The Cisco UCS Fabric Interconnect behaves as a switching device between the servers and the network, and the Cisco UCS Manager is embedded in the fabric interconnect, providing server hardware state abstraction. This section covers switching and server network profile configurations.

UCS Virtual LAN

A virtual LAN (VLAN) is 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 switch port can belong to a VLAN. Unicast, broadcast, and multicast packets are forwarded and flooded only to end stations in the VLAN. Each VLAN is considered a logical network, and packets destined for stations that do not belong to the VLAN must be forwarded through a router or bridge.

VLANs are typically associated with IP subnetworks. For example, all of 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. Additionally, you can configure VLANs to be in the active state, which is passing traffic, or in the suspended state, in which the VLANs are not passing packets. By default, the VLANs are in the active state and pass traffic.

You can use the Cisco UCS Manager to manage VLANs by doing the following:

Configure named VLANs

Assign VLANS to an access or trunk port.

Create, delete, and modify VLANs.

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

The native VLAN and the default VLAN are not the same. Native refers to VLAN traffic without an 802.1q header and can be assigned or not. The native VLAN is the only VLAN that is not tagged in a trunk, and the frames are transmitted unchanged.

You can tag everything and not use a native VLAN throughout your network, and the VLAN or devices are reachable because switches use VLAN 1 as the native by default.

The UCS Manager – LAN Uplink Manager configuration page enables you to configure VLANs and to change the native VLAN setting. Changing the native VLAN setting requires a port flap for the change to take effect; otherwise, the port flap is continuous. When you change the native VLAN, there is a loss of connectivity for approximately 20–40 seconds.

Native VLAN guidelines are as follows:

You can configure native VLANs only on trunk ports.

You can change the native VLAN on a UCS vNIC; however, the port flaps and can lead to traffic interruptions.

Cisco recommends using the native VLAN 1 setting to prevent traffic interruptions if using the Cisco Nexus 1000v switches. The native VLAN must be the same for the Nexus 1000v port profiles and your UCS vNIC definition.

If the native VLAN 1 setting is configured, and traffic routes to an incorrect interface, there is an outage, or the switch interface flaps continuously, your disjoint Layer 2 network configuration might have incorrect settings.

Using the native VLAN 1 for management access to all of your devices can potentially cause problems if someone connects another switch on the same VLAN as your management devices.

You configure a VLAN by assigning a number to it. You can delete VLANs or 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 sub-mode but does not create the same VLAN again. Newly created VLANs remain unused until you assign ports to the specific VLAN. All of the ports are assigned to VLAN 1 by default. Depending on the range of the VLAN, you can configure the following parameters for VLANs (except for the default VLAN):