A conceptual row in the inetIcmpMsgTable. A row with an inetIcmpMsgIfIndex value of zero indicates a system-wide value; a row with a non-zero cInetIcmpMsgIfIndex indicates an interface-specific value. A system may provide both system-wide and interface-specific values, in which case it is important to note that the system-wide value may not be equal to the sum of the interface-specific values across all interfaces due to e.g. dynamic interface creation/deletion. If the system keeps track of individual ICMP code values (e.g. destination unreachable, code administratively prohibited), it creates several rows for each inetIcmpMsgType, each with an appropriate value of cInetIcmpMsgCode. A row with the special value of cInetIcmpMsgCode, 256, counts all packets with type cInetIcmpMsgType that aren't counted in rows with a value of cInetIcmpMsgCode other than 256.