Interface Index(ifIndex) changes when router is rebooted
It's a well-known "feature" that interface ifindex value will change after certain JUNOS upgrades. However, the same problem is present when one reboots Juniper device- some interfaces will change ifindex value. I have heard it happens with M40, MX960, M7i, with newer switches and probably with other platforms as well and with variety of JUNOS versions . As ifindex value has to be persistent in order to use it for SNMP based monitoring solutions(for example Nagios), this is a very annoying problem 
In Cisco IOS, there is a command snmp-server ifindex persist, which tells IOS to keep ifindex value unchanged even after reboot. In JUNOS, as far as I know, something like this should be built in by design. There is a file /var/db/dcd.snmp_ix, where all the ifindex values are mapped. As /var is mounted to /dev/adX, it should survive reboot. However, still sometimes ifindex values are changed! Any experience/comments with this issue? As this behavior has been present for years, is there finally some sort of fix or workaround?
In Cisco IOS, there is a command snmp-server ifindex persist, which tells IOS to keep ifindex value unchanged even after reboot. In JUNOS, as far as I know, something like this should be built in by design. There is a file /var/db/dcd.snmp_ix, where all the ifindex values are mapped. As /var is mounted to /dev/adX, it should survive reboot. However, still sometimes ifindex values are changed! Any experience/comments with this issue? As this behavior has been present for years, is there finally some sort of fix or workaround?