[j-nsp] Interface Index(ifIndex) changes when router is rebooted

[martin]

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"(http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080134eec.shtml),
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 as 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 other than
monitoring based on interface names?

WBR,
Martin