A conceptual row in the icmpMsgStatsTable.

The system should track each ICMP type value, even if that ICMP type is not supported by the system. However, a given row need not be instantiated unless a message of that type has been processed, i.e., the row for icmpMsgStatsType=X MAY be instantiated before but MUST be instantiated after the first message with Type=X is received or transmitted. After receiving or transmitting any succeeding messages with Type=X, the relevant counter must be incremented.