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What is dot1q native VLAN?
The IEEE 802.1Q trunking protocol describes something called the native VLAN. All native VLAN traffic is untagged; it doesn’t have an 802.1Q tag on the Ethernet frame. When you look at it in Wireshark, it will look the same, just like any standard Ethernet frame.
Does CDP use native VLAN?
It uses the main interface since it is in VLAN 1 by default and VLAN 1 is considered the native VLAN on the router. The CDP packets in this default situation are sent untagged.
What is dot1q tagging?
The 802.1Q tagging protocol allows the Ethernet frame size to increase by four bytes to a range of 68 to 1522 bytes. This size increase is due to the insertion of a four-byte VLAN tag into the frame. The tags, which include a VLAN Identifier (VID), are attached to each Ethernet frame by MAC address.
What happens if you apply this command VLAN dot1q tag native?
Control traffic continues to be accepted untagged on the native VLAN on a trunked port, when the vlan dot1q tag native command is enabled. If you enable 802.1Q tagging on one switch and disable it on another switch, all traffic is dropped; you must identically configure 802.1Q tagging on each switch.
Why do we use native VLAN?
Conclusion. Finally, we can conclude that the basic purpose of native VLAN is to serve it as a common identifier on opposing ends of a trunk link. To carry untagged traffic which is generated by a computer device attached to a switch port, which is configured with the native VLAN.
What happens if native VLAN mismatch?
Connectivity issues occur in the network if a native VLAN mismatch exists. Data traffic for VLANs, other than the two native VLANs configured, successfully propagates across the trunk link, but data associated with either of the native VLANs does not successfully propagate across the trunk link.
Do you need native Dot1q for Cisco router on stick?
Native VLAN is required. If you configure “router on a stick” using subinterfaces simply use “encapsulation dot1Q x native” on the subinterface belonging to the VLAN which is native on the switch end of the line.
What does the native VLAN Dot1q tag command do?
Keep in mind that the vlan dot1q tag native command applies only to tagging frames on trunk ports. It has no effect on access ports – these ports will continue operating in untagged mode.
Can a Cisco router tag a native VLAN?
Cisco routers know that by default, VLAN 1 is treated as a native VLAN by Catalyst switches, so whenever you configure encapsulation dot1q 1 on a subinterface, the router will add the native keyword automatically, and there is no direct way of telling the router to not to do that.
Can a Cisco VLAN be compatible with 802.1Q?
In order to be compatible with 802.1Q, each device has to implement this concept, resulting into Cisco’s native VLANs on trunks. Tagged frames are still valid Ethernet frames with their source and destination MAC addresses exposed, and low end switches will switch them just like normal frames.