6.3.6. Selective Clock Acceleration Mechanism (original) (raw)

Connected: An Internet Encyclopedia
6.3.6. Selective Clock Acceleration Mechanism

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6.3.6. Selective Clock Acceleration Mechanism

The definition of the SNMPv2 security protocols requires that, if either of the timestamp values for the originating or receiving parties on a received, validated message exceeds the corresponding local notion of the clock for that party, then the local notion of the clock for that party is adjusted forward to correspond to said timestamp value. This mechanism is neither strictly necessary nor sufficient to the security of the protocol; rather, it fosters the clock synchronization on which valid message delivery depends - thereby enhancing the effectiveness of the protocol in a management context.

    if (msgIsValidated) {
           if (timestampOfReceivedMsg >
                 party->localNotionOfClock) {
                 party->localNotionOfClock =
                       timestampOfReceivedMsg;
           }
    }

The effect of this mechanism is to synchronize local notions of a party clock more closely in the case where a sender's notion is more advanced than a receiver's. In the opposite case, this mechanism has no effect on local notions of a party clock and either the received message is validly delivered or not according to other mechanisms of the protocol.

Operation of this mechanism does not, in general, improve the probability of validated delivery for messages generated by party participants whose local notion of the party clock is relatively less advanced. In this case, queries from a management station may not be validly delivered and the management station needs to react appropriately (e.g., by use of the strategy described in section 5.3). In contrast, the delivery of SNMPv2 trap messages generated by an agent that suffers from a less advanced notion of a party clock is more problematic, for an agent may lack the capacity to recognize and react to security failures that prevent delivery of its messages. Thus, the inherently unreliable character of trap messages is likely to be compounded by attempts to provide for their validated delivery.

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Connected: An Internet Encyclopedia
6.3.6. Selective Clock Acceleration Mechanism