What exactly is a Nexus 4000?

Someone mentioned a while ago in a comment to one of my blog posts that the Nexus 4000 switch already supports multihop FCoE. Now that we know what multihop FCoE really is, let’s see how Nexus 4000 fits into the picture.

The Cisco Nexus 4000 Series Design Guide starts with a confusing set of claims:

  • The Cisco Nexus 4000 Series Switches provide the Fibre Channel Forwarder (FCF) function.
  • Nexus 4000 is a FCoE Initialization Protocol (FIP) snooping bridge.

You have to dig deep into the design & configuration section of the same document to realize that:

  • Nexus 4000 cannot provide standalone FCoE functionality; it has to be connected to a Nexus 5000 switch.
  • NX-OS for Nexus-4000 does not have the fcoe feature.
  • You cannot configure FCoE on an individual interface of a Nexus 4000 with the fcoe mode command.
  • The only FCoE-related parameter you can configure on a Nexus 4000 is fip-snooping.

The obvious conclusion: Nexus 4000 is a FIP snooping bridge and thus has nothing to do with multihop FCoE. You could replace it with any DCB-compliant bridge and get the same results.

Speculation: you might even be able to tweak Nexus 5000 to use the 802.3x PAUSE mechanism instead of PFC and work without LLDP ... just don’t act surprised when TAC tells you that configuration is unsupported.

Another sad realization: It looks like the current release of NX-OS cannot create dynamic VF_ports. Even when the servers are not directly attached to the Nexus 5000, you have to create a VFC interface for each individual server and bind it to the server’s MAC address with the bind mac-address configuration command.


  1. And now that IBM has bought Blade Networks, the Nexus 4000 will most likely be discontinued by IBM. They MIGHT keep it in the product line, but I wouldn't be betting a data centre strategy on that module being available in a year.
  2. They didn't even want to sell it to us when we wanted to buy the Nexus 4000I telling us there was no such thing (beginning of 2010).

    However, I doubt that anything except the Nexus line will be able to handle vPCs. If they discontinue the Nexus 4k there's no reason to buy IBM BladeCenters any more if you happen to have a Nexus core network.
  3. Usually vPC is run internally between a pair of switches higher up in the network and the NX4K (or any other access-layer switch) would not see it ... unless, of course, you'd connect a blade server to two NX4Ks and use link aggregation between the server and the NX4K.
  4. IBM are still selling N4k for BladeCenter, but I don't know if they exist on new PureSystem technology.
    The bad thing on N4k is they don't support vPC, so you can't do an LACP PC from blades to N4k.
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