I have a DSL modem/router with a built-in 4-port LAN switch. The modem/router is used only in bridge mode, so it acts only as a modem not as a router. I have a separate router that connects to it via one of the LAN switch ports. The separate router runs PPPoE to establish internet connectivity through the bridged modem.

Can I safely use the other three ports on the modem as ordinary LAN ports? I know I can use them, because I do, and it all works nicely.

But I don't know if any LAN traffic leaks out through the modem when doing this. Is it even possible for that to happen, given that the modem is just a PPPoE bridge ?

Thanks