if Test Table

1.3.6.1.2.1.31.1.3

This table contains one entry per interface. It defines objects which allow a network manager to instruct an agent to test an interface for various faults. Tests for an interface are defined in the media-specific MIB for that interface. After invoking a test, the object ifTestResult can be read to determine the outcome. If an agent can not perform the test, ifTestResult is set to so indicate. The object ifTestCode can be used to provide further test-specific or interface-specific (or even enterprise-specific) information concerning the outcome of the test. Only one test can be in progress on each interface at any one time. If one test is in progress when another test is invoked, the second test is rejected. Some agents may reject a test when a prior test is active on another interface. Before starting a test, a manager-station must first obtain 'ownership' of the entry in the ifTestTable for the interface to be tested. This is accomplished with the ifTestId and ifTestStatus objects as follows: try_again: get (ifTestId, ifTestStatus) while (ifTestStatus != notInUse) /* * Loop while a test is running or some other * manager is configuring a test. */ short delay get (ifTestId, ifTestStatus) } /* * Is not being used right now -- let's compete * to see who gets it. */ lock_value = ifTestId if ( set(ifTestId = lock_value, ifTestStatus = inUse, ifTestOwner = 'my-IP-address') == FAILURE) /* * Another manager got the ifTestEntry -- go * try again */ goto try_again; /* * I have the lock */ set up any test parameters. /* * This starts the test */ set(ifTestType = test_to_run); wait for test completion by polling ifTestResult when test completes, agent sets ifTestResult agent also sets ifTestStatus = 'notInUse' retrieve any additional test results, and ifTestId if (ifTestId == lock_value+1) results are valid A manager station first retrieves the value of the appropriate ifTestId and ifTestStatus objects, periodically repeating the retrieval if necessary, until the value of ifTestStatus is 'notInUse'. The manager station then tries to set the same ifTestId object to the value it just retrieved, the same ifTestStatus object to 'inUse', and the corresponding ifTestOwner object to a value indicating itself. If the set operation succeeds then the manager has obtained ownership of the ifTestEntry, and the value of the ifTestId object is incremented by the agent (per the semantics of TestAndIncr). Failure of the set operation indicates that some other manager has obtained ownership of the ifTestEntry. Once ownership is obtained, any test parameters can be setup, and then the test is initiated by setting ifTestType. On completion of the test, the agent sets ifTestStatus to 'notInUse'. Once this occurs, the manager can retrieve the results. In the (rare) event that the invocation of tests by two network managers were to overlap, then there would be a possibility that the first test's results might be overwritten by the second test's results prior to the first results being read. This unlikely circumstance can be detected by a network manager retrieving ifTestId at the same time as retrieving the test results, and ensuring that the results are for the desired request. If ifTestType is not set within an abnormally long period of time after ownership is obtained, the agent should time-out the manager, and reset the value of the ifTestStatus object back to 'notInUse'. It is suggested that this time-out period be 5 minutes. In general, a management station must not retransmit a request to invoke a test for which it does not receive a response; instead, it properly inspects an agent's MIB to determine if the invocation was successful. Only if the invocation was unsuccessful, is the invocation request retransmitted. Some tests may require the interface to be taken off- line in order to execute them, or may even require the agent to reboot after completion of the test. In these circumstances, communication with the management station invoking the test may be lost until after completion of the test. An agent is not required to support such tests. However, if such tests are supported, then the agent should make every effort to transmit a response to the request which invoked the test prior to losing communication. When the agent is restored to normal service, the results of the test are properly made available in the appropriate objects. Note that this requires that the ifIndex value assigned to an interface must be unchanged even if the test causes a reboot. An agent must reject any test for which it cannot, perhaps due to resource constraints, make available at least the minimum amount of information after that test completes.