Ytdyklly

I want to connect three of my computers in a LAN as nodes in a single VLAN. How do I do it? I know I can create a VLAN using the

vconfig add [interface name] [vlan id]

command. But how do I connect the other computers to the same VLAN?
Is the VLAN id, a local reference in a particular computer or is it visible to all computers in the VLAN?

For physical servers, it is best to define a VLAN on your network / infra-structure.

Furthermore if you define a VLAN at interface level on your servers they won't be able to talk with your router to leave that network as the router won't be part of that VLAN. That is as you are defining a Virtual LAN, only the elements that belong to that Virtual LAN are able to exchange data between them.

For creating VLANs, the network infra-structure will have also to support VLANs (e.g. your switch). Some cheaper/domestic equipments do not support VAN tagging (802.1Q).

Put simply, usually in a physical situation like yours, VLANs are defined at the switch level. Normally all the switch ports where the servers that take part of that VLAN are connected and their router (if not dealing with a switch layer 3 e.g. a switch router), are tagged with that VLAN.

Usually it only may make sense dealing with VLANs at Linux level when:

1) your router is a linux box;

2) you are in a test network.

Nonetheless, if you still insist in creating a VLAN for testing, you have to:

1) load the relevant kernel mode

modprobe 8021q

2) Add the interface to the required VLAN (5 for instance)

vconfig add eth0 5

You will have a result an interface called eth0.5.

All the servers that you want added to the same VLAN will have to be configured with the vlan id 5.

Likewise, if you want groups of different VLANs, you will use different VLAN ids, and will group the servers that belong to that VLANs accordingly.

I will leave here a link: HowTo: Configure Linux Virtual Local Area Network (VLAN)

Please do note, for larger networks, separating networks into VLANs may require proper planning, and involve dynamic more complicated protocols, however that is out of the scope of this question and Unix&Linux.

As yet another footnote, there are iOT devices and cheap router/switch/AP devices as thr TPLink and ASUS wifi APs with multiple ethernet ports that support cheap switch chipsets controlled from Linux.

Normally that chipsets whilst they support some sort of VLAN functionality, they just do an internal form of VLAN (internal to the equipment/to the chipset), and do not support 802.1Q.

For instance, in the Lamobo/Banana PI R1, such chipset is the BCM53125.

In that case, all the switches would be created only at the Linux (router) switch level, and the other servers/switch/routers would known nothing about VLANs.