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Connecting a Nexus 2148 to a Nexus 5010

The Cisco Nexus 2000 series fabric extender (or “fex”) is an implementation of network interface virtualization. Because the Nexus 2000 fabric extender acts as a remote line card to the upstream IV-capable bridge (a Nexus 5000 series switch, typically), all the configuration takes place on the upstream bridge. In this post, I’ll describe how to connect a Nexus 2148T to a Nexus 5010. In reality, the process is incredibly simple and not really worthy of a blog post, but in the interest of completeness I’ll document it here.

The key to making the fabric extender work is the switchport mode fex-fabric command, used on a specific interface to let the Nexus 5000 know that a fabric extender is connected to that port:

nexus(config)# interface eth2/1  
nexus(config-if)# switchport mode fex-fabric

You can use the switchport mode fex-fabric command on a specific interface, as shown above, or on a port-channel:

nexus(config)# interface port-channel 2  
nexus(config-if)# switchport mode fex-fabric  
nexus(config-if)# interface eth2/1  
nexus(config-if)# switchport mode fex-fabric  
nexus(config-if)# channel-group 2 mode on  
nexus(config-if)# interface eth2/2  
nexus(config-if)# switchport mode fex-fabric  
nexus(config-if)# channel-group 2 mode on  
nexus(config-if)# interface port-channel 2  
nexus(config-if)# fex associate 100

In this example, I created a port-channel with two interfaces and associated the fabric extender to the port-channel, providing link-level redundancy for the connection between the Nexus 2148 and the upstream Nexus 5010.

To verify that the fabric extender is coming online properly, you can use a few different commands. The show fex detail command produces some useful output (only the first several lines are included here):

FEX: 100 Description: FEX0100 state: Online  
FEX version: 4.2(1)N1(1) [Switch version: 4.2(1)N1(1)]  
FEX Interim version: 4.2(1)N1(1)  
Switch Interim version: 4.2(1)N1(1)  
Extender Model: N2K-C2148T-1GE,  Extender Serial: JAF1321ANJN  
Part No: 73-12009-05  
Card Id: 70, Mac Addr: 00:0d:ec:cf:03:42, Num Macs: 64  
Module Sw Gen: 12594  [Switch Sw Gen: 21]  
post level: complete  
 pinning-mode: static    Max-links: 1  
Fabric port for control traffic: Eth2/1  
Fabric interface state:  
Po2 - Interface Up. State: Active  
Eth2/1 - Interface Up. State: Active

And that’s really about it. Yes, there are more advanced configurations—I’m interested in exploring the use of virtual port-channels upstream of a Nexus 2000 series fabric extender to multiple Nexus 5000 switches—but this will get you started.

Feel free to post corrections, suggestions, or any other feedback in the comments!

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