General Questions

We have a net48xx where we're trying to implement VLAN's on sis2. We have successfully implemented this on other net48xx devices.
All devices in the subnet behind sis2 are reachable with the interface having a VLAN801 tag when the interface assignment is sis2, but when we change the interface assignment from sis2 to "VLAN801 on sis2" we can no longer reach the subnet.
So, it appears that VLAN tagging isn't working but how do we find out why and fix it?

I assume it's plugged into a switch that supports vlans and is configured correctly ?

if you don't setup vlans and just use the sis2 interface, are the machines reachable ?

Yes, the switches should support the VLAN config.

You're right, when we use sis2 everything works fine but when I set up the VLAN's it all stops....