Cisco network engineer Note: VLAN Technology

Basic concepts of VLAN

1. VLAN is based on a switched network. user terminal devices on the network are divided into several logical working groups. Each logical Working Group is a VLAN.

2. VLAN technology provides the function of dynamically organizing the working environment. It simplifies the physical structure of the network, improves the manageability and security of the network, and improves the network performance.

Technical Features of VLAN

1) VLANs work at the data link layer.

2) each VLAN is an independent logical network segment and an independent broadcast domain. VLAN broadcast information is only sent to members of the same VLAN.

3) each VLAN is an independent logical network with a unique subnet number. No direct communication is allowed between VLANs and must be completed through layer-3 routing.

VLAN ID

1. VLAN names are usually identified by VLANIDVLAN numbers) and VLANnameVLAN names.

2. VLANID is represented by 12 bits.

3. VLANname is represented by 32 characters.

VLANTrunk

1. Virtual LAN relay VLANTrunk) technology isVswitchThere is a physical link between the vswitch and between the vswitch and the vro, and a technology for transmitting multiple VLAN information on this physical link.

2. The standard mechanism of VLANTrunk is frame tag. The frame tag specifies a unique VLANID for each frame as the identifier, indicating which VLAN the frame belongs.

3. Trunk functions must be implemented between switching devices and must comply with the same VLAN protocol. Currently, common VLAN protocols for switching devices include ① ISL and ② 802.10 ③ 802.1Q.

4. 802.1Q is the most widely used.

VLAN division method

VLAN division is achieved by defining VLAN members in the entire network by using software. Currently, VLAN division is commonly used in the following three methods:

1) VLAN Based on Ports

VLAN division based on ports means defining VLAN members based on switch ports. Each switch port belongs to one VLAN. The Network Administrator statically specifies the VLAN to the port of the switch. These connection ports maintain the specified VLAN settings until the Administrator changes it again.

This method, also known as static VLAN, is the most common VLAN division method.

2) MAC address-based

VLAN allocation based on MAC addresses is defined by the MAC addresses of each device connected to a vswitch. Because it can divide VLANs by end users, it is often referred to as a user-based VLAN division method. This division method usually requires a VLAN configuration server that stores VLAN management databases. Dynamically set the connection port and corresponding VLAN settings. In dynamic VLAN division, the switch port can be set automatically. When VLAN is divided based on MAC addresses, a switch port may belong to multiple VLANs.

3) Based on the layer-3 protocol type or address

In VLAN division, VLAN members are defined based on the network layer protocol type TCP/IP, IPX, and DECNET. VLAN members can also be defined based on network addresses. It also facilitates application-based VLAN composition.