Physically my setup looks like this:
┌──────┐ ether3┌────────┐
│Switch├────────────┤750UP r2│
└─┬──┬─┘ └──┬───┬─┘
│ │ │ │ether1
┌─────────┐ │ │ │ │ ┌────┐
│DSL Modem├──┘ │ │ └───┤PC 2│
└─────────┘ │ │ └────┘
│ │ether2
┌────┐ │ │ ┌────┐
│PC 1├─────┘ └───────┤PC 3│
└────┘ └────┘
I put ether1, 2 and 3 in a bridge and set this bridge as the interface for the PPPoE client. This works fine. Just for good measure I’d like to prevent PC 2 and 3 to make PPPoE connections. (Obviously nothing can be done about PC 1.)
I tried setting the interface of the PPPoE client to ether3 but then it says “Client is on slave interface”.