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SQL Server Browser service

  • Artikkeli

Applies to: SQL Server - Windows only

The SQL Server Browser program runs as a Windows service. SQL Server Browser listens for incoming requests for SQL Server resources and provides information about SQL Server instances installed on the computer. SQL Server Browser contributes to the following actions:

For each instance of the Database Engine and SQL Server Analysis Services (SSAS), the SQL Server Browser service (sqlbrowser) provides the instance name and the version number. SQL Server Browser is installed with SQL Server.

SQL Server Browser can be configured during setup or using SQL Server Configuration Manager. By default, the SQL Server Browser service starts automatically:

  • When upgrading an installation.
  • When installing on a cluster.
  • When installing a named instance of the Database Engine, including all instances of SQL Server Express.
  • When installing a named instance of SSAS.

Background

Before SQL Server 2000 (8.x), only one instance of SQL Server could be installed on a computer. SQL Server listened for incoming requests on port 1433, assigned to SQL Server by the official Internet Assigned Numbers Authority (IANA). Only one instance of SQL Server can use a port, so when SQL Server 2000 (8.x) introduced support for multiple instances of SQL Server, SQL Server Resolution Protocol (SSRP) was developed to listen on User Datagram Protocol (UDP) port 1434. This listener service responds to client requests with the names of the installed instances and the ports or named pipes used by the instance.

To resolve limitations of the SSRP system, SQL Server 2005 (9.x) introduced the SQL Server Browser service as a replacement for SSRP.

How SQL Server Browser works

When an instance of SQL Server starts and the TCP/IP protocol is enabled for SQL Server, the server is assigned a TCP/IP port. SQL Server listens on a specific named pipe if the named pipes protocol is enabled. This port or named pipe is used by that specific instance to exchange data with client applications. TCP/IP port 1433 and pipe \sql\query are assigned to the default instance during installation. The server administrator can change the port or named pipe using SQL Server Configuration Manager.

Because only one instance of SQL Server can use a port or pipe, different port numbers and pipe names are assigned for named instances, including SQL Server Express. When enabled, named instances and SQL Server Express are configured to use dynamic ports by default. That is, an available port is assigned when SQL Server starts.

If you want, a specific port can be assigned to an instance of SQL Server. Clients can specify a specific port when connecting to SQL Server. However, if the port is dynamically assigned, the port number can change anytime the SQL Server is restarted, so the correct port number is unknown to the client.

Upon startup, the SQL Server Browser starts and claims UDP port 1434. SQL Server Browser reads the registry, identifies all instances of SQL Server on the computer, and notes the ports and named pipes they use. When a server has two or more network cards, SQL Server Browser returns the first enabled port it encounters for SQL Server. SQL Server Browser supports ipv6 and ipv4.

When SQL Server clients request SQL Server resources, the client network library sends a UDP message to the server using port 1434. SQL Server Browser responds with the TCP/IP port or named pipe of the requested instance. The network library on the client application then completes the connection by sending a request to the server using the port or named pipe of the desired instance.

Learn how to start and stop the SQL Server Browser service in the article Start, stop, pause, resume, restart SQL Server services.

Use SQL Server Browser

If the SQL Server Browser service isn't running, you can still connect to the SQL Server if you provide the correct port number or named pipe. For instance, you can connect to the default instance of SQL Server with TCP/IP if it's running on port 1433.

However, if the SQL Server Browser service isn't running, the following connections don't work:

  • Any component that tries to connect to a named instance without fully specifying all the parameters (such as the TCP/IP port or named pipe).
  • Any component that generates or passes server\instance information that other components could later use to reconnect.
  • Connecting to a named instance without providing the port number or pipe.
  • DAC to a named instance or the default instance if not using TCP/IP port 1433.
  • The Online Analytical Processing (OLAP) redirector service.
  • Enumerating servers in SQL Server Management Studio or Azure Data Studio.

Suppose you're using SQL Server in a client-server scenario (for example, when your application is accessing SQL Server across a network). If you stop or disable the SQL Server Browser service, you must assign a specific port number to each instance and write your client application code to use that port number. This approach has the following problems:

  • You must update and maintain client application code to ensure it's connecting to the proper port.
  • The port you choose for each instance might be used by another service or application on the server, causing the instance of SQL Server to be unavailable.

Clusters and SQL Server Browser

SQL Server Browser isn't a clustered resource and doesn't support failover from one cluster node to the other. Therefore, if there's a cluster, SQL Server Browser should be installed and turned on for each cluster node. On clusters, the SQL Server Browser listens on IP_ANY.

Note

When listening on IP_ANY, when you enable listening on specific IPs, the user must configure the same TCP port on each IP because SQL Server Browser returns the first IP/port pair it encounters.

Install, uninstall, and run from the command line

By default, the SQL Server Browser program is installed at C:\Program Files (x86)\Microsoft SQL Server\90\Shared\sqlbrowser.exe.

The SQL Server Browser service is uninstalled when the last instance of SQL Server is removed.

SQL Server Browser can be started from the command prompt for troubleshooting by using the -c switch:

<drive>\<path>\sqlbrowser.exe -c

Security

The SQL Server Browser Service is crucial in facilitating network communication with SQL Server instances.

Security measures for SQL Server Browser Service include:

  • Configuring firewalls to allow its traffic.
  • Restricting access to trusted IP addresses.
  • Regularly applying updates to patch vulnerabilities.
  • Additionally, it's essential to implement strong authentication and authorization policies to prevent unauthorized access and maintain the integrity of your SQL Server environment.

Account privileges

SQL Server Browser listens on a UDP port and accepts unauthenticated requests using SQL Server Resolution Protocol (SSRP). SQL Server Browser should be run in the security context of a low-privileged user to minimize exposure to a malicious attack. The sign in account can be changed by using the SQL Server Configuration Manager.

The minimum user rights for SQL Server Browser are:

  • Deny access to this computer from the network.
  • Deny sign in locally.
  • Deny sign in as a batch job.
  • Deny Log On Through Terminal Services.
  • Sign in as a service.
  • Read and write the SQL Server registry keys related to network communication (ports and pipes).

Default account

Setup configures SQL Server Browser to use the account selected for services during setup. Other possible accounts include:

  • Any domain\local account.
  • The local service account.
  • The local system account (not recommended as it has unnecessary privileges).

Hide SQL Server

Hidden instances are instances of SQL Server that support only shared memory connections. For SQL Server, set the HideInstance flag to indicate that SQL Server Browser shouldn't respond with information about this server instance.

Use a firewall

To communicate with the SQL Server Browser service on a server behind a firewall, open UDP port 1434 and the TCP/IP port used by SQL Server (for example, 1433). For information about working with a firewall, see Configure the Windows Firewall to Allow SQL Server Access.

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