[SOLVED] Device in tagged VLAN


currently I'm a bit stuck maybe someone have a nice idea/help for me.

I have the Following setup:

  • IOT Device with a customized LEDE 17.01 on it.
  • Cisco VLAN capable L3 Switch

If i use this setup trough two untagged Network Ports it is working like a charm.
However when I use them trough Tagged Network Ports, my Device cannot set his IP Address.
On the Server side I see the DHCP Discover & Offer messages in logs but the client does not set his IP.
And if a configure the virtual network interface on the device manually, it's also does not working, the interface comes up but i cannot ping at all the router or the server. I have tested lots of configs but i't does not seems to work, i have also read the manual here on this site. Maybe someone has an idea

Currently i use this network configuration:

config interface 'lan'
        option ifname   eth0
        option force_link 1
        option proto    static
        option ipaddr
        option netmask
        option vlan_enable 1
config device 'eth0.21'     
        option name 'eth0.21'
config interface 'eth0.21'  
        option ifname eth0  
        option vid 21        
        option type 8021q    
        option name eth0.21  
config interface 'wan'      
        option ifname   eth0.21
        option proto    dhcp             
        option metric   2

The device has an hardware error....