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Orbi WiFi 7 RBE973
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Re: Trunk Vs. Untagged multiple VLANs

tantony
Luminary

Trunk Vs. Untagged multiple VLANs

Sorry if I'm in the wrong forum. 

 

Let's say I have 2 VLANs.  VLAN 5 = IT, VLAN 10 = Admin

 

What's the difference between making a port trunk (T), then adding both VLANs, and making a port untagged (U), and adding both VLANs.  They do the same thing correct?  I can't seem to figure out what difference it makes.  I know trunk (T) can carry multiple VLANs, but if I untag (U) a port and make it members of both VLANs, it does the same thing correct?

 

For example:

 

Port 23:

VLANs 5,10 both (T), PVID 5

 

Port 23:

VLANs 5,10 both (U), PVID 5

 

They both do the same thing?

Message 1 of 6

Accepted Solutions
schumaku
Guru

Re: Trunk Vs. Untagged multiple VLANs


@tantony wrote:

Port 23:

VLANs 5,10 both (T), PVID 5

 

Port 23:

VLANs 5,10 both (U), PVID 5

 

They both do the same thing?


No.

 

The first is a direct "trunk" type port carrying multiple tagged VLANs.

 

The second one is a config you should avoid in general - as it does create some asymmetrical VLAN ... while the VLAN ID 5 (with PVID 5) will work for incoming and outgoing traffic, there will be also VLAN ID 10 traffic flowing off the switch, but not back to that VLAN. Simple: You can't have more than one VLAN untagged on a port. Anything else is of theoretical and academic value only.

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Message 2 of 6

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schumaku
Guru

Re: Trunk Vs. Untagged multiple VLANs


@tantony wrote:

Port 23:

VLANs 5,10 both (T), PVID 5

 

Port 23:

VLANs 5,10 both (U), PVID 5

 

They both do the same thing?


No.

 

The first is a direct "trunk" type port carrying multiple tagged VLANs.

 

The second one is a config you should avoid in general - as it does create some asymmetrical VLAN ... while the VLAN ID 5 (with PVID 5) will work for incoming and outgoing traffic, there will be also VLAN ID 10 traffic flowing off the switch, but not back to that VLAN. Simple: You can't have more than one VLAN untagged on a port. Anything else is of theoretical and academic value only.

Message 2 of 6
tantony
Luminary

Re: Trunk Vs. Untagged multiple VLANs

@schumaku 

 

Thank you.  So just to make sure I understand it clearly, method 2, where I made port 23 untagged (U) with both VLANs, might or might not work depending on the circumstances, but is not a good practice.  

Message 3 of 6
schumaku
Guru

Re: Trunk Vs. Untagged multiple VLANs

Take the second one as an academical solution only. For us, the aim of VLANs is to create independent broadcast domains - with the second config you mix things up.

Message 4 of 6
tantony
Luminary

Re: Trunk Vs. Untagged multiple VLANs

@schumaku 

 

Thank you

Message 5 of 6
schumaku
Guru

Re: Trunk Vs. Untagged multiple VLANs

Just to clarify: You can have one VLAN ID (same PVID) untagged, and one or more additional VLANs tagged on that same port, too.

Message 6 of 6
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