On Mon, 3 Oct 2005, Aseem Rastogi wrote:
i have been following this post rather keenly. it now seems to have died down. but still i am not able to understand what is a vlan interface.
VLANs is IEEE 802.1Q, dividing Ethernet into 4097 virtual Ethernet networks. (the normal untagged network + 4096 .1q tagged networks = 4097)
VLAN is normally only used within and between switches, but it is also possible to use between the switch and a server/host allowing the server to participate in multiple VLANs on the switch.
This is configured on the Linux side using vconfig, creating one vritual network interface per such virtual Ethernet being used between the server and the switch. The virtual interfaces created by vconfig is true virtual interfaces and can even have a different MAC address than the physical interface if you like (defaults to use the same MAC however). These virtual interfaces is named like physicalinterface.vlannumber (i.e. eth0.45 for the VLAN with the .1q tag 45 on the eth0 physical connection).
More information on the VLAN support in Linux can be found from http://www.candelatech.com/~greear/vlan.html. The needed software is also available in most distributions (the kernel driver is available in the kernel since many years back).
can somebody please give me some pointer where i can read about this. vlan i thought is a l2 concept and should have nothing to do with l3.
vlan is indeed purely a l2 concept, using a slightly different Ethernet frame format than normal Ethernet allowing for multiple virtual Ethernet networks to be transported over the same cable.
IP-aliases on the other hand is purely a l3 concept, allowing you to have more than one IP address on the same interface, optionally labelled with a name (interface:name) for administrative purposes. The (optional) label on an IP-alias has no significant meaning other than as a reminder to the administrator, and to produce confusing results when using ifconfig (ifconfig has the odd habit of displaying the named ip-aliases as if they were separate interfaces).
Regards Henrik
