Why is possible set more VLANS to one port as Untagged?

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Why is possible set more VLANS to one port as Untagged?
Why is possible set more VLANS to one port as Untagged?
2020-03-08 16:41:22 - last edited 2020-03-11 09:06:57
Model: TL-SG108E
Hardware Version: V4
Firmware Version: 20181120

Hi

 

Why is possible set more VLANS to one port as Untagged? I expect only one VLAN can be untagged on one port. 

 

Thanks

 

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Re:Why is possible set more VLANS to one port as Untagged?-Solution
2020-03-10 19:57:45 - last edited 2020-03-11 09:06:57

@PeterK2, it's pretty easy to set up an asymmetric VLAN.

 

The TL-SG108E also has an own menu entry for a pre-defined asymmetric VLAN, it's Multi-Tenant Unit VLAN (MTU VLAN). It works as follows:

 

Let's assume that port 1 is the uplink to the router providing Internet access and ports 2 to 8 are assigned to several tenant units.

The goal is to isolate the tenant units against each other, but to let them share the Internet router.

 

So we assign each port an own VLAN, that's VLAN 1 for port 1, VLAN 2 for port 2, etc.

 

PVID of each port is it's primary VLAN, that's 1 for port 1, 2 for port 2, etc. We achieved isolation between the ports by this setup.

 

Now, we assign ports 2-8 membership in VLAN 1, too, so that they can receive traffic from the Internet router.

To allow the Internet router to receive traffic from the other ports, we assign it membership of all other VLANs, that's 2, 3, 4, 5, 6, 7 and 8.

 

All ports are untagged VLAN members since the connected devices don't use VLAN tags usually (technically they could do so, but it would not make much sense in this setup).

 

Ingress frames on port 7 get tagged with VID=7 (due to the PVID) and will be forwarded to port 1, which is a member of VLAN 7.

Ingress frames on port 1 get tagged with VID=1 and will be forwarded to any of the other ports.

 

Thus, we have ports isolated against each other and can share a common resource on port 1.

 

Have a nice day, too!

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Re:Why is possible set more VLANS to one port as Untagged?
2020-03-10 06:27:57

@PeterK2, you need untagged ports in more than one VLANs if you want to use an asymmetric VLAN setup.

 

In general, devices always should only offer a mechanism, but not enforce a policy. An asymmetric VLAN is a policy and TP-Link switches offer a mechanism to implement such a policy. There is nothing wrong with it – if you don't need such a setting, just don't use it.

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Re:Why is possible set more VLANS to one port as Untagged?
2020-03-10 08:55:08

 

@R1D2 thanks, I will learn about asymmetric VLAN.

 

have a nice day.

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Re:Why is possible set more VLANS to one port as Untagged?-Solution
2020-03-10 19:57:45 - last edited 2020-03-11 09:06:57

@PeterK2, it's pretty easy to set up an asymmetric VLAN.

 

The TL-SG108E also has an own menu entry for a pre-defined asymmetric VLAN, it's Multi-Tenant Unit VLAN (MTU VLAN). It works as follows:

 

Let's assume that port 1 is the uplink to the router providing Internet access and ports 2 to 8 are assigned to several tenant units.

The goal is to isolate the tenant units against each other, but to let them share the Internet router.

 

So we assign each port an own VLAN, that's VLAN 1 for port 1, VLAN 2 for port 2, etc.

 

PVID of each port is it's primary VLAN, that's 1 for port 1, 2 for port 2, etc. We achieved isolation between the ports by this setup.

 

Now, we assign ports 2-8 membership in VLAN 1, too, so that they can receive traffic from the Internet router.

To allow the Internet router to receive traffic from the other ports, we assign it membership of all other VLANs, that's 2, 3, 4, 5, 6, 7 and 8.

 

All ports are untagged VLAN members since the connected devices don't use VLAN tags usually (technically they could do so, but it would not make much sense in this setup).

 

Ingress frames on port 7 get tagged with VID=7 (due to the PVID) and will be forwarded to port 1, which is a member of VLAN 7.

Ingress frames on port 1 get tagged with VID=1 and will be forwarded to any of the other ports.

 

Thus, we have ports isolated against each other and can share a common resource on port 1.

 

Have a nice day, too!

༺ 0100 1101 0010 10ཏ1 0010 0110 1010 1110 ༻
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Re:Why is possible set more VLANS to one port as Untagged?
2020-03-11 09:13:54

Perfect, now I understand it :) Marked as Best solution, thank you.

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