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Monitoring a Running Traceroute Test

When traceRouteCtlAdminStatus is successfully set to enabled, the following is done before the acknowledgment of the SNMP Set request is sent back to the client:

  • traceRouteResultsEntry is created if it does not already exist.
  • traceRouteResultsOperStatus transitions to enabled.

For more information, see the following sections:

traceRouteResultsTable

While the test is running, this traceRouteResultsTable keeps track of the status of the test. The value of traceRouteResultsOperStatus is enabled while the test is running and disabled when it has stopped.

The value of traceRouteCtlAdminStatus remains enabled until you set it to disabled. Thus, to get the status of the test, you must examine traceRouteResultsOperStatus.

The traceRouteCtlFrequency variable can be used to schedule many tests for one traceRouteCtlEntry. After a test ends normally (you did not stop the test) and traceRouteCtlFrequency number of seconds has elapsed, the test is started again just as if you had set traceRouteCtlAdminStatus to enabled. If you intervene at any time between repeated tests (you set traceRouteCtlAdminStatus to disabled or traceRouteCtlRowStatus to notInService), the repeat feature is disabled until another test is started and ends normally. A value of 0 for traceRouteCtlFrequency indicates this repeat feature is not active.

traceRouteResultsIpTgtAddr and traceRouteResultsIpTgtAddrType are set to the value of the resolved destination address when the value of traceRouteCtlTargetAddressType is dns. When a test starts successfully and traceRouteResultsOperStatus transitions to enabled:

  • traceRouteResultsIpTgtAddr is set to null-string.
  • traceRouteResultsIpTgtAddrType is set to unknown.

traceRouteResultsIpTgtAddr and traceRouteResultsIpTgtAddrType are not set until traceRouteCtlTargetAddress can be resolved to a numeric address. To retrieve these values, poll traceRouteResultsIpTgtAddrType for any value other than unknown after successfully setting traceRouteCtlAdminStatus to enabled.

At the start of a test, traceRouteResultsCurHopCount is initialized to traceRouteCtlInitialTtl, and traceRouteResultsCurProbeCount is initialized to 1. Each time a probe result is determined, traceRouteResultsCurProbeCount increases by 1. While the test is running, the value of traceRouteResultsCurProbeCount reflects the current outstanding probe for which results have not yet been determined.

The traceRouteCtlProbesPerHop number of probes is sent for each time-to-live (TTL) value. When the result of the last probe for the current hop is determined, provided that the current hop is not the destination hop, traceRouteResultsCurHopCount increases by 1, and traceRouteResultsCurProbeCount resets to 1.

At the start of a test, if this is the first time this test has been run for this traceRouteCtlEntry, traceRouteResultsTestAttempts and traceRouteResultsTestSuccesses are initialized to 0.

At the end of each test execution, traceRouteResultsOperStatus transitions to disabled, and traceRouteResultsTestAttempts increases by 1. If the test was successful in determining the full path to the target, traceRouteResultsTestSuccesses increases by 1, and traceRouteResultsLastGoodPath is set to the current time.

traceRouteProbeResultsTable

Each entry in traceRouteProbeHistoryTable is indexed by five variables:

  • The first two variables, traceRouteCtlOwnerIndex and traceRouteCtlTestName, are the same ones used for traceRouteCtlTable and to identify the test.
  • The third variable, traceRouteProbeHistoryIndex, is a counter, starting from 1 and wrapping at FFFFFFFF. The maximum number of entries is limited by traceRouteCtlMaxRows.
  • The fourth variable, traceRouteProbeHistoryHopIndex, indicates which hop this probe is for (the actual time-to-live or TTL value). Thus, the first traceRouteCtlProbesPerHop number of entries created when a test starts have a value of traceRouteCtlInitialTtl for traceRouteProbeHistoryHopIndex.
  • The fifth variable, traceRouteProbeHistoryProbeIndex, is the probe for the current hop. It ranges from 1 to traceRouteCtlProbesPerHop.

While a test is running, as soon as a probe result is determined, the next probe is sent. A maximum of traceRouteCtlTimeOut seconds elapses before a probe is marked with status requestTimedOut and the next probe is sent. There is never more than one outstanding probe per traceroute test. Any probe result coming back after a probe times out is ignored.

