Different Interface OIDs, same IOS

[ronit]

Hello. We have an estate of C9200 switches. They are all running the same IOS version 17.03.04b. Strangely, the interface OIDs for some of them are offset, see example below (Vlan 1 for one of them is in the middle, for the other at the end).

This is wreaking havoc with our NMS

Is this normal, or is it a bug? Is there any way via configuration to freeze the OIDs across the estate?

[marce1000]

 - From  a Cisco viewpoint it is probably not too important and may for instance relate to a vlan(s)(1) being effectively defined and configured/used (or not).

 M.

[ronit]

Aren't the OIDs defined at first boot? If so, shouldn't this be independent of the configuration?

[marce1000]

 - I don't  think so  , because vlan-interfaces can be added and configured after boot (too). Albeit unrelated to initial post , note also that OID's are for instance  generated on devices where line cards can be added or removed , then OID's become kind of 'dynamic'.

 M.

[ronit]

I verified that "interface vlan 1" is created and "shutdown" on all the switches consistently. Also, these are fixed config switches with no support for linecards and modules, so all this is very strange.

[balaji.bandi]

OID is standard, its based in the information available SNMP walk will get it, check the one showing VLAN 1 ( show run config, also show ip interface briend, show interface status  - get is that information showing correct just to validate ?)

[ronit]

Just verified "show vlan", "show ip int brief", they are exactly the same for both switches. What I will do is remove "vlan 1" from the database and also "interface vlan 1" as we don't use this Vlan.

[ronit]

I have a feeling this has something to do with the way the switches were initially stacked. In one case, Vlan 1 appears before the second stack, in the other case Vlan 1 appears after the second stack. Looks like something to do with the sequence.

[ronit]

I found the answer.

Scenario 1

1. We boot up the switches from scratch for the first time, or factory reset the switch using “wr erase” and then reboot
2. After the switch boots up, we connect the stack cables
3. In the above case, Vlan 1 is allocated an OID between Stack unit 1 interfaces and Stack unit 2 interfaces. This is because Switch 1 booted up without switch 2 and allocated Vlan 1 an OID before Switch 2 interfaces were allocated OIDs

Scenario 2

1. We connect the switches via stack cable
2. We boot up the switches from scratch for the first time, or factory reset the switch using “wr erase” and then reboot
3. In the above case, Vlan 1 is allocated an OID after both Stack unit 1 interfaces and Stack unit 2 interfaces. This is because Switch 1 booted up with switch 2 and allocated Switch 2 interfaces a OIDs before Vlan 1 was allocated OIDs

I tested this multiple times and found consistent behaviour. So basically, to get consistently OIDs, all switches in the estate need to follow the exact sequence of first boot+connecting stack cables