We had two machines. one worked, the other gave connection issues.
without InstantClient:
SQLNET.CRYPTO_CHECKSUM_CLIENT=ACCEPTED
SQLNET.CRYPTO_CHECKSUM_SERVER=ACCEPTED
Connection fails.
SQLNET.CRYPTO_CHECKSUM_CLIENT=REQUIRED
SQLNET.CRYPTO_CHECKSUM_SERVER=REQUIRED
Connection fails
SQLNET.CRYPTO_CHECKSUM_CLIENT=REJECTED
SQLNET.CRYPTO_CHECKSUM_SERVER=REJECTED
Connection works.
With instantClient 23:
Connection works on all.
hope that helps?