Re-assignment of indices

When a router reboots, the SNMP agent on this router often assigns a different index number to a particular instance of one of its interfaces. For example, an interface named Serial1/0.1 has an ifIndex value of 25. Thus, the OID variable

interfaces.ifTable.ifEntry.ifInOctets.25

represents the number of inbound octets received on this Serial1/0.1 interface. Accordingly, a PI tag called tag1 may be configured with an extended descriptor such as:

OID_I=ifInOctets.25

After a router reboot, the Serial1/0.1 interface may be assigned an ifIndex of 31. Therefore, the number of inbound octets received on the interface is now given by the OID

interfaces.ifTable.ifEntry.ifInOctets.31

However, the tag tag1 is still configured with an extended descriptor containing the ifIndex of 25. As a result, tag1 is no longer is collecting data for Serial1/0.1. In addition, it may be difficult to realize that the ifIndex for Serial1/0.1 has changed from 25 to 31.