VLAN - require any configuration on server side/host level ?

[SJ K]

Hi all,

I always thought VLAN separate broadcast domain, and create "virtual" LANs across 1 physical switch.

Also, it is a configuration to be done on the network switch side, any packet that goes into a VLAN interface, will be tagged automatically according to the VLAN it is connected.

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However from the link below ->
http://www.linuxhorizon.ro/vlans.html

It seems like VLAN is done on the server side/host OS as well.

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Q1) can i confirm if we need to set any configuration on OS level for VLANs ? If no, what is the link above trying to achieve ?

Regards
Noob

[Cisco Freak]

Hi,

I am not sure about the Linux config in that link, but I can confirm you that VLAN DOESN'T need any special configuration at the server/PC level in most of the cases.

VLAN is created and maintained in the switch level. The machines/PCs are unaware of the VLAN setup. They will generate untagged frames and when the switch receive this frame on that switchport, the switch will tag in the proper VLAN of that switchport. However a certain devices like Cisco IP phones are well aware of VLAN that belong to and they tag packets in that voice VLAN from the phone itself.

Also the systems like VMware ESXi which is hosting many virtual machines that belong to different VLANs are capable of VLAN tagging from the ESXi machine level itself. Otherwise the switch will not have a clue to which the VLAN data to be tagged.

CF

[SJ K]

Hi CF and Jon,

Thank you for the marvelous replies.

Regards,
Noob

[Jon Marshall · Accepted solution]

With a normal client connection, as CF says, there is no need for any special vlan configuration on the host.

However I think that link is referring to using a trunk from the host to the switch.

Hopefully you read my other response before this one but when I talk about trunk above I'm not talking about how Unix refers to a trunk, I am using Cisco terminology.

A trunk in Cisco terminology is a link that can carry traffic for multiple vlans. And you can run a trunk to a host device and then that device can send and receive traffic for multiple vlans.

It's not often done with PCs but it is more common with servers although a lot of servers still are only a member of one vlan.

Without wishing to confuse you a common setup in the Cisco world is an etherchannel trunk between switches ie. a single logical link made up of multiple physical links that can carry traffic for multiple vlans.

Jon

[SJ K]

Hi Cisco Freak and Jon,

Thanks for the reply!

Yeap, I have understand what a trunk and etherchannel mean in cisco / networking terms now.

Over here, in the link above, the host device/server is doing some VLAN tagging.

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I am thinking why would it be setup this way ?

Is the server acting as some kind of a gateway that carry/receive traffic from different VLAN (through the switch trunk) , then ? what can it do next ?

Look at the  L3 portion and route to other interfaces ?

or

is it because the server is generating data designated for different VLANs and is sending the frames through 1 etherchannel link (hence it needs to tag in the VLAN information 1st) ?

Sorry I am very new and trying to conceptualize what's going on before going deeper.

Thanks.

Regards,
Noob

[Cisco Freak · Accepted solution]

Hi,

Please think the case of an ESXi server which is hosting 10 VM guest virtual machines each belonging to 10 different VLANs. In this case the the actual switchport where the ESXi physical sever is gonna get connected will have a trunk port configured in the switchport level.

Here trunk mean the server will pass all the 10 VLAN information to the EXSi and all the L2 frames that switch is gonna send to the server will have 802.1q vlan tag to identify the tag.

Similarly when the return traffic comes from the server, the ESXi will also tag the frame to the proper vlan from which the data originated.

CF