A VLAN is a group of end stations in a switched network that is logically segmented by function, project team, or application, without the limitation to the physical locations of the users. VLANs have the same attributes as physical LANs, but you can group end stations even if they are not physically located on the same LAN segment.

Any port can belong to a VLAN; all unicast, broadcast, and multicast packets are forwarded and flooded only to end stations in that VLAN. Each VLAN is considered a logical network. If a packet destination address does not belong to the VLAN, it must be forwarded through a router.

The following figure shows VLANs as logical networks. In this diagram, the stations in the engineering department are assigned to one VLAN, the stations in the marketing department are assigned to another VLAN, and the stations in the accounting department are assigned to yet another VLAN.

Figure 1. VLANs as Logically Defined Networks

VLANs are usually associated with IP subnetworks. For example, all the end stations in a particular IP subnet belong to the same VLAN. To communicate between VLANs, you must route the traffic.

By default, a newly created VLAN is operational. To disable the VLAN use the shutdown command. Additionally, you can configure VLANs to be in the active state (passing traffic), or the suspended state (in which the VLANs are not passing packets). By default, the VLANs are in the active state and pass traffic.

Note	The VLAN Trunking Protocol (VTP) mode is OFF. VTP BPDUs are dropped on all interfaces of the switch. This process has the effect of partitioning VTP domains if other switches have VTP turned on.

A VLAN can also be configured as a switched virtual interface (SVI). In this case, the switch ports in the VLAN are represented by a virtual interface to a routing or bridging system. The SVI can be configured for routing, in which case it supports Layer 3 protocols for processing packets from all switch ports associated with the VLAN, or for in-band management of the switch.

The Cisco Nexus device supports VLAN numbers 1 to 4094 in accordance with the IEEE 802.1Q standard. These VLANs are organized into ranges. The switch is physically limited in the number of VLANs it can support. The hardware also shares this available range with its VSANs. For information about VLAN and VSAN configuration limits, see the configuration limits documentation for your device.

The following table describes the details of the VLAN ranges.

Note	You cannot configure the internally allocated VLANs (reserved VLANs).

Note	VLANs 3968 to 4049 and 4094 are reserved for internal use; these VLANs cannot be changed or used.

Cisco NX-OS allocates a group of 82 VLAN numbers for those features, such as multicast and diagnostics, that need to use internal VLANs for their operation. By default, the system allocates VLANs numbered 3968 to 4049 for internal use. VLAN 4094 is also reserved for internal use by the switch.

You cannot use, modify, or delete any of the VLANs in the reserved group. You can display the VLANs that are allocated internally and their associated use.

VLANs are numbered from 1 to 4094. All configured ports belong to the default VLAN when you first bring up the switch. The default VLAN (VLAN1) uses only default values. You cannot create, delete, or suspend activity in the default VLAN.

You create a VLAN by assigning a number to it. You can delete VLANs as well as move them from the active operational state to the suspended operational state. If you attempt to create a VLAN with an existing VLAN ID, the switch goes into the VLAN submode but does not create the same VLAN again.

Newly created VLANs remain unused until ports are assigned to the specific VLAN. All the ports are assigned to VLAN1 by default.

Depending on the range of the VLAN, you can configure the following parameters for VLANs (except the default VLAN):

• VLAN name

• Shutdown or not shutdown

When you delete a specified VLAN, the ports associated to that VLAN are shut down and no traffic flows. However, the system retains all the VLAN-to-port mapping for that VLAN, and when you reenable, or recreate, the specified VLAN, the system automatically reinstates all the original ports to that VLAN.

Note	Commands entered in the VLAN configuration submode are immediately executed. VLANs 3968 to 4049 and 4094 are reserved for internal use; these VLANs cannot be changed or used.

You can create or delete all VLANs except the default VLAN and those VLANs that are internally allocated for use by the switch. Once a VLAN is created, it is automatically in the active state.

Note	When you delete a VLAN, ports associated to that VLAN shut down. The traffic does not flow and the packets are dropped.

Note	If VTP is enabled, it must be in transparent or in off mode. VTP cannot be in client or server mode. For more details about VTP, see the Configuring VTP chapter.

Beginning with Cisco NX-OS Release 7.3(0)N1(1), the length of VLAN name that you can configure is increased from 32 to 128 characters. In the earlier release version, you could configure the length of VLAN name up to 32 characters.

To configure or modify the VLAN for the following parameters, you must be in the VLAN configuration submode:

• Name

  Note	VLAN name can be either a short name (up to 32 characters) or long name (up to 128 characters). To configure VLAN long-name of up to 128 characters, you must enable system vlan long-name command.

• Shut down

Note	You cannot create, delete, or modify the default VLAN or the internally allocated VLANs. Additionally, some of these parameters cannot be modified on some VLANs.

After you have completed the configuration of a VLAN, assign ports to it.

Use one of the following commands to verify the configuration: