Can you provide the configuration of the 3 ports on the switch side and the port configuration on the MX side?
Sounds like there may be a misconfiguration of the ports. Maybe a native vlan mismatch.
Like the others have said, you could simplify your configuration by configuring one port on the switch as a trunk with all the VLANs you need. On the MX side, configure one port similarly. Then you could use one connection to carry three different networks. Just make sure both sides have the same native vlan.
CWNE #210
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