FEX Forwarding

The Cisco Nexus 2000 (that is, the 2200 or 2300 platform) Series fabric extender does not perform any local switching. All traffic is sent to the parent switch, which provides central forwarding and policy enforcement, including host-to-host communications between two systems that are connected to the same fabric extender, as shown in Figure 2-12.

  

Figure 2-12 FEX Forwarding

The forwarding model facilitates feature consistency between the fabric extender and its parent Cisco Nexus device. The fabric extender provides end-host connectivity into the network fabric. As a result, BPDU Guard is enabled on all its host interfaces. If you connect a bridge or switch to a host interface, that interface is placed in an error-disabled state when a BPDU is received. You cannot disable BPDU Guard on the host interfaces of the fabric extender.

The fabric extender supports egress multicast replication from the network to the host. Packets sent from the parent switch for multicast addresses attached to the fabric extender are replicated by the fabric extender ASICs and then sent to corresponding hosts.

Two methods (the static pinning fabric interface connection and the dynamic fabric interface connection) allow the traffic from an end host to the parent switch to be distributed when going through the Cisco Nexus 2000 Series fabric extender.

Static Pinning

Static pinning provides a deterministic relationship between the host interfaces and the parent switch. You configure the fabric extender to use individual fabric interface connections. In this configuration, the 10-Gigabit Ethernet fabric interfaces connect to the parent switch, as shown in Figure 2-13. You can use any number of fabric interfaces, up to the maximum available on the model of the fabric extender.

  

Figure 2-13 Static Pinning Fabric Interface Connections

When the fabric extender is brought up, its host interfaces are distributed equally among the available fabric interfaces. As a result, the bandwidth that is dedicated to each end host toward the parent switch is never changed by the switch but instead is always specified by you.

Note

The FEX static pinning fabric interface connection is not supported on Nexus 7000 and 9000 Series switches. Static pinning was supported on Nexus 5000 and 6000 Series switches, which are end-of-life/end-of-sale at the time of this writing. We have covered it here, as Nexus 5000 and 6000 Series switches are still deployed at scale at various data centers.