[j-nsp] EX4200 virtual chassis problem, master going into linecard mode

[Victor Sudakov]

Tobias Heister wrote:
> > 
> > Yes, no-split-detection did help.
> 
> I would like to add to that. My point of view is that you do not
> always disable split-detection in a two member VC.  You can do so if
> you know what that implies.
> 
> The reasoning for the remaining node going into LC mode is that only
> the portions of the VC having the majority of nodes stays up and
> operational. In a two member VC if for whatever reason one of the
> nodes looses connection to the other, we cannot have a majority so
> both sides go down. Even if it is the only node remaining.
> 
> But imagine an error scenario where the second node does not crash,
> but for whatever reason both sides stay up, but the connection
> between them gets lost. With split-detection configured, both sides
> will go down and you have a controlled service outage. When no
> split-detection is configured both sides remain up and you might
> have interesting effects happening in your network with two switches
> with the same configuration and same "identity" being up and
> forwarding. I have seen that happening in DC scenarios doing stp to
> other devices and it is not pretty!

Thank you for the explanation. However, in my case I would rather risk
an active/active configuration than have two unresponsive switches
which can only be revived through manual intervention. This is mainly
because:

1. The stacks are in remote locations, you have to ride an all-terrain
vehicle to reach them for manual intervention, or sometimes even a
helicopter.

2. The stack members are located together in one rack, so the most
likely scenarios requiring failover will be a) one switch hardware
failure or b) a failure of one of the UPSes or invertors.

3. An active/active situation can be easily mitigated remotely by
shutting down a port on the uplink.

> 
> So always check the implications of what the command are doing. If
> in your case an active/active split scenario (for worst case) works
> out better than a completely offline VC, that is perfectly fine. I
> have seen lots of scenarios where it would not be the expected or
> wanted behavior. But in my world a VC is no real redundancy method
> it is just stacking-NG for additional ports under one MGMT so i
> would have two VCs if i relay need redundancy in most setups. But
> that is just me ;)

I guess, in my case a completely offline VC is unacceptable.

-- 
Victor Sudakov,  VAS4-RIPE, VAS47-RIPN
AS43859