The client cannot locate the specified SQL Server instance, preventing the connection.
SQL Error 26 – “Error Locating Server/Instance Specified” means the client can’t find the SQL Server instance named in your connection string. Enable SQL Browser, verify instance name, open port 1433/UDP 1434 in the firewall, and allow TCP/IP in SQL Server Configuration Manager to resolve the error.
A network-related or instance-specific error occurred while establishing a connection to SQL Server. Error 26 – Error Locating Server/Instance Specified.
SQL Error 26 originates from the SQL Server Native Client when it cannot discover the server name or named instance provided in a connection string. The client sends a UDP broadcast on port 1434 to the SQL Browser service, expecting to receive the TCP port of the instance.
If no reply arrives or the name mapping fails, the driver aborts the connection and raises Error 26 before authentication is attempted.
The message is platform-agnostic and appears in SSMS, .NET apps, Docker containers, sqlcmd, Azure DevOps pipelines, and any tool using ODBC, Ole DB, or SqlClient.
Because discovery fails early, troubleshooting focuses on network configuration, instance visibility, and firewall rules—not login credentials.
Error 26 is commonly triggered when SQL Browser is stopped or blocked, TCP/IP protocol is disabled, the instance name is misspelled, dynamic ports are not known, or a firewall discards UDP 1434 or the instance’s TCP port.
Client/server version mismatches and VPN or container networks that lack UDP broadcast support also cause discovery failures.
Start by confirming the instance name in the connection string: “Server=MyHost\\MyInstance”. Use SQL Server Configuration Manager to verify the instance listens on TCP and note its port. Ensure the SQL Browser service is running. Add inbound rules for UDP 1434 and the instance’s TCP port on Windows Firewall or cloud security groups.
Finally, test connectivity with sqlcmd using “-S tcp:Host,Port” to bypass discovery.
Local development machines often disable SQL Browser to reduce surface area. Re-enable it or specify “tcp:.” with explicit port. In Docker Compose, publish UDP 1434 and the TCP port so the host network can reach the containerized SQL Server. On corporate VPNs, multicast/UDP is blocked; switch to explicit port syntax or host file mapping.
In Azure SQL Managed Instance, use the fully qualified DNS name; SQL Browser is not exposed.
Favor explicit TCP syntax “tcp:server,port” in production connection strings to eliminate dependency on SQL Browser. Automate firewall rules in IaC templates. Monitor the SQL Browser Windows-Service and alert on stoppage. Use predictable static ports instead of dynamic ports where compliance allows.
Store connection parameters centrally in Galaxy Collections so engineers reuse validated strings.
Galaxy’s connection manager validates instance names during setup and surfaces Error 26 diagnostics inline. Shared, endorsed connection profiles prevent typos, while the AI copilot suggests the correct “tcp:host,port” syntax. Teams quickly troubleshoot via Galaxy’s run history and collaboration features, eliminating guesswork and downtime.
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The UDP listener that maps instance names to ports is not running, so discovery fails immediately and Error 26 appears.
Even if SQL Browser runs, a local or network firewall that blocks UDP 1434 prevents the client from receiving the port information.
If TCP/IP protocol is disabled in SQL Server Network Configuration, only shared memory works, causing remote clients to raise Error 26.
Typos, missing backslashes, or using the wrong host name result in the client querying a non-existent instance and triggering the error.
Instances using dynamic ports may pick a port not yet opened in the firewall, making the returned port unreachable and raising Error 26.
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Raised when the client finds the server but the TCP handshake or login packet fails.
Often follows Error 26 if discovery succeeds but connection still blocked.
Thrown when the host name cannot be resolved via DNS or NetBIOS, unlike Error 26 which deals with instance discovery.
Occurs after the client successfully reaches the server, but authentication fails; not a discovery issue.
Similar symptom but specific to Named Pipes protocol when \\Server\pipe\sql\query cannot be reached.
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No. Error 26 only indicates the client cannot find the instance. The server may be running but unreachable due to network or configuration issues.
UDP 1434 exposes instance port numbers. Mitigate risk by using explicit ports and disabling SQL Browser on public networks.
Yes. Starting the SQL Browser service or opening firewall ports usually resolves the error without touching the database engine.
Many VPNs block UDP broadcasts. Use the “tcp:server,port” format or configure split tunneling to allow UDP 1434.
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