Tagged or Untagged Port for a IP phone server

YiHsien · December 2023

Hi all,

My office has a NEC SL2100 phone system, and we have created a VLAN (VLAN ID=2) for it.

All IP phone are at tagged port and the phone server is at a untagged port with PVID=2. And this server's port is excluded/prohibited from all other VLANs.

I found that the phone cannot connect to its server if I change the server's port from untagged to tagged. I am just so curious that why the connection will only work when server's port is untagged. I thought it will work no matter it is a tagged or untagged port.

Could anyone clarify this for me?

Thank you very much.

Zyxel_Melen · December 2023

Hi @YiHsien,

According to your result I found that the phone cannot connect to its server if I change the server's port from untagged to tagged, It seems your server is a VLAN-aware device that has a VLAN 2 interface. If the server receives a packet without a VLAN tag, it will not be sent to VLAN 2 interface but to another interface without VLAN.

YiHsien · December 2023

Thanks Melen,

Our server works with untagged port.

I am confused that why a a VLAN-aware device will only work under a untagged port? (it doesn't work under a tagged port)

Thanks again.

Zyxel_Melen · December 2023

Hi @YiHsien,

Please allow me to rephrase my previous explanation since I misinterpreted your description. Since your phone can reach the phone server when the switch port is untagged, this seems your server is a VLAN-unaware device. When it receives a packet with a VLAN tag, it will ignore this packet. If you want the phone server to handle the VLAN tag packet, the server's NIC needs to support VLAN.

YiHsien · December 2023

Hi Melan,

Thank you for reply.

Do you mean since the server is a VLAN-unaware device, it can only be connected to a untagged port (because if it receives a packet with a VLAN tag, that packet will be ignored so the connection will fail)?

Zyxel_Melen · December 2023

Hi @YiHsien,

Yes, the server seems like a VLAN-unaware device, so, it can only be connected to an untagged port.

Tagged or Untagged Port for a IP phone server

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