Re: Connection between Ex4300 and MX security appliance

I assume that the connection between the ex4300 and the ex3300 is a layer 2 trunk port.

So here you would simply add the new VLAN to both switches and include this VLAN on that existing trunk port.

The complications from with the connection from the ex4300 to MX.

I assume this existing connection is a layer 3 routed link with the ip address indicated on both ends and an untagged port.

So the simple solution is to connect a different pair of ports on the ex4300 and MX and use this as a layer 2 connection adding the new vlan here for transit.  This could also be configured as a trunk port to transport future other layer 2 vlans as needed.