About VLAN 0

I have a query regarding "VLAN 0". What is this VLAN 0 and is that configurable in a swich? Please through some light on this

Usually called "Native VLAN". By default, it's either VLAN 0 or VLAN 1, but you can change that. You can say it's the default VLAN.

When frames get sent out of trunk ports, they are tagged. These tags are part of the 802.1q standard and contain the VLAN ID of the VLAN that the this frame belongs to. Thats how the receiving port knows what VLAN this frame belongs to. However, native vlan frames are NOT tagged. The receiving trunk port will see that the frame is not tagged, so it will assume that the frame belongs to the Native VLAN (in other words, the default VLAN).

Thx Ammar

Actually My real question is in a cisco swich can an operator cofigure this VLAN 0 ?

No, I tried it on a simulated Cisco 2950 Switch. It didn't accept it. But it accepts vlan 1. I'll try on my home switch today and update you.

It rejects it on my 2950 too saying it's out of range

[code:1]Switch(config)#vlan 0
Command rejected: Bad VLAN list - character #2 (EOL) delimits a VLAN
number (0) out of the range 1..4094.
[/code:1]

I think VLAN 0 might be a loose misnomer for VLAN 1. As S0lo's last post shows, the range for valid VLAN IDs on Cisco kit is 1 to 4094 with VLAN 1 being the default VLAN. I suspect VLAN 1 might be what people are talking about when they refer to VLAN 0.

However, to muddy the water, Cisco's documentation for the 3750 reveals that there IS a VLAN 0 - but only when you're using VOIP:

The command switchport voice vlan {vlan-id | dot1p | none | untagged} configures how the Cisco IP Phone carries voice traffic:

•vlan-id—Configure the Cisco IP Phone to forward all voice traffic through the specified VLAN. By default, the Cisco IP Phone forwards the voice traffic with an 802.1Q priority of 5. Valid VLAN IDs are from 1 to 4094.

•dot1p—Configure the Cisco IP Phone to use 802.1p priority tagging for voice traffic and to use the default native VLAN (VLAN 0) to carry all traffic. By default, the Cisco IP Phone forwards the voice traffic with an 802.1p priority of 5.

Remarkable. I never knew that.