DHCP Monitor

The DHCP monitor checks the availability and response time of DHCP servers.

You assign service level classifications according to the time it takes for the DHCP server to respond to a request from the DHCP monitor, by using either the total, lookup, or response time.

Table 1. DHCP monitor files
Monitor files	Name or Location
Monitor executable	`nco_m_dhcp`
Properties file	$ISMHOME/etc/props/dhcp.props
Rules file	$ISMHOME/etc/rules/dhcp.rules
Log file	$ISMHOME/log/dhcp.log

Guidelines for Configuring the DHCP monitor: The DHCP monitor tests DHCP services by acting as a limited DHCP client. It sends a DHCP INFORM request to the target DHCP server on the same network by using UDP as the transport protocol over an established connection, and awaits a corresponding DHCP ACK from the server. The monitor doesn’t request an IP address, or affect the expiry on existing IP addresses.
Note: Monitored DHCP servers must support DHCP INFORM requests and be RFC2131 compliant.

The DHCP monitor must run as root because it binds to a port less than 1024.

Limitation: The DHCP monitor can’t use any network interface that is configured by using a DHCP client. Instead, configure the monitor to use a network interface whose IP address isn’t assigned dynamically.

Configuring the DHCP Monitor Service Test

Table 2. DHCP monitor configuration
Field	Description
server	The host name of the DHCP server. Example is dhcp1.mycompany.com
localip	The IP address network interface that the monitor uses to perform the test. Example is 192.168.n.n
description	A text field for providing descriptive information on the element. Example is DHCP monitor
port	The port number of the DHCP server and the default value is 67.
localport	The port number that the monitor uses to perform the test and the default value is 68.
timeout	The time, in seconds, to wait for the server to respond and the default value is 30.
retries	The number of times the monitor must retry the connection to the DHCP server before quitting and the default value is 0. Example is 2.
poll	The time, in seconds, between each poll of the server by using the current profile element and default value is 300.
failureretests	The number of times to retest before indicating a failure and the default value is 0.
retestinterval	The time, in seconds, to wait between each retest on failure and the default value is 30.

In addition to the test results common to all elements, the DHCP monitor generates a set of test results that contain data specific to DHCP service tests.

Table 3. DHCP monitor elements
Element	Description
`$clientIP*ClientIp`	The IP address of the host where the monitor is running.
`$lookupTime*`(`LookupTime`)	The time taken to obtain the IP address of the host server.
`$responseTime*ResponseTime`	The time between when the connection is established and the first byte of data is received.
`$retries`	The maximum number of retries, as specified during the monitor configuration.
`$router`	The IP address of the router as returned by the DHCP server.

Status messages

The DHCP monitor provides status messages in the ResultMessage attribute when using IBM® Application Performance Management. These messages indicate the result of the test.

Table 4. DHCP monitor status messages
Message	Description
`Received DHCPACK` `Received DHCPNAK`	A DHCP server responds to the DHCP inform request sent by the monitor.
`This monitor requires root privileges to run`	Log in as root.
`Did not receive valid DHCP MESSAGE`	Unrecognized response from the DHCP server.
`Did not receive valid DHCP MESSAGE TYPE`	Unrecognized response from the DHCP server (`DHCPACK` or `DHCPNAK` expected).
`Invalid transaction ID` `Received response to request not originating from this monitor - ignored`	Received a reply from a DHCP server to a message that didn’t originate from this monitor.
`Unexpected op-code returned`	Received an unexpected message on this port.
`Connection failed`	The server name that is specified is invalid.
`Failed to send request to DHCP server`	The operating system can’t identify specifically why the request might not be sent to the server so returns this status message that indicates a problem with the network.
`No Response from server`	The DHCP server isn’t responding.