When the frame reaches the switch port, the switch will add the VLAN tag. When a frame leaves an untagged port, the switch strips the VLAN tag from the frame.
The traffic is then forwarded as normal. An example of this is when two switches are connected, and pass tagged traffic. The sender will send a frame with a VLAN tag. For example, a broadcast may be received on VLAN In this case, the switch will flood the frame to all other ports configured with VLAN In some cases, an untagged frame will arrive on a tagged port. The switch assigns any untagged frame that arrives on a tagged port to the native VLAN.
Consider this Example. The ports that the hosts connect to are trunk ports, with native VLAN 15 configured. Carrying untagged traffic has its uses. This happens when one switch wants to send information to another switch. An example of switch-to-switch communication is CDP. CDP is a Cisco protocol used to share information about connected devices.
In this case, if there is a trunk link between two switches, how does the sending switch decide which VLAN to use? In short, it sends untagged traffic, which is on the native VLAN. Be aware that there are other VLAN types and uses, which fall outside the scope of this article. There are also different ways of using data VLANs. This is sometimes used by service providers to keep customer traffic separate.
It may also be used to extend the number of available VLANs. When two switches are connected via trunk ports, and the native VLAN between the two does not match, the switch logs an error like this:. The question is, does this cause a problem? The short answer is; no. There are two types of frames that could pass through this link; tagged and untagged.
Any tagged traffic will be passed without being changed, due to this being a trunk link. Therefore, the only concern here is for untagged traffic. In this example, the two switches are connected with a trunk link.
You see Native VLAN was created when hubs where still being used, and you would normally have two switches connected to each other by a hub. Devices that are unable to tag frames might be connected to the hub and as you know hubs can not tag frames, now a switch would receive untagged frames, causing the problem that Native VLAN is trying to solve, see below image:.
View solution in original post. To be more precise: " You see Native VLAN was created when hubs where still being used, and you would normally have two switches connected to each other by a hub. Devices that are unable to tag frames might be connected to the hub and as you know hubs can not tag frames, now a switch would receive untagged frames, causing the problem that Native VLAN is trying to solve, see below image ".
Yeah, but that was in back in time when were hubs are used, and there are not in use anymore. All devices that I would connect to the modern catalyst switch, can be connected to access port with assigned vlan. So this is the reason that I still do not understand use of native vlan today. Are there any situation not to assigned vlan on access port for any devices?
Thank you for your time. Thanks for your accurate response. My problem was with the second part of your answer which was solved. Buy or Renew. Find A Community. Cisco Community. Join us in congratulating October's Spotlight Award Winners!
Turn on suggestions. Why do we and the switch manufacturers just tag everything, and disallow untagged frames on trunk link in the first place?
And now we are having 2 VLAN-capable devices on both ends of a trunk link. So why would we use native VLAN? VLANs are common now but they never would have been adopted without this. Most end-devices PCs, printers, etc. Having a native VLAN would allow end-devices to connect to an interface configured as a trunk. Sign up or log in Sign up using Google. Sign up using Facebook. Sign up using Email and Password. Post as a guest Name.
Email Required, but never shown. The Overflow Blog. Podcast Explaining the semiconductor shortage, and how it might end. If you need to pass frames tagged VLAN 1, you will not be able to, by default. The solution is to change the default VLAN to another value. VLANs keep traffic from different networks separated when traversing shared links and devices within a topology. This process, also known as VLAN tagging , is invaluable to limiting broadcast network traffic, and securing network segments.
Why would you change the native VLAN? If this is of a concern you should use a different native VLAN on trunk ports between switches. For safety, this should be a VLAN not in use in the network.
You want every valid VLAN to be tagged between switches. What is the value of the native VLAN? You can specify a value within the range of
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