Virtual LAN

A virtual network , commonly called vLAN (for Virtual LAN), is a logical Data-processing network independent. Many VLANs can coexist on same a Commutateur network (switch).

Interest of VLANs

  • Segmentation : to reduce the size of a field of broadcast

  • Flexibility : Possibility of working with the level 2 (connection layer) (Address MAC) or with the level 3 (IP). VLANs function on the level of layer 2 of OSI model. However, a VLAN is often configured to be connected directly to a network IP, which gives the impression to work rather on the level of layer 3. The VLAN' S can be also based on the physical ports of the switches (attention not to confuse the ports " physiques" with the ports " logiques" of the protocol) (in English: " port-based" ) what corresponds to level 1 of OSI model and not to the number of port of the level 4 (for example: port 80 in TCP which " pointe" towards the service HTTP).

  • Safety : to allow to create a logical unit isolated to improve safety. The only means to communicate between machines belonging to of VLANs different is then to pass by a Routeur.

So that VLANs are propagated on various switches starting from one only physical bond via " trunk ", the organization IEEE (which also deals of the standardization of Ethernet and the Wi-Fi) developed the standard 802.1Q. IEEE 802.1Q (which succeeds ISL) is the prevalent protocol today.

In the context of VLANs, the term “trunk” indicates a bond of network supporting of VLANs multiples between 2 switches or between a switch and a router, that functions by using an adapted protocol. Indeed to take account of multiple connections on a bond, the screens of a VLAN must be identified with a common protocol.

Two protocols:

  • the protocol IEEE 802.1Q adds a label to the heading of the Ethernet package, marking it like pertaining to a certain VLAN, this is the method preferred in 2007 and the only valid option in an environment with equipment of multiple suppliers.
  • There is also a protocol owner Cisco (of Cisco industrial property) for Virtualisation of lan (VLAN). It is called: '''ISL''' "Inter Switch Link", it encapsulates the screen Ethernet with its own encapsulation, and marks the screen like pertaining to a specific VLAN, in a network made up of equipment of commutation of the Cisco mark.

See too

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