Cat6500 FEX, or Smart Install?

I was surprised when I got a broschure in Cisco Live London 2013 that said Catalyst 6500 is supposed to support FEXes (Fabric Extenders) in the future. Does it make sense?

A FEX is a device that looks like a data center LAN switch but it is not designated as a switch. FEX needs a parent switch to work. Currently FEXes are supported by Cisco Nexus 5000, 6000 and 7000 series switches. Basically FEX is like an external line card for the parent switch. It can only be configured in the parent switch. The interfaces between the switch and the FEX are called fabric ports and they are 10G (or 40G as of Nexus 6000) ethernet ports functioning in the special “fex-fabric” mode. FEX can also be a module in a supported blade chassis, just like there are Catalyst 3000 series switches available for some blade chassis.

Let me now have a disclaimer: I am not necessarily good at repeating what the manufacturers  – in this case, Cisco – are thinking, so my story here does maybe not correspond to the story that is presented by Cisco. Talk to your Cisco representative if you want the current and official Cisco story for product placement.

So to put things simple: in the data centers, where you previously used standalone Catalyst LAN switches, you could now use Nexus switches and FEXes, and you would gain a consolidated management view by having many physical devices managed by just a fex devices (the parent switches).

A totally irrelevant but nice photo of an iron ore train in Sweden. Photo by David Gubler (

Catalyst 6500 is an old and trustworthy work horse in the data centers and for many uses it has nowadays been replaced by a Nexus series implementation. Instead, Catalyst 6500 is now seen as a campus backbone or aggregation switch.

For me the campus networks are like this:

  • connected devices are end users with single NICs, not servers
  • bandwidth requirements are generally moderate so oversubscription between the access and core levels can be high
  • access switches are redundantly connected to the backbone or aggregation switches, either by direct fiber connections to two directions or by having a limited number of access switches connected as a chain and then connecting the chain to the backbone or aggregation switches by its ends
  • fiber connections from the building distribution facilities to the floor distribution facilities can be long and difficult (= expensive) to redesign and implement
  • campus environments are basically long-lived implementations whereas data centers are frequently redesigned while moving and/or outsourcing.

In the data centers you can relatively easily order a new fiber panel (or patch fiber) to connect to the necessary connection points within the data center so when the network is built along the lifespan of the data center it is possible to implement almost any kind of physical and logical infrastructure.

In the campus networks however the physical nature of the environment is emphasized due to the points mentioned above.

Again, Catalyst 6500 is nowadays mostly directed to campus networks. So what could be the use case for FEXes with Catalyst 6500? I don’t see it very clearly because I don’t like the idea of a failing Catalyst 6500 bringing down the whole access layer as well. In data centers I can kind of tolerate it because the servers are dual-connected with teaming or link aggregation anyway, and I can either dual-home the FEXes or distribute the FEXes accordingly. But in a campus network I don’t see the use case for FEXes.

Instead, there is the Smart Install feature in IOS and IOS-XE. As mentioned in

“Smart Install is a plug-and-play configuration and image-management feature that provides zero-touch deployment for new switches. You can ship a switch to a location, place it in the network and power it on with no configuration required on the device.”

Basically the Smart Install concept consists of things like DHCP server, TFTP server, Smart Install director and Smart Install clients.

If a client switch is failed you can just replace the switch with another identical switch and the network configures the switch automatically, based on the reported CDP information and the saved configuration file. Or, if you add a new switch the standard configuration is automatically applied and you can then do the customizations if needed.

It makes the Smart Install client switches behave much like the FEXes if you think about the ease of deployment.

The Smart Install feature is currently supported on the Catalyst switches and ISR and ISR G2 routers:

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