VLAN

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VLAN, acronym for virtual LAN (Virtual Local Area Network), is a method for creating independent logical networks within the same physical network. 1 Several VLANs can coexist on a single physical switch or on a single physical network. They are useful for reducing the size of the broadcast domain and aid in network management by separating logical segments from a local area network (e.g. departments of a company) that should not exchange data using the local network (although they might Do it through a router or layer switch 3 and 4).

A VLAN consists of two or more computer networks that behave as if they are connected to the same switch even though they are physically connected to different segments of a local area network (LAN). Network administrators configure VLANs using software instead of hardware, which makes them extremely strong.

Classification 

Although the most common are port-based VLANs (level 1), virtual local area networks can be classified into four types according to the level of the OSI hierarchy in which they operate:

• Level 1 VLAN (per port). Also known as "port switching". It specifies which switch ports belong to the VLAN, the members of that VLAN are those that connect to those ports. It does not allow the mobility of the users, it would have to reconfigure the VLANs if the user moves physically. It is the most common and the one explained in depth in this article.
• Level 2 VLANs by MAC addresses. Hosts are assigned to a VLAN based on their MAC address . It has the advantage that it is not necessary to reconfigure the switching device if the user changes its location, that is, it is connected to another port of that or another device. The main drawback is that if there are hundreds of users you would have to assign the members one by one.
• Level 2 VLANs per protocol type. The VLAN is determined by the content of the protocol type field of the MAC frame. For example, you would associate VLAN 1 to IPv4 protocol, VLAN 2 to IPv6 protocol, VLAN 3 to AppleTalk , VLAN 4 to IPX ...
• Level 3 VLANs per subnet address (virtual subnet). The level 3 header is used to map the VLAN to which it belongs. In this type of VLAN are the packets, not the stations, which belong to the VLAN. Stations with multiple network protocols (level 3) will be in multiple VLANs.
• VLAN of higher levels . A VLAN is created for each application: FTP , multimedia streams, email ... VLAN membership can be based on a combination of factors such as ports, MAC addresses, subnet, time of day, access mode, security