3

I want to connect FEX directly to Nexus 7k as dual home.. but recommendation says not to connect FEX with 7k as Dual home.. I want to know the reason.. Please help.

1
  • Did any answer help you? if so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin
    Commented Aug 11, 2017 at 2:51

1 Answer 1

5

Dual-homing to a single N7k is a supported topology so I'm guessing you mean dual-homing to two N7ks.

The reason it isn't supported should be posed as a different question: 'Why WOULD you dual home a FEX to two separate N7ks?'

Remember, a FEX should only be thought of as a remote linecard of the upstream Nexus switch i.e. it doesn't perform local forwarding between ports. The topology you are describing would be like sharing a linecard between two chassis, something that doesn't really happen (I know people could argue that this happens in VSS or nV though).

If you have a server with a single NIC then you can only connect it to a single switch anyway. So even though you want to add redundancy upstream, you will still have a single point of failure where it connects to the FEX. Cisco's rationale is that if you really want HA for a server then you would have two NICs on it. Each NIC would be connected to a separate FEX that are each dual-homed to a separate N7k.

That doesn't go to say that this may become a supported topology in the future however.

3
  • the FEX, like linecards, does do local forwarding, however, it's not a free-standing switch -- without a "sup" (n7k), the forwarding tables will be unpopulated.
    – Ricky
    Commented Jan 19, 2015 at 4:49
  • 1
    The Cisco Nexus 2000 Series Fabric Extender does not perform any local switching. All traffic is sent to the parentswitch that provides central forwarding and policy enforcement, including host-to-host communications between two systems that are connected to the same Fabric Extender. Source, page 19: cisco.com/c/en/us/td/docs/switches/datacenter/nexus2000/sw/…
    – mbud
    Commented Jan 19, 2015 at 4:56
  • That's the most idiotic thing I've seen. If ever there was a reason to avoid a FEX, that'd be it. So, it's ~50 orders of magnitude stupider than a linecard, yet costs 4x that of a real, full function switch.
    – Ricky
    Commented Jan 19, 2015 at 5:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.