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What happens to a tagged frame if it is received on a native VLAN?
“If an 802.1Q trunk port receives a tagged frame with the VLAN ID the same as the native VLAN, it drops the frame. Consequently, when configuring a switch port on a Cisco switch, configure devices so that they do not send tagged frames on the native VLAN.”
What is frame tagging in VLAN?
Frame tagging is used to identify the VLAN that the frame belongs to in a network with multiple VLANs. The VLAN ID is placed on the frame when it reaches a switch from an access port, which is a member of a VLAN.
How does native VLAN tagging work in trunk?
I can confirm that if vlan dot1q tag native is configured, a trunk always performs tagging on the outgoing frames (i.e. the native VLAN setting is ignored and all frames are tagged with the corresponding tag value). Untagged frames arriving at a trunk port will be dropped without being forwarded further.
In Figure 1, a native or normal Ethernet frame is compared to a VLAN-tagged Ethernet frame. The lengths of each field, in bytes, is shown next to the field name. The VLAN tag subtracts four bytes from the total MTU length of the Ethernet frame, but this is seldom a problem if kept in mind.
Which is the VLAN associated with untagged packets?
The Native VLAN is the VLAN associated with all untagged packets on a tagged/trunk port. Depending on the vendor, the Native VLAN is usually the same as the default VLAN on the switch e.g. VLAN 1. This can be changed on a per-port basis.
What happens when a frame leaves an untagged port?
When the frame reaches the switch port, the switch will add the VLAN tag. The switch port is configured with a VLAN ID that it will put into the tag. Most switch ports will use this mode by default, with VLAN ID 1. When a frame leaves an untagged port, the switch strips the VLAN tag from the frame. The traffic is then forwarded as normal.