...because the documentation knows better than you if your ISP needs a VLAN and if your modem supplies it in that case?
There are two cases:
1. your ISP does not need a VLAN - then your use the NIC device without one.
2. your ISP needs a VLAN - then you can do one of two things:
a. if your modem supports it, you can set the VLAN in the modem and your NIC device without VLAN.
b. if your modem does not support it or you do not want to lose modem access via the untagged VLAN, you can use the NIC device with VLAN.
I prefer 2b if needed for the reason given.
There are two cases:
1. your ISP does not need a VLAN - then your use the NIC device without one.
2. your ISP needs a VLAN - then you can do one of two things:
a. if your modem supports it, you can set the VLAN in the modem and your NIC device without VLAN.
b. if your modem does not support it or you do not want to lose modem access via the untagged VLAN, you can use the NIC device with VLAN.
I prefer 2b if needed for the reason given.
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