Question on the "UNTAGGED TRAFFIC/FRAMES" associated with the "NATIVE VLAN" on switches....

[mxdkper66]

What phenomena, mechanism, technology, or perhaps “end-devices” is solely responsible in generating or creating "UNTAGGED TRAFFIC (or untagged frames)" to begin with, which are automatically associated with the “NATIVE VLAN” on the associated, or configured TRUNK ports of switches used to physically connect to each other from which “ALL VLANs (tagged and untagged) can traverse across between these very same physical switches?

[luis_cordova]

Hi @mxdkper66,

In simple words, almost all final devices do not assign a vlan number to traffic.

In fact, it is the L2 devices that assign a number of vlan to the traffic, according to the configuration entered in the access port.

Now, there are L2 devices that are not administrable, so the traffic that passes through them is left with no vlan number.

In those cases, as well as a security measure, it is very important to configure a native vlan.

Regards

[mxdkper66]

Thanks for your response "luis_cordova."  So, "ALL endpoint devices (i.e. computers, servers, tablets, printers, etc.)" for the most part, don't assign, or create VLAN "tags, identifiers or #s" whatsoever when physically connected to existing switchports on a Cisco catalyst switch, whether those same switchports are configured for the Cisco "default configuration" or whether those same switchports have been modified by a Network Administrator and do have and show a specific "VLAN ID#" associated with them?  That's my first question.  My second question is this.....could it be that MOST "untagged traffic" traversing a NATIVE VLAN is traffic (or frames) associated with a particular protocol's overhead (i.e. CDP, SPT (spanning tree), SNMP, or something of the like)?  Just wondering....

[luis_cordova]

Hi @mxdkper66,

ALL endpoint devices (i.e. computers, servers, tablets, printers, etc.)" for the most part, don't assign, or create VLAN "tags

A: Effectively, by default all final devices send traffic without tag.

An exception to this are IP telephones, which learn the voice vlan configured in the switch port and send voice traffic with the assigned voice vlan number.

whether those same switchports are configured for the Cisco "default configuration" or whether those same switchports have been modified by a Network Administrator and do have and show a specific "VLAN ID#" associated with them? 

A: Yes, the traffic of the final devices adopts the number of vlan configured in the port of the switch.
By default, in the managed switches, the vlan number is 1.

could it be that MOST "untagged traffic" traversing a NATIVE VLAN is traffic (or frames) associated with a particular protocol's overhead?

A: In general, control protocols use vlan 1, so they have an associated vlan number.
There are times when some send frames with no vlan number, but, it is complicated to explain.
I leave this link for reference: https://learningnetwork.cisco.com/thread/121642

Regards

[mxdkper66 · Accepted solution]

Thank you so very much "luis_cordova" in your valuable feedback and explanations.  It really has helped me better understand and comprehend the nature or realm of this switching phenomena here that we discussed.....THANK YOU!

[luis_cordova]

Hi @mxdkper66,

I ask you to mark the discussion as solved, since that helps other users with similar doubts.

In addition, the votes of help motivate us to continue helping.

Regards

[luis_cordova]

Hi @mxdkper66,

The idea is that you mark as the correct answer one that I did (or the person who attends your discussion).

This makes the users find the answer to their doubts faster.

Regards