Error 26 means the client can’t locate the specified SQL Server instance due to protocol, firewall, or Browser-service issues.
SQL Network Interfaces Error 26 occurs when the SQL Server client cannot locate the target server or instance. Verify the server\instance name, start the SQL Server Browser service, enable TCP/IP, and open UDP 1434 plus the instance’s TCP port to resolve the issue.
SQL Network Interfaces, error: 26 - Error Locating Server/Instance Specified
The message “SQL Network Interfaces, error: 26 – Error Locating Server/Instance Specified” means the SQL Server client libraries could not find or connect to the named SQL Server instance.
The handshake fails before login is attempted.
The error usually appears in .NET applications, SQLCMD, or third-party tools when trying to reach a remote or named-instance SQL Server over TCP/IP or Shared Memory.
Fixing it quickly restores application uptime and prevents timeouts that cascade through dependent services.
Most cases trace back to disabled SQL Server Browser service, blocked UDP 1434 traffic, or mis-typed instance names.
If the target server uses a dynamic TCP port, clients cannot resolve the port without Browser.
Firewall, VPN, or network misconfiguration can drop packets before they reach the server. Local connection attempts fail when protocols such as TCP/IP are disabled in SQL Server Configuration Manager.
Confirm the server name is correct: ServerName\\InstanceName for named instances, or ServerName,port for default instances on non-default ports.
Use SQLCMD or ping to test network resolution.
Enable SQL Server Browser in SQL Server Configuration Manager, set its Startup Type to Automatic, and start the service so clients can discover dynamic ports.
Open UDP 1434 and the instance’s TCP port in Windows Firewall or corporate firewalls.
Verify that TCP/IP and Named Pipes protocols are enabled for the instance, then restart the SQL Server service.
On-prem machines in the same LAN: Opening UDP 1434 and enabling Browser resolves 80% of cases.
Azure SQL Managed Instance: Use the fully-qualified host name and ensure outbound firewall rules allow 3342 and 1433; Browser is not required.
Docker containers: Map container port 1433 to a host port and connect with host.docker.internal,1433.
Standardize on fixed TCP ports for all SQL Server instances and document them in DNS aliases.
Automate firewall rule creation in Infrastructure-as-Code scripts.
Monitor SQL Server Browser and SQL Server services with your observability stack. Alert on service stops or port changes. Use Galaxy’s built-in query sharing to publish tested connection strings that teammates can reuse.
SQL Server Error 53 indicates a network path issue; verify DNS and firewalls. Error 18456 appears when login fails after the network connection succeeds.
Error 40 combines both network and server errors; follow the same port and Browser checks.
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Clients cannot resolve dynamic ports when the Browser service is stopped or set to Disabled.
Firewalls dropping UDP packets prevent the Browser from answering port-discovery requests.
Typos in the connection string or using an outdated DNS alias lead the client to query the wrong host.
If protocols are turned off in SQL Server Configuration Manager, the server silently ignores connection attempts.
When SQL Server listens on a dynamic port, the port must be allowed through local and network firewalls.
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Signals a network-level failure; often fixed by the same firewall and port checks.
Wrapper error that combines error 26 with additional provider details.
Occurs after the network handshake when authentication to the server fails.
Indicates the target machine actively refused the TCP connection, usually because the port isn’t listening.
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No. The server may be running but unreachable because Browser is disabled, firewalls block UDP 1434, or the wrong instance name is supplied.
Yes. Specify the TCP port with the format ServerName,Port. Fixed ports simplify firewall rules and remove the Browser dependency.
The error can occur with any protocol, but TCP/IP is most common. Enabling Named Pipes locally may offer a temporary workaround.
Galaxy’s connection manager validates instance names, detects open ports, and stores tested connection strings in shared Collections, reducing misconfigurations that trigger Error 26.
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