Sorry, Control Port?
Isilon doesn’t have Management ports, or management interfaces. All management is done in-band. Because you’re likely talking about doing NDMP-based backups to a DataDomain, I assume that you’re talking about the network interfaces for your 3-way NDMP. So all that’s necessary to accomplish what you’re describing is to:
#1 Ensure that your backup application, NetBackup, NetWorker, etc. is using a smart connect zone name to talk to the Isilon cluster.
#2 Ensure that there are enough IP addresses for the new interfaces un-used on the static smartconnect zone on the Isilon Cluster.
#3 Add the network interfaces for the new nodes to that SmartConnect Zone/Pool. (Assuming they are cabled, and switch ports are cabled correctly).
That’s it. I hope that helps!