Nutanix Discovery on Cisco 7K Switches

Nutanix nodes are configured by default to use IPv6 link-local addresses and use IPv6 neighbor discovery in order to make the process of expanding clusters very easy.  Simply connect the new node to the network, and as long as the existing Nutanix cluster and the new node being added resides on the same layer 2 segment, you should be able to discover the new node without doing any other configuration.  This enables an administrator to configure the IPv4 addresses from their desk without having to stay in the datacenter with a crash cart.  Pretty nifty, right?

I have seen this feature become unavailable a couple of times where by the necessary IPv6 traffic is not being allowed on the network. When I have seen this customers did not realize or even intend for this to be the case.  In all of these situations, this was the result of OMF (optimize multicast flood) configured on the Cisco 7K switches.  This is the default configuration so it will always be a problem if not addressed! One customer, using Cisco 7K switches as their access layer, discovery would not work at all for them.  In the other case, the customer did not align their Nutanix clusters to the boundaries of the Cisco 5K switches in a leaf/spine configuration (a best practice, but not feasible for them).  Discovery partially worked, but only within the boundary of any one single Cisco 5K, which basically segmented the traffic and caused confusion.

At first this can be daunting to figure out because everything else you would expect works just fine. Communication appears to work, for example, pings respond just fine (once IPs are manually configured).  After the right levels of google-fu, we came across this article online:  Long story short, the default configuration of a Cisco 7K blocks IPv6 communication, and you will need to disable OMF on the Cisco 7K.  The actual configuration item is: no ip igmp snooping optimised-multicast-flood.

Hopefully google hits on this page with more common search attempts for Nutanix discovery not working.

Comment ( 1 )

  1. ReplyPeter
    For those who do not want to enable the command globally it looks like can also be done on specific VLAN interfaces.

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