SNMP EngineID Changed on version downgrade

wbenton-0 · ‎06-23-2008

I was using a Cisco 2970 running IOS 12.2(44)SE but had to downgrade it to IOS 12.2(25)SEB4 for testing purposes.

In doing so, the SNMP EngineID of the device changed. Only the last 2 bytes changed, but it changed none the less.

Prev Engine ID running 12.2(44)SE was xxxxcc340 but after downgrading to 12.2(25)SEB4, it changed to xxxxcc301.

Is this normal or is this just something special with this device and/or the above listed IOS's?

I inquire because when the SNMP EngineID changes, my configuration for remote engineID also needs to be changed and with that, all users and groups for that device must also be re-created to work with the new EngineID.

Finally, the NMS server must also re-learn the new EngineID as well making it one big PITA.

Is this true for ALL upgrades as well as downgrades regardless of platform or what?

Any info appreciated.

Walt

owillins · ‎06-27-2008

Try to reconfigure or reboot then you will see the same SNMP EngineID .

http://www.cisco.com/en/US/docs/switches/lan/catalyst2960/software/release/12.2_44_se/configuration/guide/swsnmp.html

wbenton-0 · ‎06-29-2008

If I reconfigure the device to use the following

Cisco2970G24(config)#snmp-server engineID local xxxxxxxx340

It WILL accept the new setting and continue to operate normally, or if I re-create the users and groups and get the NMS to re-learn the new engineID, the NMS will operate properly.

And of course, I did a reboot after upgrading! Rebooting DOES NOT set the engineID back to what it used to be. That's why my original post and question. Which by the way is still unanswered.

Is this a common phenomenon with ALL devices or just this one? I'd hate to have to do this for every device we had to upgrade the IOS for.

With hundreds of users and hundreds of devices, it's a burdensome task to have to either re-configure the machine. Regardless of which way is done, re-configuration is required after the upgrade/downgrade.

1) Reconfigure the local engineID to match the one prior to it being upgraded/downgraded.

2) Reconfigure the local users/groups and re-learn the new engineID by the NMS.

Both require a reconfiguration. A process I would prefer NOT to do unless necessary.

Which goes directly back to my initial question of whether this is common amongst all devices and all IOS upgrades or just this particular one?

Note 1: When I re-upgraded the device back to the latest IOS, the engineID went back to it's original number, but the downgraded version had a different engineID... regardless of how many times I rebooted it.

Note 2: If I purposefully configure the device using the local engineID of the actual machine, if the local engineID specified is the same as the actual machine's default engineID... when I perform a show run config, the local engineID configuration is not memorized and not stored because it matches the device's actual default engineID. If however, I change the local engineID to something other than the physical engineID, it is stored and used from then on.

Thus if this is a common phenomenon when upgrading IOS that the engineID changes, then you should store the local specified engineID even if it matches the default engineID. That way, even if the default engineID changes upon an upgrade/downgrade, the local setting would not require a re-configure!!!

Walt

wbenton-0 · ‎07-02-2008

I've included a powerpoint explaining exactly what happens. Rebootingthe device does NOT solve the problem.