This usually happens when setting up a connection through a firewall.

The reason for this is when you have auditing enabled, queries or DML to the SYS.AUD$ table may trigger larger than normal TCP packets.  When these packets go through the firewall, the 'fixup' can possibly modify the packet incorrectly and cause it to be corrupted which then breaks Oracle Net.

There are a few workarounds available.  You must evaluate and test each workaround individually based on the requirements of each environment.

Here are the 4 possible workarounds starting with the most commonly used one.

1.   Turn off database auditing

2.   If you must maintain auditing and cannot disable the 'fixup' feature, work with the network administrators to evaluate the MTU for the firewall and size the Oracle TCP packets to be below the current setting.

3.   Disable the 'fixup' feature and /or consult with the firewall vendor regarding patches/fixes to the feature.

4.   Employ alternate firewall configurations or policy settings.