SCAN & RAC: Clients Receiving ORA-12545 or Host resolution errors

When a client establishes a connection to a SCAN listener, the connection is routed to a VIP listener on any node in the cluster in an effort to load balance the connections.

The client receives a "redirect" packet with the address for the VIP listener to which it has been routed.

If the client must be able to resolve whatever hostname is presented to it inside this packet.

Occasionally, with remote connections to RAC, we see the ORA-12545 error or TNS:  Host or object does not exist.

Often, a client trace reveals that the client reached the SCAN listener successfully but could not resolve the form