Contents

Configuring VLANs· 1

About VLANs· 1

VLAN frame encapsulation· 1

Protocols and standards· 2

Configuring a VLAN· 2

Restrictions and guidelines· 2

Creating VLANs· 2

Display and maintenance commands for VLANs· 2

Configuring VLANs

About VLANs

The Virtual Local Area Network (VLAN) technology divides a physical LAN into multiple logical LANs. It has the following benefits:

·     Security—Hosts in the same VLAN can communicate with one another at Layer 2, but they are isolated from hosts in other VLANs at Layer 2.

·     Broadcast traffic isolation—Each VLAN is a broadcast domain that limits the transmission of broadcast packets.

·     Flexibility—A VLAN can be logically divided on a workgroup basis. Hosts in the same workgroup can be assigned to the same VLAN, regardless of their physical locations.

VLAN frame encapsulation

To identify Ethernet frames from different VLANs, IEEE 802.1Q inserts a four-byte VLAN tag between the destination and source MAC address (DA&SA) field and the Type field.

Figure 1 VLAN tag placement and format

‌

As shown in Figure 1, a VLAN tag includes the following fields:

·     TPID—16-bit tag protocol identifier that indicates whether a frame is VLAN-tagged. By default, the hexadecimal TPID value 8100 identifies a VLAN-tagged frame. A device vendor can set the TPID to a different value. For compatibility with a neighbor device, set the TPID value on the device to be the same as the neighbor device. For more information about setting the TPID value, see "Configuring QinQ."

·     Priority—3-bit long, identifies the 802.1p priority of the frame.

·     CFI—1-bit long canonical format indicator that indicates whether the MAC addresses are encapsulated in the standard format when packets are transmitted across different media. Available values include:

¡     0 (default)—The MAC addresses are encapsulated in the standard format.

¡     1—The MAC addresses are encapsulated in a non-standard format.

This field is always set to 0 for Ethernet.

·     VLAN ID—12-bit long, identifies the VLAN to which the frame belongs. The VLAN ID range is 0 to 4095. VLAN IDs 0 and 4095 are reserved, and VLAN IDs 1 to 4094 are user configurable.

The way a network device handles an incoming frame depends on whether the frame has a VLAN tag and the value of the VLAN tag (if any).

Ethernet supports encapsulation formats Ethernet II, 802.3/802.2 LLC, 802.3/802.2 SNAP, and 802.3 raw. The Ethernet II encapsulation format is used here. For information about the VLAN tag fields in other frame encapsulation formats, see related protocols and standards.

For a frame that has multiple VLAN tags, the device handles it according to its outermost VLAN tag and transmits its inner VLAN tags as the payload.

Protocols and standards

IEEE 802.1Q, IEEE Standard for Local and Metropolitan Area Networks: Virtual Bridged Local Area Networks

Configuring a VLAN

Restrictions and guidelines

·     As the system default VLAN, VLAN 1 cannot be created or deleted.

·     Before you delete a dynamic VLAN or a VLAN locked by an application, you must first remove the configuration from the VLAN.

Creating VLANs

1.     Enter system view.

system-view

2.     Create one or multiple VLANs.

¡     Create a VLAN and enter its view.

vlan vlan-id

¡     Create multiple VLANs and enter VLAN view.

Create VLANs.

vlan { vlan-id-list | all }

Enter VLAN view.

vlan vlan-id

By default, only the system default VLAN (VLAN 1) exists.

3.     (Optional.) Set a name for the VLAN.

name text

By default, the name of a VLAN is VLAN vlan-id. The vlan-id argument specifies the VLAN ID in a four-digit format. If the VLAN ID has fewer than four digits, leading zeros are added. For example, the name of VLAN 100 is VLAN 0100.

4.     (Optional.) Configure the description for the VLAN.

description text

By default, the description of a VLAN is VLAN vlan-id. The vlan-id argument specifies the VLAN ID in a four-digit format. If the VLAN ID has fewer than four digits, leading zeros are added. For example, the default description of VLAN 100 is VLAN 0100.

Display and maintenance commands for VLANs

Execute display commands in any view and reset commands in user view.

‌