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I am trying to setup a NUC computer (using ubuntu 18.04) such that:

  • ethernet port is connected to a port of a switch set in mirroring mode: The mirroring port only sends mirrored packets, and can't not be used to send from the computer to the network.
  • wifi interface is used for access to the network and internet.

When I set the port in mirroring mode, the computer looses access to the internet as it prioritize the ethernet interface and can't reach the network from that mirrored port.

I tried to use the metrics in the /etc/network/interfaces file to deprioritize the ethernet interface as below:

# interfaces(5) file used by ifup(8) and ifdown(8)
auto lo
iface lo inet loopback

auto eno1
iface eno1 inet static
    address 192.168.1.30
    netmask 255.255.255.0
    gateway 192.168.1.1
    dns-nameservers 192.168.1.1
    metric 700

The wifi interface is managed by NetworkManager. My resulting route is:

user@host: route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         192.168.1.1     0.0.0.0         UG    600    0        0 wlp58s0
0.0.0.0         192.168.1.1     0.0.0.0         UG    700    0        0 eno1
169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 eno1
192.168.1.0     0.0.0.0         255.255.255.0   U     0      0        0 eno1
192.168.1.0     0.0.0.0         255.255.255.0   U     600    0        0 wlp58s0

But when I set the port in mirroring mode, the computer looses connectivity, which I assume is because the destination 192.168.1.0 still has the eno1 interface with highest metric of 0? And I am not sure how to change that.

What I am doing wrong? Is it possible to achieve what I am trying to do? Is the metrics approach the wrong way?

Thanks for any pointers

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