Question regarding correct VLAN configuration

Hi guys,

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I'm a sysadmin for a SMB and haven't done alot of networking recently.

I have done some research and I think I know hot do do it but I would really appreciate a second opinion.

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At the moment we have a firewall (sophos xg) with 6 interfaces which are all in use.

We have configured VLANS on the switches but not on the firewall.

The connection firewall -> switch is for each VLAN an untagged port on the switch to the firewall port.

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Now I need to create 3 additional VLANs and I'm not sure how to configure it.

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I know I need to create the VLANs on the Firewall and attach them to a port.

But what's about the Port on the switch? I think it needs to stay untagged on the VLAN it already had and tagged with the additional VLANS. Is that correct?

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Thanks in advance