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Can someone please explain what the point of having untagged and PVID options are (specifically on Netgear switches).

When you set a VLAN up, you need to set which ports it applies too, which I understand, but I don’t quite get why I need to enable both PVID and untagged options on a certain port. They won’t work without the other (or so it seems), so why not simply just have PVID or untagged options on their own.

I am fairly new to VLANs, so don’t understand all the ins and outs, but am trying to figure out why this is needed at all. If any am missing something, please let me know…or is this simply something that Netgear (or anyone else for that matter) do VLANs.

so for instance, I have port 1 with a PVID of 1, untagged with VLAN 1 and Tagged with VLAN 5 and then port 5 with PVID 5 and untagged with VLAN 5. Why can’t I simply just have tagged and untagged, or tagged and PVID?

Thanks

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OK, here is the general guides when talking about vlans (all systems).

Switch to switch links (ports) are typically tagged, with the link members of all vlans that must cross the link.

Switch to device links (ports) are typically untagged, with the ports PVID set to the desired vlan.

There is an exception to the above guidance when dealing with voip phone and a computer on the same switch port. Setting the ports PVID to vlan 1 and tagging with vlan 5 falls under this exception. This is done to tag voip traffic but untag data lan traffic.

Both ends of the link must be either tagged or untagged for communications to happen. You can’t have the switch tagging and the computer set to untagged (exception for the exception above)

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Thanks, yes I do understand this, but what is the point of having untagged and PVID options, they always seem to be the same (are they not)?

Why not just have one or the other?

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I don’t know the netgear, but some switch mfg have different modes for their ports (access [allows only untagged], trunk [allows only tagged], general [allows both tagged and untagged]).

In access mode untagging removes all vlan tag information and the PVID tell the port which vlan to connect to. In this mode they should be connected lock step. The pvid is more important on the General mode where it tells the port, if you see any untagged data assume it belongs to vlan X. You would use this in the example of a switch → voip phone → desktop computer. The Voip phone is setup to tag voip traffic and the computer has nothing special setup. The computer will only interact with untagged data so then when this traffic hits the switch port untagged, the switch knows to connect it to the data vlan inside the switch. When the switch see the voip traffic already tagged it just passes it on. It is a little confusing to have tagged data and untagged data going out the same port. But there are use cases for each setup.

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Hi,

I believe I have the same question as the original poster, but I’d like to ask the question differently:

Given that a port can be untagged for only one (1) VLAN, in what cases would you ever want the PVID to differ from the untagged VLAN ID?

If you take the example provided in one of the above replies, where you have a port tagged for VLAN 2 (VoIP VLAN) and untagged for VLAN 1 (primary computer VLAN), you would then plug in a VLAN-aware IP phone into the switch and a PC into the IP phone’s switch. The PC’s traffic is untagged, and the phone’s traffic is tagged as VLAN 2. The phone will forward the PC’s untagged traffic to the switch, which will default it to VLAN 1.

Since the switch config already knows that the port is untagged for VLAN 1, why then the need to also provide PVID? In what cases would the PVID be set to a value other than that of the port’s untagged VLAN ID?

thanks

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Hi Denobot,

I think you’re mixing up PVID and VVID in the “multi-vlan access port” (study it-know it) scenario where you’d have host-phone-switchport. This is still an access port although there is a tagged frame passed out of the switch. The switch will handle the voice vlan differently than a standard access vlan, and the configuration points that out.

This is a good read on your example:

Group Study: Good Explanation of the Voice VLAN | CCIE Pursuit Blog %uFEFF

%uFEFF

Back to the original question, which it seems that you’re just unsure how an ethernet frame gets tagged/untagged and when it needed. George1421 explained it well.

Any time traffic leaves a host (default ethernet handling for untagged source host; pc, non-trunked server…) the frame will be untagged, and the switchport should be configured as an access port. This is the point when the switchport gains interest in this PVID config (port vlan ID) and sets a tag in the frame header as the ingress traffic passes through the switch to its destination. It’s the same operation for switchport egress traffic on an access port as well; the switchport see’s the mode access option configured (cisco), and then removes the vlan tag from the frame, sending an untagged ethernet frame toward the server/pc host.

If the server needs to connect to a switchport to allow for multiple vlans (excluding voice vlans), the switchport will be configured mode trunk (cisco). This will allow for at least 1 vlan-id on the port, plus the native vlan. The native vlan is untagged and is used for control traffic like cdp, lldp, stp…so there isn’t a configuration holdup for these fundamental services to work. As traffic passes through this trunk interface, you would see your (at least 1) tagged vlan, and untagged traffic (understanding this is traffic from the native vlan).

If more assistance is needed, please open a new thread and I’m sure your question will be addressed.

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Since none of these answers really answers the OP’s question (and since it’s confusing), I will elaborate here.
From reading their documentation, it seems like the “VLAN Membership” only concerns EGRESS traffic (coming from the switch to the devices). The “Port PVID” only concerns INGRESS traffic (devices going to the switch).That is why you can only select one VID for any given port under “Port PVID”… because an untagged packet can only be sent to one VLAN. You can select multiple untagged VIDs for a single port using the “VLAN Membership”, which merely designates what should happen to the VID when a packet exits the switch on a specific port from a specific VLAN.

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