Why does dladm rename-link fail with "invalid argument"?

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http://unix.stackexchange.com – I am running Solaris 11.1 (in a VM) and have two NICs installed. At a root console, if I type dladm show-phys, it lists net0 and net1 and some info for each. I want to name the links more descriptively, as the networking setup in this VM will likely be changed later. So, at the root console I enter: dladm rename-link net1 sandirect This yields the error: dladm: rename operation failed: invalid argument Why can't I rename the link? (HowTos)