The MTU is only increased between the router and DSL modem to account for PPPoE overhead, so that the MTU inside the PPPoE tunnel (and thus to the internet) can

The MTU is only increased between the router and DSL modem to account for PPPoE overhead, so that the MTU inside the PPPoE tunnel (and thus to the internet) can be a standard 1500 (otherwise it would be 1492).