Native Vs Default VLAN:

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This is an often-confused point for people new to the Networking, in particular to people coming up the Cisco track, due to Cisco's over emphasis on this point. It is more or less just a terminology thing.

Explanation:

The 802.1q standard defines a method of tagging traffic between two switches to distinguish which traffic belongs to which VLANs.

In Cisco terms, this is what happens on a "trunk" port. I've seen other vendors refer to this as a "tagged" port [Eg. Brocade ICX Series]

In this context, it means the same: adding an identifier to frames to indicate what VLAN the frame belongs to. Terminology aside, the main think to keep in mind is a VLAN tag is necessary, because often the traffic traversing two switches belongs to multiple VLANs, and there must be a way to determine which 1's and 0's belong to which VLAN.

But what happens if a trunk port, who is expecting to receive traffic that includes the VLAN tag, receives traffic with no tag?

In the predecessor to 802.1q, known as ISL (cisco proprietary, but archaic, no one supports it anymore, not even Cisco), untagged traffic on a trunk would simply be dropped. ISL has no concept of a native VLAN.

802.1q however, provided for a way to not only receive this traffic, but also associate it to a VLAN of your choosing. This method is known as setting a Native VLAN.

Effectively, you configure your trunk port with a Native VLAN, and whatever traffic arrives on that port without an existing VLAN tag, gets associated to your Native VLAN.

As with all configuration items, if you do not explicitly configure something, usually some sort of default behavior exists. In the case of Cisco (and most vendors), the Default Native VLAN is VLAN 1. Which is to say, if you do not set a Native VLAN explicitly, any untagged traffic received on a trunk port is automatically placed in VLAN 1.

The trunk port is the "opposite" (sort of) from what is known as an Access Port. An access port sends and expects to receive traffic with no VLAN tag. The way this can work, is that an access port also only ever sends and expects to receive traffic belonging to one VLAN.

The access port is statically configured for a particular VLAN, and any traffic received on that port is internally associated on the Switch itself as belonging to a particular VLAN (despite not tagging traffic for that VLAN when it leaves the switch port).

Now, to add to the confusing mix. Cisco books will often refer to the "default VLAN". The Default VLAN is simply the VLAN which all Access Ports are assigned to until they are explicitly placed in another VLAN. In the case of Cisco switches (and most other Vendors), the Default VLAN is usually VLAN 1. Typically, this VLAN is only relevant on an Access port, which is a port that sends and expects to receive traffic without a VLAN tag (also referred to an 'untagged port' by other vendors).

So, to summarize:

• The Native VLAN can change. You can set it to anything you like.
• The Access Port VLAN can change. You can set it to anything you like.
• The Default Native VLAN is always 1, this cannot be change, because its set that way by Cisco
• The Default VLAN is always 1, this cannot be changed, because it is set that way by Cisco.

Some More Info. On this Topic:

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• We speak about the native VLAN in terms of data frames and not management frames such as CDP, STP, VTP

• The ONLY difference between a regular VLAN and the native VLAN is that frames from/to the native VLAN are carried untagged; this is it.

• The IEEE 802.1q TRUNKING encapsulation standard says the NATIVE VLAN represents traffic sent and received on an interface running 802.1q encapsulation that does not have a tag.  So although the NATIVE VLAN exists also on access ports, its role is relevant only on trunk ports.

• NATIVE VLAN can be modified on a per-port basis or it can be "disabled", meaning you can configure some higher-end switches to tag all frames,  so there is not NATIVE VLAN.

• Native vlan should be same on both the ends.

For a More Detailed understanding of Native Vlan,802.1q, Tagged, Untagged ports  refer to the below link.

Native Vlan, 802.1q ,Tagged and Untagged Ports Etc.

Question:

Let’s say there was a 802.1Q Trunk between two Switches and the native VLAN command (switch port trunk native vlan x) was used on both ends as required. What affect does that have on VLAN 1...? Does this mean that VLAN X and VLAN 1 are both carrying less (untagged) overhead across the Trunk link...? Furthermore, all defined VLANs will still continue to propagate across the Trunk thanks to VLAN 1.

Answer:

When a switch port is configured with the default native vlan, you will really not see a native vlan configured in the configuration on that port. This is the equivalent of "switchport trunk native vlan 1".

In this case any traffic on vlan 1 that is leaving the switch is untagged. Any untagged traffic coming into the switch is assumed to be on vlan 1.

If we changed it to say vlan 10, then any traffic on vlan 10 that was leaving a switch would be untagged. Any traffic arriving untagged would be assumed to be on vlan 10. Additionally, in this case, traffic leaving the switch that was on vlan 1 would be tagged just as any other traffic except the traffic that was from vlan 10. As stated, any traffic arriving untagged would be assumed to be part of vlan 10, and therefore cannot be part of vlan 1.

There is only one native vlan per trunk. This must match on both ends of the trunk and is responsible for all of the untagged traffic. The native vlan could also be called the untagged vlan.

Nice Explanation on Native Vlan with quick Vedio:
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