Each probe can:

  • Result in a response from a host acknowledging the probe
  • Time out with no response from a host acknowledging the probe
  • Fail to be sent

Each probe status is recorded in traceRouteProbeHistoryTable with traceRouteProbeHistoryStatus set accordingly.

Probes that result in a response from a host record the following data:

  • traceRouteProbeHistoryResponse—Round-trip time (RTT)
  • traceRouteProbeHistoryHAddrType—The type of HAddr (next argument)
  • traceRouteProbeHistoryHAddr—The address of the hop

All probes, regardless of whether a response for the probe is received, have the following recorded:

  • traceRouteProbeHistoryStatus—What happened and why
  • traceRouteProbeHistoryLastRC—Return code (RC) value of the ICMP packet
  • traceRouteProbeHistoryTime—Timestamp when the probe result was determined

When a probe cannot be sent, traceRouteProbeHistoryResponse is set to 0. When a probe times out, traceRouteProbeHistoryResponse is set to the difference between the time when the probe was discovered to be timed out and the time when the probe was sent.

traceRouteHopsTable

Entries in traceRouteHopsTable are indexed by three variables:

  • The first two, traceRouteCtlOwnerIndex and traceRouteCtlTestName, are the same ones used for traceRouteCtlTable and identify the test.
  • The third variable, traceRouteHopsHopIndex, indicates the current hop, which starts at 1 (not traceRouteCtlInitialTtl).

When a test starts, all entries in traceRouteHopsTable with the given traceRouteCtlOwnerIndex and traceRouteCtlTestName are deleted. Entries in this table are only created if traceRouteCtlCreateHopsEntries is set to true.

A new traceRouteHopsEntry is created each time the first probe result for a given TTL is determined. The new entry is created whether or not the first probe reaches a host. The value of traceRouteHopsHopIndex is increased by 1 for this new entry.

Note: Any traceRouteHopsEntry can lack a value for traceRouteHopsIpTgtAddress if there are no responses to the probes with the given TTL.

Each time a probe reaches a host, the IP address of that host is available in the probe result. If the value of traceRouteHopsIpTgtAddress of the current traceRouteHopsEntry is not set, then the value of traceRouteHopsIpTgtAddress is set to this IP address. If the value of traceRouteHopsIpTgtAddress of the current traceRouteHopsEntry is the same as the IP address, then the value does not change. If the value of traceRouteHopsIpTgtAddress of the current traceRouteHopsEntry is different from this IP address, indicating a path change, a new traceRouteHopsEntry is created with:

  • traceRouteHopsHopIndex variable increased by 1
  • traceRouteHopsIpTgtAddress set to the IP address

    Note: A new entry for a test is added to traceRouteHopsTable each time a new TTL value is used or the path changes. Thus, the number of entries for a test may exceed the number of different TTL values used.

When a probe result is determined, the value traceRouteHopsSentProbes of the current traceRouteHopsEntry increases by 1. When a probe result is determined, and the probe reaches a host:

  • The value traceRouteHopsProbeResponses of the current traceRouteHopsEntry is increased by 1.
  • The following variables are updated:
    • traceRouteResultsMinRtt—Minimum round-trip time
    • traceRouteResultsMaxRtt—Maximum round-trip time
    • traceRouteResultsAverageRtt—Average round-trip time
    • traceRouteResultsRttSumOfSquares—Sum of squares of round-trip times
    • traceRouteResultsLastGoodProbe—Timestamp of the last response

      Note: Only probes that reach a host affect the round-trip time values.

Generating Traps

For any trap to be generated, the appropriate bit of traceRouteCtlTrapGeneration must be set. You must also configure a trap group to receive remote operations. Traps are generated under the following conditions:

  • traceRouteHopsIpTgtAddress of the current probe is different from the last probe with the same TTL value (traceRoutePathChange).
  • A path to the target could not be determined (traceRouteTestFailed).

A path to the target was determined (traceRouteTestCompleted).

For information about how to configure a trap group to receive remote operations, see Configuring SNMP Trap Groups and Example: Setting Trap Notification for Remote Operations.


Published: 2010-04-27

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