SNMP - Index shuffling
When a device boots up, SNMP assigns a particular index to identify each individual interface on that network device. These indexes are used by SNMP to identify the specific interface for which it’s collecting statistics.
Shuffling of these indexes can occur during a reboot or a minor software upgrade. This is especially true if virtual interfaces, SVIs, tunnels, or loopback interfaces have been configured over the lifetime of the device. When a reboot occurs, the order that the indexes have been assigned may change.
This means that the index previously assigned to a particular interface might be assigned to a different interface after the reboot or upgrade. This can cause confusion and inaccuracies in your network monitoring, as the SNMP manager might collect data for the wrong interface.
The following command can be used to prevent this shuffling:
snmp-server ifindex persist
It causes the device to maintain the indexes assigned to all interfaces ensuring that the same index is assigned back to the same interface even after a reboot or software upgrade, hence maintaining accuracy in your network monitoring. Once this command is issued, it appears in the running config like so:
snmp ifmib ifindex persist