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I read tutorial about VLAN configuring. The author talks about VLAN id and uses it in following actions:

My VLAN ID is 5. So I need to copy file /etc/sysconfig/network-scripts/ifcfg-eth0 to /etc/sysconfig/network-scripts/ifcfg-eth0.5

I can't find information about why VLAN id is 5 in this case? How do I know what is VLAN id in my case? And from what VLAN id depends? I run Ubuntu 12.04 if it important.

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It sounds like you're not in a network with vlans. If you manage your own network (for instance, at home), you probably won't have any vlans.

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Actually I just want some theory. – I159 Jun 24 '13 at 12:51
Vlan numbering is arbitrary. To oversimplify, you can take two completely separate physical networks and combine them, but leave them separate by vlan-tagging the traffic over shared links. This is probably much better explained elsewhere with graphics. I've never configured a subinterface in Linux, so I can't really comment on that part. – Joe Fruchey Jun 24 '13 at 14:43

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