Is there any information in the user manual about this for the DGS?
According to
this manual:
- VLANs, see pages 24ff
- Link aggregation, see page 32
Looks like LACP isn't supported, hence you have to configure a static LAG.
The VLAN configuration for any port that is a member of the LAG must be identical! Just configure any port of the LAG to be a tagged member of any of the three desired VLANs. Set the PVID value of any LAG member port to a dummy VLAN that is different from any of the three VLANs (PVID doesn't matter here, because there is no untagged ingress traffic to the LAG member ports).
For VLANs use 802.1Q and don't activate "Port-Based VLAN"