This is the Rn — the relative name, the single path segment that, appended to the parent object's Dn, produces the full Dn for the master extension key UCS generates to sign/authenticate the VM-FEX control channel to the VMM. It's the naming key a management tool actually walks the tree with to reach the master extension key, distinct from the full Dn which also encodes everything above it. For instance the Rn segment might simply be 'extkey', which only becomes the full path 'sys/vm-mgmt/extkey' once it's appended to the parent Dn 'sys/vm-mgmt'.