Features
Error 26 means the client cannot locate or reach the named SQL Server instance.
SQL Network Interfaces, error 26 occurs when the client cannot discover or reach the specified SQL Server instance. Enable SQL Browser, open UDP 1434/TCP 1433 in firewalls, verify the instance name, and use the correct server string (SERVER\INSTANCE).
A network-related or instance-specific error occurred while establishing a connection to SQL Server. The server was not found or was not accessible. Verify that the instance name is correct and that SQL Server is configured to allow remote connections. (provider: SQL Network Interfaces, error: 26 – Error Locating Server/Instance Specified)
“Error 26” signals that the SQL Client libraries cannot find or contact the named SQL Server instance. The connection request dies before authentication, so no login packet reaches the server.The failure is critical because applications stop while waiting for a database handle. Production outages and data-flow interruptions follow if it is not fixed fast.
Disabled SQL Browser blocks instance discovery. Named instances depend on SQL Browser to return the TCP port number that clients must dial.Firewalls often drop UDP 1434 or the dynamic TCP port assigned to the instance, making the server invisible on the network.Typos or missing instance names in connection strings mislead the driver, forcing a blind search that ends in error 26.Remote connections may be disabled at the server level or limited to certain protocols, preventing TCP/IP hand-shake.
First, confirm the target machine and instance are powered on and running sqlservr.exe. Then test connectivity locally with sqlcmd –S .\\Instance.Next, enable SQL Browser (Services → SQL Server Browser → Start) so clients can resolve the port number.Open inbound UDP 1434 and the instance’s TCP port (default 1433) on Windows Firewall or any network firewall.Validate the connection string: use Server=HOSTNAME\\INSTANCE;Database=MyDB;Trusted_Connection=True;. For default instances, omit \\INSTANCE.Finally, restart the SQL Server service or refresh the DNS cache if the server name was recently changed.
Azure VMs: add 1433 and 1434 to the Network Security Group rules.Connection from Docker container: publish host ports and use the host IP, not “localhost”.VPN users: push split-tunnel rules that allow UDP broadcast to 1434 or hard-code the port in the connection string, e.g., tcp:MyServer,51433.Galaxy users: Galaxy’s desktop app surfaces detailed connection logs. Use them to view the precise client stack trace and verify transport protocol selection.
Keep SQL Browser running on hosts that provide named instances.Standardize on fixed TCP ports instead of dynamic ones and document them.Automate firewall rules with configuration management to ensure every environment opens required ports.Monitor SQL Server connection failures using Extended Events or sys.dm_os_ring_buffers. Alert instantly when error 26 spikes.
Error 53: “network path not found” is thrown when the host can’t be reached; verify DNS and firewall.Error 40: “could not open a connection” appears when the port is blocked or SQL Server is down; similar fixes apply.Error 18456: login failed—occurs later in the chain after the server is found but credentials are wrong.
SQL Browser service stopped.
UDP 1434 or TCP 1433 blocked by Windows Firewall or network ACL.
Incorrect server\instance name in connection string.
Remote connections disabled in SQL Server Configuration Manager.
DNS misconfiguration or stale cache.
Error 53 – Network path not found; Error 40 – Could not open a connection; Error 18456 – Login failed for user; Error 11001 – SQL Network Interfaces: No such host is known
Named instances use dynamic ports, and clients rely on SQL Browser over UDP 1434 to learn that port. If SQL Browser is unavailable, discovery fails and error 26 is raised.
Yes. Configure the instance to listen on a fixed port and append that port in the connection string (tcp:ServerName,51433), eliminating the need for SQL Browser and UDP 1434.
Shared memory only works locally. Remote clients still need TCP/IP, so enabling it will not resolve error 26 for remote connections.
Galaxy’s connection dialog captures the provider error code and surface logs. It suggests firewall checks and shows clickable help links, speeding up root-cause analysis.
.avif){kind=logo}
