VLAN | Курс "Компьютерные сети"

Introduction to VLAN Technology

Overview of VLAN

• The lecture introduces the concept of VLAN (Virtual Local Area Network), which allows a single physical network to be divided into multiple logical networks that operate independently.

• VLAN technology is implemented using switches and operates at the data link layer (Layer 2) of the OSI model.

Purpose of Segmenting Networks

• Segmenting a network into isolated parts is essential for large organizations or business centers where different departments or tenants require separate networks.

• Creating separate physical networks for each tenant can be impractical due to unknown future requirements, making logical segmentation more efficient.

Advantages of Network Isolation

• Security: Ensures that sensitive data from one tenant is not accessible to others in shared environments.

• Network Stability: Prevents experiments or failures in one segment from affecting other segments, maintaining overall network performance.

• Reduced Broadcast Traffic: Isolating networks limits broadcast traffic within each segment, improving efficiency and reducing congestion.

Implementation of VLAN in Switches

Color-Coding Ports for VLAN Identification

• Switch ports are often color-coded based on their assigned VLAN; for example, blue ports belong to the blue VLAN while yellow ports belong to the yellow VLAN.

• Devices within a specific VLAN can only communicate with each other and cannot send data across different VLAN boundaries.

Switching Mechanism

• A switch maintains a MAC address table that includes an identifier for each VLAN. This ensures that frames are only forwarded within their respective segments.

• If a device attempts to send data across different VLANs, the switch will block this transmission based on its configuration.

Challenges with Multiple Switches

Data Transmission Between Switches

• When using multiple switches, it’s crucial to include information about the originating VLAN in transmitted frames since switches need this context for proper routing.

Modifications Required for Ethernet Frames

• Standard Ethernet frames do not have space allocated for including a VLAN identifier; thus modifications were necessary as per IEEE standards (802.1Q).

Frame Processing with 802.1Q Standard

Frame Structure Changes

• The 802.1Q standard introduced changes allowing Ethernet frames to carry additional fields indicating the associated VLAN ID without disrupting existing protocols.

Process Flow During Data Transmission

Overview of VLAN Technology

Introduction to VLANs

• The discussion begins with the restoration of the old protocol value 0800, which corresponds to IVI (Internet Virtual Interface). This is crucial for network communication.

• Currently, almost all network adapters support the 802.1Q standard, allowing them to insert necessary fields such as VLAN IDs into frames.

Functionality and Implementation of VLANs

• The lecture covers how VLAN technology enables the segmentation of a single network into multiple isolated parts, enhancing security and performance.

• VLAN implementation occurs at the data link layer (Layer 2) in the OSI model through switches. There are two main types of VLAN technologies discussed.

Types of VLAN Technologies

• The first type operates within a single switch by adding special fields to the switching table.

• The second type involves tagged frames (IEEE 802.1Q), used when networks consist of multiple switches; here, the VLAN ID is included in each transmitted frame.

Standards and Frame Formats

• A specific standard, IEEE 802.1Q, modifies Ethernet frame formats to accommodate these tagged frames for effective communication across different switches.