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ArubaStack - 2 member split-stack situation

I'm configuring several stacks, each with only 2 members.  Per UG's best practice, I am disabling split-stack detection.

If a stack should split, what state (if any) will the primary and secondary transition to?

Will they continue to forward traffic independantly?

Is there any way to configure the secondary with an IP address (other than using the dedicated management interface) to remotely connect in case it splits off?

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Aruba

Re: ArubaStack - 2 member split-stack situation

Thecompnerd,
Stepping back a moment, I thought it might be good to review the behavior of split-detection first then I'll address your two questions.

In the event of a split in an existing ArubaStack, the following detail the behavior of the primary and secondary members after the split:

  1. The ArubaStack that has the most number of members will remain active while the other part (lesser number of members) will become inactive/dormant.
  2. If the ArubaStack is split evenly (meaning both sides contain an equal number of members), the side with both primary and secondary members will remain active.
  3. If the ArubaStack is split evenly (meaning both sides contain an equal number of members) and the primary and secondary members are split to each part, the part with the secondary member will become active while the part with primary becomes inactive/dormant.

So in a two member Arubastack which would only have a primary and secondary switch, we hit clause 3 which per split-detection rules, the primary will go into a dormant state. This may be undesirable as the secondary may actually be the failed switch and the primary still has an uplink to the network. With split-detection disabled as recommend in the UG, both switches would stay active.

Now in a two member stack, we still recommend using both stack ports for redundancy. So for an ArubaStack in this configuration to experience a split would either mean that someone clipped both ArubaStack links or the member's stack ports failed. Both are pretty unlikely or would symptoms of a bigger problem with the switch/ArubaStack. However even if it were to occur, more than likely the uplink off that given member would also go down and so even though both members think they are primary and have the same management IP, more than likely only one would be remotely accessible.

So to answer your second question more specifically, there is not a way to configured the secondary with a secondary management IP address only to become active during a split. The secondary which would now be a primary would just take over the management IP address for the ArubaStack. Again, this would only be an issue if either of the two failures I described above were to happen but all other functions, specifically uplinks, were still operational as it would result in a duplicate management IP.  

Best regards,

Madani

Re: ArubaStack - 2 member split-stack situation

Thanks for the very thorough reply and addressing all of my questions!

Last question. I'd like to setup alerts for any stack issues that may occur such as a stack splitting. Is there some documentation that lists all the sylsog events so I can setup some traps?
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Aruba

Re: ArubaStack - 2 member split-stack situation

Thecompnerd,

We are working on a syslog guide for our upcoming release however I would take a look at the Stacking MIB and traps. We currently have two traps:

 

wlsxStackIfStateChangeTrap
wlsxStackTopologyChangeTrap

 

These would fire off if there was a stacking interface or topology change. Both of which would be symptoms of a problem with the stack.


Best regards,

 

Madani

Guru Elite

Re: ArubaStack - 2 member split-stack situation

We also use splunk to trigger real time reports based on log events. We filter on:

 

ChassisManager ArubaS2500-48P removed

ChassisManager ArubaS2500-24P removed

ChassisManager ArubaS3500-48P removed

ChassisManager ArubaS3500-24P removed


Tim Cappalli | Aruba Security TME
@timcappalli | timcappalli.me | ACMX #367 / ACCX #480

Re: ArubaStack - 2 member split-stack situation

Perfect.  Thanks for the input, guys!

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