I researched a lot of native VLAN tagging resources, but I still don't understand what is the difference with VLAN tagging. Can anyone explain it simply?
VLAN tags are only used on trunk links. Most hosts cannot understand VLAN tags since they increase the frame size. Hosts that do understand VLAN tags may be connected with a trunk link instead of an access link.
The definition of a native VLAN frame on a trunk is that it does not contain a VLAN tag. All the frames in any other VLANs on the trunk do contain VLAN tags. Depending on the switch model and software version, each trunk link may have a different VLAN as the native VLAN, but both ends of a trunk should agree on which VLAN is the native VLAN, otherwise various problems may arise, such as traffic being sent to the wrong VLAN or incorrectly bridging two different VLANs into one broadcast domain.
The native VLAN is the VLAN that is assumed when there is not a VLAN tag. For example, if you have a VOIP phone connected to a switch, running on VLAN 10 and then your computer connected to the phone for network access. The computer will not tag the traffic, so either the phone or the switch will assign the VLAN to the untagged traffic as it passes through.