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FX2S CMC Redundancy
Hi,
I just got myself a refurbished FX2S. It has 2x FC630 and 2x FD332. Networking modules are 2x 8x 1G Passthrough.
That server is hosted in colocation. Because I pay per U, I do not have a switch on site and everything is plugged in the chassis itself. I pushed hyper-converged infrastructure to its limit :-)
One WAN link goes in a port from module A1 to blade server 1 and the other, from module A2 to server 2. I also have a cross-connection between both nodes. I also connected CMC's port 1 to blade server 1 and CMC's port 2 to blade No 2.
CMC is configured for redundancy, but port No2 remains silent as long as port No1 is up. The consequence is that if I can use the CMC and iDrac to remote install blade server No2 from virtual media and reconfigure its BIOS, Perc, etc. I can not do the same for blade No 1.
If I reboot blade No 1, I manage to ping the CMC from server No 2 but only for a few seconds. As soon as physical ports are back up, CMC returns to its port No 1 and start responding only to port blade No1. I tried to force the link down in server No1 but that is not enough for the CMC to detect the link down and do its failover. It is only a logical link down, not a hardware link down.
Is there a way to ensure CMC will answer to any of its ports ? (Active - Active)
If there is no Active - Active configuration, is there a way to prevent CMC from returning to port No 1 after a failover and wait for the next failure before switching back to its port 1 ?
Any other idea about how I can plug / configure this to be able to access CMC and iDrac from any of the blade and do it all remotely ?
Thanks for your help,
Heracles31336d93
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August 21st, 2024 19:04
Thanks for your input Erman and here is the result for anyone who would like to do black magic like I did :
1-It is possible to get access to both ports of the CMC in an active-active config
But you are warned : it is risky and should you get it wrong, you can loose access to the CMC, the entire server or can even bring down the entire network. Only physical access to the hardware will let you fix the mess by unplugging one port.
2-When configured in stacking mode, the 2 ports end up configured as a dummy Ethernet hub like you had in the old 1990s
As such, whatever comes in over one port is copied to the other. That makes both ports active and as such, both are capable of reaching CMC's internal IP
3-To cut any broadcast storm, both ports must be directly connected to a layer 3 device.
That will contain any broadcast and avoid having a broadcast storm
4-To reach the CMC over its unique IP and unique default GW, at least one of the layer 3 device must do NAT OR both devices must join to present a virtual IP as a default GW for the CMC
Using 2 firewalls here. First one is just routing while second one is NATing when reaching the CMC. That way, return packets will go through the right firewall. If reaching the CMC over first NIC, the CMC sees the real client IP address. If reaching over the 2nd firewall, CMC sees the firewall's IP address.
Again, this is at your own risk but if done properly, you will get active-active connection to the CMC.
(edited)
DELL-Erman O
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August 20th, 2024 09:16
Hello,
As I know FX2/FX2s can’t run in active-active mode. It works in active-passive mode, meaning one port is active while the other is on standby. The CMC redundancy isn’t made for active-active use, so it will always switch back to Port 1 after recovery. The ‘logical link down’ issue you’re seeing won’t cause a failover. To ensure reliable failover, use out-of-band management options when you can.
Hope that helps!
Heracles31336d93
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August 20th, 2024 20:48
Hi Erman,
Thanks for your answer. I just had another idea : should I switch the CMC 2nd port back to stacking mode, would it work ? There would be no broadcast storm because each port will be plugged in a NIC that goes nowhere. Would that allow me to reach the CMC from either port ?
DELL-Erman O
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August 21st, 2024 14:18
Hi, so from what I understand, you are thinking of putting the second port of the CMC in stacking mode, even if it is not connected to anything. This could be a neat trick. It could give you access to the CMC from both ports.I think this could work in theory, but I haven't tried it in practice. But be careful. Different CMCs can behave differently.