VLAN Configuration Guide

Chapter 1: VLAN Configuration

1.1 VLAN Introduction

Virtual LAN (VLAN) refers to a group of logically networked devices on one or more LANs that are configured to communicate as if they were attached to the same wire, even when located on different LAN segments. Established in 1999, the IEEE 802.1Q Protocol Standard Draft standardizes VLAN realization. VLANs are based on logical, not physical, connections, offering flexibility in user/host management, bandwidth allocation, and resource optimization.

Types of Virtual LANs include:

• Port-Based VLAN: Each physical switch port is configured with an access list specifying its membership in a set of VLANs.
• 802.1Q Trunk Mode: Supported on the interface.
• Access Mode Interface: Supported.

Port-Based VLAN assigns a port to a subset of VLANs supported by the switch. If this subset contains only one VLAN, the port is an access port. If it contains multiple VLANs, the port is a trunk port. A default VLAN exists among these multiple VLANs, with its ID serving as the port VLAN ID (PVID).

VLAN-allowed range is supported on the interface. The vlan-allowed parameter controls the range of VLANs a port belongs to. The vlan-untagged parameter configures a port to send packets without a VLAN tag to the corresponding VLAN.

1.2 VLAN Configuration Task List

• Adding/Deleting VLAN
• Configuring Switch Port
• Creating/Deleting VLAN Interface
• Monitoring Configuration and State of VLAN

1.3 VLAN Configuration Task

1.3.1 Adding/Deleting VLAN

A VLAN groups hosts with common requirements, enabling communication as if on the same wire, irrespective of physical location. VLANs offer the same attributes as physical LANs but allow grouping end stations across different LAN segments. A VLAN can have multiple ports, and unicast, multicast, and broadcast messages are forwarded within the same VLAN. For inter-VLAN communication, routing or bridging is required.

Commands to configure VLAN:

VLANs can be dynamically added or deleted using the VLAN management protocol GVRP.

1.3.2 Configuring Switch Port

Switch ports support three modes: access, trunk, and dot1q-tunnel.

• Access Mode: The port is subordinate to a single VLAN and handles only untagged Ethernet frames.
• Trunk Mode: The port connects to other switches and handles tagged Ethernet frames.
• dot1q-tunnel Mode: This mode treats received packets as untagged. The switch chip automatically adds the port's PVID as a new tag, allowing the switch to ignore different VLAN partitions connected to the network. Packets are then delivered unchanged to other ports in the same customer's subnetwork, enabling transparent transmission.

Each port has a default VLAN and PVID. Data received on a port without a VLAN tag belongs to that port's default VLAN.

Trunk mode allows a port to be assigned to multiple VLANs. It also enables configuration of packet forwarding types and the VLAN list the port belongs to, specifying whether packets sent on the port are tagged or untagged.

Commands to configure switch ports:

Note: Not all switches support the dot1q-tunnel feature. Some switches only allow global enabling/disabling of this feature without per-port strategy configuration.

The command to globally enable dot1q-tunnel is:

The capability for various switch models to support dot1q-tunnel is as follows:

For models not listed or for the latest models, consult FS technicians or download the latest instructions from the FS website.

1.3.3 Creating/Deleting VLAN Interface

A VLAN interface can be established for network management or Layer 3 routing. It allows specifying an IP address and mask. The command to configure a VLAN interface is:

1.3.4 Configuring Super VLAN Interface

Super VLAN technology allows hosts in different VLANs on the same switch to share the same IPv4 subnet, saving IP addresses. It classifies different VLANs into a group that shares a management interface and an IPv4 network section/gateway. VLANs within a Super VLAN group are called SubVLANs. No SubVLAN can possess the management interface by configuring an IP address.

You can configure a Super VLAN interface via the command line. The procedure is as follows:

After configuring the Super VLAN interface, you can assign an IP address to it. The Super VLAN interface also functions as a routing port and can be configured like other ports.

1.3.5 Monitoring Configuration and State of VLAN

Run the following commands in EXEC mode to monitor VLAN configuration and state:

1.4 Configuration Examples

Scenario: Six PCs (PC1-PC6) are connected to switch ports 1-6, respectively. Their IP addresses belong to the 192.168.1.0/24 network. Although PC1-PC3 and PC4-PC6 are in different Layer 2 broadcast domains, all PCs can ping each other and be managed via the IP address 192.168.1.100. This requires configuring ports 1-3 for VLAN 1 and ports 4-6 for VLAN 2. Subsequently, VLAN 1 and VLAN 2 must be added as SubVLANs to a Super VLAN.

The following configuration steps are performed on the switch:

interface fastethernet 0/1
 switchport pvid 1
!
interface fastethernet 0/2
 switchport pvid 1
!
interface fastethernet 0/3
 switchport pvid 1
!
interface fastethernet 0/4
 switchport pvid 2
!
interface fastethernet 0/5
 switchport pvid 2
!
interface fastethernet 0/6
 switchport pvid 2
!
interface supervlan 1
 subvlan 1,2
 ip address 192.168.1.100 255.255.255.0
 ip proxy-arp subvlan
    

Diagram Description: The diagram illustrates a network topology where six PCs (PC1 through PC6) are connected to a central switch. Each PC is assigned an IP address within the 192.168.1.0/24 subnet. The connections are shown as lines from each PC to specific ports on the switch (ports 1-6). The diagram visually represents the setup described in the example, highlighting the connectivity between the PCs and the switch.