Shared memory or Named Pipes connection dropped immediately after establishment. SQL Server max connections limit reached. Authentication failure during the TDS login handshake

Step 1: Check if the issue is protocol-specific — in SQL Server Configuration Manager, disable Shared Memory and force TCP/IP for all connections.. Step 2: Check the SQL Server error log for concurrent connection issues: SELECT @@MAX_CONNECTIONS, (SELECT COUNT(*) FROM sys.dm_exec_sessions) as current_connections;. Step 3: Ensure SQL Server Authentication is enabled if a SQL login is used — error 233 can mask auth failures when the handshake breaks before a proper 18456 is raised.

High severityconnection

SQL Server Error:
233

What does this error mean?

The connection was established but dropped before it could complete — often caused by shared memory protocol issues or authentication failures after handshake.

Common causes

1Shared memory or Named Pipes connection dropped immediately after establishment
2SQL Server max connections limit reached
3Authentication failure during the TDS login handshake

How to fix it

1Step 1: Check if the issue is protocol-specific — in SQL Server Configuration Manager, disable Shared Memory and force TCP/IP for all connections.
2Step 2: Check the SQL Server error log for concurrent connection issues: SELECT @@MAX_CONNECTIONS, (SELECT COUNT(*) FROM sys.dm_exec_sessions) as current_connections;
3Step 3: Ensure SQL Server Authentication is enabled if a SQL login is used — error 233 can mask auth failures when the handshake breaks before a proper 18456 is raised.

Frequently asked questions

Why does error 233 appear only sometimes?

Intermittent 233 errors often indicate a max connections race condition — the server is near its connection limit and occasionally rejects new connections. Monitor sys.dm_exec_sessions.

Does error 233 appear in Azure SQL Database?

Less commonly — Azure SQL uses TCP/IP only and handles connection limits differently. Error 233 is more characteristic of on-premises SQL Server with Shared Memory enabled.

How do I disable Shared Memory in SQL Server?

Open SQL Server Configuration Manager → SQL Server Network Configuration → Protocols for <instance> → right-click Shared Memory → Disable → restart the SQL Server service.

Source · learn.microsoft.com/en-us/sql/relational-databases/errors-events/mssqlserver-233-database-engine-error