WAN disconnects if connected to a LAN without internet

I'm trying to use a NanoPi with OpenWrt 21 installed just as a test device, with double nat.

When I connect the WAN port to a LAN without internet access (fordidden by a rule of the primary router), then the WAN interface comes up and gets an ip via dhcp.
After some seconds it disconnects, and connects again after some more seconds.

When I connect the WAN port to a LAN with internet access it stays connected.

Looks like there is a kind of watchdog, which is restarting the interface if it did not get a response from a external server...

How to switch off this unwanted behavior?


disconnects how ?

an IP assigned via DHCP cannot be revoked, so it would mean some kind of physical change, like network cable or port.

No. I would rule that out.
Same cable works with other subnet without problems.
And connecting a raspi instead of the nanopi unsing the same switch-port and the same works without any problems.

On the nanopi I see, that the connection is lost (no ip) and after a few seconds after an dhcp request the connection is establisehd again.

What is in the logs?

mea culpa

After changing the WAN to static IP, the NanoPi was unresponsive.
Then I realized that there was defined another interface with another VLAN, but the same subnet.

Sitching off this interface the NanoPi gets responsive again. Also switching back from static ip to dhcp client works like a charm.

Maybe a error message could have prevented my inability.

Sorry for your inconvenience.

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