In Tools->Netwatch add a new host +
Set the IP to monitor in the host field.
Under Down add the vlan to be down/uplike this:
interface/vlan/set vlan10 disabled=yes
interface/vlan/set vlan20 disabled=no
Under Up reverse the down
interface/vlan/set vlan10 disabled=no
interface/vlan/set vlan20 disabled=yes
NB, you can not use an IP that need the vlan to be monitored. How should it then ever enable the vlan.
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Use Splunk> to log/monitor your MikroTik Router(s). See link below. 