RE: Re: ifLastChange

From: Peter Phaal (
Date: 10/01/02

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    Based on your suggestions I've updated SFLOW-DATAGRAM:

    The new text for sequence_number resetting is as follows:

    struct flow_sample {
       unsigned int sequence_number; /* Incremented with each flow sample
                                         generated by this source_id.
                                         Note: If the agent resets the
                                               sample_pool then it must
                                               also reset the sequence_number.*/


    struct counters_sample {
       unsigned int sequence_number; /* Incremented with each counter sample
                                          generated by this source_id
                                          Note: If the agent resets any of the
                                                counters then it must also
                                                reset the sequence_number.
                                                In the case of ifIndex-based
                                                source_id's the sequence
                                                number must be reset each time
                                                changes. */


    > Rather than ifLastChange, I think the more appropriate MIB
    > variable to use
    > would be ifCounterDiscontinuityTime (see RFC 2863, section 3.1.5 for
    > details):
    > ifCounterDiscontinuityTime OBJECT-TYPE
    > SYNTAX TimeStamp
    > MAX-ACCESS read-only
    > STATUS current
    > "The value of sysUpTime on the most recent
    > occasion at which
    > any one or more of this interface's counters suffered a
    > discontinuity. The relevant counters are the specific
    > instances associated with this interface of any
    > Counter32 or
    > Counter64 object contained in the ifTable or ifXTable. If
    > no such discontinuities have occurred since the last re-
    > initialization of the local management subsystem,
    > then this
    > object contains a zero value."
    > ::= { ifXEntry 19 }
    > Requiring the sFlow sample sequence numbers to be reset seems to be an
    > equivalent solution, though. I suggest that it be documented
    > with reference
    > to ifCounterDiscontinuityTime. Essentially, for
    > ifIndex-based data sources,
    > if the value of ifCounterDiscontinuityTime changes, then the
    > counter sample
    > sequence number for the corresponding data source should be reset.
    > Also, I think the phrase "affects the sample_pool" needs some
    > clarification.
    > If I understand the intent correctly, how about saying:
    > Note: If the agent resets the
    > sample_pool value
    > then it must
    > also reset the
    > sequence_number.

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