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DHCP Performance

Updated: November 10, 2008

Applies To: Windows Server 2008

The DHCP service is critical to the success of the network infrastructure. Without properly functioning DHCP servers, IP clients can lose some or all of their ability to access or use the network. Large amounts of RAM and faster disk drives can improve DHCP server performance; therefore, you should evaluate drive access time, the average time of read/write operations, and the RAID configuration. In many cases, the speed of the server's disk drive is more important than other server requirements, such as memory and processor.

Performance monitoring is available on computers running Windows 2000, Windows Server 2003, and Windows Server 2008 operating systems to help monitor DHCP server performance on the network and to evaluate the disk performance.

Windows Server 2008 provides a set of performance counters that can be used to measure and monitor various aspects of DHCP server activity, including:

  • All types of DHCP messages sent and received by the DHCP service.

  • The average amount of processing time spent on each message packet sent and received by the DHCP server.

  • The number of message packets dropped because of internal delays at a DHCP server computer.

To access the DHCP performance counters, you must use System Monitor. By default, the performance monitoring is available after the DHCP service component is installed. The following table describes the counters used to measure DHCP performance.

 

Name Description

Packets Received/sec

The number of message packets received per second by the DHCP server. A large number indicates heavy DHCP-related message traffic to the server.

Duplicates Dropped/sec

The number of duplicated packets per second dropped by the DHCP server. This number can be affected by multiple DHCP relay agents or network interfaces forwarding the same packet to the server. A large number here indicates that either clients are probably timing out too quickly or the server is not responding quickly enough.

Packets Expired/sec

The number of packets per second that expire and are dropped by the DHCP server. When a DHCP-related message packet is internally queued for 30 seconds or more, it is determined to be stale and expired by the server. A large number here indicates that the server is either taking too long to process some packets while other packets are queued and becoming stale, or traffic on the network is too high for the server to manage.

Milliseconds per packet (avg.)

The average time, in milliseconds, used by the DHCP server to process each packet it receives. This number can vary depending on the server hardware and its I/O subsystem. A sudden or unusual increase might indicate a problem, either with the I/O subsystem becoming slower or because of intrinsic processing overhead on the server.

Active Queue Length

The current length of the internal message queue of the DHCP server. This number equals the number of unprocessed messages received by the server. A large number might indicate heavy server traffic.

Conflict Check Queue Length

The current length of the conflict check queue for the DHCP server. This queue holds messages without responses while the DHCP server performs address conflict detection. A large value here might indicate that the Conflict Detection Attempts value was set too high or that there is unusually heavy lease traffic at the server.

Discovers/sec

The number of DHCP discover messages (DHCPDISCOVER) received per second by the server. These messages are sent by clients when they start on the network and obtain a new address lease. A sudden or unusual increase indicates a large number of clients are attempting to initialize and obtain an IP address lease from the server, such as when a number of client computers start at the same time.

Offers/sec

The number of DHCP offer messages (DHCPOFFER) sent per second by the DHCP server to clients. A sudden or unusual increase in this number indicates heavy traffic on the server.

Requests/sec

The number of DHCP request messages (DHCPREQUEST) received per second by the DHCP server from clients. A sudden or unusual increase in this number indicates a large number of clients trying to renew their leases with the DHCP server. This might indicate that scope lease durations are too short.

Informs/sec

The number of DHCP information messages (DHCPINFORM) received per second by the DHCP server. DHCPINFORM messages are used when the server queries the directory service for the enterprise root and when dynamic updates are being performed on behalf of clients by the server.

Acks/sec

The number of DHCP acknowledgment messages (DHCPACK) sent per second by the server to clients. A sudden or unusual increase in this number indicates that a large number of clients are being renewed by the DHCP server. This might indicate that the scope lease durations are too short.

Nacks/sec

The number of DHCP negative acknowledgment messages (DHCPNAK) sent per second by the DHCP server to clients. A very high value might indicate potential network trouble in the form of an incorrectly configured server or clients. When servers are incorrectly configured, one possible cause is a deactivated scope. For clients, a very high value can be caused by computers moving between subnets, such as laptops or other mobile devices.

Releases/sec

The number of DHCP release messages (DHCPRELEASE) received per second by the server from clients. A high value indicates that several clients have found their address to be in conflict, possibly indicating network trouble. Temporarily enabling conflict detection can help in this situation.

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