Database Mirroring Endpoint
Connection management in Microsoft SQL Server 2005 and later versions is based on endpoints. An endpoint is a SQL Server object that enables SQL Server to communicate over the network. For database mirroring, a server instance requires its own, dedicated database mirroring endpoint. All mirroring connections on a server instance use a single database mirroring endpoint. This endpoint is a special-purpose endpoint used exclusively to receive database mirroring connections from other server instances.
Client connections to the principal server do not use the database mirroring endpoint.
Database mirroring endpoints use Transmission Control Protocol (TCP) to send and receive messages between the server instances in database mirroring sessions. Each database mirroring endpoint listens on a unique TCP port number. The database mirroring endpoint of a server instance controls the port on which that instance listens for database mirroring messages from other server instances.
Server Network Address
The network address of a server instance (its server network address) contains the port number of its endpoint, as well as the system and domain name of its host computer. Because each server has a distinct mirroring endpoint that uses a unique port, the port number uniquely identifies a specific server instance. This permits multiple server instances on a single server to participate in database mirroring (which is typically done only for testing purposes). For more information, see Specifying a Server Network Address (Database Mirroring).
The following figure illustrates how two server instances on the same server are uniquely identified. The server network addresses of both server instances contain the same system name, MYSYSTEM, and domain name, Adventure-Works.MyDomain.com. To enable the system to route connections to a server instance, a server network address includes the port number associated with the mirroring endpoint of a particular server instance.
These endpoints can be used to turn on or off all mirroring functionality for the instance.
By default, an instance of SQL Server does not contain a database mirroring endpoint. These must be created manually as part of setting up a database mirroring session. The system administrator must create a separate endpoint in each server instance that is to participate in database mirroring.
If the computer running SQL Server has a firewall, the firewall configuration must allow both incoming and outgoing connections for the port specified in the endpoint.
For database mirroring, authentication and encryption are configured on the endpoint. For more information, see Database Mirroring Transport Security.
Do not reconfigure an in-use database mirroring endpoint. The server instances use each other's endpoints to learn the state of the other systems. If the endpoint is reconfigured, it might restart, which can appear to be an error to the other server instances. This is particularly important in high-safety mode with automatic failover, in which reconfiguring the endpoint on a partner could cause a failover to occur.
To configure an endpoint for database mirroring