Hello all,
Our company recently acquired four Dell N4064F switches. We have two in one COLO facility and two in another, both places the switches are in a stack of two acting as one logical switch. It has come to our attention through testing that the cross stack LACP port-channels connecting the two stacks and connected to our corporate headquarters network temporarily go down when the stack master has a failure (powered down, etc). When one of the switches in the stack goes down, traffic should be able to continue passing through the active link in the LAG, but there is a long pause until the active link starts passing traffic again.
So when this master goes down it looks to be that spanning-tree sees a topology change and begins to go through its calculations. Once the port-channel goes to a forwarding state traffic begins passing again, but not until about 20-30 seconds later.
What I didn't understand about this is why the port-channels connecting to other switches are going down at all. Sure one of the links goes down, but not both which I would think should keep the port-channel link status still up. I came across some forums where people had this same issue with Cisco 3750s and how the command 'stack-mac persistent timer 0' can solve this. Does anyone know if there is something comparable to this on the Dell N4000 series switches? I've opened a case with Dell's support and am still waiting to hear back on it. Below is one of the forums where I found this:
supportforums.cisco.com/.../stack-mac-persistent-timer-lacp-port-channels-c3750