DHCP Events Test

DHCP provides an automated way to distribute and update IP addresses and other configuration information on a network. When you deploy Dynamic Host Configuration Protocol (DHCP) servers on your network, you can automatically provide client computers and other TCP/IP based network devices with valid IP addresses. You can also provide the additional configuration parameters these clients and devices need, called DHCP options, that allow them to connect to other network resources, such as DNS servers, WINS servers, and routers.

DHCP is a client-server technology that allows DHCP servers to assign, or lease, IP addresses to computers and other devices that are enabled as DHCP clients. With DHCP, you can do the following:

  • Lease IP addresses for a specific amount of time to DHCP clients, and then automatically renew the IP addresses when the client requests a renewal.
  • Update DHCP client parameters automatically by changing a server or scope option at the DHCP server rather than performing this action individually on all DHCP clients.
  • Reserve IP addresses for specific computers or other devices so that they always have the same IP address and also receive the most up-to-date DHCP options.
  • Exclude IP addresses or address ranges from distribution by the DHCP server so that these IP addresses and ranges can be used to statically configure servers, routers, and other devices that require static IP addresses.
  • Provide DHCP services to many subnets, if all routers between the DHCP server and the subnet for which you want to provide service are configured to forward DHCP messages.
  • Configure the DHCP server to perform DNS name registration services for DHCP clients.
  • Provide multicast address assignment for IP-based DHCP clients.

A DHCP client initiates a conversation with a DHCP server when it is seeking a new lease, renewing a lease, rebinding, or restarting. The DHCP conversation consists of a series of DHCP messages passed between the DHCP client and DHCP servers. In an environment where the Citrix NetScaler VPX/MDX is deployed, the DHCP client-server communication happens via the NetScaler appliance. Whenever communication between a DHCP client and a DHCP server suffers a setback, say for example, a DHCP client cannot renew the acquired lease as the DHCP server that provided the original lease is offline, then, the NetScaler appliance is required to initiate a communication between the DHCP client and another DHCP server. If the DHCP client has to wait for a longer period to acquire a lease, then the DHCP client jmay move out of the network by releasing its lease. If too many DHCP clients face difficulty in acquiring a lease or renewing the lease, then severe bottlenecks will be detected in the communication between the DHCP client and DHCP server. To proactively detect such communication failure, administrators can use the DHCP Events test!

This test scans the syslog file for the communication between a DHCP client and DHCP server via the NetScaler and reports the number of times the DHCP server has sent an invalid setting in lieu of a DHCP request; the number of times a lease was acquired and released by a DHCP client and the number of times a Policy Based Routing policy is still dependent on a leased IP even after the release of the lease. Using this test, administrators can analyze the communication between the DHCP server and DHCP client, identify if there are any performance bottlenecks between the DHCP client and server and rectify the same.

For this test to run and report metrics, the NetScaler appliance should be configured to create a Syslog file in a remote Syslog server, where the details of all interactions with the NetScaler appliance will be logged. To know how to configure a remote Syslog server for the use of the NetScaler appliance, refer to Creating a Syslog file in a remote Syslog server topic.

This test is disabled by default. To enable the test, follow the Agents -> Tests -> Enable/Disable menu sequence in the eG administrative interface, pick Citrix NetScaler VPX/MPX as the Component type, select Performance as the Test type, choose this test from the list of disabled tests list, and click on the < button.

Target of the test : A NetScaler VPX/MPX

Agent deploying the test : A remote agent

Outputs of the test : One set of results for the NetScaler appliance being monitored.

Configurable parameters for the test
Parameter Description

Test Period

How often should the test be executed

Host

The IP address of the host for which the test is being configured.

Port

The port at which the host listens. By default, this is NULL.

Log File Path

This test reports metrics by parsing a Syslog file. Specify the full path to the Syslog file here.

Search String

By default, the Syslog file may contain information relating to a number of servers that are inter linked with the target NetScaler appliance. In order to obtain the metrics of the target NetScaler appliance alone, specify the hostname or the IP address of the target NetScaler appliance for which the logs are to be read from the syslog file, in the Search String text box. Using this search string the information in the Syslog file may be parsed and metrics may be collected.

Search String Index

Here, specify the cursor position after which the eG agent should search for the specified Search String (or the position upto which the eG agent should ignore while searching for the specified Search String) in the syslog file. For example, if the specified Search String appears in the syslog file at the 17th position, then you may need to specify the Search String as 16.

DD Frequency

Refers to the frequency with which detailed diagnosis measures are to be generated for this test. The default is 1:1. This indicates that, by default, detailed measures will be generated every time this test runs, and also every time the test detects a problem. You can modify this frequency, if you so desire. Also, if you intend to disable the detailed diagnosis capability for this test, you can do so by specifying none against DD Frequency.

Detailed Diagnosis

To make diagnosis more efficient and accurate, the eG Enterprise suite embeds an optional detailed diagnostic capability. With this capability, the eG agents can be configured to run detailed, more elaborate tests as and when specific problems are detected. To enable the detailed diagnosis capability of this test for a particular server, choose the On option. To disable the capability, click on the Off option.

The option to selectively enable/disable the detailed diagnosis capability will be available only if the following conditions are fulfilled:

  • The eG manager license should allow the detailed diagnosis capability
  • Both the normal and abnormal frequencies configured for the detailed diagnosis measures should not be 0.
Measurements made by the test
Measurement Decription Measurement Unit Interpretation

DHCP server acquires a lease

Indicates the number of times the DHCP client acquired a lease.

Number

A DHCP-enabled client obtains a lease for an IP address from a DHCP server. Before the lease expires, the DHCP server must renew the lease for the client or the client must obtain a new lease. Leases are retained in the DHCP server database approximately one day after expiration. This grace period protects a client's lease in case the client and server are in different time zones, their internal clocks are not synchronized, or the client is off the network when the lease expires.

DHCP server releases a lease

Indicates the number of times the DHCP client released a lease.

Number

The DHCP client acquires a lease for an IP address from the DHCP server and configures its TCP/IP properties by using the DHCP option information in the reply received from the DHCP server, and completes its initialization of TCP/IP. The IP address obtained as lease from the DHCP server remains allocated to the client until the client manually releases the address, or until the lease time expires after which the DHCP server cancels the lease. Mostly, the DHCP client releases a lease when moving to a different network. A high value for this measure therefore may indicate that the DHCP clients are moving away from the network or the DHCP server is currently offline.

DHCP lease is released and a PBR is dependent on the lease IP

Indicates the number of times the DHCP client released a lease while a Policy Based Routing (PPBR) is still dependent on the leased IP.

Number

PBR is a concept that closely relates to Access Control List (ACL) on a NetScaler appliance. PBR can be leveraged to take routing decision (next hop router) based on certain criteria such as Source IP, Source Port, Destination IP, Destination Port, Protocol, Interface, VLAN and Source MAC. Using PBR, a NetScaler appliance can either ALLOW or DENY access to network packets.

DHCP server sends an invalid setting

Indicates the number of times the DHCP server sent an invalid setting.

Number

The DHCP client acquires a lease from the DHCP server and configures its TCP/IP properties by using the DHCP option information in the reply received from the DHCP server, and completes its initialization of TCP/IP. In rare cases, a DHCP server might return a negative acknowledgment to the client. This can happen if a client requests an invalid or duplicate address. If a client receives a negative acknowledgment (DHCPNack), the client must begin the entire lease process again.

This measure is a good indicator of a conflict in communication between the DHCP client and DHCP server.