Native Vlan configuration concept

Answered Question
Jan 23rd, 2011

Dear Expert,

Could you please explain what is the exact purpose we configured native vlan under the interface?

As per my understanding All the vlan will be tagged when passing through trunk port except native vlan, It's better practice to configure non-Cisco device environment.,

I don't have much understanding about native vlan configuration. Could you please help me to understand.

Regards,

STALIN P

I have this problem too.
0 votes
Correct Answer by Mahesh Gohil about 3 years 2 months ago

Hello Stalin,

For example Say you have connected computer to a trunk port and you defined computer a part of say vlan100, but

as you know computer will not understand vlan tag and communication between computer and switch fails.

If you define vlan100 as native vlan then switch will not add vlan tag while communicating with computer and you will be able

to communicate with computer.

This is very basic explanation of native vlan

Regards

mahesh

Correct Answer by sdheer about 3 years 2 months ago

Hi Stalin,

Kinldy look at the details below for Native Vlan concept explained with examples:

With 802.1Q, a trunk link can tag frames between devices that understand the
protocol. This allows for multiple VLANs to exist on a single topology.
Because 802.1Q is defined as a type of Ethernet frame, it does not require
that every device on a link speaks the 802.1Q protocol. Because Ethernet is
a shared media and more than two device could be connected on this media,
all devices on the link must still be capable of communicating even if they
do not speak the 802.1Q protocol. For this reason, 802.1Q also defines a
Native VLAN. A trunk port on a switch is defined to be in a Native VLAN, and
the 802.1Q trunk will not tag frames that are going out the port that came
in on any port that belongs to the same VLAN that is the Native VLAN on the
switch. Any Ethernet device would be capable of reading frames for the
Native VLANs. The Native VLAN is important on an 802.1Q trunk link. If both
sides of the link do not agree on the Native VLAN, the trunk will not
operate properly

A Native VLAN is nothing else than a default VLAN given that any port in a
(CISCO)switch has to assigned to one VLAN.

2. The control traffic (vtp/stp/pagp/dtp etc) is untagged and goes via vlan
1 which cant be prune or deleted. If the native vlan ona trunk is also
untagged how does the remote end determine which are contrl packets and
which are data packets belonging to untagged native vlan ?????

Answer:
------------
Once you change the native VLAN on the switch: say to 999 ( from the default
vlan 1 ) vlan 1 becomes tagged. Only the native vlan ( 999 ) is untagged.

3. By default the native vlan on a trunk is vlan 1 ? correct  whats the best
practice not to use this native vlan for trunking ?? I believe the
recommendation is just dont use vlan for anything at all so the only
traffic over that is switch control traffic ?? correct ??

Answer :
------------
By default Vlan 1 is the native vlan - it is not advisable
to use this for any other traffic. But once you change the native vlan to
say 999 then you can always use vlan 1 for regular traffic as well as this
will now be tagged, this vlan 1 can now be used as a normal tagged vlan. (
Only one vlan is untagged and that is the native vlan ).

Hope you find teh content useful

Regards,

Swati

Please rate if you find information helpful

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Correct Answer
sdheer Sun, 01/23/2011 - 21:50

Hi Stalin,

Kinldy look at the details below for Native Vlan concept explained with examples:

With 802.1Q, a trunk link can tag frames between devices that understand the
protocol. This allows for multiple VLANs to exist on a single topology.
Because 802.1Q is defined as a type of Ethernet frame, it does not require
that every device on a link speaks the 802.1Q protocol. Because Ethernet is
a shared media and more than two device could be connected on this media,
all devices on the link must still be capable of communicating even if they
do not speak the 802.1Q protocol. For this reason, 802.1Q also defines a
Native VLAN. A trunk port on a switch is defined to be in a Native VLAN, and
the 802.1Q trunk will not tag frames that are going out the port that came
in on any port that belongs to the same VLAN that is the Native VLAN on the
switch. Any Ethernet device would be capable of reading frames for the
Native VLANs. The Native VLAN is important on an 802.1Q trunk link. If both
sides of the link do not agree on the Native VLAN, the trunk will not
operate properly

A Native VLAN is nothing else than a default VLAN given that any port in a
(CISCO)switch has to assigned to one VLAN.

2. The control traffic (vtp/stp/pagp/dtp etc) is untagged and goes via vlan
1 which cant be prune or deleted. If the native vlan ona trunk is also
untagged how does the remote end determine which are contrl packets and
which are data packets belonging to untagged native vlan ?????

Answer:
------------
Once you change the native VLAN on the switch: say to 999 ( from the default
vlan 1 ) vlan 1 becomes tagged. Only the native vlan ( 999 ) is untagged.

3. By default the native vlan on a trunk is vlan 1 ? correct  whats the best
practice not to use this native vlan for trunking ?? I believe the
recommendation is just dont use vlan for anything at all so the only
traffic over that is switch control traffic ?? correct ??

Answer :
------------
By default Vlan 1 is the native vlan - it is not advisable
to use this for any other traffic. But once you change the native vlan to
say 999 then you can always use vlan 1 for regular traffic as well as this
will now be tagged, this vlan 1 can now be used as a normal tagged vlan. (
Only one vlan is untagged and that is the native vlan ).

Hope you find teh content useful

Regards,

Swati

Please rate if you find information helpful

Correct Answer
Mahesh Gohil Sun, 01/23/2011 - 21:51

Hello Stalin,

For example Say you have connected computer to a trunk port and you defined computer a part of say vlan100, but

as you know computer will not understand vlan tag and communication between computer and switch fails.

If you define vlan100 as native vlan then switch will not add vlan tag while communicating with computer and you will be able

to communicate with computer.

This is very basic explanation of native vlan

Regards

mahesh

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