Nesting, sometimes called downstream correspondent clearing, means the correspondent is providing service to institutions it never onboarded and may not be able to name. Each layer of nesting removes another institution from the correspondent’s view.
It is not prohibited, but it must be known about and controlled. Undisclosed nesting is a recurring finding in enforcement actions, because it is the mechanism by which a bank in a restricted jurisdiction obtains dollar clearing through two intermediaries that each believe they know their customer.