3767466 - SAP ASE client connections fail during login handshake although TCP connectivity is successful

A remote SAP ASE client connection fails with errors similar to:

CT-LIBRARY error: ct_connect():
network packet layer:
internal net library error:
Net-Lib protocol driver call to read data failed

or

SQL30046 [08S01]
Connection to the server has been lost.
Unresponsive Connection was disconnected during command timeout.

or

nrpacket: recv, Connection timed out

The connection appears to timeout during login processing even though:

• TCP port is reachable
• Telnet/netcat tests succeed
• ASE listener is running
• No ASE stacktrace or engine errors are reported

• SAP Adaptive Server Enterprise (ASE)
• SAP Solution Manager
• SAP ASE Open Client / ODBC Driver
• VPN, Firewall,  Network Filtering Devices

ct_connect, SQL30046, SQL30016, timeout, nrpacket, llogin timeout, network packet layer, Net-Lib protocol driver call to read data failed, application filtering, Sybase traffic blocked.  , KBA , BC-DB-SYB , Business Suite on Adaptive Server Enterprise , Problem