OMV server cannot reach remote subnet, but other clients can

Hi,

I've the following configuration: Two routers (AVM Fritz!Box) connected with a VPN tunnel at different locations. In my home network, I've a OMV box (6.9.14-1) with various docker containers where one is Home Assistant and two zigbee2mqtt containers. In my remote network, I've a Zigbee bridge, which feeds sensor data into Home Assistant. Yesterday it worked without issues.

Today, my zigbee2mqtt instance which connects to the remote subnet lost its connection and I cannot get the connection to the Zigbee bridge back online. After an awful lot of searching, I found out that the docker container cannot reach the remote subnet anymore. I don't know why, I made some container upgrades today (portainer and pihole for example). I drilled further and detected that my OMV server is also not able to reach the remote subnet while other clients like my laptop and mobile phones connected to WIFI can. My OMV box is connected by LAN.

My OMV network config is rather simple:

IPv4: DHCP

IPv6: Disabled

DNS: 8.8.8.8

That's it.

Can somebody give me a hint how I can reach the remote subnet? Do I need to enter a static route? I'm confused because the other clients have no issue reaching the remote subnet.

Under Network -> Interfaces -> Edit one cannot enter the gateway when DHCP is selected.

$ ip route show
default via 192.168.178.1 dev eth0 proto dhcp src 192.168.178.48 metric 100 
172.17.0.0/16 dev docker0 proto kernel scope link src 172.17.0.1 
172.18.0.0/16 dev br-a41bf823d8e3 proto kernel scope link src 172.18.0.1 
172.19.0.0/16 dev br-69d1eafa12e0 proto kernel scope link src 172.19.0.1 linkdown 
172.20.0.0/16 dev br-59170f87c8e4 proto kernel scope link src 172.20.0.1 
172.21.0.0/16 dev br-b2103c2c29b1 proto kernel scope link src 172.21.0.1 
172.24.0.0/16 dev br-fd6aca8e7f28 proto kernel scope link src 172.24.0.1 linkdown 
172.28.0.0/16 dev br-f3c82608098a proto kernel scope link src 172.28.0.1 linkdown 
172.30.0.0/16 dev br-eda366c1b1a6 proto kernel scope link src 172.30.0.1 linkdown 
172.31.0.0/16 dev br-a2c8e834d55c proto kernel scope link src 172.31.0.1 
192.168.0.0/20 dev br-f5c788c346d1 proto kernel scope link src 192.168.0.1 
192.168.178.0/24 dev eth0 proto kernel scope link src $OMV_IP 
192.168.178.1 dev eth0 proto dhcp scope link src 192.168.178.48 metric 100 

$ traceroute 192.168.10.1
traceroute to 192.168.10.1 (192.168.10.1), 30 hops max, 60 byte packets
 1  $SERVERHOSTNAME (192.168.0.1)  3067.945 ms !H  3067.600 ms !H  3067.398 ms !H

192.168.178.0 = local network
192.168.10.0 = remote network
192.168.178.48 = OMV

However, I tried...

ip route add 192.168.10.0/24 via 192.168.178.1 dev eth0

...and it works now. Is this persistent?