How the SQLBrowser Service Works Internally?

The SQLBrowser Service is used by SQL Server for named instance name resolution and server name enumeration over TCP/IP and VIA networks.

The default instance of SQL Server is assigned the TCP Port 1433 by default to support client incoming requests. However, because more than one application/SQL Server Instances cannot share a port assignment, any named instances are given a random port number when the service is started. This random port assignment makes it difficult for clients to connect to it, because the client applications don't know what port the server is listening on. To meet this need, the SQLBrowser Service was created.

On start‐up, the SQLBrowser Service queries the registry to discover all the names and port numbers of installed servers and reserves UDP Port 1434. It then listens on UDP Port 1434 for SQL Server Resolution Protocol (SSRP) requests and responds to the requests with the list of instances and their respective port assignments so that clients can connect without knowing the port number assignment.

It is very important that no unauthenticated traffic on UDP Port 1434 be allowed on the network, because the service will respond to any request on that port.

If the SQLBrowser Service is disabled, it will be necessary to specify a static port number for all named instances of the SQL Server Service and to configure all client applications that connect to those instances with the appropriate connection information.

There will be only one SQL Browser Service for all the instances on same machine.