Ethernet VLAN

What is Ethernet Virtual Local Area Network (VLAN) ?
- Creation of an Ethernet VLAN

VLANs are created on Layer 2 switches to control broadcasts and enforce the use of a Layer 3 device for communications. Each VLAN is created in the local switch's database for use. If a VLAN is not known to a switch, that switch cannot transfer traffic across any of its ports for that VLAN. VLANs are created by number, and there are two ranges of usable VLAN numbers (normal range 1-1000 and extended range 1025-4096). When a VLAN is created, you can also give it certain attributes such as a VLAN name, VLAN type, and its operational state. To create a VLAN, use the following steps.

1. Configure VTP.

VTP is a protocol used by Cisco switches to maintain a consistent database between switches for trunking purposes. VTP is not required to create VLANs; however, Cisco has set it up to act as a conduit for VLAN configuration between switches as a default to make administration of VLANs easier. Because of this, you must first either configure VTP with a domain name or disable VTP on the switch. VTP is explained in detail in section "6-4: VLAN Trunking Protocol."

2.Create the VLAN.

VLANs are created by number. The two ranges of VLANs are as follows:

• The standard range consists of VLANs 1 to 1000.
  
• The extended range consists of VLANs 1025 to 4096.

Extended VLANs are currently supported only on switches running COS software version 6.1 or greater. When you create a VLAN, you have many options to consider. Many options are valid only for FDDI and Token Ring VLANs. Some of the items configured deal with options, such as private VLANs, which are discussed in other sections in this book. VLANs are created using the set vlan command for COS devices or with the vlan command in vlan database mode for IOS switches.

An Ethernet VLAN circuit can be configured using either the vlan-ccc or extended-vlan-ccc encapsulation. For extended-vlan-ccc, you cannot configure the inet family. Only the ccc family is allowed. The vlan-ccc encapsulation supports both the inet and ccc families. Ethernet interfaces in VLAN mode can have multiple logical interfaces.

For encapsulation type vlan-ccc, VLAN IDs from 512 through 1023 are reserved for CCC VLANs, allowing you to make up to 512 VLANs for the CCC connection. For the extended-vlan-ccc encapsulation type, VLAN IDs from 0 through 1023 are valid, allowing you to make up to 1024 VLANs for the CCC connection.



Some venders use the proprietary TPIDs 0x9100 and 0x9901 to encapsulate a VMAN-tagged packet into a VLAN-CCC tunnel to interconnect a geographically separated metro Ethernet network. By configuring the extended-vlan-ccc encapsulation type, a Juniper Networks router can accept all three TPIDs (0x8100, 0x9100, and 0x9901).

Configure an Ethernet VLAN circuit with the vlan-ccc encapsulation as follows:


You can configure these statements at the following hierarchy levels:

• [edit logical-routers logical-router-name interfaces]
  
• [edit interfaces]

Configure an Ethernet VLAN circuit with the extended-vlan-ccc encapsulation statement as follows: