Corosync and unmanaged switch?

Dec 8, 2022
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I'm setting up a dedicated NIC on my nodes for corosync only. I'll be creating a vlan just for corosync. My question is more a networking hardware question to fill in the gap in my understanding as I'd like to be certain.

If I connect an unmanaged switch to a port in my managed switch that connects only to the corosync vlan, will all my nodes talk directly to each other on that switch, not needing to hop back to the switch before it?

My intent is for this switch to only handle the corosync connection and nothing else.

I can put a small managed switch instead for this, but would rather keep it is simple as possible.

Thanks in advance for filling in the gap of my networking hardware knowledge.
 
These are my thoughts about this:
  1. Many unmanaged switches don't support VLAN headers and don't forward or cut the VLAN headers.
  2. You could assign an IP address to the new Interface without VLAN and change the corosync config to the News IPs.
  3. The unmanaged switch should be able to Run disconnected from your managed switch.
  4. If you still want to connect it to your managed switch and it doesn't support VLAN, you can set the default VLAN for the one port at your managed to your unmanaged switch to the new VLAN ID. Thus all devices behind will communicate without VLAN headers. But if they send packages to the managed network they will get the new VLAN header.
 
These are my thoughts about this:
  1. Many unmanaged switches don't support VLAN headers and don't forward or cut the VLAN headers.
  2. You could assign an IP address to the new Interface without VLAN and change the corosync config to the News IPs.
  3. The unmanaged switch should be able to Run disconnected from your managed switch.
  4. If you still want to connect it to your managed switch and it doesn't support VLAN, you can set the default VLAN for the one port at your managed to your unmanaged switch to the new VLAN ID. Thus all devices behind will communicate without VLAN headers. But if they send packages to the managed network they will get the new VLAN header.
Hey,
Thanks for taking the time. I was actually planning to do it the way you mention in option 4. I pretty much assumed that was the necessary way to have that unmanaged switch handle traffic on the other VLAN. My question was more, as I don't just want to assume my own knowledge, whether devices connected on an unmanaged switch will directly communicate over that switch without sending traffic back to the main switch first to determine that they are all located on the unmanaged switch.

As for option 3, I had thought about that and wondered if that would actually work. I assume no reason corosync needs actual internet, really just needs to be able to communicate directly with each other.

I will say, a small managed switch is cheap, I just didn't want to eat up an unnecessary IP on my network, but it does seem like a rather foolish concern in truth. I'm no where near running out of licenses.
 
Hi, I can tell you: Option 3 works! But consider to use a second switch as a fallback:
https://pve.proxmox.com/wiki/Cluster_Manager#pvecm_redundancy
best regards

Thank you for confirming option 3 works. This would actually be the third fallback switch (though technically the first switch as I'll be putting it as Ring0).

So would I just assign each device an IP on that NIC in the interface config as though it was connected to an actual network with DHCP? Just give them addresses in say 192.168.3.x which is currently an unused subnet I was going to use for this?
 

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