Not sure if this is a bug in netplan or is expected behavior.

I have tried this using a bare metal computer and also VMware Workstation 14.x and both USB and a PCI WiFi cards have the same Mac address as the Lan card which ends up eventually causing connectivity problems.

On other computers that are running either Windows or Linux the command arp -a will show duplicate Mac addresses, If I remember correctly arp -a immediately after the WiFi connected would show the right Mac but after less than an hour would show the Lan Mac.

I copied and pasted the config file below into the forum and I assure you that I revived no errors after running sudo netplan generate and then sudo netplan apply any formatting errors are due to the forum.

    network:
  version: 2
  renderer: networkd
  ethernets:
    ens33:
        dhcp4: no
        dhcp6: no
        addresses: [192.168.200.99/24, 192.168.200.3/24]
        nameservers:
              addresses: [ 8.8.8.8, 1.1.1.1]

# WiFi Static
network:
  version: 2
  renderer: networkd
  wifis:
    wlx666:
      dhcp4: no
      dhcp6: no
      optional: true
      addresses: [192.168.200.21/24]
      gateway4: 192.168.200.1
      nameservers:
        addresses: [8.8.8.8, 1.1.1.1]
      access-points:
        MyAcessPointSSID:
          password: password123456

EDIT: Adding arp results

Before setup of Wifi on Ubuntu 18.04 server

## Ubuntu 18.04 server
pi11@sml:~$ arp -a
TVremote (192.168.200.221)  at 0c:b3:19(remoed) [ether] on ens33
TV9 (192.168.200.9)         at 94:e9:79(remoed) [ether] on ens33
LEDE (192.168.200.1)        at 30:b5:c2(remoed) [ether] on ens33
Media (192.168.200.101)     at 4c:72:b9(remoed) [ether] on ens33
i5 (192.168.200.105)        at 10:60:4b(remoed) [ether] on ens33

## Windows 10 computer
PS C:\Users\Owner> arp -a 

Interface: 192.168.200.105 --- 0x9
  Internet Address      Physical Address      Type
  192.168.200.1         30-b5-c2(remoed)     dynamic
  192.168.200.9         94-e9-79(remoed)     dynamic
  192.168.200.11        00-0c-29(remoed)     dynamic
  192.168.200.13        20-6a-8a(remoed)     dynamic
  192.168.200.101       4c-72-b9(remoed)     dynamic
  192.168.200.255       ff-ff-ff(remoed)     static

## Openwrt 18.06.1  router/gateway
root@LEDE:~# arp -a
IP address       HW type     Flags       HW address            Mask     Device
192.168.200.12   0x1         0x0         00:00:00(remoed)     *        br-lan
192.168.1.254    0x1         0x0         00:00:00(remoed)     *        wan
192.168.1.1      0x1         0x2         84:1b:5e(remoed)     *        wan
192.168.200.9    0x1         0x2         94:e9:79(remoed)     *        br-lan
192.168.200.11   0x1         0x2         00:0c:29(remoed)     *        br-lan # Ubuntu 18.04 server Lan
192.168.200.105  0x1         0x2         10:60:4b(remoed)     *        br-lan
192.168.200.221  0x1         0x2         0c:b3:19(remoed)     *        br-lan
192.168.1.102    0x1         0x0         00:00:00(remoed)     *        wan
192.168.200.13   0x1         0x2         20:6a:8a(remoed)     *        br-lan
192.168.200.101  0x1         0x2         4c:72:b9(remoed)     *        br-lan  

After setup of Wifi on Ubuntu 18.04 server

## Ubuntu 18.04 server
pi11@sml:~$ arp -a
LEDE (192.168.200.1)         at 30:b5:c2:(remoed) [ether] on ens33
i5 (192.168.200.105)         at 10:60:4b:(remoed) [ether] on ens33
LEDE (192.168.200.1)         at 30:b5:c2:(remoed) [ether] on wlxd666
Media (192.168.200.101)      at 4c:72:b9:(remoed) [ether] on ens33
? (192.168.200.60)           at <incomplete> on ens33
? (192.168.200.60)           at <incomplete> on wlxd666



## Windows 10 computer
PS C:\Users\Owner> arp -a
Interface: 192.168.200.105 --- 0x9
  Internet Address      Physical Address      Type
  192.168.200.1         30-b5-c2-(remoed)     dynamic
  192.168.200.9         94-e9-79-(remoed)     dynamic
  192.168.200.11        00-0c-29-(remoed)     dynamic # Ubuntu 18.04 server Lan
  192.168.200.13        20-6a-8a-(remoed)     dynamic
  192.168.200.21        00-0c-29-(remoed)     dynamic # Ubuntu 18.04 server WiFi
  192.168.200.101       4c-72-b9-(remoed)     dynamic
  192.168.200.175       00-0c-29-(remoed)     dynamic # Ubuntu 18.04 server WiFi
  192.168.200.255       ff-ff-ff-(remoed)     static

## Openwrt 18.06.1  router/gateway
root@FLOWER:~# arp -a
IP address       HW type     Flags       HW address            Mask     Device
192.168.200.12   0x1         0x0         00:00:00:(remoed)     *        br-lan
192.168.1.254    0x1         0x0         00:00:00:(remoed)     *        wan
192.168.1.1      0x1         0x2         84:1b:5e:(remoed)     *        wan
192.168.200.9    0x1         0x2         94:e9:79:(remoed)     *        br-lan
192.168.200.11   0x1         0x2         00:0c:29:(remoed)     *        br-lan # Ubuntu 18.04 server
192.168.200.105  0x1         0x2         10:60:4b:(remoed)     *        br-lan
192.168.200.221  0x1         0x2         0c:b3:19:(remoed)     *        br-lan
192.168.1.102    0x1         0x0         00:00:00:(remoed)     *        wan
192.168.200.13   0x1         0x2         20:6a:8a:(remoed)     *        br-lan
192.168.200.101  0x1         0x2         4c:72:b9:(remoed)     *        br-lan
192.168.200.21   0x1         0x2         00:0c:29:(remoed)     *        br-lan # Ubuntu 18.04 server

After setting this up the Wifi card got another IP address from my DHCP server

pi11@sml:~$ ip -br a | grep wlxd666
wlxd666  UP             192.168.200.21/24 192.168.200.175/24 

pi11@sml:~$ ip link show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: ens33: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
link/ether 00:0c:29:(removed) brd ff:ff:ff:ff:ff:ff
3: wlxd666: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP mode DORMANT group default qlen 1000
link/ether d8:5d:4c:8e:05:2d brd ff:ff:ff:ff:ff:ff
  • Can you please add the output of arp -a of the dupes and also the output of ip link show on the computer with wlx666 and ens33. – Thomas Oct 6 at 9:29
  • Added more info to my original post. as requested thanks for your interest – user221429 Oct 8 at 5:47
  • You did realize that the IP addresses show with arp -a do not match the ones you have configured? That points to that a second method is active to configure your devices like NetworkManager or /etc/network/interfaces. – Thomas Oct 8 at 6:09
  • Network manager is not installed, As far as I know Ubuntu server 18.04 does not come with it When I add a static IP for the wifi I end up with 2 IP's, In this case the one I set and the other it gets from my DHCP server. – user221429 Oct 8 at 21:59

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