anchor.diff:  
             with subtest("Wait until we have an ip address on each interface"):
                 client.wait_until_succeeds("ip addr show dev eth1 | grep -q '192.168.1'")
  +
  +          with subtest("ensure MTU is set"):
  +              assert "mtu 1343" in client.succeed("ip link show dev eth1")
   
             with subtest("Test vlan 1"):
                 client.wait_until_succeeds("ping -c 1 192.168.1.1")
  
positive.code:           ipv4.addresses = [ { address = "192.168.1.1"; prefixLength = 24; } ];
            ipv6.addresses = [ { address = "2001:1470:fffd:2096::"; prefixLength = 64; } ];
            virtual = true;
          };
          networking.interfaces.tun0 = {
            ipv4.addresses = [ { address = "192.168.1.2"; prefixLength = 24; } ];
            ipv6.addresses = [ { address = "2001:1470:fffd:2097::"; prefixLength = 64; } ];
            virtual = true;
          };
        };
  
  
negative.code:           useDHCP = false;
            interfaces.eth1 = {
              ipv4.addresses = mkOverride 0 [ ];
              mtu = 1343;
              useDHCP = true;
            };
            interfaces.eth2.ipv4.addresses = mkOverride 0 [ ];
  