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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?
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.
6 Replies
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.
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.
I was actually wondering why my Netgear switch allows multiple untagged VLANs on the same port.
What is the point of that?
I never do that, I only just have on untagged VLAN per port (and I always forget that I also need to set the port's PVID to that VLAN... my other switches only allow me to set 1 untagged VLAN and that is the PVID, with Netgear I have to do both since they allow multiple untagged VLANs).
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