Setting up an adsl modem as a gateway of last resort?

Question

Computer networks

There are some vlan'ov routed by Cisco SG300. The tsiska has a "last resort" gateway on .0.2/24 (vlan10), on which the Zyxel P660RT3 adsl modem hangs. The port into which this modem is plugged in is configured as access for vlan 10. The modem pings from the cisco, the Internet does not. From any machine from other than the tenth vlan'a the modem does not respond. There is no Internet. Nothing at all was configured on the modem, except for the PPoE connection to the Internet and the ip-address of the modem itself.
Task: to provide network access to the Internet. In short, the execution logic seems to me like this: traffic arrives at the cisco, if the traffic does not go to any of the vlans, it is sent to the "last resort" gateway, i.e. to the adsl modem, which takes this traffic to the Internet.
How to implement? Configs, if needed, will be tomorrow.

Answer 1

Well probably at least it is necessary to specify on the modem routes to grids in other VLANs?