Brocade Network OS Administrator’s Guide v4.1.1 - Manual (Page 378)

frames that arrive on an ISL. If the frame exists in the fabric, it must have been allowed to enter the
fabric at the edge. In fabric cluster mode, Network OS 4.0.0 configuration rules still apply; the user
must configure VLANs on every RBridge.
Mixed fabric interoperability
Releases prior to Network OS 4.1.0 can support only 802.1Q VLAN configurations. However, although
Network OS 4.1.0 can support both 802.1Q VLANs and VFs, CLI support for a given VF configuration
depends on the participating RBridge’s capability. This is because the Brocade VDX 6720 series and
VDX 6730 series can support only 802.1Q VLAN configurations, whereas the Brocade VDX 6740
series and VDX 8770 series can support any VF configuration.
A VCS Fabric can be in one of three states, which are determined from the participating RBridge’s
capability and the VF state of the fabric. The VF state can change when an RBridge joins or leaves the
fabric. VF configurations are supported only when a fabric is in the VF-enabled state, as summarized
below.
• VF-incapable: Fabric has mixed platforms (VDX 6720, 6730, 6740, 8770) or mixed releases
(Network OS 4.1.0 and earlier). Support is for 802.1Q VLANs only.
• VF-capable: Fabric has VDX 6740 and 8770 RBridges all with Network OS 4.1.0. By default,
support is for 802.1Q VLANs only. Use the vcs virtual-fabric enable command to bring fabric to
the VF-enabled state and support VFs.
• VF-enabled: Fabric is enabled to support VF configuration. In this state, pre-Network OS 4.1.0
RBridges and VDX 6720 and VDX 6730 RBridges cannot join the fabric.
The following summarizes VF states by platform and release:
Switch/platform joining fabric VF-incapable fabric VF-capable fabric VF-enabled fabric
VDX 6720/6730 Yes Yes No
Pre-4.1.0 VDX 6740/8770 Yes Yes No
4.1.0 VDX 6740/8770 Yes Yes Yes
Virtual Fabrics operations
This section summarizes the fundamental behavior of Virtual Fabrics.
Enabling and disabling a Virtual Fabric
Virtual Fabrics can be enabled only in logical chassis cluster mode. In a VF-incapable fabric, ISL
encapsulation is based on C-TAGs. In a VF-enabled fabric, ISL encapsulation is based on Fine-Grain
Labels (FGLs), using both C-TAGs and S-TAGs. The VF is enabled only when the user issues the vcs
virtual-fabric enable command. This enables the transition from one encapsulation type to another
without disrupting existing traffic.
Enabling VFs
To ensure that there is no data disruption, the ISL encapsulation transition must be coordinated at the
fabric level without toggling the link state. When the fabric is in a VF-capable state, the user executes
the fabric-wide vcs virtual-fabric enable command to enable this transition. The command is
distributed to all RBridges in the fabric and is executed in multiple stages across nodes.
Virtual Fabrics operations
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