[SOLVED] Can't access Proxmox GUI from another network interface

[0x0C]

Hello,

This is probably a newbie question...

I did all the Proxmox setup using the onboard NIC [vmbr0] (connected to my ISP router) but now I want to virtualize OPNsense. For this I added a 2 port PCIE NIC card to the computer and configured each Ethernet port in its own proxmox virtual bridge ([vmbr10] and [vmbr11]).

I used one of the added virtual bridge [vmbr10] as my WAN in OPNsense and the other virtual bridge [vmbr11] for the OPNsense LAN. Connecting a computer to the LAN works without issues.

But now I would like to disconnect the onboard ethernet [vmbr0] as this connection is redundant with the WAN port.
When I disconnect it, the OPNsense VM still works but I can NOT access the Proxmox GUI anymore.

Reconnecting the onboard ethernet gives back access to the GUI so I still have access to Proxmox to cahnge the configuration but I can't figure out how to make it work without the onboard NIC.

Thanks for your help

PS: sorry if my english is not the best

 

[DC-CA1]

Your default gateway is set on vmbr0 instead of vmbr1 so your default route is sending traffic to vmbr0

 

[0x0C]

Thank you for your answer @DC-CA1
Here is a screenshot of my config, I think my default gateway is defined correctly


And here is a crude schematic of my networks


Situation 1: Red link is connected
- I can access proxmox GUI on PC1 via IPs 192.168.0.95, 192.168.0.97 and 192.168.1.15 => good
- I can access proxmox GUI on PC2 via IPs 192.168.0.95 and 192.168.0.97 => good too

Situation 2: Red link is DISconnected
- I can access proxmox GUI on PC1 via IP 192.168.1.15
- neither PC1 or PC2 have access to proxmox GUI while using IPs 192.168.0.95 and 192.168.0.97 => seems weird

Now that I think of it maybe this is the intended behavior but it seems strange to me

 

[B.Otto]

I suppose the problem lies in the fact that you have two different interfaces with an IP address in the same subnet. That usually causes routing problems, since the routing table is set up as an association 'destination subnet xxx' -> 'send via interface yyy'.

In your case both vmbr0 and vmbr10 have addresses in the subnet 192.168.0.0/24 and that will confuse the routing table. I suppose since the vmbr0 bridge was there first, the association is 'send packets to subnet 192.168.0.0/24 via interface vmbr0' and that will fail if you disconnect the corresponding NIC.

In general never assign two IP addresses of the same subnet to different interfaces. Putting two IP addresses of the same subnet on the same interface is usually okay, though.

 

[0x0C]

I suppose the problem lies in the fact that you have two different interfaces with an IP address in the same subnet. That usually causes routing problems, since the routing table is set up as an association 'destination subnet xxx' -> 'send via interface yyy'.

In your case both vmbr0 and vmbr10 have addresses in the subnet 192.168.0.0/24 and that will confuse the routing table. I suppose since the vmbr0 bridge was there first, the association is 'send packets to subnet 192.168.0.0/24 via interface vmbr0' and that will fail if you disconnect the corresponding NIC.

In general never assign two IP addresses of the same subnet to different interfaces. Putting two IP addresses of the same subnet on the same interface is usually okay, though.

Thank you very much!

Now that you've said it, it's obvious!

I removed the IP address assigned to the onboard nic and it worked right away