Cisco Nexus 5000 Series NX-OS Software Configuration Guide

Understanding VLANs

Note VLAN Trunking Protocol (VTP) mode is OFF. VTP BPDUs are dropped on all interfaces of a Cisco Nexus 5000 Series switch, which partitions VTP domains if other switches have VTP turned on.

A VLAN is a group of end stations in a switched network that is logically segmented by function, project team, or application, without regard 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, and unicast, broadcast, and multicast packets are forwarded and flooded only to end stations in that VLAN. Each VLAN is considered a logical network. Packets destined for stations that do not belong to the VLAN must be forwarded through a router.

Figure 1-1 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 1-1 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; that is, the VLAN is in the no shutdown condition. Additionally, you can configure VLANs to be in the active state, which is 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.

Understanding VLAN Ranges

The Cisco Nexus 5000 Series switch supports VLAN numbers 1to 4094 in accordance with the IEEE 802.1Q standard. These VLANs are organized into ranges. You use each range slightly differently. The switch is physically limited in the number of VLANs it can support. The hardware also shares this available range with its VSANs. For details of the number of supported VLANs and VSANs, see the “Configuration Limits” section.

Table 1-1 describes the details of the VLAN ranges.

Note VLANs 3968 to 4047 and 4094 are reserved for internal use; these VLANs cannot be changed or used.

Cisco NX-OS allocates a group of 80 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 4047 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.

Creating, Deleting, and Modifying VLANs

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, and 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 moving 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. Beginning with Cisco release 5.1 for Nexus 5000 series devices, you must exit the VLAN configuration submode for configuration changes to take effect.

Note VLANs 3968 to 4047 and 4094 are reserved for internal use; these VLANs cannot be changed or used.

Creating and Deleting a VLAN

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.

To create a VLAN, perform this task:

This example shows how to create a range of VLANs from 15 to 20:

Note You can also create and delete VLANs in the VLAN configuration submode.

To delete a VLAN, perform this task:

Entering the VLAN Submode and Configuring the VLAN

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

• Name
• 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; see the “Understanding VLAN Ranges” section for complete information.

To enter the submode and configure the VLAN, perform this task:

This example shows how to configure optional parameters for VLAN 5:

Adding Ports to a VLAN

After you have completed the configuration of a VLAN, assign ports to it. To add ports, perform this task:

This example shows how to configure an Ethernet interface to join VLAN 5: