQUEST packet 3
DHCP Server1 broadcasts a DHCPACK packet 4
DHCP Client
DHCP Server1
DHCP Server2
DHCP Server2
DHCP Server1
DHCP Client
DHCP client broadcasts a DHCPDISCOVER packet 1
DHCP servers broadcast a DHCPOFFER packet 2
DHCP client broadcasts a DHCPREQUEST packet 3
DHCP Server1 broadcasts a DHCPACK packet 4

7. How DHCP Lease Renewal Works
DHCP Client
DHCP Server1
DHCP Server2
DHCP client sends a DHCPREQUEST packet 1
DHCP Server1 sends a DHCPACK packet 2
50% of lease duration has expired
DHCP Client
DHCP Server1
DHCP Server2
100% of lease duration has expired
50% of lease duration has expired
87.5% of 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
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
DHCP Client sends a DHCPREQUEST packet 1
DHCP Server1 sends a DHCPACK packet 2

8. DHCP Server Authorization
DHCP authorization is the process of registering the DHCP Server service in the Active Directory domain to support DHCP clients
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
DHCP Server1
Authorized
Services DHCP requests
DHCP Server2
Unauthorized
Does not service DHCP requests
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

9. Configuring DHCP Scopes
What Are DHCP Scopes?
What Are Superscopes and Multicast Scopes?
What Is a DHCP Reservation?
DHCP Sizing and Availability

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

11. 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
Workstation 1
File and Print Server
Subnet A
Subnet B
DHCP Server
Workstation 2
IP Address1: Leased to Workstation 1
IP Address2: Leased to Workstation 2
IP Address3: Reserved for File and Print Server

12. DHCP Sizing and Availability
DHCP Clients
DHCP Server1
DHCP Server2
DHCP Sizing and Availability
DHCP Server1 has 80% of addresses as follows:
Scope range:
Excluded addresses:
DHCP Server2 has 20% of addresses as follows:
Excluded addresses:

13. Configuring DHCP Options
What Are DHCP Options?
What Are DHCP Class-Level Options?
How DHCP Options Are Applied

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

15. 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

16. 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

17. DHCP Server Configuration Options

18. Monitoring and Troubleshooting DHCP
Overview of Monitoring DHCP
Discussion: Common DHCP Issues
What Are DHCP Statistics?
What Is a DHCP Audit Log File?
Monitoring DHCP Server Performance

19. 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

20. 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
10 minutes

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

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

23. Monitoring DHCP Server Performance
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
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
Create a DHCP performance baseline
Check the standard counters for server performance
Review DHCP server counters for significant changes in DHCP traffic

24. Configuring DHCP Security
Preventing an Unauthorized Computer from Obtaining a Lease
Restricting Unauthorized, Non-Microsoft DHCP Servers from Leasing IP Addresses
Restricting DHCP Administration

25. Preventing an Unauthorized Computer from Obtaining a Lease
To prevent an unauthorized computer 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

26. Restricting Unauthorized, Non-Microsoft DHCP Servers from Leasing IP Addresses
DHCP Clients
Rogue DHCP server
Legitimate DHCP server
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

27. 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

28. Summary Overview of the DHCP Server Role Configuring DHCP Scopes
Configuring DHCP Options
Managing a DHCP Database
Monitoring and Troubleshooting DHCP
Configuring DHCP Security 35