SAP to External Oracle DB returns ORA-03135

Hi,

We have a CRM 7.0 / NW 7.01 system running with a local Oracle 11.2.0.3 patch 10 database that pulls data from an external non-SAP Oracle Database. The data that is pulled from this external database is used to update SAP CRM objects and this is performed nightly. The external Oracle database is owned and controlled by our customer and they recently cloned the system and upgraded it to Oracle 11.2.0.1 (previously 10.2). After configuring the local tnsnames.ora to point to the upgraded external database (new IP address), the test program ADBC_TEST_CONNECTION returns ORA-03135: connection lost contact.

So far we have verified the following:

- latest patch on client side

- tnsnames.ora is correctly configured (our connection to the old database still works, and the only change was the IP address)

- TNSping to the external DB is successful

- connection to external database using sqlplus works (using the same login information as entered in the DB Connection in SAP t-code DBCO)

- the CRM system and the host for the external DB are on the same internal corporate network, so there should not be firewall issues

- latest DBSL installed on client side

- followed SAP Note 1261329 and verified that the configuration of the client side is correct

- if the wrong password is entered in the DB Connection in t-code DBCO, ADBC_TEST_CONNECTION will return "incorrect password" from the Oracle server

- the response from the external Oracle database with the ORA-03135 error was instantaneous, so there's not wait time and then a timeout

Has anyone encountered this issue before and know how to resolve it? ORA-03135 usually means it's a firewall issue or a timeout issue but we believe we've eliminated those possibilities. We believe that the SAP system is able to connect to the DB but we are getting kicked out immediately.