This is normally handled with a router. Fortunately, if your 1234P is second generation with firmware R10.8.0 and higher, you have Layer 3 lite available. Three simple steps:
1. In golbal configuration, turn on routing by issuing a "IP Routing" statement.
2. create vlan interfaces that match the desired vlans that you are using to route traffic and assign an appropriate ip address to the interfaces. Make sure to enable the interface. I sometime forget.
Then you can use the switch's vlan interface IP address as the default gateway for devices on their respective vlans.
3. Finally, add a route 0.0.0.0 /0 with the gateway address of your router for internet access. You may also need to add a route statement in your router so that it is aware of the networks of your vlans. Layer 3 lite on the NetVanta supports static routing, but not any of the routing protocols such as RIP and OSPF.
If your 1234 is first generation, then you will need to rely on a separate router to route traffic from VLAN 10 to 1 & 20. In that case, I would suggest putting one of the switch ports in Trunk Mode, and delivering the vlans to the router (assuming the router has that capability. Almost all of the NetVanta routers do).
I hope this helps.
Thank you. This solved my problem. I was able to upgrade the firmware and turn on the ip routing.