•
The FEX local check is bypassed if it is running its backup image.
•
The parent switch performs SFP validation again when the fabric interface is brought up. It keeps the
fabric interface down if SFP validation fails.
After an interface on the parent switch is configured in fex-fabric mode, all other features that were configured
on that port and are not relevant to this mode are deactivated. If the interface is reconfigured to remove
fex-fabric mode, the previous configurations are reactivated.
Per class flow control mode is enabled by default on the fabric interfaces. When a fabric interface is
configured on the parent switch, PFC mode is enabled by default and cannot be changed.
Note
For a 2248PQ, all fabric interfaces need to be bundled into a single fabric port channel. They cannot be
used to connect the parent switch as individual ports.
Note
For more information about PFC, see the Quality of Service Configuration Guide for your device.
Oversubscription
In a switching environment, oversubscription is the practice of connecting multiple devices to the same
interface to optimize port usage. An interface can support a connection that runs at its maximum speed. Because
most interfaces do not run at their maximum speeds, you can take advantage of unused bandwidth by sharing
ports. Oversubscription, which is a function of the available fabric interfaces to active host interfaces, provides
cost-effective scalability and flexibility for Ethernet environments.
The Cisco Nexus 2148T Fabric Extender has 4 10-Gigabit Ethernet fabric interfaces and 48 1000BASE-T
(1-Gigabit) Ethernet host interfaces. With this system, you can have any number of configurations. For
example, you can configure the following:
•
No oversubscription (40 host interfaces for four fabric interfaces)
•
1.2 to 1 oversubscription (48 host interfaces for four fabric interfaces)
•
4.8 to 1 oversubscription (48 host interfaces for one fabric interface)
The Cisco Nexus 2248TP Fabric Extender has 4 10-Gigabit Ethernet fabric interfaces and 48 100/1000BASE-T
(100-Mb/1-Gigabit) Ethernet host interfaces. When its host interfaces are running in Gigabit Ethernet mode,
it offers similar configurations to the Cisco Nexus 2148T.
The Cisco Nexus 2248TP can be run with no oversubscription when its host interfaces are running in 100-Mb
mode.
The Cisco Nexus 2248PQ Fabric Extender has 16 10-Gigabit Ethernet fabric interfaces and 48 10-Gigabit
Ethernet host interfaces. All host interfaces use all of the available fabric interfaces. (Static pinning is not
supported. Port-channel mode is only supported on fabric interfaces.) When all host interfaces are sending
traffic to all fabric interfaces, the maximum oversubscription ratio for the Cisco Nexus 2248PQ is 3:1.
The Cisco Nexus 2232PP Fabric Extender has 8 10-Gigabit Ethernet fabric interfaces and 32 10-Gigabit
Ethernet host interfaces. All host interfaces use all of the available fabric interfaces. When all host interfaces
are sending traffic to all fabric interfaces, the maximum oversubscription ratio for the Cisco Nexus 2232PP
is 4:1.
Cisco Nexus 6000 Series NX-OS Layer 2 Switching Configuration Guide, Release 7.x
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Configuring the Fabric Extender
Oversubscription
